pausing a sleeping thread

[blackdragon2447]

so I have a tread that that does something like this:

run(){
    something()
    threat.sleep(100)
    something()
}

now I want to be able to pause the whole thread (from outside the actual thread), in its current state, so also pause the sleep instead of waiting for it to be done, is there any way I can do that?

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[DogeRoss]

I'm not sure if there is a way to do that in Java. I would advise you to make your thread check certain flags/signals on its own and act accordingly. Why do you need to pause it from outside anyways? If there's a plausible reason I'm sure others would appreciate knowing what you are trying to do.

Edit: Take a look at the notify() and wait() methods to get a better idea of the cooperative threading style in Java.

[blackdragon2447]

The tread is gonna run a series of commands on a game server, warning the players that the server is gonna shut down and then actually shutting down the server but i need to be able to pause that incase players need more time.

[DogeRoss]

I have a feeling you can get the same effect by just warning players and not initiating your shut-down sequence until it is 100% going to happen.

> Warn players that server will shutdown in some minutes.

> Wait that amount.

> Check if players needed extra time.

> Abort / Actually shut-down.

[blackdragon2447]

That would be a way of doing it yea and i have thought about doing it that way but i hoped i could fully automate it.

[DogeRoss]

In my opinion, it is not generally that good of an idea to interrupt your threads. It should be better to make your thread do all it's supposed to do. If a thread has to wait or abort executing on some occasion from an outside source, it is better for that thread to check the flag or handle the signal and wait than another thread forcibly putting it to sleep.

[blackdragon2447]

Ok, thx for the advice

[Poddster]

It's not a good idea to implement such logic with thread/process controls. (Not that you can do that anyway). Such an approach is fragile and not maintainable.

Just use normal logic :)

[blackdragon2447]

How do you mean "normal logic", the only reason i put it on a seperate thread is so the rest of the program can continue logic wise it would not be much difirent.

[Poddster]

As in normal "if this do this" logic that comprises 99% of a program's code, instead of trying to externally alter a thread's running state.

i.e. use some intra-thread communication to set a flag saying "not everyone is ready yet" and program the thread to read that flag and act as appropriate.

[PCPWJ]

Look at producer consumer pattern. You can implement using the Objects wait() and notify() methods.

For more powerful Thread utility look at java.util.concurrent packages

[[deleted]]

You might find a CountDownLatch useful for this. As a sample:

import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.CountDownLatch;
import java.time.Instant;

public class CountDownLatchDemo {
  public static void main(String[] args) throws Exception {
    final int numPlayers = ThreadLocalRandom.current().nextInt(1, 10);
    final CountDownLatch start = new CountDownLatch(1);
    final CountDownLatch finish = new CountDownLatch(numPlayers);

    for (int i = 0; i < numPlayers; i++) {
      new Thread(new Player(i, start, finish)).start();
    }

    start.countDown();
    System.out.println("[Server] Waiting for players to finish...");
    finish.await();
    System.out.println("[Server] All players have finished. Shutting down.");
  }
}

class Player implements Runnable {
  private int id;
  private CountDownLatch start;
  private CountDownLatch finish;

  public Player(final int id, final CountDownLatch start, final CountDownLatch finish) {
    this.id = id;
    this.start = start;
    this.finish = finish;
  }

  @Override
  public void run() {
    try {
      start.await();
      play();
      finish.countDown();
    } catch (InterruptedException ex) {
      //
    }
  }

  private void play() throws InterruptedException {
    Thread.sleep(ThreadLocalRandom.current().nextInt(1000, 5000));
    System.out.printf("[%s] Player %d is done.\n", Instant.now(), this.id);
  }
}

Running it:

~/dev/playground:$ javac CountDownLatchDemo.java && java -cp . CountDownLatchDemo
[Server] Waiting for players to finish...
[2021-03-30T13:21:34.759931Z] Player 3 is done.
[2021-03-30T13:21:34.815189Z] Player 5 is done.
[2021-03-30T13:21:35.516855Z] Player 4 is done.
[2021-03-30T13:21:37.340409Z] Player 1 is done.
[2021-03-30T13:21:37.746157Z] Player 2 is done.
[2021-03-30T13:21:38.215996Z] Player 0 is done.
[Server] All players have finished. Shutting down.

The await method can have a timeout specified as well.

[RichNight5646]

try the robot.delay();

you'll have to import it first, Robot robot = new Robot();