IOS GCD使用实例大全

　　GCD是大家在IOS开发过程中经常使用的一种多线程管理机制。原理这里就不多说了，大家关心的大部分都是它的使用，下面主要介绍GCD的主要方法及其实例。

1.认识主队列，感受串行队列的运行,运行结果打印的是 1，2，3，4，顺序执行。

dispatch_queue_t mainQueue = dispatch_get_main_queue();
dispatch_async(mainQueue, ^{
    NSLog(@"1");
});
dispatch_async(mainQueue, ^{
    NSLog(@"2");
});
dispatch_async(mainQueue, ^{
    NSLog(@"3");
});
dispatch_async(mainQueue, ^{
    NSLog(@"4");
});

2.认识全局队列，体验并发队列的运行，运行结果随机打印：2，3，1，4，随机执行。

dispatch_queue_t defaultQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(defaultQueue, ^{
    NSLog(@"1");
});
dispatch_async(defaultQueue, ^{
    NSLog(@"2");
});
dispatch_async(defaultQueue, ^{
    NSLog(@"3");
});
dispatch_async(defaultQueue, ^{
    NSLog(@"4");
});

3.创建自定义队列

dispatch_queue_t concurrentQueue = dispatch_queue_create("com.bjsxt.concurrentQueue", DISPATCH_QUEUE_CONCURRENT);
    
dispatch_async(concurrentQueue, ^{
    NSLog(@"4");
    dispatch_sync(concurrentQueue, ^{
        [NSThread sleepForTimeInterval:3];
        NSLog(@"5");
    });
    NSLog(@"6");
});

4.GCD在单例中的运用dispatch_once

static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
    NSLog(@"onceToken");
});

5.延迟加载dispatch_after

double delayInSeconds = 2.0;
dispatch_queue_t mainQueue = dispatch_get_main_queue();
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW,delayInSeconds * NSEC_PER_SEC);
dispatch_after(popTime, mainQueue, ^{
    NSLog(@"延时执行的2秒");
});

6.调度组dispatch_group_t

dispatch_group_t group = dispatch_group_create();
dispatch_queue_t defaultQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_group_async(group, defaultQueue, ^{
    [NSThread sleepForTimeInterval:3];
    NSLog(@"1");
});
dispatch_group_async(group, defaultQueue, ^{
    [NSThread sleepForTimeInterval:2];
    NSLog(@"2");
});
dispatch_group_notify(group, defaultQueue, ^{
    NSLog(@"3");
});

7.dispatch_barrier_async 在前面的任务执行结束后它才执行，而且它后面的任务等它执行完成之后才会执行.

dispatch_queue_t queue = dispatch_queue_create("com.bjsxt.barrierExecute", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^{
    [NSThread sleepForTimeInterval:2];
    NSLog(@"1");
});
dispatch_async(queue, ^{
    [NSThread sleepForTimeInterval:4];
    NSLog(@"2");
});
dispatch_barrier_async(queue, ^{
    NSLog(@"3");
    [NSThread sleepForTimeInterval:4];
    
});
dispatch_async(queue, ^{
    [NSThread sleepForTimeInterval:1];
    NSLog(@"4");
});

8.执行某个代码dispatch_apply

dispatch_queue_t defaultQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_apply(5, defaultQueue, ^(size_t i) {
        NSLog(@"%lu",i);
});