Rework FlushSync to return early if commands have been processed since the last update

ppapi/c/dev/ppb_context_3d_trusted_dev.h

 // Copyright (c) 2011 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 PPAPI_C_DEV_PPB_CONTEXT_3D_TRUSTED_DEV_H_
 #define PPAPI_C_DEV_PPB_CONTEXT_3D_TRUSTED_DEV_H_
 
 #include "ppapi/c/dev/ppb_context_3d_dev.h"
 #include "ppapi/c/pp_bool.h"
 #include "ppapi/c/pp_instance.h"
@@ skipping 24 matching lines @@
 
   // 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_t token;
 
   // Error status.
   PPB_Context3DTrustedError error;
+
+  // 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_t generation;
 };
 
 struct PPB_Context3DTrusted_Dev {
   // Creates a raw Context3D resource. A raw Context3D is intended to be used
   // with the trusted interface, through the command buffer (for proxying). In
   // particular, when a Surface3D is bound to a raw context, SwapBuffers has no
   // effect.
   PP_Resource (*CreateRaw)(PP_Instance instance_id,
                            PP_Config3D_Dev config,
                            PP_Resource share_context,
@@ skipping 25 matching lines @@
   int32_t (*CreateTransferBuffer)(PP_Resource context, uint32_t size);
 
   // Destroy a transfer buffer and recycle the handle.
   PP_Bool (*DestroyTransferBuffer)(PP_Resource context, int32_t id);
 
   // Get the transfer buffer associated with a handle.
   PP_Bool (*GetTransferBuffer)(PP_Resource context,
                                int32_t id,
                                int* shm_handle,
                                uint32_t* shm_size);
+
+  // Like FlushSync, but returns before processing commands if the get offset is
+  // different than last_known_get. Allows synchronization with the command
+  // processor without forcing immediate command execution.
+  struct PP_Context3DTrustedState (*FlushSyncFast)(PP_Resource context,

[piman, 2011/04/27 21:28:39]

This was added instead of replacing FlushSync because of the NaCl circular
dependency. Next step is to get NaCl to use this new function, so that we can
remove the old one once deps roll, and then maybe another round to rename
FlushSyncFast to FlushSync.

+                                                   int32_t put_offset,
+                                                   int32_t last_known_get);
 };
 
 #endif  // PPAPI_C_DEV_PPB_CONTEXT_3D_TRUSTED_DEV_H_