Implement the content/renderer and content/browser part of the Device Motion API.

content/renderer/shared_memory_seqlock_reader.h

+// Copyright (c) 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 CONTENT_RENDERER_SHARED_MEMORY_SEQLOCK_READER_H_
+#define CONTENT_RENDERER_SHARED_MEMORY_SEQLOCK_READER_H_
+
+#include "base/logging.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/shared_memory.h"
+#include "content/common/shared_memory_seqlock_buffer.h"
+
+namespace internal {
+
+class SharedMemorySeqLockReaderBase  {
+ protected:
+  SharedMemorySeqLockReaderBase();
+  virtual ~SharedMemorySeqLockReaderBase();
+
+  void* InitializeSharedMemory(
+      base::SharedMemoryHandle shared_memory_handle,
+      size_t buffer_size);
+
+  bool FetchFromBuffer(content::OneWriterSeqLock* seqlock, void* final,
+      void* temp, void* from, size_t size);
+
+  static const int kMaximumContentionCount = 10;
+  base::SharedMemoryHandle renderer_shared_memory_handle_;
+  scoped_ptr<base::SharedMemory> renderer_shared_memory_;
+};
+
+}  // namespace internal
+
+namespace content {
+
+// Template argument Data should be a pod-like structure only containing
+// data fields, such that it is copyable by memcpy method.
+template<typename Data>
+class SharedMemorySeqLockReader
+    : private internal::SharedMemorySeqLockReaderBase {
+ public:
+  SharedMemorySeqLockReader() : buffer_(0) { }
+  virtual ~SharedMemorySeqLockReader() { }
+
+  bool GetLatestData(Data* data) {
+    DCHECK(buffer_);
+    DCHECK(sizeof(*data) == sizeof(*temp_buffer_));
+    return FetchFromBuffer(&buffer_->seqlock, data, temp_buffer_.get(),
+        &buffer_->data, sizeof(*temp_buffer_));
+  }
+
+  bool Initialize(base::SharedMemoryHandle shared_memory_handle) {
+    if (void* memory = InitializeSharedMemory(
+        shared_memory_handle, sizeof(SharedMemorySeqLockBuffer<Data>))) {
+      buffer_ = static_cast<SharedMemorySeqLockBuffer<Data>*>(memory);
+      temp_buffer_.reset(new Data);
+      return true;
+    }
+    return false;
+  }
+
+ private:
+  SharedMemorySeqLockBuffer<Data>* buffer_;
+  scoped_ptr<Data> temp_buffer_;
+
+  DISALLOW_COPY_AND_ASSIGN(SharedMemorySeqLockReader);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_SHARED_MEMORY_SEQLOCK_READER_H_