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.
11 #define MAX_QUEUE_SIZE 16
13 /** A mutex that guards |g_queue|. */
14 static pthread_mutex_t g_queue_mutex;
16 /** A condition variable that is signalled when |g_queue| is not empty. */
17 static pthread_cond_t g_queue_not_empty_cond;
19 /** A circular queue of messages from JavaScript to be handled.
21 * If g_queue_start < g_queue_end:
22 * all elements in the range [g_queue_start, g_queue_end) are valid.
23 * If g_queue_start > g_queue_end:
24 * all elements in the ranges [0, g_queue_end) and
25 * [g_queue_start, MAX_QUEUE_SIZE) are valid.
26 * If g_queue_start == g_queue_end, and g_queue_size > 0:
27 * all elements in the g_queue are valid.
28 * If g_queue_start == g_queue_end, and g_queue_size == 0:
29 * No elements are valid. */
30 static char* g_queue[MAX_QUEUE_SIZE];
32 /** The index of the head of the queue. */
33 static int g_queue_start = 0;
35 /** The index of the tail of the queue, non-inclusive. */
36 static int g_queue_end = 0;
38 /** The size of the queue. */
39 static int g_queue_size = 0;
41 /** Return whether the queue is empty.
43 * NOTE: this function assumes g_queue_mutex lock is held.
44 * @return non-zero if the queue is empty. */
45 static int IsQueueEmpty() { return g_queue_size == 0; }
47 /** Return whether the queue is full.
49 * NOTE: this function assumes g_queue_mutex lock is held.
50 * @return non-zero if the queue is full. */
51 static int IsQueueFull() { return g_queue_size == MAX_QUEUE_SIZE; }
53 /** Initialize the message queue. */
54 void InitializeMessageQueue() {
55 pthread_mutex_init(&g_queue_mutex, NULL);
56 pthread_cond_init(&g_queue_not_empty_cond, NULL);
59 /** Enqueue a message (i.e. add to the end)
61 * If the queue is full, the message will be dropped.
63 * NOTE: this function assumes g_queue_mutex is _NOT_ held.
64 * @param[in] message The message to enqueue.
65 * @return non-zero if the message was added to the queue. */
66 int EnqueueMessage(char* message) {
67 pthread_mutex_lock(&g_queue_mutex);
69 /* We shouldn't block the main thread waiting for the queue to not be full,
70 * so just drop the message. */
72 pthread_mutex_unlock(&g_queue_mutex);
77 g_queue[g_queue_end] = message;
78 g_queue_end = (g_queue_end + 1) % MAX_QUEUE_SIZE;
81 pthread_cond_signal(&g_queue_not_empty_cond);
83 pthread_mutex_unlock(&g_queue_mutex);
88 /** Dequeue a message and return it.
90 * This function blocks until a message is available. It should not be called
93 * NOTE: this function assumes g_queue_mutex is _NOT_ held.
94 * @return The message at the head of the queue. */
95 char* DequeueMessage() {
98 pthread_mutex_lock(&g_queue_mutex);
100 while (IsQueueEmpty()) {
101 pthread_cond_wait(&g_queue_not_empty_cond, &g_queue_mutex);
104 message = g_queue[g_queue_start];
105 g_queue_start = (g_queue_start + 1) % MAX_QUEUE_SIZE;
108 pthread_mutex_unlock(&g_queue_mutex);