线程，先执行完一个， 在执行下一个。

dispatch_queue_t queue= dispatch_queue_create("当前页面名字C.queue", DISPATCH_QUEUE_CONCURRENT);

dispatch_sync(queue, ^{

// 测试

//for (int i = 0; i < 2; ++i) {

//NSLog(@"1------%@",[NSThread currentThread]);

//}

});

dispatch_sync(queue, ^{

// 测试

//for (int i = 0; i < 2; ++i) {

//NSLog(@"1------%@",[NSThread currentThread]);

//}

});