Use DiscardableMemoryManager on Android.

base/memory/discardable_memory_ashmem.cc

+// 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.
+
+#include "base/memory/discardable_memory_ashmem.h"
+
+#include "base/memory/discardable_memory_allocator_android.h"
+
+namespace base {
+namespace internal {
+
+DiscardableMemoryAshmem::DiscardableMemoryAshmem(
+    size_t size,
+    DiscardableMemoryAllocator* allocator,
+    DiscardableMemoryManager* manager)
+    : allocator_(allocator),
+      manager_(manager) {
+  manager_->Register(this, size);
+}
+
+DiscardableMemoryAshmem::~DiscardableMemoryAshmem() {
+  // Note that this will call Purge() below while the manager's mutex is
+  // acquired which allows the ashmem allocator not to have any mutex.
+  manager_->Unregister(this);
+  DCHECK(!ashmem_chunk_);
+}
+
+bool DiscardableMemoryAshmem::Initialize() {
+  return Lock() == DISCARDABLE_MEMORY_LOCK_STATUS_SUCCESS;
+}
+
+DiscardableMemoryLockStatus DiscardableMemoryAshmem::Lock() {
+  bool purged = false;
+  if (!manager_->AcquireLock(this, &purged))
+    return DISCARDABLE_MEMORY_LOCK_STATUS_FAILED;
+
+  return purged ? DISCARDABLE_MEMORY_LOCK_STATUS_PURGED
+                : DISCARDABLE_MEMORY_LOCK_STATUS_SUCCESS;
+}
+
+void DiscardableMemoryAshmem::Unlock() {
+  manager_->ReleaseLock(this);
+}
+
+void* DiscardableMemoryAshmem::Memory() const {
+  DCHECK(ashmem_chunk_);
+  return ashmem_chunk_->Memory();
+}
+
+// Note that the methods below are called by the manager while its internal
+// mutex is acquired which means that they don't need extra synchronization.
+
+bool DiscardableMemoryAshmem::AllocateAndAcquireLock(size_t bytes) {
+  if (ashmem_chunk_)
+    return ashmem_chunk_->Lock();
+
+  ashmem_chunk_ = allocator_->Allocate(bytes);
+  return !!ashmem_chunk_;
+}
+
+void DiscardableMemoryAshmem::ReleaseLock() {
+  ashmem_chunk_->Unlock();
+}
+
+void DiscardableMemoryAshmem::Purge() {
+  ashmem_chunk_.reset();
+}
+
+}  // namespace internal
+}  // namespace base