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

ppapi/c/dev/ppb_context_3d_trusted_dev.h

Index: ppapi/c/dev/ppb_context_3d_trusted_dev.h
diff --git a/ppapi/c/dev/ppb_context_3d_trusted_dev.h b/ppapi/c/dev/ppb_context_3d_trusted_dev.h
index f8a0d9cf0f660a0e37b3084ffe32bee07bef134e..6b7ed822f04163a25566b9ed73486aeb7984f917 100644
--- a/ppapi/c/dev/ppb_context_3d_trusted_dev.h
+++ b/ppapi/c/dev/ppb_context_3d_trusted_dev.h
@@ -42,6 +42,11 @@ struct PP_Context3DTrustedState {
 
   // 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 {
@@ -87,6 +92,13 @@ struct PPB_Context3DTrusted_Dev {
                                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_