1 /*
   2  * Copyright (c) 2005, 2017, 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/cmsHeap.hpp"
  27 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
  28 #include "gc/cms/concurrentMarkSweepThread.hpp"
  29 #include "gc/cms/vmCMSOperations.hpp"
  30 #include "gc/shared/gcLocker.inline.hpp"
  31 #include "gc/shared/gcTimer.hpp"
  32 #include "gc/shared/gcTraceTime.inline.hpp"
  33 #include "gc/shared/isGCActiveMark.hpp"
  34 #include "runtime/interfaceSupport.hpp"

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