components/html_viewer/discardable_memory_allocator.h

   1 // Copyright 2015 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef COMPONENTS_HTML_VIEWER_DISCARDABLE_MEMORY_ALLOCATOR_H_
   6 #define COMPONENTS_HTML_VIEWER_DISCARDABLE_MEMORY_ALLOCATOR_H_
   7
   8 #include <list>
   9
  10 #include "base/memory/discardable_memory_allocator.h"
  11 #include "base/synchronization/lock.h"
  12
  13 namespace html_viewer {
  14
  15 // A discarable memory allocator which will unallocate chunks on new
  16 // allocations.
  17 class DiscardableMemoryAllocator : public base::DiscardableMemoryAllocator {
  18  public:
  19   explicit DiscardableMemoryAllocator(size_t desired_max_memory);
  20   ~DiscardableMemoryAllocator() override;
  21
  22   // Overridden from DiscardableMemoryAllocator:
  23   scoped_ptr<base::DiscardableMemory> AllocateLockedDiscardableMemory(
  24       size_t size) override;
  25
  26  private:
  27   class DiscardableMemoryChunkImpl;
  28   friend class DiscardableMemoryChunkImpl;
  29
  30   // Called by DiscardableMemoryChunkImpl when they are unlocked. This puts them
  31   // at the end of the live_unlocked_chunks_ list and passes an iterator to
  32   // their position in the unlocked chunk list.
  33   std::list<DiscardableMemoryChunkImpl*>::iterator NotifyUnlocked(
  34       DiscardableMemoryChunkImpl* chunk);
  35
  36   // Called by DiscardableMemoryChunkImpl when they are locked. This removes the
  37   // passed in unlocked chunk list.
  38   void NotifyLocked(std::list<DiscardableMemoryChunkImpl*>::iterator it);
  39
  40   // Called by DiscardableMemoryChunkImpl when it's destructed. It must be
  41   // unlocked, by definition.
  42   void NotifyDestructed(std::list<DiscardableMemoryChunkImpl*>::iterator it);
  43
  44   // The amount of memory we can allocate before we try to free unlocked
  45   // chunks. We can go over this amount if all callers keep their discardable
  46   // chunks locked.
  47   const size_t desired_max_memory_;
  48
  49   // Protects all members below, since this class can be called on the main
  50   // thread and impl side painting raster threads.
  51   base::Lock lock_;
  52
  53   // A count of the sum of memory. Used to trigger discarding the oldest
  54   // memory.
  55   size_t total_live_memory_;
  56
  57   // The number of locked chunks.
  58   int locked_chunks_;
  59
  60   // A linked list of unlocked allocated chunks so that the tail is most
  61   // recently accessed chunks.
  62   std::list<DiscardableMemoryChunkImpl*> live_unlocked_chunks_;
  63
  64   DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryAllocator);
  65 };
  66
  67 }  // namespace html_viewer
  68
  69 #endif  // COMPONENTS_HTML_VIEWER_DISCARDABLE_MEMORY_ALLOCATOR_H_