Android- Thread.join() causes Application to hang

Question

I have a thread which handles my game loop, when i call .join() on this thread the application stops responding. I've been trying to fix a problem where the programs never get to the code, I.E the thread never ends.

System.out.println("YAY");

My Thread for the Game Loop:

This thread successfully prints out "Game Ended" but never seems to finish.

Runnable startGameLoop = new Runnable() {//game loop
          @Override
          public void run() {

              AiFactory ai = new AiFactory();
              final Button play = (Button) findViewById(R.id.Play);
              final Button pass = (Button) findViewById(R.id.Pass);

              while(finish==false){
                  try {
                        Thread.sleep(500);
                  } catch (InterruptedException e) {
                        e.printStackTrace();
                  }
                  currentPlayer = game.getPlayer();

                  if(currentPlayer.isPlayer()==false){

                      //System.out.println("passCount:" +game.getPasscount());
                      ai.decide(nextPlay, game.getPreviousPlayed(), currentPlayer, game.getPasscount() );
                      if(nextPlay.size()!=0){
                          runOnUiThread(new Runnable(){
                            public void run(){
                                changeArrow();
                                if(nextPlay.size() ==1){
                                    play1Card();
                                }
                                else if(nextPlay.size()==2){
                                    play2Card();
                                }
                                else if(nextPlay.size()==3){
                                    play3Card();
                                }
                                else if(nextPlay.size()==5){
                                    play5Card();
                                }
                            }
                      }
                      else{
                          game.addPassCount();
                          game.nextTurn();
                          runOnUiThread(new Runnable(){
                                public void run(){
                                    changeArrow();
                                }
                            });
                      }     
                   }
                   else if (currentPlayer.isPlayer()==true){
                      runOnUiThread(new Runnable(){
                            public void run(){
                                changeArrow();
                                play.setClickable(true);
                                 if(game.getPasscount()==3){
                                     pass.setClickable(false);
                                 }
                                 else{
                                     pass.setClickable(true);
                                 }
                            }
                        });
                  }

             }
             System.out.println("Game Ended");
          }
     };

Starting and joining the thread to the main thread:

     Thread myThread = new Thread(startGameLoop);

     myThread.start();
     try {
        myThread.join();
    } catch (InterruptedException e) {
            // TODO Auto-generated catch block
        e.printStackTrace();
    }

     System.out.println("YAY");
}

To my understanding .join() makes the current thread wait till the new thread has finished before carrying on.

Sorry if this is a stupid question, i'm quite new to threading.

Answer 1

Thread.join makes the current thread wait until the thread you call it on ends. It does not cause the thread you call it on to end. So if that thread is never ending (as you say at the top), calling join will make it hang forever.

If you want to actually end the thread, call cancel on it. But that requires your thread to occasionally call isCanceled() and exit its run function if it returns true.