rev 4551 : 8015237: Parallelize string table scanning during strong root processing
Summary: Parallelize the scanning of the intern string table by having each GC worker claim a given number of buckets. Changes were also reviewed by Per Liden <per.liden@oracle.com>.
Reviewed-by: tschatzl, stefank, twisti

   1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
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  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
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  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/symbolTable.hpp"
  27 #include "classfile/systemDictionary.hpp"
  28 #include "code/codeCache.hpp"
  29 #include "gc_interface/collectedHeap.inline.hpp"
  30 #include "memory/sharedHeap.hpp"
  31 #include "oops/oop.inline.hpp"
  32 #include "runtime/fprofiler.hpp"
  33 #include "runtime/java.hpp"
  34 #include "services/management.hpp"
  35 #include "utilities/copy.hpp"
  36 #include "utilities/workgroup.hpp"
  37 
  38 SharedHeap* SharedHeap::_sh;
  39 
  40 // The set of potentially parallel tasks in strong root scanning.
  41 enum SH_process_strong_roots_tasks {
  42   SH_PS_Universe_oops_do,
  43   SH_PS_JNIHandles_oops_do,
  44   SH_PS_ObjectSynchronizer_oops_do,
  45   SH_PS_FlatProfiler_oops_do,
  46   SH_PS_Management_oops_do,
  47   SH_PS_SystemDictionary_oops_do,
  48   SH_PS_jvmti_oops_do,

  49   SH_PS_CodeCache_oops_do,
  50   // Leave this one last.
  51   SH_PS_NumElements
  52 };
  53 
  54 SharedHeap::SharedHeap(CollectorPolicy* policy_) :
  55   CollectedHeap(),
  56   _collector_policy(policy_),
  57   _perm_gen(NULL), _rem_set(NULL),
  58   _strong_roots_parity(0),
  59   _process_strong_tasks(new SubTasksDone(SH_PS_NumElements)),
  60   _workers(NULL)
  61 {
  62   if (_process_strong_tasks == NULL || !_process_strong_tasks->valid()) {
  63     vm_exit_during_initialization("Failed necessary allocation.");
  64   }
  65   _sh = this;  // ch is static, should be set only once.
  66   if ((UseParNewGC ||
  67       (UseConcMarkSweepGC && CMSParallelRemarkEnabled) ||
  68        UseG1GC) &&
  69       ParallelGCThreads > 0) {
  70     _workers = new FlexibleWorkGang("Parallel GC Threads", ParallelGCThreads,
  71                             /* are_GC_task_threads */true,
  72                             /* are_ConcurrentGC_threads */false);
  73     if (_workers == NULL) {
  74       vm_exit_during_initialization("Failed necessary allocation.");
  75     } else {
  76       _workers->initialize_workers();
  77     }
  78   }
  79 }
  80 
  81 int SharedHeap::n_termination() {
  82   return _process_strong_tasks->n_threads();
  83 }
  84 
  85 void SharedHeap::set_n_termination(int t) {
  86   _process_strong_tasks->set_n_threads(t);
  87 }
  88 
  89 bool SharedHeap::heap_lock_held_for_gc() {
  90   Thread* t = Thread::current();
  91   return    Heap_lock->owned_by_self()
  92          || (   (t->is_GC_task_thread() ||  t->is_VM_thread())
  93              && _thread_holds_heap_lock_for_gc);
  94 }
  95 
  96 void SharedHeap::set_par_threads(uint t) {
  97   assert(t == 0 || !UseSerialGC, "Cannot have parallel threads");
  98   _n_par_threads = t;
  99   _process_strong_tasks->set_n_threads(t);
 100 }
 101 
 102 class AssertIsPermClosure: public OopClosure {
 103 public:
 104   virtual void do_oop(oop* p) {
 105     assert((*p) == NULL || (*p)->is_perm(), "Referent should be perm.");
 106   }
 107   virtual void do_oop(narrowOop* p) { ShouldNotReachHere(); }
 108 };
 109 static AssertIsPermClosure assert_is_perm_closure;
 110 
 111 #ifdef ASSERT
 112 class AssertNonScavengableClosure: public OopClosure {
 113 public:
 114   virtual void do_oop(oop* p) {
 115     assert(!Universe::heap()->is_in_partial_collection(*p),
 116       "Referent should not be scavengable.");  }
 117   virtual void do_oop(narrowOop* p) { ShouldNotReachHere(); }
 118 };
 119 static AssertNonScavengableClosure assert_is_non_scavengable_closure;
 120 #endif
 121 
 122 void SharedHeap::change_strong_roots_parity() {
 123   // Also set the new collection parity.
 124   assert(_strong_roots_parity >= 0 && _strong_roots_parity <= 2,
 125          "Not in range.");
 126   _strong_roots_parity++;
 127   if (_strong_roots_parity == 3) _strong_roots_parity = 1;
 128   assert(_strong_roots_parity >= 1 && _strong_roots_parity <= 2,
 129          "Not in range.");
 130 }
 131 
 132 SharedHeap::StrongRootsScope::StrongRootsScope(SharedHeap* outer, bool activate)
 133   : MarkScope(activate)
 134 {
 135   if (_active) {
 136     outer->change_strong_roots_parity();
 137     // Zero the claimed high water mark in the StringTable
 138     StringTable::clear_parallel_claimed_index();
 139   }
 140 }
 141 
 142 SharedHeap::StrongRootsScope::~StrongRootsScope() {
 143   // nothing particular
 144 }
 145 
 146 void SharedHeap::process_strong_roots(bool activate_scope,
 147                                       bool collecting_perm_gen,
 148                                       ScanningOption so,
 149                                       OopClosure* roots,
 150                                       CodeBlobClosure* code_roots,
 151                                       OopsInGenClosure* perm_blk) {
 152   StrongRootsScope srs(this, activate_scope);
 153   // General strong roots.
 154   assert(_strong_roots_parity != 0, "must have called prologue code");
 155   // _n_termination for _process_strong_tasks should be set up stream
 156   // in a method not running in a GC worker.  Otherwise the GC worker
 157   // could be trying to change the termination condition while the task
 158   // is executing in another GC worker.
 159   if (!_process_strong_tasks->is_task_claimed(SH_PS_Universe_oops_do)) {
 160     Universe::oops_do(roots);
 161     // Consider perm-gen discovered lists to be strong.
 162     perm_gen()->ref_processor()->weak_oops_do(roots);
 163   }
 164   // Global (strong) JNI handles
 165   if (!_process_strong_tasks->is_task_claimed(SH_PS_JNIHandles_oops_do))
 166     JNIHandles::oops_do(roots);
 167 
 168   // All threads execute this; the individual threads are task groups.
 169   if (CollectedHeap::use_parallel_gc_threads()) {
 170     Threads::possibly_parallel_oops_do(roots, code_roots);
 171   } else {
 172     Threads::oops_do(roots, code_roots);
 173   }
 174 
 175   if (!_process_strong_tasks-> is_task_claimed(SH_PS_ObjectSynchronizer_oops_do))
 176     ObjectSynchronizer::oops_do(roots);
 177   if (!_process_strong_tasks->is_task_claimed(SH_PS_FlatProfiler_oops_do))
 178     FlatProfiler::oops_do(roots);
 179   if (!_process_strong_tasks->is_task_claimed(SH_PS_Management_oops_do))
 180     Management::oops_do(roots);
 181   if (!_process_strong_tasks->is_task_claimed(SH_PS_jvmti_oops_do))
 182     JvmtiExport::oops_do(roots);
 183 
 184   if (!_process_strong_tasks->is_task_claimed(SH_PS_SystemDictionary_oops_do)) {
 185     if (so & SO_AllClasses) {
 186       SystemDictionary::oops_do(roots);
 187     } else if (so & SO_SystemClasses) {
 188       SystemDictionary::always_strong_oops_do(roots);
 189     }
 190   }
 191 
 192   // All threads execute the following. A specific chunk of buckets
 193   // from the StringTable are the individual tasks.
 194   if (so & SO_Strings || (!collecting_perm_gen && !JavaObjectsInPerm)) {
 195     if (CollectedHeap::use_parallel_gc_threads()) {
 196       StringTable::possibly_parallel_oops_do(roots);
 197     } else {
 198       StringTable::oops_do(roots);
 199     }
 200   }
 201   if (JavaObjectsInPerm) {
 202     // Verify the string table contents are in the perm gen
 203     if (CollectedHeap::use_parallel_gc_threads()) {
 204       NOT_PRODUCT(StringTable::possibly_parallel_oops_do(&assert_is_perm_closure));
 205     } else {
 206       NOT_PRODUCT(StringTable::oops_do(&assert_is_perm_closure));
 207     }
 208   }
 209 
 210   if (!_process_strong_tasks->is_task_claimed(SH_PS_CodeCache_oops_do)) {
 211     if (so & SO_CodeCache) {
 212       // (Currently, CMSCollector uses this to do intermediate-strength collections.)
 213       assert(collecting_perm_gen, "scanning all of code cache");
 214       assert(code_roots != NULL, "must supply closure for code cache");
 215       if (code_roots != NULL) {
 216         CodeCache::blobs_do(code_roots);
 217       }
 218     } else if (so & (SO_SystemClasses|SO_AllClasses)) {
 219       if (!collecting_perm_gen) {
 220         // If we are collecting from class statics, but we are not going to
 221         // visit all of the CodeCache, collect from the non-perm roots if any.
 222         // This makes the code cache function temporarily as a source of strong
 223         // roots for oops, until the next major collection.
 224         //
 225         // If collecting_perm_gen is true, we require that this phase will call
 226         // CodeCache::do_unloading.  This will kill off nmethods with expired
 227         // weak references, such as stale invokedynamic targets.
 228         CodeCache::scavenge_root_nmethods_do(code_roots);
 229       }
 230     }
 231     // Verify that the code cache contents are not subject to
 232     // movement by a scavenging collection.
 233     DEBUG_ONLY(CodeBlobToOopClosure assert_code_is_non_scavengable(&assert_is_non_scavengable_closure, /*do_marking=*/ false));
 234     DEBUG_ONLY(CodeCache::asserted_non_scavengable_nmethods_do(&assert_code_is_non_scavengable));
 235   }
 236 
 237   if (!collecting_perm_gen) {
 238     // All threads perform this; coordination is handled internally.
 239 
 240     rem_set()->younger_refs_iterate(perm_gen(), perm_blk);
 241   }
 242   _process_strong_tasks->all_tasks_completed();
 243 }
 244 
 245 class AlwaysTrueClosure: public BoolObjectClosure {
 246 public:
 247   void do_object(oop p) { ShouldNotReachHere(); }
 248   bool do_object_b(oop p) { return true; }
 249 };
 250 static AlwaysTrueClosure always_true;
 251 
 252 class SkipAdjustingSharedStrings: public OopClosure {
 253   OopClosure* _clo;
 254 public:
 255   SkipAdjustingSharedStrings(OopClosure* clo) : _clo(clo) {}
 256 
 257   virtual void do_oop(oop* p) {
 258     oop o = (*p);
 259     if (!o->is_shared_readwrite()) {
 260       _clo->do_oop(p);
 261     }
 262   }
 263   virtual void do_oop(narrowOop* p) { ShouldNotReachHere(); }
 264 };
 265 
 266 // Unmarked shared Strings in the StringTable (which got there due to
 267 // being in the constant pools of as-yet unloaded shared classes) were
 268 // not marked and therefore did not have their mark words preserved.
 269 // These entries are also deliberately not purged from the string
 270 // table during unloading of unmarked strings. If an identity hash
 271 // code was computed for any of these objects, it will not have been
 272 // cleared to zero during the forwarding process or by the
 273 // RecursiveAdjustSharedObjectClosure, and will be confused by the
 274 // adjusting process as a forwarding pointer. We need to skip
 275 // forwarding StringTable entries which contain unmarked shared
 276 // Strings. Actually, since shared strings won't be moving, we can
 277 // just skip adjusting any shared entries in the string table.
 278 
 279 void SharedHeap::process_weak_roots(OopClosure* root_closure,
 280                                     CodeBlobClosure* code_roots,
 281                                     OopClosure* non_root_closure) {
 282   // Global (weak) JNI handles
 283   JNIHandles::weak_oops_do(&always_true, root_closure);
 284 
 285   CodeCache::blobs_do(code_roots);
 286   if (UseSharedSpaces && !DumpSharedSpaces) {
 287     SkipAdjustingSharedStrings skip_closure(root_closure);
 288     StringTable::oops_do(&skip_closure);
 289   } else {
 290     StringTable::oops_do(root_closure);
 291   }
 292 }
 293 
 294 void SharedHeap::set_barrier_set(BarrierSet* bs) {
 295   _barrier_set = bs;
 296   // Cached barrier set for fast access in oops
 297   oopDesc::set_bs(bs);
 298 }
 299 
 300 void SharedHeap::post_initialize() {
 301   ref_processing_init();
 302 }
 303 
 304 void SharedHeap::ref_processing_init() {
 305   perm_gen()->ref_processor_init();
 306 }
 307 
 308 // Some utilities.
 309 void SharedHeap::print_size_transition(outputStream* out,
 310                                        size_t bytes_before,
 311                                        size_t bytes_after,
 312                                        size_t capacity) {
 313   out->print(" %d%s->%d%s(%d%s)",
 314              byte_size_in_proper_unit(bytes_before),
 315              proper_unit_for_byte_size(bytes_before),
 316              byte_size_in_proper_unit(bytes_after),
 317              proper_unit_for_byte_size(bytes_after),
 318              byte_size_in_proper_unit(capacity),
 319              proper_unit_for_byte_size(capacity));
 320 }
--- EOF ---