gpu: Reuse transfer buffers more aggresively

gpu/command_buffer/common/command_buffer.h

 // Copyright (c) 2012 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 "gpu/command_buffer/common/buffer.h"
 #include "gpu/command_buffer/common/constants.h"
 #include "gpu/gpu_export.h"
 
 namespace base {
 class SharedMemory;
 }
 
 namespace gpu {
 
 // Common interface for CommandBuffer implementations.
 class GPU_EXPORT CommandBuffer {
  public:
   struct State {
     State()
         : num_entries(0),
           get_offset(0),
           put_offset(0),
           token(-1),
+          async_token(0),
           error(error::kNoError),
           context_lost_reason(error::kUnknown),
           generation(0) {
     }
 
     // Size of the command buffer in command buffer entries.
     int32 num_entries;
 
     // The offset (in entries) from which the reader is reading.
     int32 get_offset;
 
     // The offset (in entries) at which the writer is writing.
     int32 put_offset;
 
     // The current token value. This is used 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.
     int32 token;
 
+    // The current async token. This used by the reader to synchronize with the
+    // writer that the action associated with the async token has been
+    // completed.
+    uint32 async_token;

[reveman, 2014/01/22 17:30:04]

is there a good reason this is unsigned but |token| is signed?

+
     // Error status.
     error::Error error;
 
     // Lost context detail information.
     error::ContextLostReason context_lost_reason;
 
     // Generation index of this state. The generation index is incremented every
     // time a new state is retrieved from the command processor, so that
     // consistency can be kept even if IPC messages are processed out-of-order.
     uint32 generation;
@@ skipping 53 matching lines @@
   // Destroy a transfer buffer. The ID must be positive.
   virtual void DestroyTransferBuffer(int32 id) = 0;
 
   // Get the transfer buffer associated with an ID. Returns a null buffer for
   // ID 0.
   virtual Buffer GetTransferBuffer(int32 id) = 0;
 
   // Allows the reader to update the current token value.
   virtual void SetToken(int32 token) = 0;
 
+  // Allows the reader to update the current async token value.
+  virtual void SetAsyncToken(uint32 token) = 0;
+
   // Allows the reader to set the current parse error.
   virtual void SetParseError(error::Error) = 0;
 
   // Allows the reader to set the current context lost reason.
   // NOTE: if calling this in conjunction with SetParseError,
   // call this first.
   virtual void SetContextLostReason(error::ContextLostReason) = 0;
 
 // The NaCl Win64 build only really needs the struct definitions above; having
 // GetLastError declared would mean we'd have to also define it, and pull more
 // of gpu in to the NaCl Win64 build.
 #if !defined(NACL_WIN64)
   // TODO(apatrick): this is a temporary optimization while skia is calling
   // RendererGLContext::MakeCurrent prior to every GL call. It saves returning 6
   // ints redundantly when only the error is needed for the CommandBufferProxy
   // implementation.
   virtual error::Error GetLastError();
 #endif
 
  private:
   DISALLOW_COPY_AND_ASSIGN(CommandBuffer);
 };
 
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_COMMON_COMMAND_BUFFER_H_