[heap] introduce ArrayBufferTracker

src/heap/array-buffer-tracker.h

+// Copyright 2015 the V8 project 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 V8_HEAP_ARRAY_BUFFER_TRACKER_H_
+#define V8_HEAP_ARRAY_BUFFER_TRACKER_H_
+
+#include <map>
+
+#include "src/globals.h"
+
+namespace v8 {
+namespace internal {
+
+// Forward declarations.
+class Heap;
+class JSArrayBuffer;
+
+class ArrayBufferTracker {
+ public:
+  explicit ArrayBufferTracker(Heap* heap) : heap_(heap) {}
+  ~ArrayBufferTracker();
+
+  inline Heap* heap() { return heap_; }
+
+  // The following methods are used to track raw C++ pointers to externally
+  // allocated memory used as backing store in live array buffers.
+
+  // A new ArrayBuffer was created with |data| as backing store.
+  void RegisterNew(JSArrayBuffer* buffer);
+
+  // The backing store |data| is no longer owned by V8.
+  void Unregister(JSArrayBuffer* buffer);
+
+  // A live ArrayBuffer was discovered during marking/scavenge.
+  void MarkLive(JSArrayBuffer* buffer);
+
+  // Frees all backing store pointers that weren't discovered in the previous
+  // marking or scavenge phase.
+  void FreeDead(bool from_scavenge);
+
+  // Prepare for a new scavenge phase. A new marking phase is implicitly
+  // prepared by finishing the previous one.
+  void PrepareDiscoveryInNewSpace();
+
+  // An ArrayBuffer moved from new space to old space.
+  void Promote(JSArrayBuffer* buffer);
+
+ private:
+  Heap* heap_;
+
+  // |live_array_buffers_| maps externally allocated memory used as backing
+  // store for ArrayBuffers to the length of the respective memory blocks.
+  //
+  // At the beginning of mark/compact, |not_yet_discovered_array_buffers_| is
+  // a copy of |live_array_buffers_| and we remove pointers as we discover live
+  // ArrayBuffer objects during marking. At the end of mark/compact, the
+  // remaining memory blocks can be freed.
+  std::map<void*, size_t> live_array_buffers_;
+  std::map<void*, size_t> not_yet_discovered_array_buffers_;
+
+  // To be able to free memory held by ArrayBuffers during scavenge as well, we
+  // have a separate list of allocated memory held by ArrayBuffers in new space.
+  //
+  // Since mark/compact also evacuates the new space, all pointers in the
+  // |live_array_buffers_for_scavenge_| list are also in the
+  // |live_array_buffers_| list.
+  std::map<void*, size_t> live_array_buffers_for_scavenge_;
+  std::map<void*, size_t> not_yet_discovered_array_buffers_for_scavenge_;
+};
+}
+}  // namespace v8::internal
+#endif  // V8_HEAP_ARRAY_BUFFER_TRACKER_H_