native_client_sdk/src/examples/demo/nacl_io_demo/queue.h

   1 /* Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2  * Use of this source code is governed by a BSD-style license that can be
   3  * found in the LICENSE file.
   4  */
   5
   6 #ifndef QUEUE_H_
   7 #define QUEUE_H_
   8
   9 #include "ppapi/c/pp_var.h"
  10
  11 /* This file implements a single-producer/single-consumer queue, using a mutex
  12  * and a condition variable.
  13  *
  14  * There are techniques to implement a queue like this without using memory
  15  * barriers or locks on x86, but ARM's memory system is different from x86, so
  16  * we cannot make the same assumptions about visibility order of writes. Using a
  17  * mutex is slower, but also simpler.
  18  *
  19  * We make the assumption that messages are only enqueued on the main thread
  20  * and consumed on the worker thread. Because we don't want to block the main
  21  * thread, EnqueueMessage will return zero if the message could not be enqueued.
  22  *
  23  * DequeueMessage will block until a message is available using a condition
  24  * variable. Again, this may not be as fast as spin-waiting, but will consume
  25  * much less CPU (and battery), which is important to consider for ChromeOS
  26  * devices. */
  27
  28 void InitializeMessageQueue();
  29 int EnqueueMessage(struct PP_Var message);
  30 struct PP_Var DequeueMessage();
  31
  32 #endif /* QUEUE_H_ */