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