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// Copyright (c) 2006-2008 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/shared_memory.h"
#include "base/task.h"
namespace command_buffer {
// Common interface for CommandBuffer implementations.
class CommandBuffer {
CommandBuffer() {
virtual ~CommandBuffer() {
// Initialize the command buffer with the given ring buffer. Takes ownership
// of ring buffer.
virtual bool Initialize(::base::SharedMemory* ring_buffer) = 0;
// Gets the shared memory ring buffer object for the command buffer.
virtual ::base::SharedMemory* GetRingBuffer() = 0;
virtual int32 GetSize() = 0;
// The writer calls this to update its put offset. This function returns the
// reader's most recent get offset. Does not return until after the put offset
// change callback has been invoked. Returns -1 if the put offset is invalid.
virtual int32 SyncOffsets(int32 put_offset) = 0;
// Returns the current get offset. This can be called from any thread.
virtual int32 GetGetOffset() = 0;
// Sets the current get offset. This can be called from any thread.
virtual void SetGetOffset(int32 get_offset) = 0;
// Returns the current put offset. This can be called from any thread.
virtual int32 GetPutOffset() = 0;
// Sets a callback that should be posted on another thread whenever the put
// offset is changed. The callback must not return until some progress has
// been made (unless the command buffer is empty), i.e. the
// get offset must have changed. It need not process the entire command
// buffer though. This allows concurrency between the writer and the reader
// while giving the writer a means of waiting for the reader to make some
// progress before attempting to write more to the command buffer. Avoiding
// the use of a synchronization primitive like a condition variable to
// synchronize reader and writer reduces the risk of deadlock.
// Takes ownership of callback. The callback is invoked on the plugin thread.
virtual void SetPutOffsetChangeCallback(Callback0::Type* callback) = 0;
// Create a shared memory transfer buffer and return a handle that uniquely
// identifies it or -1 on error.
virtual int32 CreateTransferBuffer(size_t size) = 0;
// Destroy a shared memory transfer buffer and recycle the handle.
virtual void DestroyTransferBuffer(int32 id) = 0;
// Get the shared memory associated with a handle.
virtual ::base::SharedMemory* GetTransferBuffer(int32 handle) = 0;
// Get the current token value. This is used for by the writer to defer
// changes to shared memory objects until the reader has reached a certain
// point in the command buffer. The reader is responsible for updating the
// token value, for example in response to an asynchronous set token command
// embedded in the command buffer. The default token value is zero.
virtual int32 GetToken() = 0;
// Allows the reader to update the current token value.
virtual void SetToken(int32 token) = 0;
// Get the current parse error and reset it to zero. Zero means no error. Non-
// zero means error. The default error status is zero.
virtual int32 ResetParseError() = 0;
// Allows the reader to set the current parse error.
virtual void SetParseError(int32 parse_error) = 0;
// Returns whether the command buffer is in the error state.
virtual bool GetErrorStatus() = 0;
// Allows the reader to set the error status. Once in an error state, the
// command buffer cannot recover and ceases to process commands.
virtual void RaiseErrorStatus() = 0;
} // namespace command_buffer