1 /*
   2  * Copyright (c) 2005, 2015, 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.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   // The caller may block while communicating
  42   // with the SLT thread in order to acquire/release the PLL.
  43   SurrogateLockerThread* slt = ConcurrentMarkSweepThread::slt();
  44   if (slt != NULL) {
  45     slt->manipulatePLL(SurrogateLockerThread::acquirePLL);
  46   } else {
  47     SurrogateLockerThread::report_missing_slt();
  48   }
  49 }
  50 
  51 void VM_CMS_Operation::release_and_notify_pending_list_lock() {
  52   // The caller may block while communicating
  53   // with the SLT thread in order to acquire/release the PLL.
  54   ConcurrentMarkSweepThread::slt()->
  55     manipulatePLL(SurrogateLockerThread::releaseAndNotifyPLL);
  56 }
  57 
  58 void VM_CMS_Operation::verify_before_gc() {
  59   if (VerifyBeforeGC &&
  60       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
  61     GCTraceTime tm("Verify Before", false, false, _collector->_gc_timer_cm);
  62     HandleMark hm;
  63     FreelistLocker x(_collector);
  64     MutexLockerEx  y(_collector->bitMapLock(), Mutex::_no_safepoint_check_flag);
  65     GenCollectedHeap::heap()->prepare_for_verify();
  66     Universe::verify();
  67   }
  68 }
  69 
  70 void VM_CMS_Operation::verify_after_gc() {
  71   if (VerifyAfterGC &&
  72       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
  73     GCTraceTime tm("Verify After", false, false, _collector->_gc_timer_cm);
  74     HandleMark hm;
  75     FreelistLocker x(_collector);
  76     MutexLockerEx  y(_collector->bitMapLock(), Mutex::_no_safepoint_check_flag);
  77     Universe::verify();
  78   }
  79 }
  80 
  81 bool VM_CMS_Operation::lost_race() const {
  82   if (CMSCollector::abstract_state() == CMSCollector::Idling) {
  83     // We lost a race to a foreground collection
  84     // -- there's nothing to do
  85     return true;
  86   }
  87   assert(CMSCollector::abstract_state() == legal_state(),
  88          "Inconsistent collector state?");
  89   return false;
  90 }
  91 
  92 bool VM_CMS_Operation::doit_prologue() {
  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 (needs_pll()) {
  99     acquire_pending_list_lock();
 100   }
 101   // Get the Heap_lock after the pending_list_lock.
 102   Heap_lock->lock();
 103   if (lost_race()) {
 104     assert(_prologue_succeeded == false, "Initialized in c'tor");
 105     Heap_lock->unlock();
 106     if (needs_pll()) {
 107       release_and_notify_pending_list_lock();
 108     }
 109   } else {
 110     _prologue_succeeded = true;
 111   }
 112   return _prologue_succeeded;
 113 }
 114 
 115 void VM_CMS_Operation::doit_epilogue() {
 116   assert(Thread::current()->is_ConcurrentGC_thread(), "just checking");
 117   assert(!CMSCollector::foregroundGCShouldWait(), "Possible deadlock");
 118   assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
 119          "Possible deadlock");
 120 
 121   // Release the Heap_lock first.
 122   Heap_lock->unlock();
 123   if (needs_pll()) {
 124     release_and_notify_pending_list_lock();
 125   }
 126 }
 127 
 128 //////////////////////////////////////////////////////////
 129 // Methods in class VM_CMS_Initial_Mark
 130 //////////////////////////////////////////////////////////
 131 void VM_CMS_Initial_Mark::doit() {
 132   if (lost_race()) {
 133     // Nothing to do.
 134     return;
 135   }
 136   HS_PRIVATE_CMS_INITMARK_BEGIN();
 137   GCIdMark gc_id_mark(_gc_id);
 138 
 139   _collector->_gc_timer_cm->register_gc_pause_start("Initial Mark");
 140 
 141   GenCollectedHeap* gch = GenCollectedHeap::heap();
 142   GCCauseSetter gccs(gch, GCCause::_cms_initial_mark);
 143 
 144   VM_CMS_Operation::verify_before_gc();
 145 
 146   IsGCActiveMark x; // stop-world GC active
 147   _collector->do_CMS_operation(CMSCollector::CMS_op_checkpointRootsInitial, gch->gc_cause());
 148 
 149   VM_CMS_Operation::verify_after_gc();
 150 
 151   _collector->_gc_timer_cm->register_gc_pause_end();
 152 
 153   HS_PRIVATE_CMS_INITMARK_END();
 154 }
 155 
 156 //////////////////////////////////////////////////////////
 157 // Methods in class VM_CMS_Final_Remark_Operation
 158 //////////////////////////////////////////////////////////
 159 void VM_CMS_Final_Remark::doit() {
 160   if (lost_race()) {
 161     // Nothing to do.
 162     return;
 163   }
 164   HS_PRIVATE_CMS_REMARK_BEGIN();
 165   GCIdMark gc_id_mark(_gc_id);
 166 
 167   _collector->_gc_timer_cm->register_gc_pause_start("Final Mark");
 168 
 169   GenCollectedHeap* gch = GenCollectedHeap::heap();
 170   GCCauseSetter gccs(gch, GCCause::_cms_final_remark);
 171 
 172   VM_CMS_Operation::verify_before_gc();
 173 
 174   IsGCActiveMark x; // stop-world GC active
 175   _collector->do_CMS_operation(CMSCollector::CMS_op_checkpointRootsFinal, gch->gc_cause());
 176 
 177   VM_CMS_Operation::verify_after_gc();
 178 
 179   _collector->save_heap_summary();
 180   _collector->_gc_timer_cm->register_gc_pause_end();
 181 
 182   HS_PRIVATE_CMS_REMARK_END();
 183 }
 184 
 185 // VM operation to invoke a concurrent collection of a
 186 // GenCollectedHeap heap.
 187 void VM_GenCollectFullConcurrent::doit() {
 188   assert(Thread::current()->is_VM_thread(), "Should be VM thread");
 189   assert(GCLockerInvokesConcurrent || ExplicitGCInvokesConcurrent, "Unexpected");
 190 
 191   GenCollectedHeap* gch = GenCollectedHeap::heap();
 192   if (_gc_count_before == gch->total_collections()) {
 193     // The "full" of do_full_collection call below "forces"
 194     // a collection; the second arg, 0, below ensures that
 195     // only the young gen is collected. XXX In the future,
 196     // we'll probably need to have something in this interface
 197     // to say do this only if we are sure we will not bail
 198     // out to a full collection in this attempt, but that's
 199     // for the future.
 200     assert(SafepointSynchronize::is_at_safepoint(),
 201       "We can only be executing this arm of if at a safepoint");
 202     GCCauseSetter gccs(gch, _gc_cause);
 203     gch->do_full_collection(gch->must_clear_all_soft_refs(), GenCollectedHeap::YoungGen);
 204   } // Else no need for a foreground young gc
 205   assert((_gc_count_before < gch->total_collections()) ||
 206          (GC_locker::is_active() /* gc may have been skipped */
 207           && (_gc_count_before == gch->total_collections())),
 208          "total_collections() should be monotonically increasing");
 209 
 210   MutexLockerEx x(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
 211   assert(_full_gc_count_before <= gch->total_full_collections(), "Error");
 212   if (gch->total_full_collections() == _full_gc_count_before) {
 213     // Nudge the CMS thread to start a concurrent collection.
 214     CMSCollector::request_full_gc(_full_gc_count_before, _gc_cause);
 215   } else {
 216     assert(_full_gc_count_before < gch->total_full_collections(), "Error");
 217     FullGCCount_lock->notify_all();  // Inform the Java thread its work is done
 218   }
 219 }
 220 
 221 bool VM_GenCollectFullConcurrent::evaluate_at_safepoint() const {
 222   Thread* thr = Thread::current();
 223   assert(thr != NULL, "Unexpected tid");
 224   if (!thr->is_Java_thread()) {
 225     assert(thr->is_VM_thread(), "Expected to be evaluated by VM thread");
 226     GenCollectedHeap* gch = GenCollectedHeap::heap();
 227     if (_gc_count_before != gch->total_collections()) {
 228       // No need to do a young gc, we'll just nudge the CMS thread
 229       // in the doit() method above, to be executed soon.
 230       assert(_gc_count_before < gch->total_collections(),
 231              "total_collections() should be monotonically increasing");
 232       return false;  // no need for foreground young gc
 233     }
 234   }
 235   return true;       // may still need foreground young gc
 236 }
 237 
 238 
 239 void VM_GenCollectFullConcurrent::doit_epilogue() {
 240   Thread* thr = Thread::current();
 241   assert(thr->is_Java_thread(), "just checking");
 242   JavaThread* jt = (JavaThread*)thr;
 243   // Release the Heap_lock first.
 244   Heap_lock->unlock();
 245   release_and_notify_pending_list_lock();
 246 
 247   // It is fine to test whether completed collections has
 248   // exceeded our request count without locking because
 249   // the completion count is monotonically increasing;
 250   // this will break for very long-running apps when the
 251   // count overflows and wraps around. XXX fix me !!!
 252   // e.g. at the rate of 1 full gc per ms, this could
 253   // overflow in about 1000 years.
 254   GenCollectedHeap* gch = GenCollectedHeap::heap();
 255   if (_gc_cause != GCCause::_gc_locker &&
 256       gch->total_full_collections_completed() <= _full_gc_count_before) {
 257     // maybe we should change the condition to test _gc_cause ==
 258     // GCCause::_java_lang_system_gc or GCCause::_dcmd_gc_run,
 259     // instead of _gc_cause != GCCause::_gc_locker
 260     assert(GCCause::is_user_requested_gc(_gc_cause),
 261            "the only way to get here if this was a System.gc()-induced GC");
 262     assert(ExplicitGCInvokesConcurrent, "Error");
 263     // Now, wait for witnessing concurrent gc cycle to complete,
 264     // but do so in native mode, because we want to lock the
 265     // FullGCEvent_lock, which may be needed by the VM thread
 266     // or by the CMS thread, so we do not want to be suspended
 267     // while holding that lock.
 268     ThreadToNativeFromVM native(jt);
 269     MutexLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
 270     // Either a concurrent or a stop-world full gc is sufficient
 271     // witness to our request.
 272     while (gch->total_full_collections_completed() <= _full_gc_count_before) {
 273       FullGCCount_lock->wait(Mutex::_no_safepoint_check_flag);
 274     }
 275   }
 276 }
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