1.創(chuàng)建異步線(xiàn)程

NSLog(@"hello world 1");
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        sleep(1);
        NSLog(@"hello world 2");
    });
    NSLog(@"hello world 3");

屏幕快照 2017-09-28 下午3.11.55.png

2.創(chuàng)建同步線(xiàn)程

NSLog(@"hello world 1");
    dispatch_sync(dispatch_get_global_queue(0, 0), ^{
        sleep(1);
        NSLog(@"hello world 2");
    });
    NSLog(@"hello world 3");

屏幕快照 2017-09-28 下午3.11.27.png

3.創(chuàng)建主線(xiàn)程

dispatch_async(dispatch_get_main_queue(), ^{
        //刷新界面代碼
    });

4.GCD只執(zhí)行一次

static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        //只執(zhí)行一次代碼
    });

5.線(xiàn)程延遲調(diào)用

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(5.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{

        NSLog(@"## 在主線(xiàn)程延遲5秒調(diào)用 ##");
    });

6.信號(hào)量

dispatch_semaphore_create //創(chuàng)建一個(gè)semaphore 通過(guò)dispatch_semaphore_create 函數(shù)創(chuàng)建一個(gè)Semaphore并初始化信號(hào)的總量。

dispatch_semaphore_signal　//發(fā)送一個(gè)信號(hào) 通過(guò)dispatch_semaphore_signal 函數(shù)發(fā)送一個(gè)信號(hào)，讓信號(hào)總量加1。

dispatch_semaphore_wait　　//等待信號(hào) 通過(guò)dispatch_semaphore_wait可以使總信號(hào)量減1，當(dāng)信號(hào)總量為0時(shí)就會(huì)一直等待，否則就可以正常執(zhí)行

dispatch_semaphore_t semaoh = dispatch_semaphore_create(0);
dispatch_async(dispatch_get_global_queue(0, 0), ^{
       //獲取數(shù)據(jù)  執(zhí)行信號(hào)數(shù)量+1
        dispatch_semaphore_signal(semaoh);
    });
//使總信號(hào)量減1
dispatch_semaphore_wait(semaoh, DISPATCH_TIME_FOREVER);

7.多個(gè)請(qǐng)求都結(jié)束后，在執(zhí)行界面刷新

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        
        //創(chuàng)建組
        dispatch_group_t group=dispatch_group_create();
        
        // 關(guān)聯(lián)一個(gè)任務(wù)到group
        dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            //任務(wù)一
            NSLog(@"******執(zhí)行任務(wù)一******");
        });
        
        // 關(guān)聯(lián)一個(gè)任務(wù)到group
        dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            //任務(wù)二
            NSLog(@"******執(zhí)行任務(wù)二******");
        });
        
        // 等待組中的任務(wù)執(zhí)行完畢,回到主線(xiàn)程執(zhí)行block回調(diào)
        dispatch_group_notify(group, dispatch_get_main_queue(), ^{
            //任務(wù)三 回到主線(xiàn)程刷新界面
            dispatch_async(dispatch_get_main_queue(), ^{
            //刷新界面代碼
    });
    });

8. dispatch_barrier_async的使用

dispatch_barrier_async是在前面的任務(wù)執(zhí)行結(jié)束后它才執(zhí)行，而且它后面的任務(wù)等它執(zhí)行完成之后才會(huì)執(zhí)行

dispatch_queue_t queue = dispatch_queue_create("create_asy_queue", DISPATCH_QUEUE_CONCURRENT);
    dispatch_async(queue, ^{
        NSLog(@"任務(wù)一");
    });
    dispatch_async(queue, ^{
        NSLog(@"任務(wù)二");
    });
    dispatch_barrier_async(queue, ^{
        NSLog(@"dispatch_barrier_async");
        //FIXEM:任務(wù)一和二都執(zhí)行完了，才執(zhí)行
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"刷新界面");
        });
        
    });
    dispatch_async(queue, ^{
        //FIXEM:界面刷新完了，才執(zhí)行
        [NSThread sleepForTimeInterval:1];
        NSLog(@"任務(wù)三");
    });