dispatch_semaphore

信号量使用详解

最新推荐文章于 2025-02-27 18:30:18 发布

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最新推荐文章于 2025-02-27 18:30:18 发布

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原文链接：http://www.cnblogs.com/wxm5558/p/7763922.html

本文介绍了信号量的基本概念及其在控制并发任务中的应用。通过两个示例展示了如何利用信号量限制最大下载并发数以及如何实现任务的顺序执行。适用于希望了解信号量机制及其实现细节的开发者。

信号量

wait减1，signal加1，它是线程安全的，下面从网上找了两个例子，这个很灵活

一个是可以控制最大下载并发数

一个是可以一个一个的执行任务

- (void)testMaxConcurrent
{
    dispatch_group_t group = dispatch_group_create();
    dispatch_semaphore_t semaphore = dispatch_semaphore_create(10);
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    for (int i = 0; i < 100; i++)
    {
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        dispatch_group_async(group, queue, ^{
            NSLog(@"%i",i);
            sleep(2);
            dispatch_semaphore_signal(semaphore);
        });
    }
    dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
//    dispatch_release(group);
//    dispatch_release(semaphore);
}

-(void)dispatchSignal
{
    dispatch_semaphore_t semaphore = dispatch_semaphore_create(1);
    dispatch_queue_t quene = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(quene, ^{
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        NSLog(@"run task 1");
        sleep(1);
        NSLog(@"complete task 1");
        dispatch_semaphore_signal(semaphore);
    });
  
    dispatch_async(quene, ^{
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        NSLog(@"run task 2");
        sleep(1);
        NSLog(@"complete task 2");
        dispatch_semaphore_signal(semaphore);
    });
    
    dispatch_async(quene, ^{
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        NSLog(@"run task 3");
        sleep(1);
        NSLog(@"complete task 3");
        dispatch_semaphore_signal(semaphore);
    });
}

转载于:https://www.cnblogs.com/wxm5558/p/7763922.html