Taking strict turns in a cards game

Question

I am implementing a cards game on the web and the clients are threads . how do I make them alternate strictly in turns on the server. Is there any way I can identify which thread it is and block its information.

Answer 1

You can identify which thread is running with static method Thread.getCurrentThread() (or it can call the synchronized method with some arguments identifying it). It is easy then to have it wait if it is not ist turn. The server is passive, it has no specific thread. It knows of all players thread and of their ordering. Player threads will run its play method. In this method, they will wait until their turn has come.
Here are too little classes that will sketch the system:
import java.util.Date;
public class GameServer extends Thread {
  private final Thread[] players;
  int currentPlayerIndex = 0;
  public GameServer() {
    players = new Thread[4];
    for (int p = 0; p < players.length; p++){
      players[p] = new PlayerThread(this, "Player " + (p+1));
      players[p].start();
  public synchronized void play(String playerName, long thinkTime){
    try{
      long waitStart = new Date().getTime();
      while(Thread.currentThread() != players[currentPlayerIndex])
        wait();
      long waitTime = new Date().getTime() - waitStart;
      System.out.println(playerName + " is playing. "
          + " Took " + thinkTime + " ms to think"
          + " Had then to wait for " + waitTime + " ms.");
      currentPlayerIndex = (currentPlayerIndex + 1) % players.length;
      notifyAll();
    } catch (InterruptedException e){
      e.printStackTrace();
  public static void main(String[] args){
    GameServer server = new GameServer();
}Here is player thread
public class PlayerThread extends Thread {
  private final GameServer server;
  public PlayerThread(GameServer aServer, String name) {
    super(name);
    server = aServer;
  public void run(){
    try {
      while(true){
        long thinkTime = Math.round(3000 * Math.random());
        Thread.sleep(thinkTime); // think
        server.play(getName(), thinkTime);
    } catch (InterruptedException e){
  }Two points:
1) This has to be improved to resist one player thread going down. Otherwise, when its turn comes, over will wait forever. You might need to be more careful with InterruptedException, and to set up a ThreadGroup for players so that you be notified with uncaughtException.
2) If players work the way I wrote them, you cannot do your scheduling with priorities. If a thread is sleeping (or waiting for some resource, or user input), giving it a high priority will not make its wait shorter. Another thread which happens to get its resource or input quicker will run first.. Better use priorities only as hints for optimization rather than for strongly constrained synchronization.