GCD使用小结

- (void)test1 {
    //创建一个并发队列
    //并发队列+异步任务:创建多个线程，并发执行
    dispatch_queue_t queue = dispatch_queue_create("tqh.com", DISPATCH_QUEUE_CONCURRENT);
    //一步创建一个任务，任务不会立即执行
    dispatch_async(queue, ^{
        NSLog(@"1--%@--",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"2--%@--",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"3--%@--",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"4--%@--",[NSThread currentThread]);
    });
    NSLog(@"结束");
    //number = 4, name = (null) 无序
}

- (void)test2 {
    //并发队列+同步任务：不会开启新线程，在父线程中同步执行各个子线程，也就是逐一执行，并且是添加过任务后立即执行，之后才能添加下一个任务
    dispatch_queue_t queue = dispatch_queue_create("tqh.com", DISPATCH_QUEUE_CONCURRENT);
    dispatch_sync(queue, ^{
        NSLog(@"1--%@--",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"2--%@--",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"3--%@--",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"4--%@--",[NSThread currentThread]);
    });
    NSLog(@"结束");
    //number = 1, name = main 有序
}

- (void)test3 {
    //串行队列+同步任务：不会开启新线程，在父线程中同步执行各个子线程，也就是逐一执行，并且是添加过任务后立即执行，之后才能添加下一个任务
    dispatch_queue_t queue = dispatch_queue_create("tqh.com", DISPATCH_QUEUE_SERIAL);
    dispatch_sync(queue, ^{
        NSLog(@"1--%@--",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"2--%@--",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"3--%@--",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"4--%@--",[NSThread currentThread]);
    });
    NSLog(@"结束");
    //number = 1, name = main 有序
}

- (void)test4 {
    //串行队列+异步任务：创建新线程，但是只会创建一个新线程，所有的任务都是在这个子线程里执行，执行顺序按照添加任务 的先后顺序，并且不是立即执行，而是等整个方法
    dispatch_queue_t queue = dispatch_queue_create("tqh.com", DISPATCH_QUEUE_SERIAL);
    dispatch_async(queue, ^{
        NSLog(@"1--%@--",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"2--%@--",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"3--%@--",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"4--%@--",[NSThread currentThread]);
    });
    NSLog(@"结束");
    //number = 2,name = (null),创建了一个线程 有序
}

- (void)test5 {
    //主队列+异步任务：不会创建新线程，所有的任务都是在这个父线程里执行，执行顺序按照添加任务 的先后顺序，并且不是立即执行，而是等整个方法结束后依次执行
    dispatch_queue_t queue = dispatch_get_main_queue();
    dispatch_async(queue, ^{
        NSLog(@"1--%@--",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"2--%@--",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"3--%@--",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"4--%@--",[NSThread currentThread]);
    });
    NSLog(@"结束");
    //number = 1, name = main 有序
}

- (void)test6 {
    //这个会产生问题,死锁，添加任务到主队列的任务要求立即执行，但是主队列是串行队列，当前任务要求执行完当前任务在执行新添加的任务。结果就是:两个任务互相等待，产生死锁
    dispatch_queue_t queue = dispatch_get_main_queue();
    dispatch_sync(queue, ^{
        NSLog(@"1--%@--",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"2--%@--",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"3--%@--",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"4--%@--",[NSThread currentThread]);
    });
    NSLog(@"结束");
    //没有打印信息
}

//延时执行：没有NSObject和NsTimer精确度高
- (void)test7 {
    NSLog(@"%@",[NSDate date]);
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        NSLog(@"%@",[NSDate date]);
    });
}

//一次性代码

- (void)test8 {
    for (int i = 0; i < 10; i ++) {
        [self onece];
    }
    //只走了第一次
}

- (void)onece {
    static dispatch_once_t once;
    dispatch_once(&once, ^{
        NSLog(@"只走一次%@",[NSThread currentThread]);
    });
    NSLog(@"----------------");
}

//快速迭代,顺序不稳定

- (void)test9 {
    dispatch_apply(10, dispatch_get_global_queue(0, 0), ^(size_t  index) {
        NSLog(@"%ld %@",index,[NSThread currentThread]);
    });
    //无序
}

//队列组
- (void)test10 {
    dispatch_group_t group = dispatch_group_create();
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    // 先执行3个耗时操作
    dispatch_group_async(group, queue, ^{
        for (int i = 0 ; i < 1000; i ++) {
            NSLog(@"1--%@--",[NSThread currentThread]);
        }
    });
    
    dispatch_group_async(group, queue, ^{
        for (int i = 0 ; i < 1000; i ++) {
            NSLog(@"2--%@--",[NSThread currentThread]);
        }
    });
    dispatch_group_async(group, queue, ^{
        for (int i = 0 ; i < 1000; i ++) {
            NSLog(@"3--%@--",[NSThread currentThread]);
        }
    });
    // 等到以上任务完成后才会执行这个notify任务
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        NSLog(@"最后执行main--%@--",[NSThread currentThread]);
    });
}