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