XCode调试多线程遭遇海森伯效应一例

 1 dispatch_async(dispatch_get_global_queue(0, 0), ^{
 2         
 3                 dispatch_async(dispatch_get_main_queue(), ^{
 4                     ...
 5                     [self myMethod];
 6                    
 7                 });
 8 
 9 -(void)myMethod
10 {
11     self.view.frame = CGRectMake(0, 20, 320, 460); //在该行加断点，会导致调试过程中该方法执行两遍。