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