iOS block 同步执行(2)

<pre>

1. • (CLPlacemark*)getStartplacemark
2. {
3. //先创建一个semaphore
4. dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
5. dispatch_semaphore_t semaphore = dispatch_semaphore_create(1);

6. __block CLPlacemark* start;
   

7. [self.geoCoder geocodeAddressString:_SourceText.text completionHandler:^(NSArray *placemarks, NSError *error) {      
   

8.   CLPlacemark *startPlaceMark = [placemarks firstObject];
   

9.     start = startPlaceMark;
   

11.    //发出已完成的信号
    

12.     dispatch_semaphore_signal(semaphore);
    

13. }];
    

15. //等待执行，不会占用资源
    

16. dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
    

17. return start;
    

18. }

</pre>

https://www.zybuluo.com/MicroCai/note/64272