base: Add free list implementation to browser-wide discardable memory system.

content/common/discardable_shared_memory_heap.h

+// Copyright 2014 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 CONTENT_COMMON_DISCARDABLE_SHARED_MEMORY_HEAP_H_
+#define CONTENT_COMMON_DISCARDABLE_SHARED_MEMORY_HEAP_H_
+
+#include <bitset>
+
+#include "base/containers/hash_tables.h"
+#include "base/containers/linked_list.h"
+#include "base/memory/linked_ptr.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/scoped_vector.h"
+#include "content/common/content_export.h"
+
+namespace base {
+class DiscardableSharedMemory;
+}
+
+namespace content {
+
+// Implements a heap of discardable shared memory. A free list is used to keep
+// track of free blocks.
+class CONTENT_EXPORT DiscardableSharedMemoryHeap {
+ public:
+  class CONTENT_EXPORT Span : public base::LinkNode<Span> {
+   public:
+    ~Span();
+
+    base::DiscardableSharedMemory* shared_memory() {
+      return shared_memory_.get();
+    }
+    size_t start() const { return start_; }
+    size_t length() const { return length_; }
+
+   private:
+    friend class DiscardableSharedMemoryHeap;
+
+    Span(linked_ptr<base::DiscardableSharedMemory> shared_memory,
+         size_t start,
+         size_t length);
+
+    linked_ptr<base::DiscardableSharedMemory> shared_memory_;
+    size_t start_;
+    size_t length_;
+
+    DISALLOW_COPY_AND_ASSIGN(Span);
+  };
+
+  explicit DiscardableSharedMemoryHeap(size_t block_size);
+  ~DiscardableSharedMemoryHeap();
+
+  // Grow heap using |memory| and return a span for this new memory.
+  // |memory| must be aligned to the block size and |size| must be a
+  // multiple of the block size.
+  scoped_ptr<Span> Grow(scoped_ptr<base::DiscardableSharedMemory> memory,
+                        size_t size);
+
+  // Merge |span| into the free list. This will coalesce |span| with
+  // neighboring spans in free list when possible.
+  void MergeIntoFreeList(scoped_ptr<Span> span);
+
+  // Split an allocated span into two spans, one of length |blocks| followed
+  // by another span of length "span->length - blocks" blocks. Modifies |span|
+  // to point to the first span of length |blocks|. Return second span.
+  scoped_ptr<Span> Split(Span* span, size_t blocks);
+
+  // Search free list for span that satisfies the request for |blocks| of
+  // memory. If found, the span is removed from the free list and returned.
+  scoped_ptr<Span> SearchFreeList(size_t blocks);
+
+  // Delete span and release memory if possible.
+  void DeleteSpan(scoped_ptr<Span> span);
+
+ private:
+  scoped_ptr<Span> RemoveFromFreeList(Span* span);
+  scoped_ptr<Span> Carve(Span* span, size_t blocks);
+  void RegisterSpan(Span* span);
+
+  size_t block_size_;
+
+  // Mapping from first/last block of span to Span instance.
+  typedef base::hash_map<size_t, Span*> SpanMap;
+  SpanMap spans_;
+
+  // Linked-list of free discardable memory regions.
+  base::LinkedList<Span> free_spans_;
+
+  DISALLOW_COPY_AND_ASSIGN(DiscardableSharedMemoryHeap);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_COMMON_DISCARDABLE_SHARED_MEMORY_HEAP_H_