Switch to using a ScheduledThreadPoolExecutor instead of a Timer for scheduled tasks. This will allow 2 * CPU count threads to handle background tasks instead of using a single thread, which could cause the server to effectively die if a task gets stuck for some reason. This addresse the symptom of #89, but not the cause (which is yet to be determined).

src/net/socialgamer/cah/CahModule.java

@@ -29,7 +29,9 @@ import java.util.Collections;
 import java.util.HashSet;
 import java.util.Properties;
 import java.util.Set;
-import java.util.Timer;
+import java.util.concurrent.ScheduledThreadPoolExecutor;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.atomic.AtomicInteger;
 
 import net.socialgamer.cah.data.GameManager;
 import net.socialgamer.cah.data.GameManager.GameId;
@@ -65,10 +67,24 @@ public class CahModule extends AbstractModule {
     })
         .annotatedWith(BanList.class)
         .toInstance(Collections.synchronizedSet(new HashSet<String>()));
-    bind(Timer.class)
-        .toInstance(new Timer("timer-task", true));
     bind(Properties.class)
         .toInstance(properties);
+
+    final ScheduledThreadPoolExecutor threadPool =
+        new ScheduledThreadPoolExecutor(2 * Runtime.getRuntime().availableProcessors(),
+            new ThreadFactory() {
+              final AtomicInteger threadCount = new AtomicInteger();
+
+              @Override
+              public Thread newThread(final Runnable r) {
+                final Thread t = new Thread(r);
+                t.setDaemon(true);
+                t.setName("timer-task-" + threadCount.incrementAndGet());
+                return t;
+              }
+            });
+    threadPool.setRemoveOnCancelPolicy(true);
+    bind(ScheduledThreadPoolExecutor.class).toInstance(threadPool);
   }
 
   /**

src/net/socialgamer/cah/SafeTimerTask.java

@@ -1,11 +1,9 @@
 package net.socialgamer.cah;
 
-import java.util.TimerTask;
-
 import org.apache.log4j.Logger;
 
 
-public abstract class SafeTimerTask extends TimerTask {
+public abstract class SafeTimerTask implements Runnable {
 
   private static final Logger logger = Logger.getLogger(SafeTimerTask.class);
 

src/net/socialgamer/cah/StartupUtils.java

@@ -27,7 +27,8 @@ import java.io.File;
 import java.io.FileReader;
 import java.util.Date;
 import java.util.Properties;
-import java.util.Timer;
+import java.util.concurrent.ScheduledThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
 
 import javax.servlet.ServletContext;
 import javax.servlet.ServletContextEvent;
@@ -83,8 +84,9 @@ public class StartupUtils extends GuiceServletContextListener {
     final ServletContext context = contextEvent.getServletContext();
 
     final Injector injector = (Injector) context.getAttribute(INJECTOR);
-    final Timer timer = injector.getInstance(Timer.class);
-    timer.cancel();
+    final ScheduledThreadPoolExecutor timer = injector
+        .getInstance(ScheduledThreadPoolExecutor.class);
+    timer.shutdownNow();
 
     context.removeAttribute(INJECTOR);
     context.removeAttribute(DATE_NAME);
@@ -97,8 +99,9 @@ public class StartupUtils extends GuiceServletContextListener {
     final ServletContext context = contextEvent.getServletContext();
     final Injector injector = getInjector();
     final UserPing ping = injector.getInstance(UserPing.class);
-    final Timer timer = injector.getInstance(Timer.class);
-    timer.schedule(ping, PING_START_DELAY, PING_CHECK_DELAY);
+    final ScheduledThreadPoolExecutor timer = injector
+        .getInstance(ScheduledThreadPoolExecutor.class);
+    timer.scheduleAtFixedRate(ping, PING_START_DELAY, PING_CHECK_DELAY, TimeUnit.MILLISECONDS);
     serverStarted = new Date();
     context.setAttribute(INJECTOR, injector);
     context.setAttribute(DATE_NAME, serverStarted);

src/net/socialgamer/cah/UserPing.java

@@ -23,7 +23,7 @@
 
 package net.socialgamer.cah;
 
-import java.util.Timer;
+import java.util.concurrent.ScheduledThreadPoolExecutor;
 
 import net.socialgamer.cah.data.ConnectedUsers;
 
@@ -38,10 +38,10 @@ import com.google.inject.Inject;
 public class UserPing extends SafeTimerTask {
 
   private final ConnectedUsers users;
-  private final Timer globalTimer;
+  private final ScheduledThreadPoolExecutor globalTimer;
 
   @Inject
-  public UserPing(final ConnectedUsers users, final Timer globalTimer) {
+  public UserPing(final ConnectedUsers users, final ScheduledThreadPoolExecutor globalTimer) {
     this.users = users;
     this.globalTimer = globalTimer;
   }

src/net/socialgamer/cah/data/Game.java

@@ -33,7 +33,9 @@ import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
-import java.util.Timer;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.ScheduledThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
@@ -146,8 +148,8 @@ public class Game {
    * Lock to prevent missing timer updates.
    */
   private final Object roundTimerLock = new Object();
-  private volatile SafeTimerTask lastTimerTask;
-  private final Timer globalTimer;
+  private volatile ScheduledFuture<?> lastScheduledFuture;
+  private final ScheduledThreadPoolExecutor globalTimer;
 
   private int scoreGoal = 8;
   private final Set<CardSet> cardSets = new HashSet<CardSet>();
@@ -169,7 +171,7 @@ public class Game {
    */
   @Inject
   public Game(@GameId final Integer id, final ConnectedUsers connectedUsers,
-      final GameManager gameManager, final Timer globalTimer) {
+      final GameManager gameManager, final ScheduledThreadPoolExecutor globalTimer) {
     this.id = id;
     this.connectedUsers = connectedUsers;
     this.gameManager = gameManager;
@@ -902,10 +904,10 @@ public class Game {
 
   private void killRoundTimer() {
     synchronized (roundTimerLock) {
-      if (lastTimerTask != null) {
-        logger.trace(String.format("Killing timer task %s", lastTimerTask));
-        lastTimerTask.cancel();
-        lastTimerTask = null;
+      if (null != lastScheduledFuture) {
+        logger.trace(String.format("Killing timer task %s", lastScheduledFuture));
+        lastScheduledFuture.cancel(false);
+        lastScheduledFuture = null;
       }
     }
   }
@@ -914,8 +916,7 @@ public class Game {
     synchronized (roundTimerLock) {
       killRoundTimer();
       logger.trace(String.format("Scheduling timer task %s after %d ms", task, timeout));
-      lastTimerTask = task;
-      globalTimer.schedule(task, timeout);
+      lastScheduledFuture = globalTimer.schedule(task, timeout, TimeUnit.MILLISECONDS);
     }
   }
 

test/net/socialgamer/cah/data/GameManagerTest.java

@@ -35,7 +35,7 @@ import static org.junit.Assert.assertNull;
 
 import java.util.Collection;
 import java.util.HashMap;
-import java.util.Timer;
+import java.util.concurrent.ScheduledThreadPoolExecutor;
 
 import net.socialgamer.cah.HibernateUtil;
 import net.socialgamer.cah.data.GameManager.GameId;
@@ -65,7 +65,7 @@ public class GameManagerTest {
   private ConnectedUsers cuMock;
   private User userMock;
   private int gameId;
-  private final Timer timer = new Timer("junit-timer", true);
+  private final ScheduledThreadPoolExecutor timer = new ScheduledThreadPoolExecutor(1);
 
   @Before
   public void setUp() throws Exception {

test/net/socialgamer/cah/data/GameTest.java

@@ -36,7 +36,7 @@ import static org.junit.Assert.assertTrue;
 
 import java.util.Collection;
 import java.util.HashMap;
-import java.util.Timer;
+import java.util.concurrent.ScheduledThreadPoolExecutor;
 
 import net.socialgamer.cah.data.Game.TooManyPlayersException;
 import net.socialgamer.cah.data.QueuedMessage.MessageType;
@@ -55,7 +55,7 @@ public class GameTest {
   private Game game;
   private ConnectedUsers cuMock;
   private GameManager gmMock;
-  private final Timer timer = new Timer("junit-timer", true);
+  private final ScheduledThreadPoolExecutor timer = new ScheduledThreadPoolExecutor(1);
 
   @Before
   public void setUp() throws Exception {