GCD使用基础 三

dispatch_after

dispatch_after延迟将任务提交到队列中，注意不是事先将任务添加到队列中然后再延迟执行。

dispatch_queue_t serialQueue = dispatch_queue_create("serialQueue", DISPATCH_QUEUE_SERIAL);
dispatch_sync(serialQueue, ^{
        NSLog(@"任务1，%@", [NSThread currentThread]);
    });

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(5*NSEC_PER_SEC)), serialQueue, ^{
        NSLog(@"5秒后提交该block,%@", [NSThread currentThread]);
    });
dispatch_sync(serialQueue, ^{
        NSLog(@"任务2，%@", [NSThread currentThread]);
    });
/**
dispatch_time_t
dispatch_time（）创建时间
DISPATCH_TIME_NOW从现在开始计算
NSEC_PER_SEC=1秒
*/
dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2*NSEC_PER_SEC));
dispatch_after(time, serialQueue, ^{
        NSLog(@"2秒后提交该block，%@", [NSThread currentThread]);
    });

dispatch_after

从打印日志可以看出，所有任务都是添加到串行队列中的，由串行队列的特性可知：先进入对的任务结束，才会执行后面的任务，可验证dispatch_after是将任务延时添加到队列中。

DISPATCH_TIME_NOW是指执行到该行代码时开始计算。

dispatch_queue_t serialQueue = dispatch_queue_create("serialQueue", DISPATCH_QUEUE_SERIAL);
dispatch_sync(serialQueue, ^{
        NSLog(@"任务1，%@", [NSThread currentThread]);
    });

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(5*NSEC_PER_SEC)), serialQueue, ^{
        NSLog(@"5秒后提交该block,%@", [NSThread currentThread]);
    });
dispatch_sync(serialQueue, ^{
        NSLog(@"任务2，%@", [NSThread currentThread]);
        sleep(10);
    });
/**
dispatch_time_t
dispatch_time（）创建时间
DISPATCH_TIME_NOW从现在开始计算
NSEC_PER_SEC=1秒
*/
dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2*NSEC_PER_SEC));
dispatch_after(time, serialQueue, ^{
        NSLog(@"2秒后提交该block，%@", [NSThread currentThread]);
    });

DISPATCH_TIME_NOW

从两次的打印日志中也可以看出，dispatch_after是另外开辟了一条线程执行的。

dispatch_group_t

dispatch_group_t：调度组，可以将队列中的任务放到调度组中，由调度组来控制任务的执行。

dispatch_queue_t concurrentQueue = dispatch_queue_create("concurrentQueue", DISPATCH_QUEUE_CONCURRENT);
dispatch_group_t group = dispatch_group_create();
dispatch_group_async(group, concurrentQueue, ^{
        NSLog(@"任务1%@", [NSThread currentThread]);
    });
dispatch_group_async(group, concurrentQueue, ^{
        NSLog(@"任务2%@", [NSThread currentThread]);
    });
dispatch_group_async(group, concurrentQueue, ^{
        NSLog(@"任务3%@", [NSThread currentThread]);
    });
dispatch_group_notify(group, concurrentQueue, ^{
        NSLog(@"调度组中concurrentQueue队列的所有任务执行完毕%@", [NSThread currentThread]);
    });

调度组1

• dispatch_group_async：创建一个异步任务将其放在concurrentQueue队列中，并关联到调度组中。
• dispatch_group_notify：concurrentQueue队列中所有关联到调度组中的任务结束时执行。

---

dispatch_queue_t concurrentQueue = dispatch_queue_create("concurrentQueue", DISPATCH_QUEUE_CONCURRENT);
dispatch_group_enter(group);
dispatch_async(concurrentQueue, ^{
        NSLog(@"任务1%@", [NSThread currentThread]);
        dispatch_group_leave(group);
    });

dispatch_group_enter(group);
dispatch_async(concurrentQueue, ^{
        NSLog(@"任务2%@", [NSThread currentThread]);
        dispatch_group_leave(group);
    });
    
dispatch_group_enter(group);
dispatch_async(concurrentQueue, ^{
        NSLog(@"任务3%@", [NSThread currentThread]);
        dispatch_group_leave(group);
    });

调度组2

• dispatch_group_enter：任务入组。
• dispatch_group_leave：任务出组。

dispatch_group_enter和dispatch_group_leave需要成对出现。

---

dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3*NSEC_PER_SEC));
dispatch_group_t group = dispatch_group_create();
dispatch_group_enter(group);
dispatch_async(concurrentQueue, ^{
        NSLog(@"任务1%@", [NSThread currentThread]);
        dispatch_group_leave(group);
    });

dispatch_group_enter(group);
dispatch_async(concurrentQueue, ^{
        NSLog(@"任务2%@", [NSThread currentThread]);
        dispatch_group_leave(group);
    });
    
dispatch_group_enter(group);
dispatch_async(concurrentQueue, ^{
        sleep(5);
        NSLog(@"任务3%@", [NSThread currentThread]);
        dispatch_group_leave(group);
    });

dispatch_group_notify(group, concurrentQueue, ^{
        NSLog(@"调度组中concurrentQueue队列的所有任务执行完毕%@", [NSThread currentThread]);
    });
dispatch_async(dispatch_get_global_queue(0, 0), ^{
        dispatch_group_wait(group, time);
        NSLog(@"顶多等你三秒，调度组不结束我就干自己的事去了");
    });

调度组3
dispatch_group_wait：在指定时间或调度组结束时，执行下面的任务。可以应用在网络请求时间较长时的处理。

dispatch_apply

dispatch_apply：重复提交任务到队列中。

dispatch_apply(10, serialQueue, ^(size_t i) {
        NSLog(@"在线程中循环10次执行该block%ld%@", i, [NSThread currentThread]);
    });

串行队列重复提交

在当前线程中执行，不会开辟新的线程。

---

dispatch_apply(10, concurrentQueue, ^(size_t i) {
        NSLog(@"在线程中循环10次执行该block%ld%@", i, [NSThread currentThread]);
    });

会开辟新的线程，异步执行任务。

并行队列重复提交

其他

• dispatch_queue_get_label：获取队列的名字。

//获取指定队列的名字
NSLog(@"%s", dispatch_queue_get_label(serialQueue));

//获取当前队列的名字
NSLog(@"%s", dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL));