third_party/WebKit/Source/platform/heap/GCInfo.cpp

// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "platform/heap/GCInfo.h"

#include "platform/heap/Handle.h"
#include "platform/heap/Heap.h"

namespace blink {

// GCInfo indices start from 1 for heap objects, with 0 being treated
// specially as the index for freelist entries and large heap objects.
int GCInfoTable::s_gcInfoIndex = 0;

size_t GCInfoTable::s_gcInfoTableSize = 0;
GCInfo const** s_gcInfoTable = nullptr;

void GCInfoTable::ensureGCInfoIndex(const GCInfo* gcInfo,
                                    size_t* gcInfoIndexSlot) {
  ASSERT(gcInfo);
  ASSERT(gcInfoIndexSlot);
  // Keep a global GCInfoTable lock while allocating a new slot.
  DEFINE_THREAD_SAFE_STATIC_LOCAL(Mutex, mutex, new Mutex);
  MutexLocker locker(mutex);

  // If more than one thread ends up allocating a slot for
  // the same GCInfo, have later threads reuse the slot
  // allocated by the first.
  if (*gcInfoIndexSlot)
    return;

  int index = ++s_gcInfoIndex;
  size_t gcInfoIndex = static_cast<size_t>(index);
  RELEASE_ASSERT(gcInfoIndex < GCInfoTable::maxIndex);
  if (gcInfoIndex >= s_gcInfoTableSize)
    resize();

  s_gcInfoTable[gcInfoIndex] = gcInfo;
  releaseStore(reinterpret_cast<int*>(gcInfoIndexSlot), index);
}

void GCInfoTable::resize() {
  static const int gcInfoZapValue = 0x33;
  // (Light) experimentation suggests that Blink doesn't need
  // more than this while handling content on popular web properties.
  const size_t initialSize = 512;

  size_t newSize = s_gcInfoTableSize ? 2 * s_gcInfoTableSize : initialSize;
  ASSERT(newSize < GCInfoTable::maxIndex);
  s_gcInfoTable = reinterpret_cast<GCInfo const**>(WTF::Partitions::fastRealloc(
      s_gcInfoTable, newSize * sizeof(GCInfo), "GCInfo"));
  ASSERT(s_gcInfoTable);
  memset(reinterpret_cast<uint8_t*>(s_gcInfoTable) +
             s_gcInfoTableSize * sizeof(GCInfo),
         gcInfoZapValue, (newSize - s_gcInfoTableSize) * sizeof(GCInfo));
  s_gcInfoTableSize = newSize;
}

void GCInfoTable::init() {
  RELEASE_ASSERT(!s_gcInfoTable);
  resize();
}

#if DCHECK_IS_ON()
void assertObjectHasGCInfo(const void* payload, size_t gcInfoIndex) {
  HeapObjectHeader::checkFromPayload(payload);
#if !defined(COMPONENT_BUILD)
  // On component builds we cannot compare the gcInfos as they are statically
  // defined in each of the components and hence will not match.
  ASSERT(HeapObjectHeader::fromPayload(payload)->gcInfoIndex() == gcInfoIndex);
#endif
}
#endif

}  // namespace blink