Make CommandBuffer::Flush asynchronous, and add CommandBuffer::FlushSync with former semantics.

gpu/command_buffer/common/command_buffer.h

 // Copyright (c) 2009 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 GPU_COMMAND_BUFFER_COMMON_COMMAND_BUFFER_H_
 #define GPU_COMMAND_BUFFER_COMMON_COMMAND_BUFFER_H_
 
 #include "../common/buffer.h"
 #include "../common/constants.h"
 
@@ skipping 43 matching lines @@
 
   // Initialize the command buffer with the given size.
   virtual bool Initialize(int32 size) = 0;
 
   // Gets the ring buffer for the command buffer.
   virtual Buffer GetRingBuffer() = 0;
 
   // Returns the current status.
   virtual State GetState() = 0;
 
+  // The writer calls this to update its put offset. This ensures the reader
+  // sees the latest added commands, and will eventually process them.
+  virtual void Flush(int32 put_offset) = 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 State Flush(int32 put_offset) = 0;
+  // As opposed to Flush(), this function guarantees that the reader has
+  // processed some commands before returning (assuming the command buffer isn't
+  // empty and there is no error).
+  virtual State FlushSync(int32 put_offset) = 0;
 
   // Sets the current get offset. This can be called from any thread.
   virtual void SetGetOffset(int32 get_offset) = 0;
 
   // Create a transfer buffer and return a handle that uniquely
   // identifies it or -1 on error.
   virtual int32 CreateTransferBuffer(size_t size) = 0;
 
   // Destroy a transfer buffer and recycle the handle.
   virtual void DestroyTransferBuffer(int32 id) = 0;
 
   // Get the transfer buffer associated with a handle.
   virtual Buffer GetTransferBuffer(int32 handle) = 0;
 
   // Allows the reader to update the current token value.
   virtual void SetToken(int32 token) = 0;
 
   // Allows the reader to set the current parse error.
   virtual void SetParseError(error::Error) = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(CommandBuffer);
 };
 
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_COMMON_COMMAND_BUFFER_H_