请教多线程 GCD 关于异步同步与串行相关的问题
```
dispatch_queue_t queue = dispatch_queue_create("com.serial.com", DISPATCH_QUEUE_SERIAL);
NSLog(@"1-%@",[NSThread currentThread]);
dispatch_async(queue,^ {
NSLog(@"2-%@",[NSThread currentThread]);
dispatch_sync(queue,^{
NSLog(@"3-%@",[NSThread currentThread]);
});
NSLog(@"4-%@",[NSThread currentThread]);
});
NSLog(@"5-%@",[NSThread currentThread]);
``` print 152
执行到 dispatch_sync(queue,^{ 就结束了。
