1 /*
   2  * Copyright (c) 2005, 2016, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   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
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  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).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  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
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
  27 #include "gc/cms/concurrentMarkSweepThread.hpp"
  28 #include "gc/cms/vmCMSOperations.hpp"
  29 #include "gc/shared/gcLocker.inline.hpp"
  30 #include "gc/shared/gcTimer.hpp"
  31 #include "gc/shared/gcTraceTime.inline.hpp"
  32 #include "gc/shared/isGCActiveMark.hpp"
  33 #include "runtime/interfaceSupport.hpp"
  34 #include "runtime/os.hpp"
  35 #include "utilities/dtrace.hpp"
  36 
  37 //////////////////////////////////////////////////////////
  38 // Methods in abstract class VM_CMS_Operation
  39 //////////////////////////////////////////////////////////
  40 void VM_CMS_Operation::acquire_pending_list_lock() {
  41   _pending_list_locker.lock();
  42 }
  43 
  44 void VM_CMS_Operation::release_and_notify_pending_list_lock() {
  45   _pending_list_locker.unlock();
  46 }
  47 
  48 void VM_CMS_Operation::verify_before_gc() {
  49   if (VerifyBeforeGC &&
  50       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
  51     GCTraceTime(Info, gc, phases, verify) tm("Verify Before", _collector->_gc_timer_cm);
  52     HandleMark hm;
  53     FreelistLocker x(_collector);
  54     MutexLockerEx  y(_collector->bitMapLock(), Mutex::_no_safepoint_check_flag);
  55     GenCollectedHeap::heap()->prepare_for_verify();
  56     Universe::verify();
  57   }
  58 }
  59 
  60 void VM_CMS_Operation::verify_after_gc() {
  61   if (VerifyAfterGC &&
  62       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
  63     GCTraceTime(Info, gc, phases, verify) tm("Verify After", _collector->_gc_timer_cm);
  64     HandleMark hm;
  65     FreelistLocker x(_collector);
  66     MutexLockerEx  y(_collector->bitMapLock(), Mutex::_no_safepoint_check_flag);
  67     Universe::verify();
  68   }
  69 }
  70 
  71 bool VM_CMS_Operation::lost_race() const {
  72   if (CMSCollector::abstract_state() == CMSCollector::Idling) {
  73     // We lost a race to a foreground collection
  74     // -- there's nothing to do
  75     return true;
  76   }
  77   assert(CMSCollector::abstract_state() == legal_state(),
  78          "Inconsistent collector state?");
  79   return false;
  80 }
  81 
  82 bool VM_CMS_Operation::doit_prologue() {
  83   assert(Thread::current()->is_ConcurrentGC_thread(), "just checking");
  84   assert(!CMSCollector::foregroundGCShouldWait(), "Possible deadlock");
  85   assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
  86          "Possible deadlock");
  87 
  88   if (needs_pending_list_lock()) {
  89     acquire_pending_list_lock();
  90   }
  91   // Get the Heap_lock after the pending_list_lock.
  92   Heap_lock->lock();
  93   if (lost_race()) {
  94     assert(_prologue_succeeded == false, "Initialized in c'tor");
  95     Heap_lock->unlock();
  96     if (needs_pending_list_lock()) {
  97       release_and_notify_pending_list_lock();
  98     }
  99   } else {
 100     _prologue_succeeded = true;
 101   }
 102   return _prologue_succeeded;
 103 }
 104 
 105 void VM_CMS_Operation::doit_epilogue() {
 106   assert(Thread::current()->is_ConcurrentGC_thread(), "just checking");
 107   assert(!CMSCollector::foregroundGCShouldWait(), "Possible deadlock");
 108   assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
 109          "Possible deadlock");
 110 
 111   // Release the Heap_lock first.
 112   Heap_lock->unlock();
 113   if (needs_pending_list_lock()) {
 114     release_and_notify_pending_list_lock();
 115   }
 116 }
 117 
 118 //////////////////////////////////////////////////////////
 119 // Methods in class VM_CMS_Initial_Mark
 120 //////////////////////////////////////////////////////////
 121 void VM_CMS_Initial_Mark::doit() {
 122   if (lost_race()) {
 123     // Nothing to do.
 124     return;
 125   }
 126   HS_PRIVATE_CMS_INITMARK_BEGIN();
 127   GCIdMark gc_id_mark(_gc_id);
 128 
 129   _collector->_gc_timer_cm->register_gc_pause_start("Initial Mark");
 130 
 131   GenCollectedHeap* gch = GenCollectedHeap::heap();
 132   GCCauseSetter gccs(gch, GCCause::_cms_initial_mark);
 133 
 134   VM_CMS_Operation::verify_before_gc();
 135 
 136   IsGCActiveMark x; // stop-world GC active
 137   _collector->do_CMS_operation(CMSCollector::CMS_op_checkpointRootsInitial, gch->gc_cause());
 138 
 139   VM_CMS_Operation::verify_after_gc();
 140 
 141   _collector->_gc_timer_cm->register_gc_pause_end();
 142 
 143   HS_PRIVATE_CMS_INITMARK_END();
 144 }
 145 
 146 //////////////////////////////////////////////////////////
 147 // Methods in class VM_CMS_Final_Remark_Operation
 148 //////////////////////////////////////////////////////////
 149 void VM_CMS_Final_Remark::doit() {
 150   if (lost_race()) {
 151     // Nothing to do.
 152     return;
 153   }
 154   HS_PRIVATE_CMS_REMARK_BEGIN();
 155   GCIdMark gc_id_mark(_gc_id);
 156 
 157   _collector->_gc_timer_cm->register_gc_pause_start("Final Mark");
 158 
 159   GenCollectedHeap* gch = GenCollectedHeap::heap();
 160   GCCauseSetter gccs(gch, GCCause::_cms_final_remark);
 161 
 162   VM_CMS_Operation::verify_before_gc();
 163 
 164   IsGCActiveMark x; // stop-world GC active
 165   _collector->do_CMS_operation(CMSCollector::CMS_op_checkpointRootsFinal, gch->gc_cause());
 166 
 167   VM_CMS_Operation::verify_after_gc();
 168 
 169   _collector->save_heap_summary();
 170   _collector->_gc_timer_cm->register_gc_pause_end();
 171 
 172   HS_PRIVATE_CMS_REMARK_END();
 173 }
 174 
 175 // VM operation to invoke a concurrent collection of a
 176 // GenCollectedHeap heap.
 177 void VM_GenCollectFullConcurrent::doit() {
 178   assert(Thread::current()->is_VM_thread(), "Should be VM thread");
 179   assert(GCLockerInvokesConcurrent || ExplicitGCInvokesConcurrent, "Unexpected");
 180 
 181   GenCollectedHeap* gch = GenCollectedHeap::heap();
 182   if (_gc_count_before == gch->total_collections()) {
 183     // The "full" of do_full_collection call below "forces"
 184     // a collection; the second arg, 0, below ensures that
 185     // only the young gen is collected. XXX In the future,
 186     // we'll probably need to have something in this interface
 187     // to say do this only if we are sure we will not bail
 188     // out to a full collection in this attempt, but that's
 189     // for the future.
 190     assert(SafepointSynchronize::is_at_safepoint(),
 191       "We can only be executing this arm of if at a safepoint");
 192     GCCauseSetter gccs(gch, _gc_cause);
 193     gch->do_full_collection(gch->must_clear_all_soft_refs(), GenCollectedHeap::YoungGen);
 194   } // Else no need for a foreground young gc
 195   assert((_gc_count_before < gch->total_collections()) ||
 196          (GCLocker::is_active() /* gc may have been skipped */
 197           && (_gc_count_before == gch->total_collections())),
 198          "total_collections() should be monotonically increasing");
 199 
 200   MutexLockerEx x(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
 201   assert(_full_gc_count_before <= gch->total_full_collections(), "Error");
 202   if (gch->total_full_collections() == _full_gc_count_before) {
 203     // Nudge the CMS thread to start a concurrent collection.
 204     CMSCollector::request_full_gc(_full_gc_count_before, _gc_cause);
 205   } else {
 206     assert(_full_gc_count_before < gch->total_full_collections(), "Error");
 207     FullGCCount_lock->notify_all();  // Inform the Java thread its work is done
 208   }
 209 }
 210 
 211 bool VM_GenCollectFullConcurrent::evaluate_at_safepoint() const {
 212   Thread* thr = Thread::current();
 213   assert(thr != NULL, "Unexpected tid");
 214   if (!thr->is_Java_thread()) {
 215     assert(thr->is_VM_thread(), "Expected to be evaluated by VM thread");
 216     GenCollectedHeap* gch = GenCollectedHeap::heap();
 217     if (_gc_count_before != gch->total_collections()) {
 218       // No need to do a young gc, we'll just nudge the CMS thread
 219       // in the doit() method above, to be executed soon.
 220       assert(_gc_count_before < gch->total_collections(),
 221              "total_collections() should be monotonically increasing");
 222       return false;  // no need for foreground young gc
 223     }
 224   }
 225   return true;       // may still need foreground young gc
 226 }
 227 
 228 
 229 void VM_GenCollectFullConcurrent::doit_epilogue() {
 230   Thread* thr = Thread::current();
 231   assert(thr->is_Java_thread(), "just checking");
 232   JavaThread* jt = (JavaThread*)thr;
 233   // Release the Heap_lock first.
 234   Heap_lock->unlock();
 235   release_and_notify_pending_list_lock();
 236 
 237   // It is fine to test whether completed collections has
 238   // exceeded our request count without locking because
 239   // the completion count is monotonically increasing;
 240   // this will break for very long-running apps when the
 241   // count overflows and wraps around. XXX fix me !!!
 242   // e.g. at the rate of 1 full gc per ms, this could
 243   // overflow in about 1000 years.
 244   GenCollectedHeap* gch = GenCollectedHeap::heap();
 245   if (_gc_cause != GCCause::_gc_locker &&
 246       gch->total_full_collections_completed() <= _full_gc_count_before) {
 247     // maybe we should change the condition to test _gc_cause ==
 248     // GCCause::_java_lang_system_gc or GCCause::_dcmd_gc_run,
 249     // instead of _gc_cause != GCCause::_gc_locker
 250     assert(GCCause::is_user_requested_gc(_gc_cause),
 251            "the only way to get here if this was a System.gc()-induced GC");
 252     assert(ExplicitGCInvokesConcurrent, "Error");
 253     // Now, wait for witnessing concurrent gc cycle to complete,
 254     // but do so in native mode, because we want to lock the
 255     // FullGCEvent_lock, which may be needed by the VM thread
 256     // or by the CMS thread, so we do not want to be suspended
 257     // while holding that lock.
 258     ThreadToNativeFromVM native(jt);
 259     MutexLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
 260     // Either a concurrent or a stop-world full gc is sufficient
 261     // witness to our request.
 262     while (gch->total_full_collections_completed() <= _full_gc_count_before) {
 263       FullGCCount_lock->wait(Mutex::_no_safepoint_check_flag);
 264     }
 265   }
 266 }