//声明一个串行队列 优先级low
dispatch_queue_t serialQueue=
dispatch_queue_create("serial_queue",DISPATCH_QUEUE_SERIAL);
dispatch_set_target_queue(serialQueue,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW,0));
//声明一个并行队列 优先级low
dispatch_queue_t concurrencyQueue = dispatch_queue_create("concurrentcy_queue",DISPATCH_QUEUE_CONCURRENCY);
dispatch_set_target_queue(concurrencyQueue,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW,0));
串行队列 内执行顺序为有序 因为在同一线程中执行
并行队列内执行顺序为无序 因为在不同线程中执行
