Reland "[heap] Fine-grained JSArrayBuffer tracking"

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/allocation.h"
 #include "src/base/platform/mutex.h"
 #include "src/globals.h"
 
 namespace v8 {
 namespace internal {
 
-// Forward declarations.
 class Heap;
 class JSArrayBuffer;
+class Page;
 
-class ArrayBufferTracker {
+class ArrayBufferTracker : public AllStatic {
  public:
-  explicit ArrayBufferTracker(Heap* heap) : heap_(heap) {}
-  ~ArrayBufferTracker();
-
-  inline Heap* heap() { return heap_; }
+  enum ProcessingMode {
+    kUpdateForwardedRemoveOthers,
+    kUpdateForwardedKeepOthers,
+  };
 
   // 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);
+  // Register/unregister a new JSArrayBuffer |buffer| for tracking.
+  static void RegisterNew(Heap* heap, JSArrayBuffer* buffer);
+  static void Unregister(Heap* heap, JSArrayBuffer* buffer);
 
-  // The backing store |data| is no longer owned by V8.
-  void Unregister(JSArrayBuffer* buffer);
+  // Frees all backing store pointers for dead JSArrayBuffers in new space.
+  static void FreeDeadInNewSpace(Heap* heap);
 
-  // A live ArrayBuffer was discovered during marking/scavenge.
-  void MarkLive(JSArrayBuffer* buffer);
+  // Frees all backing store pointers for dead JSArrayBuffer on a given page.
+  // Requires marking information to be present.
+  static void FreeDead(Page* page);
 
-  // Frees all backing store pointers that weren't discovered in the previous
-  // marking or scavenge phase.
-  void FreeDead(bool from_scavenge);
+  // Processes all array buffers on a given page. |mode| specifies the action
+  // to perform on the buffers.
+  static void ProcessBuffers(Page* page, ProcessingMode mode);
 
-  // Prepare for a new scavenge phase. A new marking phase is implicitly
-  // prepared by finishing the previous one.
-  void PrepareDiscoveryInNewSpace();
+  // Returns whether a buffer is currently tracked.
+  static bool IsTracked(JSArrayBuffer* buffer);
+};
 
-  // An ArrayBuffer moved from new space to old space.
-  void Promote(JSArrayBuffer* buffer);
+// LocalArrayBufferTracker tracks internalized array buffers.
+//
+// Never use directly but instead always call through |ArrayBufferTracker|.
+class LocalArrayBufferTracker {
+ public:
+  typedef std::pair<void*, size_t> Value;
+  typedef JSArrayBuffer* Key;
+
+  enum CallbackResult { kKeepEntry, kUpdateEntry, kRemoveEntry };
+
+  explicit LocalArrayBufferTracker(Heap* heap) : heap_(heap) {}
+  ~LocalArrayBufferTracker();
+
+  void Add(Key key, const Value& value);
+  Value Remove(Key key);
+
+  // Frees up any buffers that are currently not marked.
+  void FreeDead();
+
+  // Processes buffers one by one. The CallbackResult of the callback decides
+  // what action to take on the buffer.
+  //
+  // Callback should be of type:
+  //   CallbackResult fn(JSArrayBuffer* buffer, JSArrayBuffer** new_buffer);
+  template <typename Callback>
+  inline void Process(Callback callback);
+
+  bool IsEmpty() { return array_buffers_.empty(); }
+
+  bool IsTracked(Key key) {
+    return array_buffers_.find(key) != array_buffers_.end();
+  }
 
  private:
-  base::Mutex mutex_;
+  // TODO(mlippautz): Switch to unordered_map once it is supported on all
+  // platforms.
+  typedef std::map<Key, Value> TrackingMap;
+
   Heap* heap_;
+  TrackingMap array_buffers_;
+};
 
-  // |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 internal
 }  // namespace v8
 #endif  // V8_HEAP_ARRAY_BUFFER_TRACKER_H_