OC

/**
 * 隊(duì)列組 dispatch_group_notify
 */
- (void)groupNotify {
    NSLog(@"currentThread---%@",[NSThread currentThread]);  // 打印當(dāng)前線程
    NSLog(@"group---begin");

    dispatch_group_t group =  dispatch_group_create();

    dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        // 追加任務(wù) 1
        [NSThread sleepForTimeInterval:2];              // 模擬耗時(shí)操作
        NSLog(@"1---%@",[NSThread currentThread]);      // 打印當(dāng)前線程
    });

    dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        // 追加任務(wù) 2
        [NSThread sleepForTimeInterval:2];              // 模擬耗時(shí)操作
        NSLog(@"2---%@",[NSThread currentThread]);      // 打印當(dāng)前線程
    });

    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        // 等前面的異步任務(wù) 1阿纤、任務(wù) 2 都執(zhí)行完畢后句灌，回到主線程執(zhí)行下邊任務(wù)
        [NSThread sleepForTimeInterval:2];              // 模擬耗時(shí)操作
        NSLog(@"3---%@",[NSThread currentThread]);      // 打印當(dāng)前線程

        NSLog(@"group---end");
    });
}

/**
 * 隊(duì)列組 dispatch_group_wait
 */
- (void)groupWait {
    NSLog(@"currentThread---%@",[NSThread currentThread]);  // 打印當(dāng)前線程
    NSLog(@"group---begin");

    dispatch_group_t group =  dispatch_group_create();

    dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        // 追加任務(wù) 1
        [NSThread sleepForTimeInterval:2];              // 模擬耗時(shí)操作
        NSLog(@"1---%@",[NSThread currentThread]);      // 打印當(dāng)前線程
    });

    dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        // 追加任務(wù) 2
        [NSThread sleepForTimeInterval:2];              // 模擬耗時(shí)操作
        NSLog(@"2---%@",[NSThread currentThread]);      // 打印當(dāng)前線程
    });

    // 等待上面的任務(wù)全部完成后，會(huì)往下繼續(xù)執(zhí)行（會(huì)阻塞當(dāng)前線程）
    dispatch_group_wait(group, DISPATCH_TIME_FOREVER);

    NSLog(@"group---end");

}

/**
 * 隊(duì)列組 dispatch_group_enter欠拾、dispatch_group_leave
 */
- (void)groupEnterAndLeave {
    NSLog(@"currentThread---%@",[NSThread currentThread]);  // 打印當(dāng)前線程
    NSLog(@"group---begin");

    dispatch_group_t group = dispatch_group_create();
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_group_enter(group);
    dispatch_async(queue, ^{
        // 追加任務(wù) 1
        [NSThread sleepForTimeInterval:2];              // 模擬耗時(shí)操作
        NSLog(@"1---%@",[NSThread currentThread]);      // 打印當(dāng)前線程

        dispatch_group_leave(group);
    });

    dispatch_group_enter(group);
    dispatch_async(queue, ^{
        // 追加任務(wù) 2
        [NSThread sleepForTimeInterval:2];              // 模擬耗時(shí)操作
        NSLog(@"2---%@",[NSThread currentThread]);      // 打印當(dāng)前線程

        dispatch_group_leave(group);
    });
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        // 等前面的異步操作都執(zhí)行完畢后胰锌，回到主線程.
        [NSThread sleepForTimeInterval:2];              // 模擬耗時(shí)操作
        NSLog(@"3---%@",[NSThread currentThread]);      // 打印當(dāng)前線程

        NSLog(@"group---end");
    });
    //從 dispatch_group_enter、dispatch_group_leave
    //相關(guān)代碼運(yùn)行結(jié)果中可以看出：當(dāng)所有任務(wù)執(zhí)行完成之后藐窄，才執(zhí)行 dispatch_group_notify 中的任務(wù)格带。
    //這里的dispatch_group_enter屈呕、dispatch_group_leave 組合，其實(shí)等同于dispatch_group_async嗽桩。
}

Swift

 //MARK: ---隊(duì)列組---
    /**
    * 隊(duì)列組 dispatch_group_notify
    */
    func groupNotify() {
        let queue = DispatchQueue.main
        let group = DispatchGroup.init()
//        group( asyncSerial() )
        queue.async(group: group, execute: {
            //追加任務(wù)1
            print("追加任務(wù)1")
        })
        
        queue.async(group: group, execute: {
           //追加任務(wù)2
            print("追加任務(wù)2")
        })
        
        group.notify(queue: DispatchQueue.main) {
            // 等前面的異步任務(wù) 1种樱、任務(wù) 2 都執(zhí)行完畢后消恍，回到主線程執(zhí)行下邊任務(wù)
            print("任務(wù)3")
        }
        
    }
    /**
    * 隊(duì)列組 dispatch_group_wait
    */
    func groupWait() {
          let group = DispatchGroup.init()
          let queue = DispatchQueue.global()
        
         queue.async(group: group, execute: {
             //追加任務(wù)1
             print("追加任務(wù)1")
         })
         
         queue.async(group: group, execute: {
            //追加任務(wù)2
             print("追加任務(wù)2")
         })
         group.wait(timeout: .now()+1)
    }
    
    /**
    * 隊(duì)列組 dispatch_group_enter邑遏、dispatch_group_leave
    */
    func groupEnterAndLeave(){
        let group = DispatchGroup.init()
        let queue = DispatchQueue.global()
        
        group.enter()
        queue.async(group: group, execute: {
            //追加任務(wù)1
            print("追加任務(wù)1")
            group.leave()
        })
        
        group.enter()
        queue.async(group: group, execute: {
            //追加任務(wù)2
            print("追加任務(wù)2")
            group.leave()
        })
        
        group.notify(queue: DispatchQueue.main) {
            // 等前面的異步任務(wù) 1、任務(wù) 2 都執(zhí)行完畢后，回到主線程執(zhí)行下邊任務(wù)
            print("任務(wù)3")
        }
    }