嵌套dispatch_async（另一个dispatch_async中的dispatch_async）

Question

我该如何称呼不当dispatch_async内来电dispatch_async

dispatch_group_t downloadQueue = dispatch_group_create();
dispatch_group_async(downloadQueue,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {

NSLog(@"Main");
[NSThread sleepForTimeInterval:5.0];
NSLog(@"End");

    [self myMethod];

});
dispatch_group_notify(downloadQueue,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH,0), ^ {

    NSLog(@"FINAL");

});

这是myMethod：

-(void)myMethod
{
    dispatch_group_t group = dispatch_group_create();
    dispatch_group_async(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {
        // block1
        NSLog(@"Block1");
        [NSThread sleepForTimeInterval:5.0];
        NSLog(@"Block1 End");
    });
    dispatch_group_async(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {
        // block2
        NSLog(@"Block2");
        [NSThread sleepForTimeInterval:8.0];
        NSLog(@"Block2 End");
    });

    dispatch_group_notify(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {
        // block3
        NSLog(@"Block3");
    });
}

我的输出是：
主要
结束
1座
2座
最后
Block1结束
Block2结束
3座

但是我需要
主要
结束
1座
2座
Block1结束
Block2结束
3座
最后

Answer 1

您只需要通过您的myMethod组通知即可。 您的代码将是：

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {

    NSLog(@"Main");
    [NSThread sleepForTimeInterval:5.0];
    NSLog(@"End");

    dispatch_group_notify([self myMethod],dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH,0), ^ {

        NSLog(@"FINAL");

    });
});

-(dispatch_group_t)myMethod{

    dispatch_group_t group = dispatch_group_create();

    dispatch_group_async(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {
        // block1
        NSLog(@"Block1");
        [NSThread sleepForTimeInterval:5.0];
        NSLog(@"Block1 End");
    });


    dispatch_group_async(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {
        // block2
        NSLog(@"Block2");
        [NSThread sleepForTimeInterval:8.0];
        NSLog(@"Block2 End");
    });

    dispatch_group_notify(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {
        // block3
        NSLog(@"Block3");
    });
    return group;
}

Answer 2

您可以在myMethod使用dispatch_group_wait而不是dispatch_group_notify。 这样，仅当两个dispatch_group_async完成执行时，您的方法才会返回。