一个典型的结束子线程的方法：   用 isFinished 检测子线程是否被完全kill掉

-(IBAction)btnBack:(id)sender{    //释放内存    仅仅remove 并不会触发内存的释放        if (!(mySecondThread==nil) && !myFirstThread.isCancelled) {        [myFirstThread cancel];                 //等子线程结束再跳出循环        int i=0;        while (!myFirstThread.isFinished){            NSLog(@"mySecondThread还没有结束 %i",i++);        }    }    if (!(mySecondThread==nil) && !mySecondThread.isCancelled) {        [mySecondThread cancel];                //等子线程结束再跳出循环        int j=0;        while (!mySecondThread.isFinished){            NSLog(@"mySecondThread还没有结束 %i",j++);        }    }     // 其它操作 }