third_party/blink/renderer/platform/heap/address_cache.h

// Copyright 2018 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.

#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_ADDRESS_CACHE_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_ADDRESS_CACHE_H_

#include "third_party/blink/renderer/platform/heap/blink_gc.h"
#include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"

namespace blink {

// Negative cache for addresses outside of Blink's garbage collected heap.
// - Internally maps to pages (NormalPage) to cover a larger range of addresses.
// - Requires flushing when adding new addresses.
class PLATFORM_EXPORT AddressCache {
  USING_FAST_MALLOC(AddressCache);

 public:
  class PLATFORM_EXPORT EnabledScope {
    STACK_ALLOCATED();

   public:
    explicit EnabledScope(AddressCache*);
    ~EnabledScope();

   private:
    AddressCache* const address_cache_;
  };

  AddressCache()
      : entries_{}, enabled_(false), has_entries_(false), dirty_(false) {}

  void EnableLookup() { enabled_ = true; }
  void DisableLookup() { enabled_ = false; }

  void MarkDirty() { dirty_ = true; }
  void Flush();
  void FlushIfDirty();
  bool IsEmpty() const { return !has_entries_; }

  // Perform a lookup in the cache. Returns true if the address is guaranteed
  // to not in Blink's heap and false otherwise.
  bool Lookup(Address);

  // Add an entry to the cache.
  void AddEntry(Address);

 private:
  static constexpr size_t kNumberOfEntriesLog2 = 12;
  static constexpr size_t kNumberOfEntries = 1 << kNumberOfEntriesLog2;

  static size_t GetHash(Address);

  Address entries_[kNumberOfEntries];
  bool enabled_ : 1;
  bool has_entries_ : 1;
  bool dirty_ : 1;
};

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_ADDRESS_CACHE_H_