如何在大小变化的列表的所有元素上使用Thread.join（）？

for(Worker w:staff){
    w.start();
}
for(Worker w:staff){
    w.join();
}

synchronized(this){
    for(Worker w:staff){
        w.start();
    }
}
while(true){ //this loop will keep the supervisor running until all workers have stopped
                  //interrupts will occur when changes to the size of staff list occur
    try{
        Iterator<Worker> it;
        synchronized(this){
            it = staff.iterator();
        }
        while(it.hasNext()){
            Worker w = it.next();
            w.join();
        }
        return;
    }catch(InterruptedException ie){continue;}
}

Worker w = it.next();