PPAPI: Synchronous postMessage proposal #1

ppapi/api/ppb_messaging.idl

 /* 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 defines the <code>PPB_Messaging</code> interface implemented
  * by the browser for sending messages to DOM elements associated with a
  * specific module instance.
  */
 
 [generate_thunk]
 
 label Chrome {
-  M14 = 1.0
+  M14 = 1.0,
+  M36 = 1.1
 };
 
 /**
  * The <code>PPB_Messaging</code> interface is implemented by the browser
  * 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
    * the DOM element for the given module instance. A call to PostMessage()
    * will not block while the message is processed.
    *
    * @param[in] instance A <code>PP_Instance</code> identifying one instance
    * of a module.
    * @param[in] message A <code>PP_Var</code> containing the data to be sent to
    * JavaScript.
@@ skipping 42 matching lines @@
    *                                                    hello_world,
    *                                                    sizeof(hello_world));
    *  ppb_messaging_interface->PostMessage(instance, hello_var); // Copies var.
    *  ppb_var_interface->Release(hello_var);
    *
    * @endcode
    *
    * 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);
 };