pnacl/util/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 <inttypes.h>
  10 #include <stdbool.h>
  11
  12 /* This file implements a single-producer/single-consumer queue, using a mutex
  13  * and a condition variable.
  14  *
  15  * There are techniques to implement a queue like this without using memory
  16  * barriers or locks on x86, but ARM's memory system is different from x86, so
  17  * we cannot make the same assumptions about visibility order of writes. Using a
  18  * mutex is slower, but also simpler.
  19  *
  20  * We make the assumption that messages are only enqueued on the main thread
  21  * and consumed on the worker thread. Because we don't want to block the main
  22  * thread, EnqueueMessage will return zero if the message could not be enqueued.
  23  *
  24  * DequeueMessage will block until a message is available using a condition
  25  * variable. Again, this may not be as fast as spin-waiting, but will consume
  26  * much less CPU (and battery), which is important to consider for ChromeOS
  27  * devices. */
  28
  29 struct q_ele {
  30         char **argv;
  31         uint32_t argc;
  32 };
  33
  34 void InitializeMessageQueue(void);
  35 bool EnqueueMessage(char **argv, uint32_t argc);
  36 struct q_ele *DequeueMessage();
  37
  38 #endif /* QUEUE_H_ */