gpu: Reuse transfer buffers more aggresively

gpu/command_buffer/client/cmd_buffer_helper.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.
 
 // This file contains the command buffer helper class.
 
 #ifndef GPU_COMMAND_BUFFER_CLIENT_CMD_BUFFER_HELPER_H_
 #define GPU_COMMAND_BUFFER_CLIENT_CMD_BUFFER_HELPER_H_
 
 #include <string.h>
@@ skipping 65 matching lines @@
 
   // Inserts a new token into the command buffer. This token either has a value
   // different from previously inserted tokens, or ensures that previously
   // inserted tokens with that value have already passed through the command
   // stream.
   // Returns:
   //   the value of the new token or -1 if the command buffer reader has
   //   shutdown.
   int32 InsertToken();
 
+  // Returns true if the token has already passed.
+  // Parameters:
+  //   the value of the token to check whether it has passed
+  bool HasTokenPassed(int32 token) const {
+    if (token > token_)
+      return true;  // we wrapped
+    return last_token_read() >= token;
+  }
+
   // Waits until the token of a particular value has passed through the command
   // stream (i.e. commands inserted before that token have been executed).
   // NOTE: This will call Flush if it needs to block.
   // Parameters:
   //   the value of the token to wait for.
   void WaitForToken(int32 token);
 
+  // Get the serial number last read by the command buffer.
+  uint32 last_serial_read() const {
+    return command_buffer_->GetLastState().serial;
+  }
+
   // Called prior to each command being issued. Waits for a certain amount of
   // space to be available. Returns address of space.
   CommandBufferEntry* GetSpace(uint32 entries);
 
   // Typed version of GetSpace. Gets enough room for the given type and returns
   // a reference to it.
   template <typename T>
   T* GetCmdSpace() {
     COMPILE_ASSERT(T::kArgFlags == cmd::kFixed, Cmd_kArgFlags_not_kFixed);
     uint32 space_needed = ComputeNumEntries(sizeof(T));
@@ skipping 158 matching lines @@
   // Using C runtime instead of base because this file cannot depend on base.
   clock_t last_flush_time_;
 
   friend class CommandBufferHelperTest;
   DISALLOW_COPY_AND_ASSIGN(CommandBufferHelper);
 };
 
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_CMD_BUFFER_HELPER_H_