base/memory/discardable_memory_allocator_android.h

   1 // Copyright 2013 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 BASE_MEMORY_DISCARDABLE_MEMORY_ALLOCATOR_H_
   6 #define BASE_MEMORY_DISCARDABLE_MEMORY_ALLOCATOR_H_
   7
   8 #include <string>
   9
  10 #include "base/base_export.h"
  11 #include "base/basictypes.h"
  12 #include "base/memory/scoped_ptr.h"
  13 #include "base/memory/scoped_vector.h"
  14 #include "base/synchronization/lock.h"
  15 #include "base/threading/thread_checker.h"
  16
  17 namespace base {
  18
  19 class DiscardableMemory;
  20
  21 namespace internal {
  22
  23 // On Android ashmem is used to implement discardable memory. It is backed by a
  24 // file (descriptor) thus is a limited resource. This allocator minimizes the
  25 // problem by allocating large ashmem regions internally and returning smaller
  26 // chunks to the client.
  27 // Allocated chunks are systematically aligned on a page boundary therefore this
  28 // allocator should not be used for small allocations.
  29 //
  30 // Threading: The allocator must be deleted on the thread it was constructed on
  31 // although its Allocate() method can be invoked on any thread. See
  32 // discardable_memory.h for DiscardableMemory's threading guarantees.
  33 class BASE_EXPORT_PRIVATE DiscardableMemoryAllocator {
  34  public:
  35   // Note that |name| is only used for debugging/measurement purposes.
  36   // |ashmem_region_size| is the size that will be used to create the underlying
  37   // ashmem regions and is expected to be greater or equal than 32 MBytes.
  38   DiscardableMemoryAllocator(const std::string& name,
  39                              size_t ashmem_region_size);
  40
  41   ~DiscardableMemoryAllocator();
  42
  43   // Note that the allocator must outlive the returned DiscardableMemory
  44   // instance.
  45   scoped_ptr<DiscardableMemory> Allocate(size_t size);
  46
  47   // Returns the size of the last ashmem region which was created. This is used
  48   // for testing only.
  49   size_t last_ashmem_region_size() const;
  50
  51  private:
  52   class AshmemRegion;
  53   class DiscardableAshmemChunk;
  54
  55   void DeleteAshmemRegion_Locked(AshmemRegion* region);
  56
  57   ThreadChecker thread_checker_;
  58   const std::string name_;
  59   const size_t ashmem_region_size_;
  60   mutable Lock lock_;
  61   size_t last_ashmem_region_size_;
  62   ScopedVector<AshmemRegion> ashmem_regions_;
  63
  64   DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryAllocator);
  65 };
  66
  67 }  // namespace internal
  68 }  // namespace base
  69
  70 #endif  // BASE_MEMORY_DISCARDABLE_MEMORY_ALLOCATOR_H_