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Java example source code file (vmCMSOperations.cpp)

This example Java source code file (vmCMSOperations.cpp) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

error, gccausesetter, gctracetime, gencollectedheap, gencollectedheap::heap, heap_lock-, hs_dtrace_probe_decl, mutex\:\:_no_safepoint_check_flag, mutexlockerex, possible, usdt2, vm_cms_operation\:\:verify_after_gc, vm_cms_operation\:\:verify_before_gc

The vmCMSOperations.cpp Java example source code

/*
 * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

#include "precompiled.hpp"
#include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
#include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
#include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
#include "gc_implementation/shared/gcTimer.hpp"
#include "gc_implementation/shared/gcTraceTime.hpp"
#include "gc_implementation/shared/isGCActiveMark.hpp"
#include "memory/gcLocker.inline.hpp"
#include "runtime/interfaceSupport.hpp"
#include "runtime/os.hpp"
#include "utilities/dtrace.hpp"


#ifndef USDT2
HS_DTRACE_PROBE_DECL(hs_private, cms__initmark__begin);
HS_DTRACE_PROBE_DECL(hs_private, cms__initmark__end);

HS_DTRACE_PROBE_DECL(hs_private, cms__remark__begin);
HS_DTRACE_PROBE_DECL(hs_private, cms__remark__end);
#endif /* !USDT2 */

//////////////////////////////////////////////////////////
// Methods in abstract class VM_CMS_Operation
//////////////////////////////////////////////////////////
void VM_CMS_Operation::acquire_pending_list_lock() {
  // The caller may block while communicating
  // with the SLT thread in order to acquire/release the PLL.
  ConcurrentMarkSweepThread::slt()->
    manipulatePLL(SurrogateLockerThread::acquirePLL);
}

void VM_CMS_Operation::release_and_notify_pending_list_lock() {
  // The caller may block while communicating
  // with the SLT thread in order to acquire/release the PLL.
  ConcurrentMarkSweepThread::slt()->
    manipulatePLL(SurrogateLockerThread::releaseAndNotifyPLL);
}

void VM_CMS_Operation::verify_before_gc() {
  if (VerifyBeforeGC &&
      GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
    GCTraceTime tm("Verify Before", false, false, _collector->_gc_timer_cm);
    HandleMark hm;
    FreelistLocker x(_collector);
    MutexLockerEx  y(_collector->bitMapLock(), Mutex::_no_safepoint_check_flag);
    Universe::heap()->prepare_for_verify();
    Universe::verify();
  }
}

void VM_CMS_Operation::verify_after_gc() {
  if (VerifyAfterGC &&
      GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
    GCTraceTime tm("Verify After", false, false, _collector->_gc_timer_cm);
    HandleMark hm;
    FreelistLocker x(_collector);
    MutexLockerEx  y(_collector->bitMapLock(), Mutex::_no_safepoint_check_flag);
    Universe::verify();
  }
}

bool VM_CMS_Operation::lost_race() const {
  if (CMSCollector::abstract_state() == CMSCollector::Idling) {
    // We lost a race to a foreground collection
    // -- there's nothing to do
    return true;
  }
  assert(CMSCollector::abstract_state() == legal_state(),
         "Inconsistent collector state?");
  return false;
}

bool VM_CMS_Operation::doit_prologue() {
  assert(Thread::current()->is_ConcurrentGC_thread(), "just checking");
  assert(!CMSCollector::foregroundGCShouldWait(), "Possible deadlock");
  assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
         "Possible deadlock");

  if (needs_pll()) {
    acquire_pending_list_lock();
  }
  // Get the Heap_lock after the pending_list_lock.
  Heap_lock->lock();
  if (lost_race()) {
    assert(_prologue_succeeded == false, "Initialized in c'tor");
    Heap_lock->unlock();
    if (needs_pll()) {
      release_and_notify_pending_list_lock();
    }
  } else {
    _prologue_succeeded = true;
  }
  return _prologue_succeeded;
}

void VM_CMS_Operation::doit_epilogue() {
  assert(Thread::current()->is_ConcurrentGC_thread(), "just checking");
  assert(!CMSCollector::foregroundGCShouldWait(), "Possible deadlock");
  assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
         "Possible deadlock");

  // Release the Heap_lock first.
  Heap_lock->unlock();
  if (needs_pll()) {
    release_and_notify_pending_list_lock();
  }
}

//////////////////////////////////////////////////////////
// Methods in class VM_CMS_Initial_Mark
//////////////////////////////////////////////////////////
void VM_CMS_Initial_Mark::doit() {
  if (lost_race()) {
    // Nothing to do.
    return;
  }
#ifndef USDT2
  HS_DTRACE_PROBE(hs_private, cms__initmark__begin);
#else /* USDT2 */
  HS_PRIVATE_CMS_INITMARK_BEGIN(
                                );
#endif /* USDT2 */

  _collector->_gc_timer_cm->register_gc_pause_start("Initial Mark");

  GenCollectedHeap* gch = GenCollectedHeap::heap();
  GCCauseSetter gccs(gch, GCCause::_cms_initial_mark);

  VM_CMS_Operation::verify_before_gc();

  IsGCActiveMark x; // stop-world GC active
  _collector->do_CMS_operation(CMSCollector::CMS_op_checkpointRootsInitial, gch->gc_cause());

  VM_CMS_Operation::verify_after_gc();

  _collector->_gc_timer_cm->register_gc_pause_end();

#ifndef USDT2
  HS_DTRACE_PROBE(hs_private, cms__initmark__end);
#else /* USDT2 */
  HS_PRIVATE_CMS_INITMARK_END(
                                );
#endif /* USDT2 */
}

//////////////////////////////////////////////////////////
// Methods in class VM_CMS_Final_Remark_Operation
//////////////////////////////////////////////////////////
void VM_CMS_Final_Remark::doit() {
  if (lost_race()) {
    // Nothing to do.
    return;
  }
#ifndef USDT2
  HS_DTRACE_PROBE(hs_private, cms__remark__begin);
#else /* USDT2 */
  HS_PRIVATE_CMS_REMARK_BEGIN(
                                );
#endif /* USDT2 */

  _collector->_gc_timer_cm->register_gc_pause_start("Final Mark");

  GenCollectedHeap* gch = GenCollectedHeap::heap();
  GCCauseSetter gccs(gch, GCCause::_cms_final_remark);

  VM_CMS_Operation::verify_before_gc();

  IsGCActiveMark x; // stop-world GC active
  _collector->do_CMS_operation(CMSCollector::CMS_op_checkpointRootsFinal, gch->gc_cause());

  VM_CMS_Operation::verify_after_gc();

  _collector->save_heap_summary();
  _collector->_gc_timer_cm->register_gc_pause_end();

#ifndef USDT2
  HS_DTRACE_PROBE(hs_private, cms__remark__end);
#else /* USDT2 */
  HS_PRIVATE_CMS_REMARK_END(
                                );
#endif /* USDT2 */
}

// VM operation to invoke a concurrent collection of a
// GenCollectedHeap heap.
void VM_GenCollectFullConcurrent::doit() {
  assert(Thread::current()->is_VM_thread(), "Should be VM thread");
  assert(GCLockerInvokesConcurrent || ExplicitGCInvokesConcurrent, "Unexpected");

  GenCollectedHeap* gch = GenCollectedHeap::heap();
  if (_gc_count_before == gch->total_collections()) {
    // The "full" of do_full_collection call below "forces"
    // a collection; the second arg, 0, below ensures that
    // only the young gen is collected. XXX In the future,
    // we'll probably need to have something in this interface
    // to say do this only if we are sure we will not bail
    // out to a full collection in this attempt, but that's
    // for the future.
    assert(SafepointSynchronize::is_at_safepoint(),
      "We can only be executing this arm of if at a safepoint");
    GCCauseSetter gccs(gch, _gc_cause);
    gch->do_full_collection(gch->must_clear_all_soft_refs(),
                            0 /* collect only youngest gen */);
  } // Else no need for a foreground young gc
  assert((_gc_count_before < gch->total_collections()) ||
         (GC_locker::is_active() /* gc may have been skipped */
          && (_gc_count_before == gch->total_collections())),
         "total_collections() should be monotonically increasing");

  MutexLockerEx x(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
  assert(_full_gc_count_before <= gch->total_full_collections(), "Error");
  if (gch->total_full_collections() == _full_gc_count_before) {
    // Disable iCMS until the full collection is done, and
    // remember that we did so.
    CMSCollector::disable_icms();
    _disabled_icms = true;
    // In case CMS thread was in icms_wait(), wake it up.
    CMSCollector::start_icms();
    // Nudge the CMS thread to start a concurrent collection.
    CMSCollector::request_full_gc(_full_gc_count_before, _gc_cause);
  } else {
    assert(_full_gc_count_before < gch->total_full_collections(), "Error");
    FullGCCount_lock->notify_all();  // Inform the Java thread its work is done
  }
}

bool VM_GenCollectFullConcurrent::evaluate_at_safepoint() const {
  Thread* thr = Thread::current();
  assert(thr != NULL, "Unexpected tid");
  if (!thr->is_Java_thread()) {
    assert(thr->is_VM_thread(), "Expected to be evaluated by VM thread");
    GenCollectedHeap* gch = GenCollectedHeap::heap();
    if (_gc_count_before != gch->total_collections()) {
      // No need to do a young gc, we'll just nudge the CMS thread
      // in the doit() method above, to be executed soon.
      assert(_gc_count_before < gch->total_collections(),
             "total_collections() should be monotnically increasing");
      return false;  // no need for foreground young gc
    }
  }
  return true;       // may still need foreground young gc
}


void VM_GenCollectFullConcurrent::doit_epilogue() {
  Thread* thr = Thread::current();
  assert(thr->is_Java_thread(), "just checking");
  JavaThread* jt = (JavaThread*)thr;
  // Release the Heap_lock first.
  Heap_lock->unlock();
  release_and_notify_pending_list_lock();

  // It is fine to test whether completed collections has
  // exceeded our request count without locking because
  // the completion count is monotonically increasing;
  // this will break for very long-running apps when the
  // count overflows and wraps around. XXX fix me !!!
  // e.g. at the rate of 1 full gc per ms, this could
  // overflow in about 1000 years.
  GenCollectedHeap* gch = GenCollectedHeap::heap();
  if (_gc_cause != GCCause::_gc_locker &&
      gch->total_full_collections_completed() <= _full_gc_count_before) {
    // maybe we should change the condition to test _gc_cause ==
    // GCCause::_java_lang_system_gc, instead of
    // _gc_cause != GCCause::_gc_locker
    assert(_gc_cause == GCCause::_java_lang_system_gc,
           "the only way to get here if this was a System.gc()-induced GC");
    assert(ExplicitGCInvokesConcurrent, "Error");
    // Now, wait for witnessing concurrent gc cycle to complete,
    // but do so in native mode, because we want to lock the
    // FullGCEvent_lock, which may be needed by the VM thread
    // or by the CMS thread, so we do not want to be suspended
    // while holding that lock.
    ThreadToNativeFromVM native(jt);
    MutexLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
    // Either a concurrent or a stop-world full gc is sufficient
    // witness to our request.
    while (gch->total_full_collections_completed() <= _full_gc_count_before) {
      FullGCCount_lock->wait(Mutex::_no_safepoint_check_flag);
    }
  }
  // Enable iCMS back if we disabled it earlier.
  if (_disabled_icms) {
    CMSCollector::enable_icms();
  }
}

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