[Mac] A couple of improvements for DiscardableMemory

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_ashmem_allocator.h"
 
 namespace base {
 namespace internal {
 
 DiscardableMemoryAshmem::DiscardableMemoryAshmem(
     size_t bytes,
     DiscardableMemoryAshmemAllocator* allocator,
     DiscardableMemoryManager* manager)
     : bytes_(bytes),
       allocator_(allocator),
       manager_(manager),
       is_locked_(false) {
   manager_->Register(this, bytes_);
 }
 
 DiscardableMemoryAshmem::~DiscardableMemoryAshmem() {
   if (is_locked_)
-    manager_->ReleaseLock(this);
+    Unlock();
 
   manager_->Unregister(this);
 }
 
 bool DiscardableMemoryAshmem::Initialize() {
-  return Lock() == DISCARDABLE_MEMORY_LOCK_STATUS_PURGED;
+  return Lock() != DISCARDABLE_MEMORY_LOCK_STATUS_FAILED;
 }
 
 DiscardableMemoryLockStatus DiscardableMemoryAshmem::Lock() {
+  DCHECK(!is_locked_);
+
   bool purged = false;
   if (!manager_->AcquireLock(this, &purged))
     return DISCARDABLE_MEMORY_LOCK_STATUS_FAILED;
 
+  is_locked_ = true;
   return purged ? DISCARDABLE_MEMORY_LOCK_STATUS_PURGED
                 : DISCARDABLE_MEMORY_LOCK_STATUS_SUCCESS;
 }
 
 void DiscardableMemoryAshmem::Unlock() {
+  DCHECK(is_locked_);
   manager_->ReleaseLock(this);
+  is_locked_ = false;
 }
 
 void* DiscardableMemoryAshmem::Memory() const {
+  DCHECK(is_locked_);
   DCHECK(ashmem_chunk_);
   return ashmem_chunk_->Memory();
 }
 
 bool DiscardableMemoryAshmem::AllocateAndAcquireLock() {
-  DCHECK(!is_locked_);
-  is_locked_ = true;
-
   if (ashmem_chunk_)
     return ashmem_chunk_->Lock();
 
   ashmem_chunk_ = allocator_->Allocate(bytes_);
   return false;
 }
 
 void DiscardableMemoryAshmem::ReleaseLock() {
-  DCHECK(is_locked_);
   ashmem_chunk_->Unlock();
-  is_locked_ = false;
 }
 
 void DiscardableMemoryAshmem::Purge() {
-  DCHECK(!is_locked_);
   ashmem_chunk_.reset();
 }
 
 }  // namespace internal
 }  // namespace base