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 #include "queue.h" 7 8 #include <pthread.h> 9 #include <stdlib.h> 10 11 #include "ppapi/c/pp_var.h" 12 13 #define MAX_QUEUE_SIZE 16 14 15 /** A mutex that guards |g_queue|. */ 16 static pthread_mutex_t g_queue_mutex; 17 18 /** A condition variable that is signalled when |g_queue| is not empty. */ 19 static pthread_cond_t g_queue_not_empty_cond; 20 21 /** A circular queue of messages from JavaScript to be handled. 22 * 23 * If g_queue_start < g_queue_end: 24 * all elements in the range [g_queue_start, g_queue_end) are valid. 25 * If g_queue_start > g_queue_end: 26 * all elements in the ranges [0, g_queue_end) and 27 * [g_queue_start, MAX_QUEUE_SIZE) are valid. 28 * If g_queue_start == g_queue_end, and g_queue_size > 0: 29 * all elements in the g_queue are valid. 30 * If g_queue_start == g_queue_end, and g_queue_size == 0: 31 * No elements are valid. */ 32 static struct PP_Var g_queue[MAX_QUEUE_SIZE]; 33 34 /** The index of the head of the queue. */ 35 static int g_queue_start = 0; 36 37 /** The index of the tail of the queue, non-inclusive. */ 38 static int g_queue_end = 0; 39 40 /** The size of the queue. */ 41 static int g_queue_size = 0; 42 43 /** Return whether the queue is empty. 44 * 45 * NOTE: this function assumes g_queue_mutex lock is held. 46 * @return non-zero if the queue is empty. */ 47 static int IsQueueEmpty() { return g_queue_size == 0; } 48 49 /** Return whether the queue is full. 50 * 51 * NOTE: this function assumes g_queue_mutex lock is held. 52 * @return non-zero if the queue is full. */ 53 static int IsQueueFull() { return g_queue_size == MAX_QUEUE_SIZE; } 54 55 /** Initialize the message queue. */ 56 void InitializeMessageQueue() { 57 pthread_mutex_init(&g_queue_mutex, NULL); 58 pthread_cond_init(&g_queue_not_empty_cond, NULL); 59 } 60 61 /** Enqueue a message (i.e. add to the end) 62 * 63 * If the queue is full, the message will be dropped. 64 * 65 * NOTE: this function assumes g_queue_mutex is _NOT_ held. 66 * @param[in] message The message to enqueue. 67 * @return non-zero if the message was added to the queue. */ 68 int EnqueueMessage(struct PP_Var message) { 69 pthread_mutex_lock(&g_queue_mutex); 70 71 /* We shouldn't block the main thread waiting for the queue to not be full, 72 * so just drop the message. */ 73 if (IsQueueFull()) { 74 pthread_mutex_unlock(&g_queue_mutex); 75 return 0; 76 } 77 78 g_queue[g_queue_end] = message; 79 g_queue_end = (g_queue_end + 1) % MAX_QUEUE_SIZE; 80 g_queue_size++; 81 82 pthread_cond_signal(&g_queue_not_empty_cond); 83 84 pthread_mutex_unlock(&g_queue_mutex); 85 86 return 1; 87 } 88 89 /** Dequeue a message and return it. 90 * 91 * This function blocks until a message is available. It should not be called 92 * on the main thread. 93 * 94 * NOTE: this function assumes g_queue_mutex is _NOT_ held. 95 * @return The message at the head of the queue. */ 96 struct PP_Var DequeueMessage() { 97 struct PP_Var message; 98 99 pthread_mutex_lock(&g_queue_mutex); 100 101 while (IsQueueEmpty()) { 102 pthread_cond_wait(&g_queue_not_empty_cond, &g_queue_mutex); 103 } 104 105 message = g_queue[g_queue_start]; 106 g_queue_start = (g_queue_start + 1) % MAX_QUEUE_SIZE; 107 g_queue_size--; 108 109 pthread_mutex_unlock(&g_queue_mutex); 110 111 return message; 112 } 113
