// 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 "third_party/blink/renderer/platform/heap/gc_info.h"

#include "third_party/blink/renderer/platform/heap/heap.h"

namespace blink {

namespace {

inline uintptr_t RoundUpToPageAllocationGranularity(uintptr_t address) {
  return (address + base::kPageAllocationGranularityOffsetMask) &
         base::kPageAllocationGranularityBaseMask;
}

constexpr inline bool IsPowerOfTwo(size_t value) {
  return value > 0 && (value & (value - 1)) == 0;
}

constexpr size_t kEntrySize = sizeof(GCInfo*);
constexpr int kGcInfoZapValue = 0x33;

// Allocation and resizing are built around the following invariants.
static_assert(IsPowerOfTwo(kEntrySize),
              "GCInfoTable entries size must be power of "
              "two");
static_assert(
    0 == base::kPageAllocationGranularity % base::kSystemPageSize,
    "System page size must be a multiple of page page allocation granularity");

size_t ComputeInitialTableLimit() {
  // (Light) experimentation suggests that Blink doesn't need more than this
  // while handling content on popular web properties.
  constexpr size_t kInitialWantedLimit = 512;

  // Different OSes have different page sizes, so we have to choose the minimum
  // of memory wanted and OS page size.
  constexpr size_t memory_wanted = kInitialWantedLimit * kEntrySize;
  return RoundUpToPageAllocationGranularity(memory_wanted) / kEntrySize;
}

size_t MaxTableSize() {
  static const size_t kMaxTableSize =
      RoundUpToPageAllocationGranularity(GCInfoTable::kMaxIndex * kEntrySize);
  return kMaxTableSize;
}

}  // namespace

void GCInfoTable::EnsureGCInfoIndex(const GCInfo* gc_info,
                                    size_t* gc_info_index_slot) {
  DCHECK(gc_info);
  DCHECK(gc_info_index_slot);

  // Ensuring a new index involves current index adjustment as well
  // as potentially resizing the table, both operations that require
  // a lock.
  MutexLocker locker(table_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 (*gc_info_index_slot)
    return;

  int index = ++current_index_;
  size_t gc_info_index = static_cast<size_t>(index);
  CHECK(gc_info_index < GCInfoTable::kMaxIndex);
  if (current_index_ >= limit_)
    Resize();

  table_[gc_info_index] = gc_info;
  ReleaseStore(reinterpret_cast<int*>(gc_info_index_slot), index);
}

void GCInfoTable::Resize() {
  const size_t new_limit = (limit_) ? 2 * limit_ : ComputeInitialTableLimit();
  const size_t old_committed_size = limit_ * kEntrySize;
  const size_t new_committed_size = new_limit * kEntrySize;
  CHECK(table_);
  CHECK_EQ(0u, new_committed_size % base::kPageAllocationGranularity);
  CHECK_GE(MaxTableSize(), limit_ * kEntrySize);

  // Recommitting and zapping assumes byte-addressable storage.
  uint8_t* const current_table_end =
      reinterpret_cast<uint8_t*>(table_) + old_committed_size;
  const size_t table_size_delta = new_committed_size - old_committed_size;

  // Commit the new size and allow read/write.
  // TODO(ajwong): SetSystemPagesAccess should be part of RecommitSystemPages to
  // avoid having two calls here.
  bool ok = base::SetSystemPagesAccess(current_table_end, table_size_delta,
                                       base::PageReadWrite);
  CHECK(ok);
  ok = base::RecommitSystemPages(current_table_end, table_size_delta,
                                 base::PageReadWrite);
  CHECK(ok);

  // Zap unused values.,
  memset(current_table_end, kGcInfoZapValue, table_size_delta);

  limit_ = new_limit;
}

GCInfoTable::GCInfoTable() {
  CHECK(!table_);
  table_ = reinterpret_cast<GCInfo const**>(base::AllocPages(
      nullptr, MaxTableSize(), base::kPageAllocationGranularity,
      base::PageInaccessible));
  CHECK(table_);
  Resize();
}

#if DCHECK_IS_ON()
void AssertObjectHasGCInfo(const void* payload, size_t gc_info_index) {
  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.
  DCHECK_EQ(HeapObjectHeader::FromPayload(payload)->GcInfoIndex(),
            gc_info_index);
#endif
}
#endif

}  // namespace blink