// Copyright 2013 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 BASE_MEMORY_DISCARDABLE_MEMORY_ALLOCATOR_H_
#define BASE_MEMORY_DISCARDABLE_MEMORY_ALLOCATOR_H_
#include <string>
#include "base/base_export.h"
#include "base/basictypes.h"
#include "base/memory/scoped_ptr.h"
#include "base/memory/scoped_vector.h"
#include "base/synchronization/lock.h"
#include "base/threading/thread_checker.h"
namespace base {
class DiscardableMemory;
namespace internal {
// On Android ashmem is used to implement discardable memory. It is backed by a
// file (descriptor) thus is a limited resource. This allocator minimizes the
// problem by allocating large ashmem regions internally and returning smaller
// chunks to the client.
// Allocated chunks are systematically aligned on a page boundary therefore this
// allocator should not be used for small allocations.
//
// Threading: The allocator must be deleted on the thread it was constructed on
// although its Allocate() method can be invoked on any thread. See
// discardable_memory.h for DiscardableMemory's threading guarantees.
class BASE_EXPORT_PRIVATE DiscardableMemoryAllocator {
public:
// Note that |name| is only used for debugging/measurement purposes.
// |ashmem_region_size| is the size that will be used to create the underlying
// ashmem regions and is expected to be greater or equal than 32 MBytes.
DiscardableMemoryAllocator(const std::string& name,
size_t ashmem_region_size);
~DiscardableMemoryAllocator();
// Note that the allocator must outlive the returned DiscardableMemory
// instance.
scoped_ptr<DiscardableMemory> Allocate(size_t size);
// Returns the size of the last ashmem region which was created. This is used
// for testing only.
size_t last_ashmem_region_size() const;
private:
class AshmemRegion;
class DiscardableAshmemChunk;
void DeleteAshmemRegion_Locked(AshmemRegion* region);
ThreadChecker thread_checker_;
const std::string name_;
const size_t ashmem_region_size_;
mutable Lock lock_;
size_t last_ashmem_region_size_;
ScopedVector<AshmemRegion> ashmem_regions_;
DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryAllocator);
};
} // namespace internal
} // namespace base
#endif // BASE_MEMORY_DISCARDABLE_MEMORY_ALLOCATOR_H_