Question

I would like to check whether a certain thread has already been joined.
In the code below I have threads that finish at different times and I would like to check whether a thread has terminated and not yet been joined.

Is there a good way of checking this?

while(!allJoined){
        allJoined=true;
        for ( int i = 0; i < 10; i++ )
        {
            try {
                if(!threadList[i].isAlive() && threadList[i].NOT_YET_JOINED() ) {
                    threadList[i].join(0);
                    System.out.println("Joined t-"+i);
                } else {
                    allJoined = false;
                }

            } catch (Exception e) { 
                System.out.println("MASTER: Child interrupted."+e); 
            } 
        }
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) { 
            System.out.println("Child interrupted."); 
        } 
    }

Answer 1

Whether you have join()ed a thread is a part of your state, not the thread’s state. Imagine: you could have several threads all trying to join a given worker-thread.

Why don’t you keep a list of the threads you have already joined?

Then check that list before you join it.

Vector<Thread> joined = new Vector<Thread>();
for(int i=0;i<threadList.length;i++) {
  if(threadList[i].isAlive() && !joined.contains(threadList[i])){ 
     threadList[i].join(0);
     joined.add(threadList[i]);
  }
}

then use joined.size() to see if all are joined or not.