同步执行+并发队列

/**
 * 同步执行 + 并发队列
 * 特点：不会开启新线程，在当前线程中执行任务，执行完一个任务，再执行下一个任务。
 */
- (void)syncConcurrent {
    //打印当前线程
    NSLog(@"currentThread---%@",[NSThread currentThread]);
    NSLog(@"syncConcurrent---begin");
    dispatch_queue_t queue = dispatch_queue_create("net.bujige.testQueue", DISPATCH_QUEUE_CONCURRENT);
    dispatch_sync(queue, ^{
        // 追加任务1
        for (int i = 0; i < 2; ++i) {
            //模拟耗时操作
            [NSThread sleepForTimeInterval:4];
            //打印当前线程
            NSLog(@"1---%@",[NSThread currentThread]);
        }
    });
    dispatch_sync(queue, ^{
        // 追加任务2
        for (int i = 0; i < 2; ++i) {
            //模拟耗时操作
            [NSThread sleepForTimeInterval:3];
            //打印当前线程
            NSLog(@"2---%@",[NSThread currentThread]);
        }
    });
    dispatch_sync(queue, ^{
        // 追加任务3
        for (int i = 0; i < 2; ++i) {
            //模拟耗时操作
            [NSThread sleepForTimeInterval:2];
            //打印当前线程
            NSLog(@"3---%@",[NSThread currentThread]);
        }
    });
    NSLog(@"syncConcurrent---end");
}
运行结果：
2020-07-06 20:35:47.995878+0800 GCD[15831:3005855] currentThread---<NSThread: 0x600000f8d040>{number = 1, name = main}
2020-07-06 20:35:47.995997+0800 GCD[15831:3005855] syncConcurrent---begin
2020-07-06 20:35:51.996729+0800 GCD[15831:3005855] 1---<NSThread: 0x600000f8d040>{number = 1, name = main}
2020-07-06 20:35:55.997665+0800 GCD[15831:3005855] 1---<NSThread: 0x600000f8d040>{number = 1, name = main}
2020-07-06 20:35:58.998527+0800 GCD[15831:3005855] 2---<NSThread: 0x600000f8d040>{number = 1, name = main}
2020-07-06 20:36:01.999486+0800 GCD[15831:3005855] 2---<NSThread: 0x600000f8d040>{number = 1, name = main}
2020-07-06 20:36:03.999725+0800 GCD[15831:3005855] 3---<NSThread: 0x600000f8d040>{number = 1, name = main}
2020-07-06 20:36:06.000605+0800 GCD[15831:3005855] 3---<NSThread: 0x600000f8d040>{number = 1, name = main}
2020-07-06 20:36:06.000765+0800 GCD[15831:3005855] syncConcurrent---end