1个信号量:
- (IBAction)dispatchSingal0:(UIButton *)sender {
dispatch_semaphore_t semaphore1 = dispatch_semaphore_create(0);
dispatch_queue_t queue1 = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
// 任务1
dispatch_async(queue1, ^{
dispatch_semaphore_signal(semaphore1);
NSLog(@"run task 1");
sleep(2);
NSLog(@"任务全部执行完成 complete task 1");
dispatch_semaphore_wait(semaphore1, DISPATCH_TIME_FOREVER);
});
}
2019-11-11 10:02:12.328143+0800 123334567[3976:47598] run task 1
2019-11-11 10:02:14.333569+0800 123334567[3976:47598] 任务全部执行完成 complete task 1
由于设定的信号值为0，所以只有一个线程
2个信号量：
- (IBAction)dispatchSingal1:(UIButton *)sender {
//create(value)表示，最多几个资源可访问,现在最多可访问2个资源(0,1)
dispatch_semaphore_t semaphore = dispatch_semaphore_create(1);
dispatch_queue_t quene = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
//任务1
dispatch_async(quene, ^{
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
NSLog(@"run task 1");
sleep(2);
NSLog(@"任务全部执行完成 complete task 1");
dispatch_semaphore_signal(semaphore);
});
//任务2
dispatch_async(quene, ^{
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
NSLog(@"run task 2");
sleep(2);
NSLog(@"任务全部执行完成 complete task 2");
dispatch_semaphore_signal(semaphore);
});
}
2019-11-11 10:16:19.435266+0800 123334567[4481:54963] run task 1
2019-11-11 10:16:21.437668+0800 123334567[4481:54963] 任务全部执行完成 complete task 1
2019-11-11 10:16:21.437969+0800 123334567[4481:55783] run task 2
2019-11-11 10:16:23.439545+0800 123334567[4481:55783] 任务全部执行完成 complete task 2
由于设定的信号值为1，所以会先执行一个线程，等执行完一个，才会继续执行另一个，保证同一时间执行的线程数为1
3个信号量:
- (IBAction)dispatchSingal2:(UIButton *)sender {
//create(value)表示，最多几个资源可访问,现在最多可访问3个资源(0,1,2)
dispatch_semaphore_t semaphore = dispatch_semaphore_create(2);
dispatch_queue_t quene = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
//任务1
dispatch_async(quene, ^{
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
NSLog(@"run task 1");
sleep(1);
NSLog(@"任务全部执行完成 complete task 1");
dispatch_semaphore_signal(semaphore);
});
//任务2
dispatch_async(quene, ^{
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
NSLog(@"run task 2");
sleep(1);
NSLog(@"任务全部执行完成 complete task 2");
dispatch_semaphore_signal(semaphore);
});
//任务3
dispatch_async(quene, ^{
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
NSLog(@"run task 3");
sleep(1);
NSLog(@"任务全部执行完成 complete task 3");
dispatch_semaphore_signal(semaphore);
});
}
① 第一种情况
2019-11-11 10:20:10.961881+0800 123334567[4481:55783] run task 1
2019-11-11 10:20:10.962065+0800 123334567[4481:57698] run task 3
2019-11-11 10:20:11.966846+0800 123334567[4481:57698] 任务全部执行完成 complete task 3
2019-11-11 10:20:11.966847+0800 123334567[4481:55783] 任务全部执行完成 complete task 1
2019-11-11 10:20:11.967167+0800 123334567[4481:57697] run task 2
2019-11-11 10:20:12.971532+0800 123334567[4481:57697] 任务全部执行完成 complete task 2
------------------------------------------------------------------------------------------
② 第二种情况
2019-11-11 10:24:03.889155+0800 123334567[4798:60740] run task 1
2019-11-11 10:24:03.889277+0800 123334567[4798:60847] run task 2
2019-11-11 10:24:04.894150+0800 123334567[4798:60740] 任务全部执行完成 complete task 1
2019-11-11 10:24:04.894125+0800 123334567[4798:60847] 任务全部执行完成 complete task 2
2019-11-11 10:24:04.894492+0800 123334567[4798:60848] run task 3
2019-11-11 10:24:05.899918+0800 123334567[4798:60848] 任务全部执行完成 complete task 3
由于设定的信号值为2，先执行两个线程，等执行完一个，才会继续执行下一个，保证同一时间执行的线程数不超过2
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