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Java example source code file (vmGCOperations.cpp)

This example Java source code file (vmGCOperations.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

gc_locker\:\:is_active_and_needs_gc, gccausesetter, gencollectedheap\:\:heap, heap_lock\-, hs_dtrace_workaround_tail_call_bug, include_all_gcs, null, sharedheap\:\:heap, svcgcmarker, universe::heap, usdt2, vm_gc_operation\:\:doit_prologue

The vmGCOperations.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 "classfile/classLoader.hpp"
#include "classfile/javaClasses.hpp"
#include "gc_implementation/shared/vmGCOperations.hpp"
#include "memory/gcLocker.inline.hpp"
#include "memory/genCollectedHeap.hpp"
#include "memory/oopFactory.hpp"
#include "oops/instanceKlass.hpp"
#include "oops/instanceRefKlass.hpp"
#include "runtime/handles.inline.hpp"
#include "runtime/init.hpp"
#include "runtime/interfaceSupport.hpp"
#include "utilities/dtrace.hpp"
#include "utilities/preserveException.hpp"
#include "utilities/macros.hpp"
#if INCLUDE_ALL_GCS
#include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
#endif // INCLUDE_ALL_GCS

#ifndef USDT2
HS_DTRACE_PROBE_DECL1(hotspot, gc__begin, bool);
HS_DTRACE_PROBE_DECL(hotspot, gc__end);
#endif /* !USDT2 */

// The same dtrace probe can't be inserted in two different files, so we
// have to call it here, so it's only in one file.  Can't create new probes
// for the other file anymore.   The dtrace probes have to remain stable.
void VM_GC_Operation::notify_gc_begin(bool full) {
#ifndef USDT2
  HS_DTRACE_PROBE1(hotspot, gc__begin, full);
  HS_DTRACE_WORKAROUND_TAIL_CALL_BUG();
#else /* USDT2 */
  HOTSPOT_GC_BEGIN(
                   full);
#endif /* USDT2 */
}

void VM_GC_Operation::notify_gc_end() {
#ifndef USDT2
  HS_DTRACE_PROBE(hotspot, gc__end);
  HS_DTRACE_WORKAROUND_TAIL_CALL_BUG();
#else /* USDT2 */
  HOTSPOT_GC_END(
);
#endif /* USDT2 */
}

void VM_GC_Operation::acquire_pending_list_lock() {
  // we may enter this with pending exception set
  InstanceRefKlass::acquire_pending_list_lock(&_pending_list_basic_lock);
}


void VM_GC_Operation::release_and_notify_pending_list_lock() {

  InstanceRefKlass::release_and_notify_pending_list_lock(&_pending_list_basic_lock);
}

// Allocations may fail in several threads at about the same time,
// resulting in multiple gc requests.  We only want to do one of them.
// In case a GC locker is active and the need for a GC is already signalled,
// we want to skip this GC attempt altogether, without doing a futile
// safepoint operation.
bool VM_GC_Operation::skip_operation() const {
  bool skip = (_gc_count_before != Universe::heap()->total_collections());
  if (_full && skip) {
    skip = (_full_gc_count_before != Universe::heap()->total_full_collections());
  }
  if (!skip && GC_locker::is_active_and_needs_gc()) {
    skip = Universe::heap()->is_maximal_no_gc();
    assert(!(skip && (_gc_cause == GCCause::_gc_locker)),
           "GC_locker cannot be active when initiating GC");
  }
  return skip;
}

bool VM_GC_Operation::doit_prologue() {
  assert(Thread::current()->is_Java_thread(), "just checking");
  assert(((_gc_cause != GCCause::_no_gc) &&
          (_gc_cause != GCCause::_no_cause_specified)), "Illegal GCCause");

  acquire_pending_list_lock();
  // If the GC count has changed someone beat us to the collection
  // Get the Heap_lock after the pending_list_lock.
  Heap_lock->lock();

  // Check invocations
  if (skip_operation()) {
    // skip collection
    Heap_lock->unlock();
    release_and_notify_pending_list_lock();
    _prologue_succeeded = false;
  } else {
    _prologue_succeeded = true;
    SharedHeap* sh = SharedHeap::heap();
    if (sh != NULL) sh->_thread_holds_heap_lock_for_gc = true;
  }
  return _prologue_succeeded;
}


void VM_GC_Operation::doit_epilogue() {
  assert(Thread::current()->is_Java_thread(), "just checking");
  // Release the Heap_lock first.
  SharedHeap* sh = SharedHeap::heap();
  if (sh != NULL) sh->_thread_holds_heap_lock_for_gc = false;
  Heap_lock->unlock();
  release_and_notify_pending_list_lock();
}

bool VM_GC_HeapInspection::doit_prologue() {
  if (Universe::heap()->supports_heap_inspection()) {
    return VM_GC_Operation::doit_prologue();
  } else {
    return false;
  }
}

bool VM_GC_HeapInspection::skip_operation() const {
  assert(Universe::heap()->supports_heap_inspection(), "huh?");
  return false;
}

bool VM_GC_HeapInspection::collect() {
  if (GC_locker::is_active()) {
    return false;
  }
  Universe::heap()->collect_as_vm_thread(GCCause::_heap_inspection);
  return true;
}

void VM_GC_HeapInspection::doit() {
  HandleMark hm;
  Universe::heap()->ensure_parsability(false); // must happen, even if collection does
                                               // not happen (e.g. due to GC_locker)
                                               // or _full_gc being false
  if (_full_gc) {
    if (!collect()) {
      // The collection attempt was skipped because the gc locker is held.
      // The following dump may then be a tad misleading to someone expecting
      // only live objects to show up in the dump (see CR 6944195). Just issue
      // a suitable warning in that case and do not attempt to do a collection.
      // The latter is a subtle point, because even a failed attempt
      // to GC will, in fact, induce one in the future, which we
      // probably want to avoid in this case because the GC that we may
      // be about to attempt holds value for us only
      // if it happens now and not if it happens in the eventual
      // future.
      warning("GC locker is held; pre-dump GC was skipped");
    }
  }
  HeapInspection inspect(_csv_format, _print_help, _print_class_stats,
                         _columns);
  inspect.heap_inspection(_out);
}


void VM_GenCollectForAllocation::doit() {
  SvcGCMarker sgcm(SvcGCMarker::MINOR);

  GenCollectedHeap* gch = GenCollectedHeap::heap();
  GCCauseSetter gccs(gch, _gc_cause);
  _res = gch->satisfy_failed_allocation(_size, _tlab);
  assert(gch->is_in_reserved_or_null(_res), "result not in heap");

  if (_res == NULL && GC_locker::is_active_and_needs_gc()) {
    set_gc_locked();
  }
}

void VM_GenCollectFull::doit() {
  SvcGCMarker sgcm(SvcGCMarker::FULL);

  GenCollectedHeap* gch = GenCollectedHeap::heap();
  GCCauseSetter gccs(gch, _gc_cause);
  gch->do_full_collection(gch->must_clear_all_soft_refs(), _max_level);
}

void VM_CollectForMetadataAllocation::doit() {
  SvcGCMarker sgcm(SvcGCMarker::FULL);

  CollectedHeap* heap = Universe::heap();
  GCCauseSetter gccs(heap, _gc_cause);

  // Check again if the space is available.  Another thread
  // may have similarly failed a metadata allocation and induced
  // a GC that freed space for the allocation.
  if (!MetadataAllocationFailALot) {
    _result = _loader_data->metaspace_non_null()->allocate(_size, _mdtype);
  }

  if (_result == NULL) {
    if (UseConcMarkSweepGC) {
      if (CMSClassUnloadingEnabled) {
        MetaspaceGC::set_should_concurrent_collect(true);
      }
      // For CMS expand since the collection is going to be concurrent.
      _result =
        _loader_data->metaspace_non_null()->expand_and_allocate(_size, _mdtype);
    }
    if (_result == NULL) {
      // Don't clear the soft refs yet.
      if (Verbose && PrintGCDetails && UseConcMarkSweepGC) {
        gclog_or_tty->print_cr("\nCMS full GC for Metaspace");
      }
      heap->collect_as_vm_thread(GCCause::_metadata_GC_threshold);
      // After a GC try to allocate without expanding.  Could fail
      // and expansion will be tried below.
      _result =
        _loader_data->metaspace_non_null()->allocate(_size, _mdtype);
    }
    if (_result == NULL) {
      // If still failing, allow the Metaspace to expand.
      // See delta_capacity_until_GC() for explanation of the
      // amount of the expansion.
      // This should work unless there really is no more space
      // or a MaxMetaspaceSize has been specified on the command line.
      _result =
        _loader_data->metaspace_non_null()->expand_and_allocate(_size, _mdtype);
      if (_result == NULL) {
        // If expansion failed, do a last-ditch collection and try allocating
        // again.  A last-ditch collection will clear softrefs.  This
        // behavior is similar to the last-ditch collection done for perm
        // gen when it was full and a collection for failed allocation
        // did not free perm gen space.
        heap->collect_as_vm_thread(GCCause::_last_ditch_collection);
        _result =
          _loader_data->metaspace_non_null()->allocate(_size, _mdtype);
      }
    }
    if (Verbose && PrintGCDetails && _result == NULL) {
      gclog_or_tty->print_cr("\nAfter Metaspace GC failed to allocate size "
                             SIZE_FORMAT, _size);
    }
  }

  if (_result == NULL && GC_locker::is_active_and_needs_gc()) {
    set_gc_locked();
  }
}

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