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src/share/vm/gc/cms/concurrentMarkSweepGeneration.cpp

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 923   assert_lock_strong(freelistLock());
 924 
 925 #ifndef PRODUCT
 926   if (GenCollectedHeap::heap()->promotion_should_fail()) {
 927     return NULL;
 928   }
 929 #endif  // #ifndef PRODUCT
 930 
 931   oop res = _cmsSpace->promote(obj, obj_size);
 932   if (res == NULL) {
 933     // expand and retry
 934     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 935     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 936     // Since this is the old generation, we don't try to promote
 937     // into a more senior generation.
 938     res = _cmsSpace->promote(obj, obj_size);
 939   }
 940   if (res != NULL) {
 941     // See comment in allocate() about when objects should
 942     // be allocated live.
 943     assert(obj->is_oop(), "Will dereference klass pointer below");
 944     collector()->promoted(false,           // Not parallel
 945                           (HeapWord*)res, obj->is_objArray(), obj_size);
 946     // promotion counters
 947     NOT_PRODUCT(
 948       _numObjectsPromoted++;
 949       _numWordsPromoted +=
 950         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
 951     )
 952   }
 953   return res;
 954 }
 955 
 956 
 957 // IMPORTANT: Notes on object size recognition in CMS.
 958 // ---------------------------------------------------
 959 // A block of storage in the CMS generation is always in
 960 // one of three states. A free block (FREE), an allocated
 961 // object (OBJECT) whose size() method reports the correct size,
 962 // and an intermediate state (TRANSIENT) in which its size cannot
 963 // be accurately determined.


1046 
1047   if (UseCompressedClassPointers) {
1048     // Copy gap missed by (aligned) header size calculation below
1049     obj->set_klass_gap(old->klass_gap());
1050   }
1051   if (word_sz > (size_t)oopDesc::header_size()) {
1052     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1053                                  obj_ptr + oopDesc::header_size(),
1054                                  word_sz - oopDesc::header_size());
1055   }
1056 
1057   // Now we can track the promoted object, if necessary.  We take care
1058   // to delay the transition from uninitialized to full object
1059   // (i.e., insertion of klass pointer) until after, so that it
1060   // atomically becomes a promoted object.
1061   if (promoInfo->tracking()) {
1062     promoInfo->track((PromotedObject*)obj, old->klass());
1063   }
1064   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1065   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1066   assert(old->is_oop(), "Will use and dereference old klass ptr below");
1067 
1068   // Finally, install the klass pointer (this should be volatile).
1069   OrderAccess::storestore();
1070   obj->set_klass(old->klass());
1071   // We should now be able to calculate the right size for this object
1072   assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1073 
1074   collector()->promoted(true,          // parallel
1075                         obj_ptr, old->is_objArray(), word_sz);
1076 
1077   NOT_PRODUCT(
1078     Atomic::inc_ptr(&_numObjectsPromoted);
1079     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1080   )
1081 
1082   return obj;
1083 }
1084 
1085 void
1086 ConcurrentMarkSweepGeneration::
1087 par_promote_alloc_done(int thread_num) {
1088   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1089   ps->lab.retire(thread_num);
1090 }
1091 
1092 void


3331   virtual void do_oop(narrowOop* p);
3332 
3333   void trim_queue(size_t max);
3334   void handle_stack_overflow(HeapWord* lost);
3335   void do_yield_check() {
3336     if (_task->should_yield()) {
3337       _task->yield();
3338     }
3339   }
3340 };
3341 
3342 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3343 
3344 // Grey object scanning during work stealing phase --
3345 // the salient assumption here is that any references
3346 // that are in these stolen objects being scanned must
3347 // already have been initialized (else they would not have
3348 // been published), so we do not need to check for
3349 // uninitialized objects before pushing here.
3350 void ParConcMarkingClosure::do_oop(oop obj) {
3351   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3352   HeapWord* addr = (HeapWord*)obj;
3353   // Check if oop points into the CMS generation
3354   // and is not marked
3355   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3356     // a white object ...
3357     // If we manage to "claim" the object, by being the
3358     // first thread to mark it, then we push it on our
3359     // marking stack
3360     if (_bit_map->par_mark(addr)) {     // ... now grey
3361       // push on work queue (grey set)
3362       bool simulate_overflow = false;
3363       NOT_PRODUCT(
3364         if (CMSMarkStackOverflowALot &&
3365             _collector->simulate_overflow()) {
3366           // simulate a stack overflow
3367           simulate_overflow = true;
3368         }
3369       )
3370       if (simulate_overflow ||
3371           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {


3373         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3374         // We cannot assert that the overflow stack is full because
3375         // it may have been emptied since.
3376         assert(simulate_overflow ||
3377                _work_queue->size() == _work_queue->max_elems(),
3378               "Else push should have succeeded");
3379         handle_stack_overflow(addr);
3380       }
3381     } // Else, some other thread got there first
3382     do_yield_check();
3383   }
3384 }
3385 
3386 void ParConcMarkingClosure::do_oop(oop* p)       { ParConcMarkingClosure::do_oop_work(p); }
3387 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); }
3388 
3389 void ParConcMarkingClosure::trim_queue(size_t max) {
3390   while (_work_queue->size() > max) {
3391     oop new_oop;
3392     if (_work_queue->pop_local(new_oop)) {
3393       assert(new_oop->is_oop(), "Should be an oop");
3394       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3395       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3396       new_oop->oop_iterate(this);  // do_oop() above
3397       do_yield_check();
3398     }
3399   }
3400 }
3401 
3402 // Upon stack overflow, we discard (part of) the stack,
3403 // remembering the least address amongst those discarded
3404 // in CMSCollector's _restart_address.
3405 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3406   // We need to do this under a mutex to prevent other
3407   // workers from interfering with the work done below.
3408   MutexLockerEx ml(_overflow_stack->par_lock(),
3409                    Mutex::_no_safepoint_check_flag);
3410   // Remember the least grey address discarded
3411   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3412   _collector->lower_restart_addr(ra);
3413   _overflow_stack->reset();  // discard stack contents
3414   _overflow_stack->expand(); // expand the stack if possible
3415 }
3416 
3417 
3418 void CMSConcMarkingTask::do_work_steal(int i) {
3419   OopTaskQueue* work_q = work_queue(i);
3420   oop obj_to_scan;
3421   CMSBitMap* bm = &(_collector->_markBitMap);
3422   CMSMarkStack* ovflw = &(_collector->_markStack);
3423   int* seed = _collector->hash_seed(i);
3424   ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3425   while (true) {
3426     cl.trim_queue(0);
3427     assert(work_q->size() == 0, "Should have been emptied above");
3428     if (get_work_from_overflow_stack(ovflw, work_q)) {
3429       // Can't assert below because the work obtained from the
3430       // overflow stack may already have been stolen from us.
3431       // assert(work_q->size() > 0, "Work from overflow stack");
3432       continue;
3433     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3434       assert(obj_to_scan->is_oop(), "Should be an oop");
3435       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3436       obj_to_scan->oop_iterate(&cl);
3437     } else if (terminator()->offer_termination(&_term_term)) {
3438       assert(work_q->size() == 0, "Impossible!");
3439       break;
3440     } else if (yielding() || should_yield()) {
3441       yield();
3442     }
3443   }
3444 }
3445 
3446 // This is run by the CMS (coordinator) thread.
3447 void CMSConcMarkingTask::coordinator_yield() {
3448   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3449          "CMS thread should hold CMS token");
3450   // First give up the locks, then yield, then re-lock
3451   // We should probably use a constructor/destructor idiom to
3452   // do this unlock/lock or modify the MutexUnlocker class to
3453   // serve our purpose. XXX
3454   assert_lock_strong(_bit_map_lock);


4505         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4506         start = space->bottom();
4507         end   = space->top();
4508       } else if (nth_task == 0) {
4509         start = space->bottom();
4510         end   = chunk_array[nth_task];
4511       } else if (nth_task < (uint)chunk_top) {
4512         assert(nth_task >= 1, "Control point invariant");
4513         start = chunk_array[nth_task - 1];
4514         end   = chunk_array[nth_task];
4515       } else {
4516         assert(nth_task == (uint)chunk_top, "Control point invariant");
4517         start = chunk_array[chunk_top - 1];
4518         end   = space->top();
4519       }
4520       MemRegion mr(start, end);
4521       // Verify that mr is in space
4522       assert(mr.is_empty() || space->used_region().contains(mr),
4523              "Should be in space");
4524       // Verify that "start" is an object boundary
4525       assert(mr.is_empty() || oop(mr.start())->is_oop(),
4526              "Should be an oop");
4527       space->par_oop_iterate(mr, cl);
4528     }
4529     pst->all_tasks_completed();
4530   }
4531 }
4532 
4533 void
4534 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4535   CompactibleFreeListSpace* sp, int i,
4536   ParMarkRefsIntoAndScanClosure* cl) {
4537   // Until all tasks completed:
4538   // . claim an unclaimed task
4539   // . compute region boundaries corresponding to task claimed
4540   // . transfer dirty bits ct->mut for that region
4541   // . apply rescanclosure to dirty mut bits for that region
4542 
4543   ResourceMark rm;
4544   HandleMark   hm;
4545 


4639     // only affects the number of attempts made to get work from the
4640     // overflow list and does not affect the number of workers.  Just
4641     // pass ParallelGCThreads so this behavior is unchanged.
4642     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4643                                                 work_q,
4644                                                 ParallelGCThreads)) {
4645       // found something in global overflow list;
4646       // not yet ready to go stealing work from others.
4647       // We'd like to assert(work_q->size() != 0, ...)
4648       // because we just took work from the overflow list,
4649       // but of course we can't since all of that could have
4650       // been already stolen from us.
4651       // "He giveth and He taketh away."
4652       continue;
4653     }
4654     // Verify that we have no work before we resort to stealing
4655     assert(work_q->size() == 0, "Have work, shouldn't steal");
4656     // Try to steal from other queues that have work
4657     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4658       NOT_PRODUCT(num_steals++;)
4659       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4660       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4661       // Do scanning work
4662       obj_to_scan->oop_iterate(cl);
4663       // Loop around, finish this work, and try to steal some more
4664     } else if (terminator()->offer_termination()) {
4665         break;  // nirvana from the infinite cycle
4666     }
4667   }
4668   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4669   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4670          "Else our work is not yet done");
4671 }
4672 
4673 // Record object boundaries in _eden_chunk_array by sampling the eden
4674 // top in the slow-path eden object allocation code path and record
4675 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4676 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4677 // sampling in sample_eden() that activates during the part of the
4678 // preclean phase.
4679 void CMSCollector::sample_eden_chunk() {


5118     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5119     // only affects the number of attempts made to get work from the
5120     // overflow list and does not affect the number of workers.  Just
5121     // pass ParallelGCThreads so this behavior is unchanged.
5122     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5123                                                 work_q,
5124                                                 ParallelGCThreads)) {
5125       // Found something in global overflow list;
5126       // not yet ready to go stealing work from others.
5127       // We'd like to assert(work_q->size() != 0, ...)
5128       // because we just took work from the overflow list,
5129       // but of course we can't, since all of that might have
5130       // been already stolen from us.
5131       continue;
5132     }
5133     // Verify that we have no work before we resort to stealing
5134     assert(work_q->size() == 0, "Have work, shouldn't steal");
5135     // Try to steal from other queues that have work
5136     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5137       NOT_PRODUCT(num_steals++;)
5138       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5139       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5140       // Do scanning work
5141       obj_to_scan->oop_iterate(keep_alive);
5142       // Loop around, finish this work, and try to steal some more
5143     } else if (terminator()->offer_termination()) {
5144       break;  // nirvana from the infinite cycle
5145     }
5146   }
5147   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5148 }
5149 
5150 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5151 {
5152   GenCollectedHeap* gch = GenCollectedHeap::heap();
5153   WorkGang* workers = gch->workers();
5154   assert(workers != NULL, "Need parallel worker threads.");
5155   CMSRefProcTaskProxy rp_task(task, &_collector,
5156                               _collector.ref_processor()->span(),
5157                               _collector.markBitMap(),
5158                               workers, _collector.task_queues());


5808 // XXX: there seems to be a lot of code  duplication here;
5809 // should refactor and consolidate common code.
5810 
5811 // This closure is used to mark refs into the CMS generation in
5812 // the CMS bit map. Called at the first checkpoint. This closure
5813 // assumes that we do not need to re-mark dirty cards; if the CMS
5814 // generation on which this is used is not an oldest
5815 // generation then this will lose younger_gen cards!
5816 
5817 MarkRefsIntoClosure::MarkRefsIntoClosure(
5818   MemRegion span, CMSBitMap* bitMap):
5819     _span(span),
5820     _bitMap(bitMap)
5821 {
5822   assert(ref_processor() == NULL, "deliberately left NULL");
5823   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5824 }
5825 
5826 void MarkRefsIntoClosure::do_oop(oop obj) {
5827   // if p points into _span, then mark corresponding bit in _markBitMap
5828   assert(obj->is_oop(), "expected an oop");
5829   HeapWord* addr = (HeapWord*)obj;
5830   if (_span.contains(addr)) {
5831     // this should be made more efficient
5832     _bitMap->mark(addr);
5833   }
5834 }
5835 
5836 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
5837 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5838 
5839 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5840   MemRegion span, CMSBitMap* bitMap):
5841     _span(span),
5842     _bitMap(bitMap)
5843 {
5844   assert(ref_processor() == NULL, "deliberately left NULL");
5845   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5846 }
5847 
5848 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5849   // if p points into _span, then mark corresponding bit in _markBitMap
5850   assert(obj->is_oop(), "expected an oop");
5851   HeapWord* addr = (HeapWord*)obj;
5852   if (_span.contains(addr)) {
5853     // this should be made more efficient
5854     _bitMap->par_mark(addr);
5855   }
5856 }
5857 
5858 void ParMarkRefsIntoClosure::do_oop(oop* p)       { ParMarkRefsIntoClosure::do_oop_work(p); }
5859 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5860 
5861 // A variant of the above, used for CMS marking verification.
5862 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5863   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5864     _span(span),
5865     _verification_bm(verification_bm),
5866     _cms_bm(cms_bm)
5867 {
5868   assert(ref_processor() == NULL, "deliberately left NULL");
5869   assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5870 }
5871 
5872 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5873   // if p points into _span, then mark corresponding bit in _markBitMap
5874   assert(obj->is_oop(), "expected an oop");
5875   HeapWord* addr = (HeapWord*)obj;
5876   if (_span.contains(addr)) {
5877     _verification_bm->mark(addr);
5878     if (!_cms_bm->isMarked(addr)) {
5879       Log(gc, verify) log;
5880       ResourceMark rm;
5881       LogStream ls(log.error());
5882       oop(addr)->print_on(&ls);
5883       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5884       fatal("... aborting");
5885     }
5886   }
5887 }
5888 
5889 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5890 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5891 
5892 //////////////////////////////////////////////////
5893 // MarkRefsIntoAndScanClosure
5894 //////////////////////////////////////////////////


5908   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
5909                       mark_stack, concurrent_precleaning),
5910   _yield(should_yield),
5911   _concurrent_precleaning(concurrent_precleaning),
5912   _freelistLock(NULL)
5913 {
5914   // FIXME: Should initialize in base class constructor.
5915   assert(rp != NULL, "ref_processor shouldn't be NULL");
5916   set_ref_processor_internal(rp);
5917 }
5918 
5919 // This closure is used to mark refs into the CMS generation at the
5920 // second (final) checkpoint, and to scan and transitively follow
5921 // the unmarked oops. It is also used during the concurrent precleaning
5922 // phase while scanning objects on dirty cards in the CMS generation.
5923 // The marks are made in the marking bit map and the marking stack is
5924 // used for keeping the (newly) grey objects during the scan.
5925 // The parallel version (Par_...) appears further below.
5926 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5927   if (obj != NULL) {
5928     assert(obj->is_oop(), "expected an oop");
5929     HeapWord* addr = (HeapWord*)obj;
5930     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5931     assert(_collector->overflow_list_is_empty(),
5932            "overflow list should be empty");
5933     if (_span.contains(addr) &&
5934         !_bit_map->isMarked(addr)) {
5935       // mark bit map (object is now grey)
5936       _bit_map->mark(addr);
5937       // push on marking stack (stack should be empty), and drain the
5938       // stack by applying this closure to the oops in the oops popped
5939       // from the stack (i.e. blacken the grey objects)
5940       bool res = _mark_stack->push(obj);
5941       assert(res, "Should have space to push on empty stack");
5942       do {
5943         oop new_oop = _mark_stack->pop();
5944         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
5945         assert(_bit_map->isMarked((HeapWord*)new_oop),
5946                "only grey objects on this stack");
5947         // iterate over the oops in this oop, marking and pushing
5948         // the ones in CMS heap (i.e. in _span).
5949         new_oop->oop_iterate(&_pushAndMarkClosure);
5950         // check if it's time to yield
5951         do_yield_check();
5952       } while (!_mark_stack->isEmpty() ||
5953                (!_concurrent_precleaning && take_from_overflow_list()));
5954         // if marking stack is empty, and we are not doing this
5955         // during precleaning, then check the overflow list
5956     }
5957     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5958     assert(_collector->overflow_list_is_empty(),
5959            "overflow list was drained above");
5960 
5961     assert(_collector->no_preserved_marks(),
5962            "All preserved marks should have been restored above");
5963   }
5964 }


6006   _low_water_mark(MIN2((work_queue->max_elems()/4),
6007                        ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6008   _parPushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6009 {
6010   // FIXME: Should initialize in base class constructor.
6011   assert(rp != NULL, "ref_processor shouldn't be NULL");
6012   set_ref_processor_internal(rp);
6013 }
6014 
6015 // This closure is used to mark refs into the CMS generation at the
6016 // second (final) checkpoint, and to scan and transitively follow
6017 // the unmarked oops. The marks are made in the marking bit map and
6018 // the work_queue is used for keeping the (newly) grey objects during
6019 // the scan phase whence they are also available for stealing by parallel
6020 // threads. Since the marking bit map is shared, updates are
6021 // synchronized (via CAS).
6022 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6023   if (obj != NULL) {
6024     // Ignore mark word because this could be an already marked oop
6025     // that may be chained at the end of the overflow list.
6026     assert(obj->is_oop(true), "expected an oop");
6027     HeapWord* addr = (HeapWord*)obj;
6028     if (_span.contains(addr) &&
6029         !_bit_map->isMarked(addr)) {
6030       // mark bit map (object will become grey):
6031       // It is possible for several threads to be
6032       // trying to "claim" this object concurrently;
6033       // the unique thread that succeeds in marking the
6034       // object first will do the subsequent push on
6035       // to the work queue (or overflow list).
6036       if (_bit_map->par_mark(addr)) {
6037         // push on work_queue (which may not be empty), and trim the
6038         // queue to an appropriate length by applying this closure to
6039         // the oops in the oops popped from the stack (i.e. blacken the
6040         // grey objects)
6041         bool res = _work_queue->push(obj);
6042         assert(res, "Low water mark should be less than capacity?");
6043         trim_queue(_low_water_mark);
6044       } // Else, another thread claimed the object
6045     }
6046   }


6052 // This closure is used to rescan the marked objects on the dirty cards
6053 // in the mod union table and the card table proper.
6054 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6055   oop p, MemRegion mr) {
6056 
6057   size_t size = 0;
6058   HeapWord* addr = (HeapWord*)p;
6059   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6060   assert(_span.contains(addr), "we are scanning the CMS generation");
6061   // check if it's time to yield
6062   if (do_yield_check()) {
6063     // We yielded for some foreground stop-world work,
6064     // and we have been asked to abort this ongoing preclean cycle.
6065     return 0;
6066   }
6067   if (_bitMap->isMarked(addr)) {
6068     // it's marked; is it potentially uninitialized?
6069     if (p->klass_or_null_acquire() != NULL) {
6070         // an initialized object; ignore mark word in verification below
6071         // since we are running concurrent with mutators
6072         assert(p->is_oop(true), "should be an oop");
6073         if (p->is_objArray()) {
6074           // objArrays are precisely marked; restrict scanning
6075           // to dirty cards only.
6076           size = CompactibleFreeListSpace::adjustObjectSize(
6077                    p->oop_iterate_size(_scanningClosure, mr));
6078         } else {
6079           // A non-array may have been imprecisely marked; we need
6080           // to scan object in its entirety.
6081           size = CompactibleFreeListSpace::adjustObjectSize(
6082                    p->oop_iterate_size(_scanningClosure));
6083         }
6084       #ifdef ASSERT
6085         size_t direct_size =
6086           CompactibleFreeListSpace::adjustObjectSize(p->size());
6087         assert(size == direct_size, "Inconsistency in size");
6088         assert(size >= 3, "Necessary for Printezis marks to work");
6089         HeapWord* start_pbit = addr + 1;
6090         HeapWord* end_pbit = addr + size - 1;
6091         assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6092                "inconsistent Printezis mark");


6101     } else {
6102       // An uninitialized object.
6103       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6104       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6105       size = pointer_delta(nextOneAddr + 1, addr);
6106       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6107              "alignment problem");
6108       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6109       // will dirty the card when the klass pointer is installed in the
6110       // object (signaling the completion of initialization).
6111     }
6112   } else {
6113     // Either a not yet marked object or an uninitialized object
6114     if (p->klass_or_null_acquire() == NULL) {
6115       // An uninitialized object, skip to the next card, since
6116       // we may not be able to read its P-bits yet.
6117       assert(size == 0, "Initial value");
6118     } else {
6119       // An object not (yet) reached by marking: we merely need to
6120       // compute its size so as to go look at the next block.
6121       assert(p->is_oop(true), "should be an oop");
6122       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6123     }
6124   }
6125   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6126   return size;
6127 }
6128 
6129 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6130   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6131          "CMS thread should hold CMS token");
6132   assert_lock_strong(_freelistLock);
6133   assert_lock_strong(_bitMap->lock());
6134   // relinquish the free_list_lock and bitMaplock()
6135   _bitMap->lock()->unlock();
6136   _freelistLock->unlock();
6137   ConcurrentMarkSweepThread::desynchronize(true);
6138   _collector->stopTimer();
6139   _collector->incrementYields();
6140 
6141   // See the comment in coordinator_yield()


6148   ConcurrentMarkSweepThread::synchronize(true);
6149   _freelistLock->lock_without_safepoint_check();
6150   _bitMap->lock()->lock_without_safepoint_check();
6151   _collector->startTimer();
6152 }
6153 
6154 
6155 //////////////////////////////////////////////////////////////////
6156 // SurvivorSpacePrecleanClosure
6157 //////////////////////////////////////////////////////////////////
6158 // This (single-threaded) closure is used to preclean the oops in
6159 // the survivor spaces.
6160 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6161 
6162   HeapWord* addr = (HeapWord*)p;
6163   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6164   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6165   assert(p->klass_or_null() != NULL, "object should be initialized");
6166   // an initialized object; ignore mark word in verification below
6167   // since we are running concurrent with mutators
6168   assert(p->is_oop(true), "should be an oop");
6169   // Note that we do not yield while we iterate over
6170   // the interior oops of p, pushing the relevant ones
6171   // on our marking stack.
6172   size_t size = p->oop_iterate_size(_scanning_closure);
6173   do_yield_check();
6174   // Observe that below, we do not abandon the preclean
6175   // phase as soon as we should; rather we empty the
6176   // marking stack before returning. This is to satisfy
6177   // some existing assertions. In general, it may be a
6178   // good idea to abort immediately and complete the marking
6179   // from the grey objects at a later time.
6180   while (!_mark_stack->isEmpty()) {
6181     oop new_oop = _mark_stack->pop();
6182     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6183     assert(_bit_map->isMarked((HeapWord*)new_oop),
6184            "only grey objects on this stack");
6185     // iterate over the oops in this oop, marking and pushing
6186     // the ones in CMS heap (i.e. in _span).
6187     new_oop->oop_iterate(_scanning_closure);
6188     // check if it's time to yield
6189     do_yield_check();
6190   }
6191   unsigned int after_count =
6192     GenCollectedHeap::heap()->total_collections();
6193   bool abort = (_before_count != after_count) ||
6194                _collector->should_abort_preclean();
6195   return abort ? 0 : size;
6196 }
6197 
6198 void SurvivorSpacePrecleanClosure::do_yield_work() {
6199   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6200          "CMS thread should hold CMS token");
6201   assert_lock_strong(_bit_map->lock());
6202   // Relinquish the bit map lock


6206   _collector->incrementYields();
6207 
6208   // See the comment in coordinator_yield()
6209   for (unsigned i = 0; i < CMSYieldSleepCount &&
6210                        ConcurrentMarkSweepThread::should_yield() &&
6211                        !CMSCollector::foregroundGCIsActive(); ++i) {
6212     os::sleep(Thread::current(), 1, false);
6213   }
6214 
6215   ConcurrentMarkSweepThread::synchronize(true);
6216   _bit_map->lock()->lock_without_safepoint_check();
6217   _collector->startTimer();
6218 }
6219 
6220 // This closure is used to rescan the marked objects on the dirty cards
6221 // in the mod union table and the card table proper. In the parallel
6222 // case, although the bitMap is shared, we do a single read so the
6223 // isMarked() query is "safe".
6224 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6225   // Ignore mark word because we are running concurrent with mutators
6226   assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6227   HeapWord* addr = (HeapWord*)p;
6228   assert(_span.contains(addr), "we are scanning the CMS generation");
6229   bool is_obj_array = false;
6230   #ifdef ASSERT
6231     if (!_parallel) {
6232       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6233       assert(_collector->overflow_list_is_empty(),
6234              "overflow list should be empty");
6235 
6236     }
6237   #endif // ASSERT
6238   if (_bit_map->isMarked(addr)) {
6239     // Obj arrays are precisely marked, non-arrays are not;
6240     // so we scan objArrays precisely and non-arrays in their
6241     // entirety.
6242     if (p->is_objArray()) {
6243       is_obj_array = true;
6244       if (_parallel) {
6245         p->oop_iterate(_par_scan_closure, mr);
6246       } else {


6359   // See the comment in coordinator_yield()
6360   for (unsigned i = 0; i < CMSYieldSleepCount &&
6361                        ConcurrentMarkSweepThread::should_yield() &&
6362                        !CMSCollector::foregroundGCIsActive(); ++i) {
6363     os::sleep(Thread::current(), 1, false);
6364   }
6365 
6366   ConcurrentMarkSweepThread::synchronize(true);
6367   _bitMap->lock()->lock_without_safepoint_check();
6368   _collector->startTimer();
6369 }
6370 
6371 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6372   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6373   assert(_markStack->isEmpty(),
6374          "should drain stack to limit stack usage");
6375   // convert ptr to an oop preparatory to scanning
6376   oop obj = oop(ptr);
6377   // Ignore mark word in verification below, since we
6378   // may be running concurrent with mutators.
6379   assert(obj->is_oop(true), "should be an oop");
6380   assert(_finger <= ptr, "_finger runneth ahead");
6381   // advance the finger to right end of this object
6382   _finger = ptr + obj->size();
6383   assert(_finger > ptr, "we just incremented it above");
6384   // On large heaps, it may take us some time to get through
6385   // the marking phase. During
6386   // this time it's possible that a lot of mutations have
6387   // accumulated in the card table and the mod union table --
6388   // these mutation records are redundant until we have
6389   // actually traced into the corresponding card.
6390   // Here, we check whether advancing the finger would make
6391   // us cross into a new card, and if so clear corresponding
6392   // cards in the MUT (preclean them in the card-table in the
6393   // future).
6394 
6395   DEBUG_ONLY(if (!_verifying) {)
6396     // The clean-on-enter optimization is disabled by default,
6397     // until we fix 6178663.
6398     if (CMSCleanOnEnter && (_finger > _threshold)) {
6399       // [_threshold, _finger) represents the interval


6406       assert(is_aligned(old_threshold, CardTableModRefBS::card_size),
6407              "_threshold should always be card-aligned");
6408       _threshold = align_up(_finger, CardTableModRefBS::card_size);
6409       MemRegion mr(old_threshold, _threshold);
6410       assert(!mr.is_empty(), "Control point invariant");
6411       assert(_span.contains(mr), "Should clear within span");
6412       _mut->clear_range(mr);
6413     }
6414   DEBUG_ONLY(})
6415   // Note: the finger doesn't advance while we drain
6416   // the stack below.
6417   PushOrMarkClosure pushOrMarkClosure(_collector,
6418                                       _span, _bitMap, _markStack,
6419                                       _finger, this);
6420   bool res = _markStack->push(obj);
6421   assert(res, "Empty non-zero size stack should have space for single push");
6422   while (!_markStack->isEmpty()) {
6423     oop new_oop = _markStack->pop();
6424     // Skip verifying header mark word below because we are
6425     // running concurrent with mutators.
6426     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6427     // now scan this oop's oops
6428     new_oop->oop_iterate(&pushOrMarkClosure);
6429     do_yield_check();
6430   }
6431   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6432 }
6433 
6434 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6435                        CMSCollector* collector, MemRegion span,
6436                        CMSBitMap* bit_map,
6437                        OopTaskQueue* work_queue,
6438                        CMSMarkStack*  overflow_stack):
6439   _collector(collector),
6440   _whole_span(collector->_span),
6441   _span(span),
6442   _bit_map(bit_map),
6443   _mut(&collector->_modUnionTable),
6444   _work_queue(work_queue),
6445   _overflow_stack(overflow_stack),
6446   _skip_bits(0),


6472     if (p->klass_or_null_acquire() == NULL) {
6473       // in the case of Clean-on-Enter optimization, redirty card
6474       // and avoid clearing card by increasing  the threshold.
6475       return true;
6476     }
6477   }
6478   scan_oops_in_oop(addr);
6479   return true;
6480 }
6481 
6482 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6483   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6484   // Should we assert that our work queue is empty or
6485   // below some drain limit?
6486   assert(_work_queue->size() == 0,
6487          "should drain stack to limit stack usage");
6488   // convert ptr to an oop preparatory to scanning
6489   oop obj = oop(ptr);
6490   // Ignore mark word in verification below, since we
6491   // may be running concurrent with mutators.
6492   assert(obj->is_oop(true), "should be an oop");
6493   assert(_finger <= ptr, "_finger runneth ahead");
6494   // advance the finger to right end of this object
6495   _finger = ptr + obj->size();
6496   assert(_finger > ptr, "we just incremented it above");
6497   // On large heaps, it may take us some time to get through
6498   // the marking phase. During
6499   // this time it's possible that a lot of mutations have
6500   // accumulated in the card table and the mod union table --
6501   // these mutation records are redundant until we have
6502   // actually traced into the corresponding card.
6503   // Here, we check whether advancing the finger would make
6504   // us cross into a new card, and if so clear corresponding
6505   // cards in the MUT (preclean them in the card-table in the
6506   // future).
6507 
6508   // The clean-on-enter optimization is disabled by default,
6509   // until we fix 6178663.
6510   if (CMSCleanOnEnter && (_finger > _threshold)) {
6511     // [_threshold, _finger) represents the interval
6512     // of cards to be cleared  in MUT (or precleaned in card table).


6533                                          _overflow_stack,
6534                                          _finger,
6535                                          gfa, this);
6536   bool res = _work_queue->push(obj);   // overflow could occur here
6537   assert(res, "Will hold once we use workqueues");
6538   while (true) {
6539     oop new_oop;
6540     if (!_work_queue->pop_local(new_oop)) {
6541       // We emptied our work_queue; check if there's stuff that can
6542       // be gotten from the overflow stack.
6543       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6544             _overflow_stack, _work_queue)) {
6545         do_yield_check();
6546         continue;
6547       } else {  // done
6548         break;
6549       }
6550     }
6551     // Skip verifying header mark word below because we are
6552     // running concurrent with mutators.
6553     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6554     // now scan this oop's oops
6555     new_oop->oop_iterate(&pushOrMarkClosure);
6556     do_yield_check();
6557   }
6558   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6559 }
6560 
6561 // Yield in response to a request from VM Thread or
6562 // from mutators.
6563 void ParMarkFromRootsClosure::do_yield_work() {
6564   assert(_task != NULL, "sanity");
6565   _task->yield();
6566 }
6567 
6568 // A variant of the above used for verifying CMS marking work.
6569 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6570                         MemRegion span,
6571                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6572                         CMSMarkStack*  mark_stack):
6573   _collector(collector),


6587 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6588   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6589   assert(_span.contains(addr), "Out of bounds _finger?");
6590   _finger = addr;
6591 }
6592 
6593 // Should revisit to see if this should be restructured for
6594 // greater efficiency.
6595 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6596   // convert offset into a HeapWord*
6597   HeapWord* addr = _verification_bm->startWord() + offset;
6598   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6599          "address out of range");
6600   assert(_verification_bm->isMarked(addr), "tautology");
6601   assert(_cms_bm->isMarked(addr), "tautology");
6602 
6603   assert(_mark_stack->isEmpty(),
6604          "should drain stack to limit stack usage");
6605   // convert addr to an oop preparatory to scanning
6606   oop obj = oop(addr);
6607   assert(obj->is_oop(), "should be an oop");
6608   assert(_finger <= addr, "_finger runneth ahead");
6609   // advance the finger to right end of this object
6610   _finger = addr + obj->size();
6611   assert(_finger > addr, "we just incremented it above");
6612   // Note: the finger doesn't advance while we drain
6613   // the stack below.
6614   bool res = _mark_stack->push(obj);
6615   assert(res, "Empty non-zero size stack should have space for single push");
6616   while (!_mark_stack->isEmpty()) {
6617     oop new_oop = _mark_stack->pop();
6618     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6619     // now scan this oop's oops
6620     new_oop->oop_iterate(&_pam_verify_closure);
6621   }
6622   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6623   return true;
6624 }
6625 
6626 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6627   CMSCollector* collector, MemRegion span,
6628   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6629   CMSMarkStack*  mark_stack):
6630   MetadataAwareOopClosure(collector->ref_processor()),
6631   _collector(collector),
6632   _span(span),
6633   _verification_bm(verification_bm),
6634   _cms_bm(cms_bm),
6635   _mark_stack(mark_stack)
6636 { }
6637 
6638 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6639 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6640 
6641 // Upon stack overflow, we discard (part of) the stack,
6642 // remembering the least address amongst those discarded
6643 // in CMSCollector's _restart_address.
6644 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6645   // Remember the least grey address discarded
6646   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6647   _collector->lower_restart_addr(ra);
6648   _mark_stack->reset();  // discard stack contents
6649   _mark_stack->expand(); // expand the stack if possible
6650 }
6651 
6652 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6653   assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6654   HeapWord* addr = (HeapWord*)obj;
6655   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6656     // Oop lies in _span and isn't yet grey or black
6657     _verification_bm->mark(addr);            // now grey
6658     if (!_cms_bm->isMarked(addr)) {
6659       Log(gc, verify) log;
6660       ResourceMark rm;
6661       LogStream ls(log.error());
6662       oop(addr)->print_on(&ls);
6663       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6664       fatal("... aborting");
6665     }
6666 
6667     if (!_mark_stack->push(obj)) { // stack overflow
6668       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6669       assert(_mark_stack->isFull(), "Else push should have succeeded");
6670       handle_stack_overflow(addr);
6671     }
6672     // anything including and to the right of _finger
6673     // will be scanned as we iterate over the remainder of the


6730   _markStack->expand(); // expand the stack if possible
6731 }
6732 
6733 // Upon stack overflow, we discard (part of) the stack,
6734 // remembering the least address amongst those discarded
6735 // in CMSCollector's _restart_address.
6736 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6737   // We need to do this under a mutex to prevent other
6738   // workers from interfering with the work done below.
6739   MutexLockerEx ml(_overflow_stack->par_lock(),
6740                    Mutex::_no_safepoint_check_flag);
6741   // Remember the least grey address discarded
6742   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6743   _collector->lower_restart_addr(ra);
6744   _overflow_stack->reset();  // discard stack contents
6745   _overflow_stack->expand(); // expand the stack if possible
6746 }
6747 
6748 void PushOrMarkClosure::do_oop(oop obj) {
6749   // Ignore mark word because we are running concurrent with mutators.
6750   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6751   HeapWord* addr = (HeapWord*)obj;
6752   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6753     // Oop lies in _span and isn't yet grey or black
6754     _bitMap->mark(addr);            // now grey
6755     if (addr < _finger) {
6756       // the bit map iteration has already either passed, or
6757       // sampled, this bit in the bit map; we'll need to
6758       // use the marking stack to scan this oop's oops.
6759       bool simulate_overflow = false;
6760       NOT_PRODUCT(
6761         if (CMSMarkStackOverflowALot &&
6762             _collector->simulate_overflow()) {
6763           // simulate a stack overflow
6764           simulate_overflow = true;
6765         }
6766       )
6767       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6768         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6769         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6770         handle_stack_overflow(addr);
6771       }
6772     }
6773     // anything including and to the right of _finger
6774     // will be scanned as we iterate over the remainder of the
6775     // bit map
6776     do_yield_check();
6777   }
6778 }
6779 
6780 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
6781 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6782 
6783 void ParPushOrMarkClosure::do_oop(oop obj) {
6784   // Ignore mark word because we are running concurrent with mutators.
6785   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6786   HeapWord* addr = (HeapWord*)obj;
6787   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6788     // Oop lies in _span and isn't yet grey or black
6789     // We read the global_finger (volatile read) strictly after marking oop
6790     bool res = _bit_map->par_mark(addr);    // now grey
6791     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6792     // Should we push this marked oop on our stack?
6793     // -- if someone else marked it, nothing to do
6794     // -- if target oop is above global finger nothing to do
6795     // -- if target oop is in chunk and above local finger
6796     //      then nothing to do
6797     // -- else push on work queue
6798     if (   !res       // someone else marked it, they will deal with it
6799         || (addr >= *gfa)  // will be scanned in a later task
6800         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6801       return;
6802     }
6803     // the bit map iteration has already either passed, or
6804     // sampled, this bit in the bit map; we'll need to
6805     // use the marking stack to scan this oop's oops.


6838                                        bool           concurrent_precleaning):
6839   MetadataAwareOopClosure(rp),
6840   _collector(collector),
6841   _span(span),
6842   _bit_map(bit_map),
6843   _mod_union_table(mod_union_table),
6844   _mark_stack(mark_stack),
6845   _concurrent_precleaning(concurrent_precleaning)
6846 {
6847   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6848 }
6849 
6850 // Grey object rescan during pre-cleaning and second checkpoint phases --
6851 // the non-parallel version (the parallel version appears further below.)
6852 void PushAndMarkClosure::do_oop(oop obj) {
6853   // Ignore mark word verification. If during concurrent precleaning,
6854   // the object monitor may be locked. If during the checkpoint
6855   // phases, the object may already have been reached by a  different
6856   // path and may be at the end of the global overflow list (so
6857   // the mark word may be NULL).
6858   assert(obj->is_oop_or_null(true /* ignore mark word */),
6859          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6860   HeapWord* addr = (HeapWord*)obj;
6861   // Check if oop points into the CMS generation
6862   // and is not marked
6863   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6864     // a white object ...
6865     _bit_map->mark(addr);         // ... now grey
6866     // push on the marking stack (grey set)
6867     bool simulate_overflow = false;
6868     NOT_PRODUCT(
6869       if (CMSMarkStackOverflowALot &&
6870           _collector->simulate_overflow()) {
6871         // simulate a stack overflow
6872         simulate_overflow = true;
6873       }
6874     )
6875     if (simulate_overflow || !_mark_stack->push(obj)) {
6876       if (_concurrent_precleaning) {
6877          // During precleaning we can just dirty the appropriate card(s)
6878          // in the mod union table, thus ensuring that the object remains


6917   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6918 }
6919 
6920 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
6921 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6922 
6923 // Grey object rescan during second checkpoint phase --
6924 // the parallel version.
6925 void ParPushAndMarkClosure::do_oop(oop obj) {
6926   // In the assert below, we ignore the mark word because
6927   // this oop may point to an already visited object that is
6928   // on the overflow stack (in which case the mark word has
6929   // been hijacked for chaining into the overflow stack --
6930   // if this is the last object in the overflow stack then
6931   // its mark word will be NULL). Because this object may
6932   // have been subsequently popped off the global overflow
6933   // stack, and the mark word possibly restored to the prototypical
6934   // value, by the time we get to examined this failing assert in
6935   // the debugger, is_oop_or_null(false) may subsequently start
6936   // to hold.
6937   assert(obj->is_oop_or_null(true),
6938          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6939   HeapWord* addr = (HeapWord*)obj;
6940   // Check if oop points into the CMS generation
6941   // and is not marked
6942   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6943     // a white object ...
6944     // If we manage to "claim" the object, by being the
6945     // first thread to mark it, then we push it on our
6946     // marking stack
6947     if (_bit_map->par_mark(addr)) {     // ... now grey
6948       // push on work queue (grey set)
6949       bool simulate_overflow = false;
6950       NOT_PRODUCT(
6951         if (CMSMarkStackOverflowALot &&
6952             _collector->par_simulate_overflow()) {
6953           // simulate a stack overflow
6954           simulate_overflow = true;
6955         }
6956       )
6957       if (simulate_overflow || !_work_queue->push(obj)) {


7308   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7309   do_post_free_or_garbage_chunk(fc, size);
7310 
7311   assert(_limit >= addr + size,
7312          "A freshly garbage chunk can't possibly straddle over _limit");
7313   if (inFreeRange()) lookahead_and_flush(fc, size);
7314   return size;
7315 }
7316 
7317 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7318   HeapWord* addr = (HeapWord*) fc;
7319   // The sweeper has just found a live object. Return any accumulated
7320   // left hand chunk to the free lists.
7321   if (inFreeRange()) {
7322     assert(freeFinger() < addr, "freeFinger points too high");
7323     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7324   }
7325 
7326   // This object is live: we'd normally expect this to be
7327   // an oop, and like to assert the following:
7328   // assert(oop(addr)->is_oop(), "live block should be an oop");
7329   // However, as we commented above, this may be an object whose
7330   // header hasn't yet been initialized.
7331   size_t size;
7332   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7333   if (_bitMap->isMarked(addr + 1)) {
7334     // Determine the size from the bit map, rather than trying to
7335     // compute it from the object header.
7336     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7337     size = pointer_delta(nextOneAddr + 1, addr);
7338     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7339            "alignment problem");
7340 
7341 #ifdef ASSERT
7342       if (oop(addr)->klass_or_null_acquire() != NULL) {
7343         // Ignore mark word because we are running concurrent with mutators
7344         assert(oop(addr)->is_oop(true), "live block should be an oop");
7345         assert(size ==
7346                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7347                "P-mark and computed size do not agree");
7348       }
7349 #endif
7350 
7351   } else {
7352     // This should be an initialized object that's alive.
7353     assert(oop(addr)->klass_or_null_acquire() != NULL,
7354            "Should be an initialized object");
7355     // Ignore mark word because we are running concurrent with mutators
7356     assert(oop(addr)->is_oop(true), "live block should be an oop");
7357     // Verify that the bit map has no bits marked between
7358     // addr and purported end of this block.
7359     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7360     assert(size >= 3, "Necessary for Printezis marks to work");
7361     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7362     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7363   }
7364   return size;
7365 }
7366 
7367 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7368                                                  size_t chunkSize) {
7369   // do_post_free_or_garbage_chunk() should only be called in the case
7370   // of the adaptive free list allocator.
7371   const bool fcInFreeLists = fc->is_free();
7372   assert((HeapWord*)fc <= _limit, "sweep invariant");
7373   if (CMSTestInFreeList && fcInFreeLists) {
7374     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7375   }
7376 


7644     // In general, during recursive tracing, several threads
7645     // may be concurrently getting here; the first one to
7646     // "tag" it, claims it.
7647     if (_bit_map->par_mark(addr)) {
7648       bool res = _work_queue->push(obj);
7649       assert(res, "Low water mark should be much less than capacity");
7650       // Do a recursive trim in the hope that this will keep
7651       // stack usage lower, but leave some oops for potential stealers
7652       trim_queue(_low_water_mark);
7653     } // Else, another thread got there first
7654   }
7655 }
7656 
7657 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
7658 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7659 
7660 void CMSParKeepAliveClosure::trim_queue(uint max) {
7661   while (_work_queue->size() > max) {
7662     oop new_oop;
7663     if (_work_queue->pop_local(new_oop)) {
7664       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7665       assert(_bit_map->isMarked((HeapWord*)new_oop),
7666              "no white objects on this stack!");
7667       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7668       // iterate over the oops in this oop, marking and pushing
7669       // the ones in CMS heap (i.e. in _span).
7670       new_oop->oop_iterate(&_mark_and_push);
7671     }
7672   }
7673 }
7674 
7675 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7676                                 CMSCollector* collector,
7677                                 MemRegion span, CMSBitMap* bit_map,
7678                                 OopTaskQueue* work_queue):
7679   _collector(collector),
7680   _span(span),
7681   _bit_map(bit_map),
7682   _work_queue(work_queue) { }
7683 
7684 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {


7724       return "Par Spooling Space";
7725     case _adaptive_size_policy:
7726       return "Ergonomics";
7727     default:
7728       return "unknown";
7729   }
7730 }
7731 
7732 void CMSDrainMarkingStackClosure::do_void() {
7733   // the max number to take from overflow list at a time
7734   const size_t num = _mark_stack->capacity()/4;
7735   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7736          "Overflow list should be NULL during concurrent phases");
7737   while (!_mark_stack->isEmpty() ||
7738          // if stack is empty, check the overflow list
7739          _collector->take_from_overflow_list(num, _mark_stack)) {
7740     oop obj = _mark_stack->pop();
7741     HeapWord* addr = (HeapWord*)obj;
7742     assert(_span.contains(addr), "Should be within span");
7743     assert(_bit_map->isMarked(addr), "Should be marked");
7744     assert(obj->is_oop(), "Should be an oop");
7745     obj->oop_iterate(_keep_alive);
7746   }
7747 }
7748 
7749 void CMSParDrainMarkingStackClosure::do_void() {
7750   // drain queue
7751   trim_queue(0);
7752 }
7753 
7754 // Trim our work_queue so its length is below max at return
7755 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7756   while (_work_queue->size() > max) {
7757     oop new_oop;
7758     if (_work_queue->pop_local(new_oop)) {
7759       assert(new_oop->is_oop(), "Expected an oop");
7760       assert(_bit_map->isMarked((HeapWord*)new_oop),
7761              "no white objects on this stack!");
7762       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7763       // iterate over the oops in this oop, marking and pushing
7764       // the ones in CMS heap (i.e. in _span).
7765       new_oop->oop_iterate(&_mark_and_push);
7766     }
7767   }
7768 }
7769 
7770 ////////////////////////////////////////////////////////////////////
7771 // Support for Marking Stack Overflow list handling and related code
7772 ////////////////////////////////////////////////////////////////////
7773 // Much of the following code is similar in shape and spirit to the
7774 // code used in ParNewGC. We should try and share that code
7775 // as much as possible in the future.
7776 
7777 #ifndef PRODUCT
7778 // Debugging support for CMSStackOverflowALot
7779 


7790     return false;
7791   }
7792 }
7793 
7794 bool CMSCollector::par_simulate_overflow() {
7795   return simulate_overflow();
7796 }
7797 #endif
7798 
7799 // Single-threaded
7800 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7801   assert(stack->isEmpty(), "Expected precondition");
7802   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7803   size_t i = num;
7804   oop  cur = _overflow_list;
7805   const markOop proto = markOopDesc::prototype();
7806   NOT_PRODUCT(ssize_t n = 0;)
7807   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7808     next = oop(cur->mark());
7809     cur->set_mark(proto);   // until proven otherwise
7810     assert(cur->is_oop(), "Should be an oop");
7811     bool res = stack->push(cur);
7812     assert(res, "Bit off more than can chew?");
7813     NOT_PRODUCT(n++;)
7814   }
7815   _overflow_list = cur;
7816 #ifndef PRODUCT
7817   assert(_num_par_pushes >= n, "Too many pops?");
7818   _num_par_pushes -=n;
7819 #endif
7820   return !stack->isEmpty();
7821 }
7822 
7823 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
7824 // (MT-safe) Get a prefix of at most "num" from the list.
7825 // The overflow list is chained through the mark word of
7826 // each object in the list. We fetch the entire list,
7827 // break off a prefix of the right size and return the
7828 // remainder. If other threads try to take objects from
7829 // the overflow list at that time, they will wait for
7830 // some time to see if data becomes available. If (and


7934           suffix_tail->set_mark(markOop(cur_overflow_list));
7935         } else { // cur_overflow_list == BUSY
7936           suffix_tail->set_mark(NULL);
7937         }
7938         // ... and try to place spliced list back on overflow_list ...
7939         observed_overflow_list =
7940           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7941       } while (cur_overflow_list != observed_overflow_list);
7942       // ... until we have succeeded in doing so.
7943     }
7944   }
7945 
7946   // Push the prefix elements on work_q
7947   assert(prefix != NULL, "control point invariant");
7948   const markOop proto = markOopDesc::prototype();
7949   oop next;
7950   NOT_PRODUCT(ssize_t n = 0;)
7951   for (cur = prefix; cur != NULL; cur = next) {
7952     next = oop(cur->mark());
7953     cur->set_mark(proto);   // until proven otherwise
7954     assert(cur->is_oop(), "Should be an oop");
7955     bool res = work_q->push(cur);
7956     assert(res, "Bit off more than we can chew?");
7957     NOT_PRODUCT(n++;)
7958   }
7959 #ifndef PRODUCT
7960   assert(_num_par_pushes >= n, "Too many pops?");
7961   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
7962 #endif
7963   return true;
7964 }
7965 
7966 // Single-threaded
7967 void CMSCollector::push_on_overflow_list(oop p) {
7968   NOT_PRODUCT(_num_par_pushes++;)
7969   assert(p->is_oop(), "Not an oop");
7970   preserve_mark_if_necessary(p);
7971   p->set_mark((markOop)_overflow_list);
7972   _overflow_list = p;
7973 }
7974 
7975 // Multi-threaded; use CAS to prepend to overflow list
7976 void CMSCollector::par_push_on_overflow_list(oop p) {
7977   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
7978   assert(p->is_oop(), "Not an oop");
7979   par_preserve_mark_if_necessary(p);
7980   oop observed_overflow_list = _overflow_list;
7981   oop cur_overflow_list;
7982   do {
7983     cur_overflow_list = observed_overflow_list;
7984     if (cur_overflow_list != BUSY) {
7985       p->set_mark(markOop(cur_overflow_list));
7986     } else {
7987       p->set_mark(NULL);
7988     }
7989     observed_overflow_list =
7990       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
7991   } while (cur_overflow_list != observed_overflow_list);
7992 }
7993 #undef BUSY
7994 
7995 // Single threaded
7996 // General Note on GrowableArray: pushes may silently fail
7997 // because we are (temporarily) out of C-heap for expanding
7998 // the stack. The problem is quite ubiquitous and affects


8045 // until all work's been completed. Because we
8046 // expect the preserved oop stack (set) to be small,
8047 // it's probably fine to do this single-threaded.
8048 // We can explore cleverer concurrent/overlapped/parallel
8049 // processing of preserved marks if we feel the
8050 // need for this in the future. Stack overflow should
8051 // be so rare in practice and, when it happens, its
8052 // effect on performance so great that this will
8053 // likely just be in the noise anyway.
8054 void CMSCollector::restore_preserved_marks_if_any() {
8055   assert(SafepointSynchronize::is_at_safepoint(),
8056          "world should be stopped");
8057   assert(Thread::current()->is_ConcurrentGC_thread() ||
8058          Thread::current()->is_VM_thread(),
8059          "should be single-threaded");
8060   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8061          "bijection");
8062 
8063   while (!_preserved_oop_stack.is_empty()) {
8064     oop p = _preserved_oop_stack.pop();
8065     assert(p->is_oop(), "Should be an oop");
8066     assert(_span.contains(p), "oop should be in _span");
8067     assert(p->mark() == markOopDesc::prototype(),
8068            "Set when taken from overflow list");
8069     markOop m = _preserved_mark_stack.pop();
8070     p->set_mark(m);
8071   }
8072   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8073          "stacks were cleared above");
8074 }
8075 
8076 #ifndef PRODUCT
8077 bool CMSCollector::no_preserved_marks() const {
8078   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8079 }
8080 #endif
8081 
8082 // Transfer some number of overflown objects to usual marking
8083 // stack. Return true if some objects were transferred.
8084 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8085   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,




 923   assert_lock_strong(freelistLock());
 924 
 925 #ifndef PRODUCT
 926   if (GenCollectedHeap::heap()->promotion_should_fail()) {
 927     return NULL;
 928   }
 929 #endif  // #ifndef PRODUCT
 930 
 931   oop res = _cmsSpace->promote(obj, obj_size);
 932   if (res == NULL) {
 933     // expand and retry
 934     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 935     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 936     // Since this is the old generation, we don't try to promote
 937     // into a more senior generation.
 938     res = _cmsSpace->promote(obj, obj_size);
 939   }
 940   if (res != NULL) {
 941     // See comment in allocate() about when objects should
 942     // be allocated live.
 943     assert(oopDesc::is_oop(obj), "Will dereference klass pointer below");
 944     collector()->promoted(false,           // Not parallel
 945                           (HeapWord*)res, obj->is_objArray(), obj_size);
 946     // promotion counters
 947     NOT_PRODUCT(
 948       _numObjectsPromoted++;
 949       _numWordsPromoted +=
 950         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
 951     )
 952   }
 953   return res;
 954 }
 955 
 956 
 957 // IMPORTANT: Notes on object size recognition in CMS.
 958 // ---------------------------------------------------
 959 // A block of storage in the CMS generation is always in
 960 // one of three states. A free block (FREE), an allocated
 961 // object (OBJECT) whose size() method reports the correct size,
 962 // and an intermediate state (TRANSIENT) in which its size cannot
 963 // be accurately determined.


1046 
1047   if (UseCompressedClassPointers) {
1048     // Copy gap missed by (aligned) header size calculation below
1049     obj->set_klass_gap(old->klass_gap());
1050   }
1051   if (word_sz > (size_t)oopDesc::header_size()) {
1052     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1053                                  obj_ptr + oopDesc::header_size(),
1054                                  word_sz - oopDesc::header_size());
1055   }
1056 
1057   // Now we can track the promoted object, if necessary.  We take care
1058   // to delay the transition from uninitialized to full object
1059   // (i.e., insertion of klass pointer) until after, so that it
1060   // atomically becomes a promoted object.
1061   if (promoInfo->tracking()) {
1062     promoInfo->track((PromotedObject*)obj, old->klass());
1063   }
1064   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1065   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1066   assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below");
1067 
1068   // Finally, install the klass pointer (this should be volatile).
1069   OrderAccess::storestore();
1070   obj->set_klass(old->klass());
1071   // We should now be able to calculate the right size for this object
1072   assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1073 
1074   collector()->promoted(true,          // parallel
1075                         obj_ptr, old->is_objArray(), word_sz);
1076 
1077   NOT_PRODUCT(
1078     Atomic::inc_ptr(&_numObjectsPromoted);
1079     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1080   )
1081 
1082   return obj;
1083 }
1084 
1085 void
1086 ConcurrentMarkSweepGeneration::
1087 par_promote_alloc_done(int thread_num) {
1088   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1089   ps->lab.retire(thread_num);
1090 }
1091 
1092 void


3331   virtual void do_oop(narrowOop* p);
3332 
3333   void trim_queue(size_t max);
3334   void handle_stack_overflow(HeapWord* lost);
3335   void do_yield_check() {
3336     if (_task->should_yield()) {
3337       _task->yield();
3338     }
3339   }
3340 };
3341 
3342 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3343 
3344 // Grey object scanning during work stealing phase --
3345 // the salient assumption here is that any references
3346 // that are in these stolen objects being scanned must
3347 // already have been initialized (else they would not have
3348 // been published), so we do not need to check for
3349 // uninitialized objects before pushing here.
3350 void ParConcMarkingClosure::do_oop(oop obj) {
3351   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3352   HeapWord* addr = (HeapWord*)obj;
3353   // Check if oop points into the CMS generation
3354   // and is not marked
3355   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3356     // a white object ...
3357     // If we manage to "claim" the object, by being the
3358     // first thread to mark it, then we push it on our
3359     // marking stack
3360     if (_bit_map->par_mark(addr)) {     // ... now grey
3361       // push on work queue (grey set)
3362       bool simulate_overflow = false;
3363       NOT_PRODUCT(
3364         if (CMSMarkStackOverflowALot &&
3365             _collector->simulate_overflow()) {
3366           // simulate a stack overflow
3367           simulate_overflow = true;
3368         }
3369       )
3370       if (simulate_overflow ||
3371           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {


3373         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3374         // We cannot assert that the overflow stack is full because
3375         // it may have been emptied since.
3376         assert(simulate_overflow ||
3377                _work_queue->size() == _work_queue->max_elems(),
3378               "Else push should have succeeded");
3379         handle_stack_overflow(addr);
3380       }
3381     } // Else, some other thread got there first
3382     do_yield_check();
3383   }
3384 }
3385 
3386 void ParConcMarkingClosure::do_oop(oop* p)       { ParConcMarkingClosure::do_oop_work(p); }
3387 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); }
3388 
3389 void ParConcMarkingClosure::trim_queue(size_t max) {
3390   while (_work_queue->size() > max) {
3391     oop new_oop;
3392     if (_work_queue->pop_local(new_oop)) {
3393       assert(oopDesc::is_oop(new_oop), "Should be an oop");
3394       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3395       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3396       new_oop->oop_iterate(this);  // do_oop() above
3397       do_yield_check();
3398     }
3399   }
3400 }
3401 
3402 // Upon stack overflow, we discard (part of) the stack,
3403 // remembering the least address amongst those discarded
3404 // in CMSCollector's _restart_address.
3405 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3406   // We need to do this under a mutex to prevent other
3407   // workers from interfering with the work done below.
3408   MutexLockerEx ml(_overflow_stack->par_lock(),
3409                    Mutex::_no_safepoint_check_flag);
3410   // Remember the least grey address discarded
3411   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3412   _collector->lower_restart_addr(ra);
3413   _overflow_stack->reset();  // discard stack contents
3414   _overflow_stack->expand(); // expand the stack if possible
3415 }
3416 
3417 
3418 void CMSConcMarkingTask::do_work_steal(int i) {
3419   OopTaskQueue* work_q = work_queue(i);
3420   oop obj_to_scan;
3421   CMSBitMap* bm = &(_collector->_markBitMap);
3422   CMSMarkStack* ovflw = &(_collector->_markStack);
3423   int* seed = _collector->hash_seed(i);
3424   ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3425   while (true) {
3426     cl.trim_queue(0);
3427     assert(work_q->size() == 0, "Should have been emptied above");
3428     if (get_work_from_overflow_stack(ovflw, work_q)) {
3429       // Can't assert below because the work obtained from the
3430       // overflow stack may already have been stolen from us.
3431       // assert(work_q->size() > 0, "Work from overflow stack");
3432       continue;
3433     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3434       assert(oopDesc::is_oop(obj_to_scan), "Should be an oop");
3435       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3436       obj_to_scan->oop_iterate(&cl);
3437     } else if (terminator()->offer_termination(&_term_term)) {
3438       assert(work_q->size() == 0, "Impossible!");
3439       break;
3440     } else if (yielding() || should_yield()) {
3441       yield();
3442     }
3443   }
3444 }
3445 
3446 // This is run by the CMS (coordinator) thread.
3447 void CMSConcMarkingTask::coordinator_yield() {
3448   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3449          "CMS thread should hold CMS token");
3450   // First give up the locks, then yield, then re-lock
3451   // We should probably use a constructor/destructor idiom to
3452   // do this unlock/lock or modify the MutexUnlocker class to
3453   // serve our purpose. XXX
3454   assert_lock_strong(_bit_map_lock);


4505         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4506         start = space->bottom();
4507         end   = space->top();
4508       } else if (nth_task == 0) {
4509         start = space->bottom();
4510         end   = chunk_array[nth_task];
4511       } else if (nth_task < (uint)chunk_top) {
4512         assert(nth_task >= 1, "Control point invariant");
4513         start = chunk_array[nth_task - 1];
4514         end   = chunk_array[nth_task];
4515       } else {
4516         assert(nth_task == (uint)chunk_top, "Control point invariant");
4517         start = chunk_array[chunk_top - 1];
4518         end   = space->top();
4519       }
4520       MemRegion mr(start, end);
4521       // Verify that mr is in space
4522       assert(mr.is_empty() || space->used_region().contains(mr),
4523              "Should be in space");
4524       // Verify that "start" is an object boundary
4525       assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())),
4526              "Should be an oop");
4527       space->par_oop_iterate(mr, cl);
4528     }
4529     pst->all_tasks_completed();
4530   }
4531 }
4532 
4533 void
4534 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4535   CompactibleFreeListSpace* sp, int i,
4536   ParMarkRefsIntoAndScanClosure* cl) {
4537   // Until all tasks completed:
4538   // . claim an unclaimed task
4539   // . compute region boundaries corresponding to task claimed
4540   // . transfer dirty bits ct->mut for that region
4541   // . apply rescanclosure to dirty mut bits for that region
4542 
4543   ResourceMark rm;
4544   HandleMark   hm;
4545 


4639     // only affects the number of attempts made to get work from the
4640     // overflow list and does not affect the number of workers.  Just
4641     // pass ParallelGCThreads so this behavior is unchanged.
4642     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4643                                                 work_q,
4644                                                 ParallelGCThreads)) {
4645       // found something in global overflow list;
4646       // not yet ready to go stealing work from others.
4647       // We'd like to assert(work_q->size() != 0, ...)
4648       // because we just took work from the overflow list,
4649       // but of course we can't since all of that could have
4650       // been already stolen from us.
4651       // "He giveth and He taketh away."
4652       continue;
4653     }
4654     // Verify that we have no work before we resort to stealing
4655     assert(work_q->size() == 0, "Have work, shouldn't steal");
4656     // Try to steal from other queues that have work
4657     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4658       NOT_PRODUCT(num_steals++;)
4659       assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
4660       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4661       // Do scanning work
4662       obj_to_scan->oop_iterate(cl);
4663       // Loop around, finish this work, and try to steal some more
4664     } else if (terminator()->offer_termination()) {
4665         break;  // nirvana from the infinite cycle
4666     }
4667   }
4668   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4669   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4670          "Else our work is not yet done");
4671 }
4672 
4673 // Record object boundaries in _eden_chunk_array by sampling the eden
4674 // top in the slow-path eden object allocation code path and record
4675 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4676 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4677 // sampling in sample_eden() that activates during the part of the
4678 // preclean phase.
4679 void CMSCollector::sample_eden_chunk() {


5118     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5119     // only affects the number of attempts made to get work from the
5120     // overflow list and does not affect the number of workers.  Just
5121     // pass ParallelGCThreads so this behavior is unchanged.
5122     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5123                                                 work_q,
5124                                                 ParallelGCThreads)) {
5125       // Found something in global overflow list;
5126       // not yet ready to go stealing work from others.
5127       // We'd like to assert(work_q->size() != 0, ...)
5128       // because we just took work from the overflow list,
5129       // but of course we can't, since all of that might have
5130       // been already stolen from us.
5131       continue;
5132     }
5133     // Verify that we have no work before we resort to stealing
5134     assert(work_q->size() == 0, "Have work, shouldn't steal");
5135     // Try to steal from other queues that have work
5136     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5137       NOT_PRODUCT(num_steals++;)
5138       assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
5139       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5140       // Do scanning work
5141       obj_to_scan->oop_iterate(keep_alive);
5142       // Loop around, finish this work, and try to steal some more
5143     } else if (terminator()->offer_termination()) {
5144       break;  // nirvana from the infinite cycle
5145     }
5146   }
5147   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5148 }
5149 
5150 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5151 {
5152   GenCollectedHeap* gch = GenCollectedHeap::heap();
5153   WorkGang* workers = gch->workers();
5154   assert(workers != NULL, "Need parallel worker threads.");
5155   CMSRefProcTaskProxy rp_task(task, &_collector,
5156                               _collector.ref_processor()->span(),
5157                               _collector.markBitMap(),
5158                               workers, _collector.task_queues());


5808 // XXX: there seems to be a lot of code  duplication here;
5809 // should refactor and consolidate common code.
5810 
5811 // This closure is used to mark refs into the CMS generation in
5812 // the CMS bit map. Called at the first checkpoint. This closure
5813 // assumes that we do not need to re-mark dirty cards; if the CMS
5814 // generation on which this is used is not an oldest
5815 // generation then this will lose younger_gen cards!
5816 
5817 MarkRefsIntoClosure::MarkRefsIntoClosure(
5818   MemRegion span, CMSBitMap* bitMap):
5819     _span(span),
5820     _bitMap(bitMap)
5821 {
5822   assert(ref_processor() == NULL, "deliberately left NULL");
5823   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5824 }
5825 
5826 void MarkRefsIntoClosure::do_oop(oop obj) {
5827   // if p points into _span, then mark corresponding bit in _markBitMap
5828   assert(oopDesc::is_oop(obj), "expected an oop");
5829   HeapWord* addr = (HeapWord*)obj;
5830   if (_span.contains(addr)) {
5831     // this should be made more efficient
5832     _bitMap->mark(addr);
5833   }
5834 }
5835 
5836 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
5837 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5838 
5839 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5840   MemRegion span, CMSBitMap* bitMap):
5841     _span(span),
5842     _bitMap(bitMap)
5843 {
5844   assert(ref_processor() == NULL, "deliberately left NULL");
5845   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5846 }
5847 
5848 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5849   // if p points into _span, then mark corresponding bit in _markBitMap
5850   assert(oopDesc::is_oop(obj), "expected an oop");
5851   HeapWord* addr = (HeapWord*)obj;
5852   if (_span.contains(addr)) {
5853     // this should be made more efficient
5854     _bitMap->par_mark(addr);
5855   }
5856 }
5857 
5858 void ParMarkRefsIntoClosure::do_oop(oop* p)       { ParMarkRefsIntoClosure::do_oop_work(p); }
5859 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5860 
5861 // A variant of the above, used for CMS marking verification.
5862 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5863   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5864     _span(span),
5865     _verification_bm(verification_bm),
5866     _cms_bm(cms_bm)
5867 {
5868   assert(ref_processor() == NULL, "deliberately left NULL");
5869   assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5870 }
5871 
5872 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5873   // if p points into _span, then mark corresponding bit in _markBitMap
5874   assert(oopDesc::is_oop(obj), "expected an oop");
5875   HeapWord* addr = (HeapWord*)obj;
5876   if (_span.contains(addr)) {
5877     _verification_bm->mark(addr);
5878     if (!_cms_bm->isMarked(addr)) {
5879       Log(gc, verify) log;
5880       ResourceMark rm;
5881       LogStream ls(log.error());
5882       oop(addr)->print_on(&ls);
5883       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5884       fatal("... aborting");
5885     }
5886   }
5887 }
5888 
5889 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5890 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5891 
5892 //////////////////////////////////////////////////
5893 // MarkRefsIntoAndScanClosure
5894 //////////////////////////////////////////////////


5908   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
5909                       mark_stack, concurrent_precleaning),
5910   _yield(should_yield),
5911   _concurrent_precleaning(concurrent_precleaning),
5912   _freelistLock(NULL)
5913 {
5914   // FIXME: Should initialize in base class constructor.
5915   assert(rp != NULL, "ref_processor shouldn't be NULL");
5916   set_ref_processor_internal(rp);
5917 }
5918 
5919 // This closure is used to mark refs into the CMS generation at the
5920 // second (final) checkpoint, and to scan and transitively follow
5921 // the unmarked oops. It is also used during the concurrent precleaning
5922 // phase while scanning objects on dirty cards in the CMS generation.
5923 // The marks are made in the marking bit map and the marking stack is
5924 // used for keeping the (newly) grey objects during the scan.
5925 // The parallel version (Par_...) appears further below.
5926 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5927   if (obj != NULL) {
5928     assert(oopDesc::is_oop(obj), "expected an oop");
5929     HeapWord* addr = (HeapWord*)obj;
5930     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5931     assert(_collector->overflow_list_is_empty(),
5932            "overflow list should be empty");
5933     if (_span.contains(addr) &&
5934         !_bit_map->isMarked(addr)) {
5935       // mark bit map (object is now grey)
5936       _bit_map->mark(addr);
5937       // push on marking stack (stack should be empty), and drain the
5938       // stack by applying this closure to the oops in the oops popped
5939       // from the stack (i.e. blacken the grey objects)
5940       bool res = _mark_stack->push(obj);
5941       assert(res, "Should have space to push on empty stack");
5942       do {
5943         oop new_oop = _mark_stack->pop();
5944         assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
5945         assert(_bit_map->isMarked((HeapWord*)new_oop),
5946                "only grey objects on this stack");
5947         // iterate over the oops in this oop, marking and pushing
5948         // the ones in CMS heap (i.e. in _span).
5949         new_oop->oop_iterate(&_pushAndMarkClosure);
5950         // check if it's time to yield
5951         do_yield_check();
5952       } while (!_mark_stack->isEmpty() ||
5953                (!_concurrent_precleaning && take_from_overflow_list()));
5954         // if marking stack is empty, and we are not doing this
5955         // during precleaning, then check the overflow list
5956     }
5957     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5958     assert(_collector->overflow_list_is_empty(),
5959            "overflow list was drained above");
5960 
5961     assert(_collector->no_preserved_marks(),
5962            "All preserved marks should have been restored above");
5963   }
5964 }


6006   _low_water_mark(MIN2((work_queue->max_elems()/4),
6007                        ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6008   _parPushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6009 {
6010   // FIXME: Should initialize in base class constructor.
6011   assert(rp != NULL, "ref_processor shouldn't be NULL");
6012   set_ref_processor_internal(rp);
6013 }
6014 
6015 // This closure is used to mark refs into the CMS generation at the
6016 // second (final) checkpoint, and to scan and transitively follow
6017 // the unmarked oops. The marks are made in the marking bit map and
6018 // the work_queue is used for keeping the (newly) grey objects during
6019 // the scan phase whence they are also available for stealing by parallel
6020 // threads. Since the marking bit map is shared, updates are
6021 // synchronized (via CAS).
6022 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6023   if (obj != NULL) {
6024     // Ignore mark word because this could be an already marked oop
6025     // that may be chained at the end of the overflow list.
6026     assert(oopDesc::is_oop(obj, true), "expected an oop");
6027     HeapWord* addr = (HeapWord*)obj;
6028     if (_span.contains(addr) &&
6029         !_bit_map->isMarked(addr)) {
6030       // mark bit map (object will become grey):
6031       // It is possible for several threads to be
6032       // trying to "claim" this object concurrently;
6033       // the unique thread that succeeds in marking the
6034       // object first will do the subsequent push on
6035       // to the work queue (or overflow list).
6036       if (_bit_map->par_mark(addr)) {
6037         // push on work_queue (which may not be empty), and trim the
6038         // queue to an appropriate length by applying this closure to
6039         // the oops in the oops popped from the stack (i.e. blacken the
6040         // grey objects)
6041         bool res = _work_queue->push(obj);
6042         assert(res, "Low water mark should be less than capacity?");
6043         trim_queue(_low_water_mark);
6044       } // Else, another thread claimed the object
6045     }
6046   }


6052 // This closure is used to rescan the marked objects on the dirty cards
6053 // in the mod union table and the card table proper.
6054 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6055   oop p, MemRegion mr) {
6056 
6057   size_t size = 0;
6058   HeapWord* addr = (HeapWord*)p;
6059   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6060   assert(_span.contains(addr), "we are scanning the CMS generation");
6061   // check if it's time to yield
6062   if (do_yield_check()) {
6063     // We yielded for some foreground stop-world work,
6064     // and we have been asked to abort this ongoing preclean cycle.
6065     return 0;
6066   }
6067   if (_bitMap->isMarked(addr)) {
6068     // it's marked; is it potentially uninitialized?
6069     if (p->klass_or_null_acquire() != NULL) {
6070         // an initialized object; ignore mark word in verification below
6071         // since we are running concurrent with mutators
6072         assert(oopDesc::is_oop(p, true), "should be an oop");
6073         if (p->is_objArray()) {
6074           // objArrays are precisely marked; restrict scanning
6075           // to dirty cards only.
6076           size = CompactibleFreeListSpace::adjustObjectSize(
6077                    p->oop_iterate_size(_scanningClosure, mr));
6078         } else {
6079           // A non-array may have been imprecisely marked; we need
6080           // to scan object in its entirety.
6081           size = CompactibleFreeListSpace::adjustObjectSize(
6082                    p->oop_iterate_size(_scanningClosure));
6083         }
6084       #ifdef ASSERT
6085         size_t direct_size =
6086           CompactibleFreeListSpace::adjustObjectSize(p->size());
6087         assert(size == direct_size, "Inconsistency in size");
6088         assert(size >= 3, "Necessary for Printezis marks to work");
6089         HeapWord* start_pbit = addr + 1;
6090         HeapWord* end_pbit = addr + size - 1;
6091         assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6092                "inconsistent Printezis mark");


6101     } else {
6102       // An uninitialized object.
6103       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6104       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6105       size = pointer_delta(nextOneAddr + 1, addr);
6106       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6107              "alignment problem");
6108       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6109       // will dirty the card when the klass pointer is installed in the
6110       // object (signaling the completion of initialization).
6111     }
6112   } else {
6113     // Either a not yet marked object or an uninitialized object
6114     if (p->klass_or_null_acquire() == NULL) {
6115       // An uninitialized object, skip to the next card, since
6116       // we may not be able to read its P-bits yet.
6117       assert(size == 0, "Initial value");
6118     } else {
6119       // An object not (yet) reached by marking: we merely need to
6120       // compute its size so as to go look at the next block.
6121       assert(oopDesc::is_oop(p, true), "should be an oop");
6122       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6123     }
6124   }
6125   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6126   return size;
6127 }
6128 
6129 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6130   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6131          "CMS thread should hold CMS token");
6132   assert_lock_strong(_freelistLock);
6133   assert_lock_strong(_bitMap->lock());
6134   // relinquish the free_list_lock and bitMaplock()
6135   _bitMap->lock()->unlock();
6136   _freelistLock->unlock();
6137   ConcurrentMarkSweepThread::desynchronize(true);
6138   _collector->stopTimer();
6139   _collector->incrementYields();
6140 
6141   // See the comment in coordinator_yield()


6148   ConcurrentMarkSweepThread::synchronize(true);
6149   _freelistLock->lock_without_safepoint_check();
6150   _bitMap->lock()->lock_without_safepoint_check();
6151   _collector->startTimer();
6152 }
6153 
6154 
6155 //////////////////////////////////////////////////////////////////
6156 // SurvivorSpacePrecleanClosure
6157 //////////////////////////////////////////////////////////////////
6158 // This (single-threaded) closure is used to preclean the oops in
6159 // the survivor spaces.
6160 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6161 
6162   HeapWord* addr = (HeapWord*)p;
6163   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6164   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6165   assert(p->klass_or_null() != NULL, "object should be initialized");
6166   // an initialized object; ignore mark word in verification below
6167   // since we are running concurrent with mutators
6168   assert(oopDesc::is_oop(p, true), "should be an oop");
6169   // Note that we do not yield while we iterate over
6170   // the interior oops of p, pushing the relevant ones
6171   // on our marking stack.
6172   size_t size = p->oop_iterate_size(_scanning_closure);
6173   do_yield_check();
6174   // Observe that below, we do not abandon the preclean
6175   // phase as soon as we should; rather we empty the
6176   // marking stack before returning. This is to satisfy
6177   // some existing assertions. In general, it may be a
6178   // good idea to abort immediately and complete the marking
6179   // from the grey objects at a later time.
6180   while (!_mark_stack->isEmpty()) {
6181     oop new_oop = _mark_stack->pop();
6182     assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
6183     assert(_bit_map->isMarked((HeapWord*)new_oop),
6184            "only grey objects on this stack");
6185     // iterate over the oops in this oop, marking and pushing
6186     // the ones in CMS heap (i.e. in _span).
6187     new_oop->oop_iterate(_scanning_closure);
6188     // check if it's time to yield
6189     do_yield_check();
6190   }
6191   unsigned int after_count =
6192     GenCollectedHeap::heap()->total_collections();
6193   bool abort = (_before_count != after_count) ||
6194                _collector->should_abort_preclean();
6195   return abort ? 0 : size;
6196 }
6197 
6198 void SurvivorSpacePrecleanClosure::do_yield_work() {
6199   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6200          "CMS thread should hold CMS token");
6201   assert_lock_strong(_bit_map->lock());
6202   // Relinquish the bit map lock


6206   _collector->incrementYields();
6207 
6208   // See the comment in coordinator_yield()
6209   for (unsigned i = 0; i < CMSYieldSleepCount &&
6210                        ConcurrentMarkSweepThread::should_yield() &&
6211                        !CMSCollector::foregroundGCIsActive(); ++i) {
6212     os::sleep(Thread::current(), 1, false);
6213   }
6214 
6215   ConcurrentMarkSweepThread::synchronize(true);
6216   _bit_map->lock()->lock_without_safepoint_check();
6217   _collector->startTimer();
6218 }
6219 
6220 // This closure is used to rescan the marked objects on the dirty cards
6221 // in the mod union table and the card table proper. In the parallel
6222 // case, although the bitMap is shared, we do a single read so the
6223 // isMarked() query is "safe".
6224 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6225   // Ignore mark word because we are running concurrent with mutators
6226   assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6227   HeapWord* addr = (HeapWord*)p;
6228   assert(_span.contains(addr), "we are scanning the CMS generation");
6229   bool is_obj_array = false;
6230   #ifdef ASSERT
6231     if (!_parallel) {
6232       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6233       assert(_collector->overflow_list_is_empty(),
6234              "overflow list should be empty");
6235 
6236     }
6237   #endif // ASSERT
6238   if (_bit_map->isMarked(addr)) {
6239     // Obj arrays are precisely marked, non-arrays are not;
6240     // so we scan objArrays precisely and non-arrays in their
6241     // entirety.
6242     if (p->is_objArray()) {
6243       is_obj_array = true;
6244       if (_parallel) {
6245         p->oop_iterate(_par_scan_closure, mr);
6246       } else {


6359   // See the comment in coordinator_yield()
6360   for (unsigned i = 0; i < CMSYieldSleepCount &&
6361                        ConcurrentMarkSweepThread::should_yield() &&
6362                        !CMSCollector::foregroundGCIsActive(); ++i) {
6363     os::sleep(Thread::current(), 1, false);
6364   }
6365 
6366   ConcurrentMarkSweepThread::synchronize(true);
6367   _bitMap->lock()->lock_without_safepoint_check();
6368   _collector->startTimer();
6369 }
6370 
6371 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6372   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6373   assert(_markStack->isEmpty(),
6374          "should drain stack to limit stack usage");
6375   // convert ptr to an oop preparatory to scanning
6376   oop obj = oop(ptr);
6377   // Ignore mark word in verification below, since we
6378   // may be running concurrent with mutators.
6379   assert(oopDesc::is_oop(obj, true), "should be an oop");
6380   assert(_finger <= ptr, "_finger runneth ahead");
6381   // advance the finger to right end of this object
6382   _finger = ptr + obj->size();
6383   assert(_finger > ptr, "we just incremented it above");
6384   // On large heaps, it may take us some time to get through
6385   // the marking phase. During
6386   // this time it's possible that a lot of mutations have
6387   // accumulated in the card table and the mod union table --
6388   // these mutation records are redundant until we have
6389   // actually traced into the corresponding card.
6390   // Here, we check whether advancing the finger would make
6391   // us cross into a new card, and if so clear corresponding
6392   // cards in the MUT (preclean them in the card-table in the
6393   // future).
6394 
6395   DEBUG_ONLY(if (!_verifying) {)
6396     // The clean-on-enter optimization is disabled by default,
6397     // until we fix 6178663.
6398     if (CMSCleanOnEnter && (_finger > _threshold)) {
6399       // [_threshold, _finger) represents the interval


6406       assert(is_aligned(old_threshold, CardTableModRefBS::card_size),
6407              "_threshold should always be card-aligned");
6408       _threshold = align_up(_finger, CardTableModRefBS::card_size);
6409       MemRegion mr(old_threshold, _threshold);
6410       assert(!mr.is_empty(), "Control point invariant");
6411       assert(_span.contains(mr), "Should clear within span");
6412       _mut->clear_range(mr);
6413     }
6414   DEBUG_ONLY(})
6415   // Note: the finger doesn't advance while we drain
6416   // the stack below.
6417   PushOrMarkClosure pushOrMarkClosure(_collector,
6418                                       _span, _bitMap, _markStack,
6419                                       _finger, this);
6420   bool res = _markStack->push(obj);
6421   assert(res, "Empty non-zero size stack should have space for single push");
6422   while (!_markStack->isEmpty()) {
6423     oop new_oop = _markStack->pop();
6424     // Skip verifying header mark word below because we are
6425     // running concurrent with mutators.
6426     assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6427     // now scan this oop's oops
6428     new_oop->oop_iterate(&pushOrMarkClosure);
6429     do_yield_check();
6430   }
6431   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6432 }
6433 
6434 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6435                        CMSCollector* collector, MemRegion span,
6436                        CMSBitMap* bit_map,
6437                        OopTaskQueue* work_queue,
6438                        CMSMarkStack*  overflow_stack):
6439   _collector(collector),
6440   _whole_span(collector->_span),
6441   _span(span),
6442   _bit_map(bit_map),
6443   _mut(&collector->_modUnionTable),
6444   _work_queue(work_queue),
6445   _overflow_stack(overflow_stack),
6446   _skip_bits(0),


6472     if (p->klass_or_null_acquire() == NULL) {
6473       // in the case of Clean-on-Enter optimization, redirty card
6474       // and avoid clearing card by increasing  the threshold.
6475       return true;
6476     }
6477   }
6478   scan_oops_in_oop(addr);
6479   return true;
6480 }
6481 
6482 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6483   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6484   // Should we assert that our work queue is empty or
6485   // below some drain limit?
6486   assert(_work_queue->size() == 0,
6487          "should drain stack to limit stack usage");
6488   // convert ptr to an oop preparatory to scanning
6489   oop obj = oop(ptr);
6490   // Ignore mark word in verification below, since we
6491   // may be running concurrent with mutators.
6492   assert(oopDesc::is_oop(obj, true), "should be an oop");
6493   assert(_finger <= ptr, "_finger runneth ahead");
6494   // advance the finger to right end of this object
6495   _finger = ptr + obj->size();
6496   assert(_finger > ptr, "we just incremented it above");
6497   // On large heaps, it may take us some time to get through
6498   // the marking phase. During
6499   // this time it's possible that a lot of mutations have
6500   // accumulated in the card table and the mod union table --
6501   // these mutation records are redundant until we have
6502   // actually traced into the corresponding card.
6503   // Here, we check whether advancing the finger would make
6504   // us cross into a new card, and if so clear corresponding
6505   // cards in the MUT (preclean them in the card-table in the
6506   // future).
6507 
6508   // The clean-on-enter optimization is disabled by default,
6509   // until we fix 6178663.
6510   if (CMSCleanOnEnter && (_finger > _threshold)) {
6511     // [_threshold, _finger) represents the interval
6512     // of cards to be cleared  in MUT (or precleaned in card table).


6533                                          _overflow_stack,
6534                                          _finger,
6535                                          gfa, this);
6536   bool res = _work_queue->push(obj);   // overflow could occur here
6537   assert(res, "Will hold once we use workqueues");
6538   while (true) {
6539     oop new_oop;
6540     if (!_work_queue->pop_local(new_oop)) {
6541       // We emptied our work_queue; check if there's stuff that can
6542       // be gotten from the overflow stack.
6543       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6544             _overflow_stack, _work_queue)) {
6545         do_yield_check();
6546         continue;
6547       } else {  // done
6548         break;
6549       }
6550     }
6551     // Skip verifying header mark word below because we are
6552     // running concurrent with mutators.
6553     assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6554     // now scan this oop's oops
6555     new_oop->oop_iterate(&pushOrMarkClosure);
6556     do_yield_check();
6557   }
6558   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6559 }
6560 
6561 // Yield in response to a request from VM Thread or
6562 // from mutators.
6563 void ParMarkFromRootsClosure::do_yield_work() {
6564   assert(_task != NULL, "sanity");
6565   _task->yield();
6566 }
6567 
6568 // A variant of the above used for verifying CMS marking work.
6569 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6570                         MemRegion span,
6571                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6572                         CMSMarkStack*  mark_stack):
6573   _collector(collector),


6587 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6588   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6589   assert(_span.contains(addr), "Out of bounds _finger?");
6590   _finger = addr;
6591 }
6592 
6593 // Should revisit to see if this should be restructured for
6594 // greater efficiency.
6595 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6596   // convert offset into a HeapWord*
6597   HeapWord* addr = _verification_bm->startWord() + offset;
6598   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6599          "address out of range");
6600   assert(_verification_bm->isMarked(addr), "tautology");
6601   assert(_cms_bm->isMarked(addr), "tautology");
6602 
6603   assert(_mark_stack->isEmpty(),
6604          "should drain stack to limit stack usage");
6605   // convert addr to an oop preparatory to scanning
6606   oop obj = oop(addr);
6607   assert(oopDesc::is_oop(obj), "should be an oop");
6608   assert(_finger <= addr, "_finger runneth ahead");
6609   // advance the finger to right end of this object
6610   _finger = addr + obj->size();
6611   assert(_finger > addr, "we just incremented it above");
6612   // Note: the finger doesn't advance while we drain
6613   // the stack below.
6614   bool res = _mark_stack->push(obj);
6615   assert(res, "Empty non-zero size stack should have space for single push");
6616   while (!_mark_stack->isEmpty()) {
6617     oop new_oop = _mark_stack->pop();
6618     assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop");
6619     // now scan this oop's oops
6620     new_oop->oop_iterate(&_pam_verify_closure);
6621   }
6622   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6623   return true;
6624 }
6625 
6626 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6627   CMSCollector* collector, MemRegion span,
6628   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6629   CMSMarkStack*  mark_stack):
6630   MetadataAwareOopClosure(collector->ref_processor()),
6631   _collector(collector),
6632   _span(span),
6633   _verification_bm(verification_bm),
6634   _cms_bm(cms_bm),
6635   _mark_stack(mark_stack)
6636 { }
6637 
6638 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6639 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6640 
6641 // Upon stack overflow, we discard (part of) the stack,
6642 // remembering the least address amongst those discarded
6643 // in CMSCollector's _restart_address.
6644 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6645   // Remember the least grey address discarded
6646   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6647   _collector->lower_restart_addr(ra);
6648   _mark_stack->reset();  // discard stack contents
6649   _mark_stack->expand(); // expand the stack if possible
6650 }
6651 
6652 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6653   assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6654   HeapWord* addr = (HeapWord*)obj;
6655   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6656     // Oop lies in _span and isn't yet grey or black
6657     _verification_bm->mark(addr);            // now grey
6658     if (!_cms_bm->isMarked(addr)) {
6659       Log(gc, verify) log;
6660       ResourceMark rm;
6661       LogStream ls(log.error());
6662       oop(addr)->print_on(&ls);
6663       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6664       fatal("... aborting");
6665     }
6666 
6667     if (!_mark_stack->push(obj)) { // stack overflow
6668       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6669       assert(_mark_stack->isFull(), "Else push should have succeeded");
6670       handle_stack_overflow(addr);
6671     }
6672     // anything including and to the right of _finger
6673     // will be scanned as we iterate over the remainder of the


6730   _markStack->expand(); // expand the stack if possible
6731 }
6732 
6733 // Upon stack overflow, we discard (part of) the stack,
6734 // remembering the least address amongst those discarded
6735 // in CMSCollector's _restart_address.
6736 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6737   // We need to do this under a mutex to prevent other
6738   // workers from interfering with the work done below.
6739   MutexLockerEx ml(_overflow_stack->par_lock(),
6740                    Mutex::_no_safepoint_check_flag);
6741   // Remember the least grey address discarded
6742   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6743   _collector->lower_restart_addr(ra);
6744   _overflow_stack->reset();  // discard stack contents
6745   _overflow_stack->expand(); // expand the stack if possible
6746 }
6747 
6748 void PushOrMarkClosure::do_oop(oop obj) {
6749   // Ignore mark word because we are running concurrent with mutators.
6750   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6751   HeapWord* addr = (HeapWord*)obj;
6752   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6753     // Oop lies in _span and isn't yet grey or black
6754     _bitMap->mark(addr);            // now grey
6755     if (addr < _finger) {
6756       // the bit map iteration has already either passed, or
6757       // sampled, this bit in the bit map; we'll need to
6758       // use the marking stack to scan this oop's oops.
6759       bool simulate_overflow = false;
6760       NOT_PRODUCT(
6761         if (CMSMarkStackOverflowALot &&
6762             _collector->simulate_overflow()) {
6763           // simulate a stack overflow
6764           simulate_overflow = true;
6765         }
6766       )
6767       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6768         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6769         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6770         handle_stack_overflow(addr);
6771       }
6772     }
6773     // anything including and to the right of _finger
6774     // will be scanned as we iterate over the remainder of the
6775     // bit map
6776     do_yield_check();
6777   }
6778 }
6779 
6780 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
6781 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6782 
6783 void ParPushOrMarkClosure::do_oop(oop obj) {
6784   // Ignore mark word because we are running concurrent with mutators.
6785   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6786   HeapWord* addr = (HeapWord*)obj;
6787   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6788     // Oop lies in _span and isn't yet grey or black
6789     // We read the global_finger (volatile read) strictly after marking oop
6790     bool res = _bit_map->par_mark(addr);    // now grey
6791     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6792     // Should we push this marked oop on our stack?
6793     // -- if someone else marked it, nothing to do
6794     // -- if target oop is above global finger nothing to do
6795     // -- if target oop is in chunk and above local finger
6796     //      then nothing to do
6797     // -- else push on work queue
6798     if (   !res       // someone else marked it, they will deal with it
6799         || (addr >= *gfa)  // will be scanned in a later task
6800         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6801       return;
6802     }
6803     // the bit map iteration has already either passed, or
6804     // sampled, this bit in the bit map; we'll need to
6805     // use the marking stack to scan this oop's oops.


6838                                        bool           concurrent_precleaning):
6839   MetadataAwareOopClosure(rp),
6840   _collector(collector),
6841   _span(span),
6842   _bit_map(bit_map),
6843   _mod_union_table(mod_union_table),
6844   _mark_stack(mark_stack),
6845   _concurrent_precleaning(concurrent_precleaning)
6846 {
6847   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6848 }
6849 
6850 // Grey object rescan during pre-cleaning and second checkpoint phases --
6851 // the non-parallel version (the parallel version appears further below.)
6852 void PushAndMarkClosure::do_oop(oop obj) {
6853   // Ignore mark word verification. If during concurrent precleaning,
6854   // the object monitor may be locked. If during the checkpoint
6855   // phases, the object may already have been reached by a  different
6856   // path and may be at the end of the global overflow list (so
6857   // the mark word may be NULL).
6858   assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */),
6859          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6860   HeapWord* addr = (HeapWord*)obj;
6861   // Check if oop points into the CMS generation
6862   // and is not marked
6863   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6864     // a white object ...
6865     _bit_map->mark(addr);         // ... now grey
6866     // push on the marking stack (grey set)
6867     bool simulate_overflow = false;
6868     NOT_PRODUCT(
6869       if (CMSMarkStackOverflowALot &&
6870           _collector->simulate_overflow()) {
6871         // simulate a stack overflow
6872         simulate_overflow = true;
6873       }
6874     )
6875     if (simulate_overflow || !_mark_stack->push(obj)) {
6876       if (_concurrent_precleaning) {
6877          // During precleaning we can just dirty the appropriate card(s)
6878          // in the mod union table, thus ensuring that the object remains


6917   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6918 }
6919 
6920 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
6921 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6922 
6923 // Grey object rescan during second checkpoint phase --
6924 // the parallel version.
6925 void ParPushAndMarkClosure::do_oop(oop obj) {
6926   // In the assert below, we ignore the mark word because
6927   // this oop may point to an already visited object that is
6928   // on the overflow stack (in which case the mark word has
6929   // been hijacked for chaining into the overflow stack --
6930   // if this is the last object in the overflow stack then
6931   // its mark word will be NULL). Because this object may
6932   // have been subsequently popped off the global overflow
6933   // stack, and the mark word possibly restored to the prototypical
6934   // value, by the time we get to examined this failing assert in
6935   // the debugger, is_oop_or_null(false) may subsequently start
6936   // to hold.
6937   assert(oopDesc::is_oop_or_null(obj, true),
6938          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6939   HeapWord* addr = (HeapWord*)obj;
6940   // Check if oop points into the CMS generation
6941   // and is not marked
6942   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6943     // a white object ...
6944     // If we manage to "claim" the object, by being the
6945     // first thread to mark it, then we push it on our
6946     // marking stack
6947     if (_bit_map->par_mark(addr)) {     // ... now grey
6948       // push on work queue (grey set)
6949       bool simulate_overflow = false;
6950       NOT_PRODUCT(
6951         if (CMSMarkStackOverflowALot &&
6952             _collector->par_simulate_overflow()) {
6953           // simulate a stack overflow
6954           simulate_overflow = true;
6955         }
6956       )
6957       if (simulate_overflow || !_work_queue->push(obj)) {


7308   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7309   do_post_free_or_garbage_chunk(fc, size);
7310 
7311   assert(_limit >= addr + size,
7312          "A freshly garbage chunk can't possibly straddle over _limit");
7313   if (inFreeRange()) lookahead_and_flush(fc, size);
7314   return size;
7315 }
7316 
7317 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7318   HeapWord* addr = (HeapWord*) fc;
7319   // The sweeper has just found a live object. Return any accumulated
7320   // left hand chunk to the free lists.
7321   if (inFreeRange()) {
7322     assert(freeFinger() < addr, "freeFinger points too high");
7323     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7324   }
7325 
7326   // This object is live: we'd normally expect this to be
7327   // an oop, and like to assert the following:
7328   // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop");
7329   // However, as we commented above, this may be an object whose
7330   // header hasn't yet been initialized.
7331   size_t size;
7332   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7333   if (_bitMap->isMarked(addr + 1)) {
7334     // Determine the size from the bit map, rather than trying to
7335     // compute it from the object header.
7336     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7337     size = pointer_delta(nextOneAddr + 1, addr);
7338     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7339            "alignment problem");
7340 
7341 #ifdef ASSERT
7342       if (oop(addr)->klass_or_null_acquire() != NULL) {
7343         // Ignore mark word because we are running concurrent with mutators
7344         assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7345         assert(size ==
7346                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7347                "P-mark and computed size do not agree");
7348       }
7349 #endif
7350 
7351   } else {
7352     // This should be an initialized object that's alive.
7353     assert(oop(addr)->klass_or_null_acquire() != NULL,
7354            "Should be an initialized object");
7355     // Ignore mark word because we are running concurrent with mutators
7356     assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7357     // Verify that the bit map has no bits marked between
7358     // addr and purported end of this block.
7359     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7360     assert(size >= 3, "Necessary for Printezis marks to work");
7361     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7362     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7363   }
7364   return size;
7365 }
7366 
7367 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7368                                                  size_t chunkSize) {
7369   // do_post_free_or_garbage_chunk() should only be called in the case
7370   // of the adaptive free list allocator.
7371   const bool fcInFreeLists = fc->is_free();
7372   assert((HeapWord*)fc <= _limit, "sweep invariant");
7373   if (CMSTestInFreeList && fcInFreeLists) {
7374     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7375   }
7376 


7644     // In general, during recursive tracing, several threads
7645     // may be concurrently getting here; the first one to
7646     // "tag" it, claims it.
7647     if (_bit_map->par_mark(addr)) {
7648       bool res = _work_queue->push(obj);
7649       assert(res, "Low water mark should be much less than capacity");
7650       // Do a recursive trim in the hope that this will keep
7651       // stack usage lower, but leave some oops for potential stealers
7652       trim_queue(_low_water_mark);
7653     } // Else, another thread got there first
7654   }
7655 }
7656 
7657 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
7658 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7659 
7660 void CMSParKeepAliveClosure::trim_queue(uint max) {
7661   while (_work_queue->size() > max) {
7662     oop new_oop;
7663     if (_work_queue->pop_local(new_oop)) {
7664       assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
7665       assert(_bit_map->isMarked((HeapWord*)new_oop),
7666              "no white objects on this stack!");
7667       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7668       // iterate over the oops in this oop, marking and pushing
7669       // the ones in CMS heap (i.e. in _span).
7670       new_oop->oop_iterate(&_mark_and_push);
7671     }
7672   }
7673 }
7674 
7675 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7676                                 CMSCollector* collector,
7677                                 MemRegion span, CMSBitMap* bit_map,
7678                                 OopTaskQueue* work_queue):
7679   _collector(collector),
7680   _span(span),
7681   _bit_map(bit_map),
7682   _work_queue(work_queue) { }
7683 
7684 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {


7724       return "Par Spooling Space";
7725     case _adaptive_size_policy:
7726       return "Ergonomics";
7727     default:
7728       return "unknown";
7729   }
7730 }
7731 
7732 void CMSDrainMarkingStackClosure::do_void() {
7733   // the max number to take from overflow list at a time
7734   const size_t num = _mark_stack->capacity()/4;
7735   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7736          "Overflow list should be NULL during concurrent phases");
7737   while (!_mark_stack->isEmpty() ||
7738          // if stack is empty, check the overflow list
7739          _collector->take_from_overflow_list(num, _mark_stack)) {
7740     oop obj = _mark_stack->pop();
7741     HeapWord* addr = (HeapWord*)obj;
7742     assert(_span.contains(addr), "Should be within span");
7743     assert(_bit_map->isMarked(addr), "Should be marked");
7744     assert(oopDesc::is_oop(obj), "Should be an oop");
7745     obj->oop_iterate(_keep_alive);
7746   }
7747 }
7748 
7749 void CMSParDrainMarkingStackClosure::do_void() {
7750   // drain queue
7751   trim_queue(0);
7752 }
7753 
7754 // Trim our work_queue so its length is below max at return
7755 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7756   while (_work_queue->size() > max) {
7757     oop new_oop;
7758     if (_work_queue->pop_local(new_oop)) {
7759       assert(oopDesc::is_oop(new_oop), "Expected an oop");
7760       assert(_bit_map->isMarked((HeapWord*)new_oop),
7761              "no white objects on this stack!");
7762       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7763       // iterate over the oops in this oop, marking and pushing
7764       // the ones in CMS heap (i.e. in _span).
7765       new_oop->oop_iterate(&_mark_and_push);
7766     }
7767   }
7768 }
7769 
7770 ////////////////////////////////////////////////////////////////////
7771 // Support for Marking Stack Overflow list handling and related code
7772 ////////////////////////////////////////////////////////////////////
7773 // Much of the following code is similar in shape and spirit to the
7774 // code used in ParNewGC. We should try and share that code
7775 // as much as possible in the future.
7776 
7777 #ifndef PRODUCT
7778 // Debugging support for CMSStackOverflowALot
7779 


7790     return false;
7791   }
7792 }
7793 
7794 bool CMSCollector::par_simulate_overflow() {
7795   return simulate_overflow();
7796 }
7797 #endif
7798 
7799 // Single-threaded
7800 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7801   assert(stack->isEmpty(), "Expected precondition");
7802   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7803   size_t i = num;
7804   oop  cur = _overflow_list;
7805   const markOop proto = markOopDesc::prototype();
7806   NOT_PRODUCT(ssize_t n = 0;)
7807   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7808     next = oop(cur->mark());
7809     cur->set_mark(proto);   // until proven otherwise
7810     assert(oopDesc::is_oop(cur), "Should be an oop");
7811     bool res = stack->push(cur);
7812     assert(res, "Bit off more than can chew?");
7813     NOT_PRODUCT(n++;)
7814   }
7815   _overflow_list = cur;
7816 #ifndef PRODUCT
7817   assert(_num_par_pushes >= n, "Too many pops?");
7818   _num_par_pushes -=n;
7819 #endif
7820   return !stack->isEmpty();
7821 }
7822 
7823 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
7824 // (MT-safe) Get a prefix of at most "num" from the list.
7825 // The overflow list is chained through the mark word of
7826 // each object in the list. We fetch the entire list,
7827 // break off a prefix of the right size and return the
7828 // remainder. If other threads try to take objects from
7829 // the overflow list at that time, they will wait for
7830 // some time to see if data becomes available. If (and


7934           suffix_tail->set_mark(markOop(cur_overflow_list));
7935         } else { // cur_overflow_list == BUSY
7936           suffix_tail->set_mark(NULL);
7937         }
7938         // ... and try to place spliced list back on overflow_list ...
7939         observed_overflow_list =
7940           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7941       } while (cur_overflow_list != observed_overflow_list);
7942       // ... until we have succeeded in doing so.
7943     }
7944   }
7945 
7946   // Push the prefix elements on work_q
7947   assert(prefix != NULL, "control point invariant");
7948   const markOop proto = markOopDesc::prototype();
7949   oop next;
7950   NOT_PRODUCT(ssize_t n = 0;)
7951   for (cur = prefix; cur != NULL; cur = next) {
7952     next = oop(cur->mark());
7953     cur->set_mark(proto);   // until proven otherwise
7954     assert(oopDesc::is_oop(cur), "Should be an oop");
7955     bool res = work_q->push(cur);
7956     assert(res, "Bit off more than we can chew?");
7957     NOT_PRODUCT(n++;)
7958   }
7959 #ifndef PRODUCT
7960   assert(_num_par_pushes >= n, "Too many pops?");
7961   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
7962 #endif
7963   return true;
7964 }
7965 
7966 // Single-threaded
7967 void CMSCollector::push_on_overflow_list(oop p) {
7968   NOT_PRODUCT(_num_par_pushes++;)
7969   assert(oopDesc::is_oop(p), "Not an oop");
7970   preserve_mark_if_necessary(p);
7971   p->set_mark((markOop)_overflow_list);
7972   _overflow_list = p;
7973 }
7974 
7975 // Multi-threaded; use CAS to prepend to overflow list
7976 void CMSCollector::par_push_on_overflow_list(oop p) {
7977   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
7978   assert(oopDesc::is_oop(p), "Not an oop");
7979   par_preserve_mark_if_necessary(p);
7980   oop observed_overflow_list = _overflow_list;
7981   oop cur_overflow_list;
7982   do {
7983     cur_overflow_list = observed_overflow_list;
7984     if (cur_overflow_list != BUSY) {
7985       p->set_mark(markOop(cur_overflow_list));
7986     } else {
7987       p->set_mark(NULL);
7988     }
7989     observed_overflow_list =
7990       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
7991   } while (cur_overflow_list != observed_overflow_list);
7992 }
7993 #undef BUSY
7994 
7995 // Single threaded
7996 // General Note on GrowableArray: pushes may silently fail
7997 // because we are (temporarily) out of C-heap for expanding
7998 // the stack. The problem is quite ubiquitous and affects


8045 // until all work's been completed. Because we
8046 // expect the preserved oop stack (set) to be small,
8047 // it's probably fine to do this single-threaded.
8048 // We can explore cleverer concurrent/overlapped/parallel
8049 // processing of preserved marks if we feel the
8050 // need for this in the future. Stack overflow should
8051 // be so rare in practice and, when it happens, its
8052 // effect on performance so great that this will
8053 // likely just be in the noise anyway.
8054 void CMSCollector::restore_preserved_marks_if_any() {
8055   assert(SafepointSynchronize::is_at_safepoint(),
8056          "world should be stopped");
8057   assert(Thread::current()->is_ConcurrentGC_thread() ||
8058          Thread::current()->is_VM_thread(),
8059          "should be single-threaded");
8060   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8061          "bijection");
8062 
8063   while (!_preserved_oop_stack.is_empty()) {
8064     oop p = _preserved_oop_stack.pop();
8065     assert(oopDesc::is_oop(p), "Should be an oop");
8066     assert(_span.contains(p), "oop should be in _span");
8067     assert(p->mark() == markOopDesc::prototype(),
8068            "Set when taken from overflow list");
8069     markOop m = _preserved_mark_stack.pop();
8070     p->set_mark(m);
8071   }
8072   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8073          "stacks were cleared above");
8074 }
8075 
8076 #ifndef PRODUCT
8077 bool CMSCollector::no_preserved_marks() const {
8078   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8079 }
8080 #endif
8081 
8082 // Transfer some number of overflown objects to usual marking
8083 // stack. Return true if some objects were transferred.
8084 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8085   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,


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