queue.h revision cedac228d2dd51db4b79ea1e72c7f249408ee061 
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
28void InitializeMessageQueue();
29int EnqueueMessage(struct PP_Var message);
30struct PP_Var DequeueMessage();
31
32#endif /* QUEUE_H_ */
33