iOS block 同步执行(2)

 
 
 
  
 
   
 
    
(CLPlacemark*)getStartplacemark
 
   
 
  
{
 
  
//先创建一个semaphore
 
  
dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
 
  
dispatch_semaphore_t semaphore = dispatch_semaphore_create(1);
 
  
__block CLPlacemark* start;
 
  
[self.geoCoder geocodeAddressString:_SourceText.text completionHandler:^(NSArray *placemarks, NSError *error) {      
 
  
  CLPlacemark *startPlaceMark = [placemarks firstObject];
 
  
    start = startPlaceMark;
 
  
 
 
  
   //发出已完成的信号
 
  
    dispatch_semaphore_signal(semaphore);
 
  
}];
 
  
 
 
  
//等待执行，不会占用资源
 
  
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
 
  
return start;
 
  
}
 
 
 
 

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