主線程，執(zhí)行UI刷新

dispatch_async(dispatch_get_global_queue(0, 0), ^{
      //執(zhí)行耗時的異步操作..
      //................
      //................
      dispatch_async(dispatch_get_main_queue(), ^{
          //回到主線程宫蛆，執(zhí)行UI刷新操作
          //................
          //................
      });
  });

延時操作

 dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(10 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        //code to be executed after a specified delay code將在10后執(zhí)行
 });

dispatch_group_async隊列組實現(xiàn)多線程異步操作

1.調(diào)用隊列組的 dispatch_group_async先把任務(wù)放到隊列中全谤，然后將隊列放入隊列組中。
[或者使用隊列組的 dispatch_group_enter安皱、dispatch_group_leave組合 來實現(xiàn)dispatch_group_async]
2.當(dāng)所有任務(wù)都執(zhí)行完成之后调鬓，才執(zhí)行dispatch_group_notify block 中的任務(wù)。

#@property(nonatomic, strong) dispatch_group_t group_t;
#@property(nonatomic, strong) dispatch_queue_t queue_t;

#pragma mark dispatch_group_async
- (void)gcd_dispatch_group {
    // 打印當(dāng)前線程
    NSLog(@"當(dāng)前線程---%@",[NSThread currentThread]);
    NSLog(@"隊列組---begin");
    dispatch_group_t group =  dispatch_group_create();
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    dispatch_group_async(group, queue, ^{
        // 追加任務(wù)1111
        for (int i = 0; i < 5; ++i) {
            //模擬耗時操作
            [NSThread sleepForTimeInterval:4];
            //打印當(dāng)前線程
            NSLog(@"1111---%@",[NSThread currentThread]);
        }
    });
    
    dispatch_group_async(group, queue, ^{
        // 追加任務(wù)2222
        for (int i = 0; i < 6; ++i) {
            //模擬耗時操作
            [NSThread sleepForTimeInterval:4];
            //打印當(dāng)前線程
            NSLog(@"2222---%@",[NSThread currentThread]);
        }
    });

    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        //等前面的異步任務(wù)1酌伊、任務(wù)2都執(zhí)行完畢后腾窝，回到主線程執(zhí)行下邊任務(wù)
        NSLog(@"任務(wù)1、任務(wù)2都執(zhí)行完畢");
        for (int i = 0; i < 4; ++i) {
            // 模擬耗時操作
            [NSThread sleepForTimeInterval:2];
            // 打印當(dāng)前線程
            NSLog(@"3333---%@",[NSThread currentThread]);
        }
        NSLog(@"隊列組---end");
    });
    NSLog(@"代碼---end");
}