Thread安全

 Thread之間存取變數的時間差可能導致變數存取的錯誤

- (void)setMyVar:(id)inMyVar { 

 [myVar release];

#warmming 這裡會有時間差 

 myVar = [inMyVar retain]; 

}

可以用Lock去鎖定，或是用下列的寫法來保證線程安全

- (void)setMyVar:(id)inMyVar { 

id tmp = myVar; 

myVar = [inMyVar retain]; 

[tmp release]; 

}