Do not interrupt timer threads when cancelling timers.

core/src/main/java/net/kuujo/copycat/internal/ActiveState.java

@@ -345,7 +345,6 @@ protected void applyEntry(long index) {
   @Override
   public CompletableFuture<PollResponse> poll(PollRequest request) {
     context.checkThread();
-    logger().debug("{} - Received {}", context.getLocalMember(), request);
     return CompletableFuture.completedFuture(logResponse(handlePoll(logRequest(request))));
   }
 

core/src/main/java/net/kuujo/copycat/internal/CandidateState.java

@@ -88,7 +88,7 @@ private void resetTimer() {
 
     // Cancel the current timer task and purge the election timer of cancelled tasks.
     if (currentTimer != null) {
-      currentTimer.cancel(true);
+      currentTimer.cancel(false);
     }
 
     // When the election timer is reset, increment the current term and

core/src/main/java/net/kuujo/copycat/internal/FollowerState.java

@@ -61,20 +61,20 @@ public CompletableFuture<Void> open() {
    */
   private void startTimer() {
     LOGGER.debug("{} - Starting heartbeat timer", context.getLocalMember());
-    resetTimer();
+    resetHeartbeatTimer();
   }
 
   /**
    * Resets the heartbeat timer.
    */
-  private void resetTimer() {
+  private void resetHeartbeatTimer() {
     context.checkThread();
     if (isClosed()) return;
 
     // If a timer is already set, cancel the timer.
     if (currentTimer != null) {
       LOGGER.debug("{} - Reset heartbeat timeout", context.getLocalMember());
-      currentTimer.cancel(true);
+      currentTimer.cancel(false);
     }
 
     // Reset the last voted for candidate.
@@ -92,20 +92,20 @@ private void resetTimer() {
         transition(CopycatState.CANDIDATE);
       } else {
         // If the node voted for a candidate then reset the election timer.
-        resetTimer();
+        resetHeartbeatTimer();
       }
     }, delay, TimeUnit.MILLISECONDS);
   }
 
   @Override
   public CompletableFuture<PingResponse> ping(PingRequest request) {
-    resetTimer();
+    resetHeartbeatTimer();
     return super.ping(request);
   }
 
   @Override
   public CompletableFuture<AppendResponse> append(AppendRequest request) {
-    resetTimer();
+    resetHeartbeatTimer();
     return super.append(request);
   }
 
@@ -115,7 +115,7 @@ public CompletableFuture<AppendResponse> append(AppendRequest request) {
   private void cancelTimer() {
     if (currentTimer != null) {
       LOGGER.debug("{} - Cancelling heartbeat timer", context.getLocalMember());
-      currentTimer.cancel(true);
+      currentTimer.cancel(false);
     }
   }
 

core/src/main/java/net/kuujo/copycat/internal/LeaderState.java

@@ -251,7 +251,7 @@ public CompletableFuture<CommitResponse> commit(final CommitRequest request) {
   private void cancelPingTimer() {
     if (currentTimer != null) {
       LOGGER.debug("{} - Cancelling ping timer", context.getLocalMember());
-      currentTimer.cancel(true);
+      currentTimer.cancel(false);
     }
   }
 

core/src/main/java/net/kuujo/copycat/internal/PassiveState.java

@@ -65,17 +65,17 @@ public CompletableFuture<Void> open() {
    */
   private void startSyncTimer() {
     LOGGER.debug("{} - Setting sync timer", context.getLocalMember());
-    setSyncTimer();
+    resetSyncTimer();
   }
 
   /**
    * Sets the sync timer.
    */
-  private void setSyncTimer() {
+  private void resetSyncTimer() {
     currentTimer = context.executor().schedule(() -> {
       if (isOpen()) {
         sync();
-        setSyncTimer();
+        resetSyncTimer();
       }
     }, context.getHeartbeatInterval(), TimeUnit.MILLISECONDS);
   }
@@ -84,6 +84,9 @@ private void setSyncTimer() {
    * Synchronizes with random nodes via a gossip protocol.
    */
   private void sync() {
+    context.checkThread();
+    if (isClosed()) return;
+
     // Create a list of currently active members.
     List<ReplicaInfo> activeMembers = new ArrayList<>(context.getMembers().size());
     for (ReplicaInfo member : context.getMemberInfo()) {
@@ -136,6 +139,8 @@ private void sync() {
 
   @Override
   public CompletableFuture<SyncResponse> sync(SyncRequest request) {
+    context.checkThread();
+
     if (request.term() > context.getTerm()) {
       context.setTerm(request.term());
       context.setLeader(request.leader());
@@ -176,7 +181,7 @@ public CompletableFuture<SyncResponse> sync(SyncRequest request) {
   private void cancelSyncTimer() {
     if (currentTimer != null) {
       LOGGER.debug("{} - Cancelling sync timer", context.getLocalMember());
-      currentTimer.cancel(true);
+      currentTimer.cancel(false);
     }
   }