GCD代碼記錄霞扬，以便后用

//自定義一個(gè)queue：
- (void)customQueue{
    /*
     第二個(gè)參數(shù)傳：
     串行隊(duì)列：DISPATCH_QUEUE_SERIAL     開啟一個(gè)子線程页畦，按序執(zhí)行
     并行隊(duì)列：DISPATCH_QUEUE_CONCURRENT 開啟多個(gè)子線程，無序執(zhí)行
     同步：串行秀又、并行都會(huì)在主線程
     異步：串行涮帘、并行都會(huì)在子線程
     */
    
    //串行隊(duì)列
    dispatch_queue_t serialQueue = dispatch_queue_create("com.gcd.serialQueue", DISPATCH_QUEUE_SERIAL);
    //并發(fā)隊(duì)列
    dispatch_queue_t concurrentQueue = dispatch_queue_create("com.gcd.concurrentQueue", DISPATCH_QUEUE_CONCURRENT);
    
//可以通過dispatch_queue_get_label(dispatch_queue_t queue)獲取你創(chuàng)建queue的名字
    const char *c = dispatch_queue_get_label(concurrentQueue);
    NSLog(@"%s",c);//com.gcd.concurrentQueue

    dispatch_sync(concurrentQueue, ^{
        NSLog(@"1");
        [NSThread sleepForTimeInterval:2];
        NSLog(@"1--");
    });
    dispatch_sync(concurrentQueue, ^{
        NSLog(@"2");
        [NSThread sleepForTimeInterval:2];
        NSLog(@"2--");
    });
    dispatch_sync(concurrentQueue, ^{
        NSLog(@"3");
        [NSThread sleepForTimeInterval:4];
        NSLog(@"3--");
    });
    dispatch_sync(concurrentQueue, ^{
        NSLog(@"4");
        [NSThread sleepForTimeInterval:2];
        NSLog(@"4--");
    });
}

dispatch_group

/*
 串行隊(duì)列：DISPATCH_QUEUE_SERIAL     開啟一個(gè)子線程拼苍，按序執(zhí)行
 并行隊(duì)列：DISPATCH_QUEUE_CONCURRENT 開啟多個(gè)子線程，無序執(zhí)行
 */
- (void)dispatch_group{
    dispatch_queue_t queue = dispatch_queue_create("com.gcd.serialQueue", DISPATCH_QUEUE_SERIAL);
    dispatch_group_t group = dispatch_group_create();

    dispatch_group_async(group, queue, ^{
        NSLog(@"1");
        [NSThread sleepForTimeInterval:5];
        NSLog(@"1--");
    });
    dispatch_group_async(group, queue, ^{
        NSLog(@"2");
        [NSThread sleepForTimeInterval:8];
        NSLog(@"2--");
    });
    dispatch_group_async(group, queue, ^{
        NSLog(@"3");
        [NSThread sleepForTimeInterval:3];
        NSLog(@"3--");
    });

    dispatch_group_notify(group, queue, ^{
        NSLog(@"notify：任務(wù)都完成了");
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"回到主線程");
        });
    });
}

dispatch_group_enter和dispatch_group_leave是成對(duì)出現(xiàn)的调缨，可以按照引用計(jì)數(shù)+1疮鲫、-1理解。

/*
 串行隊(duì)列：DISPATCH_QUEUE_SERIAL     開啟一個(gè)子線程弦叶，按序執(zhí)行
 并行隊(duì)列：DISPATCH_QUEUE_CONCURRENT 開啟多個(gè)子線程俊犯，無序執(zhí)行
 注意：dispatch_group_notify會(huì)與耗時(shí)最長(zhǎng)的線程在同一個(gè)線程
 */
- (void)dispatch_group_enter{
    dispatch_queue_t queue = dispatch_queue_create("com.GCD.group", DISPATCH_QUEUE_CONCURRENT);
    dispatch_group_t group = dispatch_group_create();
    
    dispatch_group_enter(group);
    dispatch_async(queue, ^{
        sleep(5);
        NSLog(@"任務(wù)一完成");
        dispatch_group_leave(group);
    });
    
    dispatch_group_enter(group);
    dispatch_async(queue, ^{
        sleep(8);
        NSLog(@"任務(wù)二完成");
        dispatch_group_leave(group);
    });
    
    dispatch_group_enter(group);
    dispatch_async(queue, ^{
        sleep(3);
        NSLog(@"任務(wù)三完成");
        dispatch_group_leave(group);
    });
    
    dispatch_group_notify(group, queue, ^{
        NSLog(@"任務(wù)完成");
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"回到主線程");
        });
    });
}

dispatch_barrier

/*
 dispatch_barrier_sync和dispatch_barrier_async的共同點(diǎn)：
 1、都會(huì)等待在它前面插入隊(duì)列的任務(wù)（1湾蔓、2瘫析、3）先執(zhí)行完
 2砌梆、都會(huì)等待他們自己的任務(wù)（0）執(zhí)行完再執(zhí)行后面的任務(wù)（4默责、5贬循、6）
 
 dispatch_barrier_sync和dispatch_barrier_async的不共同點(diǎn)：
 在將任務(wù)插入到queue的時(shí)候，dispatch_barrier_sync需要等待自己的任務(wù)（0）結(jié)束之后才會(huì)繼續(xù)程序桃序，然后插入被寫在它后面的任務(wù)（4杖虾、5、6）媒熊，然后執(zhí)行后面的任務(wù)
 而dispatch_barrier_async將自己的任務(wù)（0）插入到queue之后奇适，不會(huì)等待自己的任務(wù)結(jié)束，它會(huì)繼續(xù)把后面的任務(wù)（4芦鳍、5嚷往、6）插入到queue
 */
- (void)dispatch_barrier{
    dispatch_queue_t queue = dispatch_queue_create("com.GCD.barrier", DISPATCH_QUEUE_CONCURRENT);
    dispatch_async(queue, ^{
        NSLog(@"1");
        [NSThread sleepForTimeInterval:3];
        NSLog(@"1--");
    });
    dispatch_async(queue, ^{
        NSLog(@"2");
        [NSThread sleepForTimeInterval:5];
        NSLog(@"2--");
    });
    dispatch_async(queue, ^{
        NSLog(@"3");
        [NSThread sleepForTimeInterval:2];
        NSLog(@"3--");
    });
    
    dispatch_barrier_async(queue, ^{
        NSLog(@"barrier");
        [NSThread sleepForTimeInterval:2];
        NSLog(@"barrier--");
        [NSThread sleepForTimeInterval:3];
        NSLog(@"barrier==");
    });
    NSLog(@"aaa");
    dispatch_async(queue, ^{
        NSLog(@"4");
        [NSThread sleepForTimeInterval:3];
        NSLog(@"4--");
    });
    NSLog(@"bbb");
    dispatch_async(queue, ^{
        NSLog(@"5");
        [NSThread sleepForTimeInterval:5];
        NSLog(@"5--");
    });
    dispatch_async(queue, ^{
        NSLog(@"6");
        [NSThread sleepForTimeInterval:2];
        NSLog(@"6--");
    });
}