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| 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 assuptions 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 | |
| 26 void InitializeMessageQueue(); | |
| 27 int EnqueueMessage(char* message); | |
| 28 char* DequeueMessage(); | |
| 29 | |
| 30 #endif /* QUEUE_H_ */ | |
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