PPAPI: Synchronous postMessage proposal #1

ppapi/api/ppb_messaging.idl

Index: ppapi/api/ppb_messaging.idl
diff --git a/ppapi/api/ppb_messaging.idl b/ppapi/api/ppb_messaging.idl
index 0f9a3aa8c2bbeb49c2341179e49771534a01a5a5..4008d730c4b55b6f0a671c7d6a307775a9ef4941 100644
--- a/ppapi/api/ppb_messaging.idl
+++ b/ppapi/api/ppb_messaging.idl
@@ -12,7 +12,8 @@
 [generate_thunk]
 
 label Chrome {
-  M14 = 1.0
+  M14 = 1.0,
+  M36 = 1.1
 };
 
 /**
@@ -20,6 +21,7 @@ label Chrome {
  * and is related to sending messages to JavaScript message event listeners on
  * the DOM element associated with specific module instance.
  */
+[version=1.0]
 interface PPB_Messaging {
   /**
    * PostMessage() asynchronously invokes any listeners for message events on
@@ -82,5 +84,55 @@ interface PPB_Messaging {
    * The browser will pop-up an alert saying "Hello world!"
    */
   void PostMessage([in] PP_Instance instance, [in] PP_Var message);
+
+  /**
+   *  Call this to prepare to receive a blocking message from JavaScript.
+   *  When JavaScript invokes postMessageAndAwaitResponse(), the callback will
+   *  be invoked (or, if a blocking completion callback was used,
+   *  WaitForBlockingMessage will return).
+   *
+   *  When the call completes, |message| will be a PP_Var containing a copy of
+   *  the data passed from JavaScript to postMessageAndAwaitResponse().
+   *
+   *  Upon receipt of the callback, the plugin must respond to the plugin by
+   *  calling RespondToBlockingMessage. The JavaScript invocation of
+   *  postMessageAndAwaitResponse will not return until the response is
+   *  received, so it is important to respond quickly.
+   *
+   *  Invocations of WaitForBlockingMessage will fail if JavaScript is still
+   *  awaiting a response to a prior invocation of the callback. Therefore, the
+   *  plugin must always call RespondToBlockingMessage before calling
+   *  WaitForBlockingMessage again.
+   *
+   *  Example usage:
+   *  void thread_func() {
+   *    while (!ShouldQuit()) {
+   *      PP_Var param = PP_MakeUndefined();
+   *      WaitForBlockingMessage(pp_instance, &param,
+   *                             PP_BlockUntilComplete());
+   *      PP_Var response = ComputeSomething(param);
+   *      RespondToBlockingMessage(pp_instance, response);
+   *      var_if.Release(param);
+   *      var_if.Release(response);
+   *    }
+   *  }
+   *
+   *  WaitForBlockingMessage will only work if called from a background thread.
+   *  If it is invoked from the main Pepper thread, the result will be
+   *  PP_ERROR_WRONG_THREAD.
+   */
+  [version=1.1]
+  int32_t WaitForBlockingMessage([in] PP_Instance instance,
+                                 [out] PP_Var message,
+                                 [in] PP_CompletionCallback callback);
+  /**
+   *  Send a response to JavaScript. This only makes sense if JavaScript is
+   *  currently blocked on postMessagAndAwaitResponse. JavaScript's
+   *  postMessageAndAwaitResponse function will return a JavaScript value
+   *  representing a copy of |response|.
+   */
+  [version=1.1]
+  void RespondToBlockingMessage([in] PP_Instance instance,
+                                [in] PP_Var response);
 };