Fix race condition in DataFetcherSharedMemoryBase

content/browser/device_orientation/data_fetcher_shared_memory_default.cc

 // 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.
 
 #include "data_fetcher_shared_memory.h"
 
 #include "base/logging.h"
 #include "content/common/device_motion_hardware_buffer.h"
 #include "content/common/device_orientation/device_orientation_hardware_buffer.h"
 
 namespace {
 
 static bool SetMotionBuffer(content::DeviceMotionHardwareBuffer* buffer,
     bool enabled) {
-  DCHECK(buffer);
+  if (!buffer)
+    return false;
   buffer->seqlock.WriteBegin();
   buffer->data.allAvailableSensorsAreActive = enabled;
   buffer->seqlock.WriteEnd();
   return true;
 }
 
 }
 
 namespace content {
 
 DataFetcherSharedMemory::DataFetcherSharedMemory() {
 }
 
 DataFetcherSharedMemory::~DataFetcherSharedMemory() {
 }
 
-bool DataFetcherSharedMemory::Start(ConsumerType consumer_type) {
-  void* buffer = GetSharedMemoryBuffer(consumer_type);
+bool DataFetcherSharedMemory::Start(ConsumerType consumer_type, void* buffer) {
   DCHECK(buffer);
 
   switch (consumer_type) {
     case CONSUMER_TYPE_MOTION:
-      return SetMotionBuffer(
-          static_cast<DeviceMotionHardwareBuffer*>(buffer), true);
+      motion_buffer_ = static_cast<DeviceMotionHardwareBuffer*>(buffer);
+      return SetMotionBuffer(motion_buffer_, true);
     case CONSUMER_TYPE_ORIENTATION:
       NOTIMPLEMENTED();
       break;
     default:
       NOTREACHED();
   }
   return false;
 }
 
 bool DataFetcherSharedMemory::Stop(ConsumerType consumer_type) {
-  void* buffer = GetSharedMemoryBuffer(consumer_type);
-  DCHECK(buffer);
 
   switch (consumer_type) {
     case CONSUMER_TYPE_MOTION:
-      return SetMotionBuffer(
-          static_cast<DeviceMotionHardwareBuffer*>(buffer), false);
+      return SetMotionBuffer(motion_buffer_, false);
     case CONSUMER_TYPE_ORIENTATION:
       NOTIMPLEMENTED();
       break;
     default:
       NOTREACHED();
   }
   return false;
 }
 
 }  // namespace content