Print the warning if amount of events in incoming queue is too big

It should simplify troubleshooting in case of slowness in event
processing logic.

src/main/java/com/sonymobile/tools/gerrit/gerritevents/GerritHandler.java

@@ -73,6 +73,10 @@ public class GerritHandler implements Coordinator, Handler {
     private final Set<GerritEventListener> gerritEventListeners = new CopyOnWriteArraySet<GerritEventListener>();
     private final List<EventThread> workers;
     private Map<String, String> ignoreEMails = new ConcurrentHashMap<String, String>();
+    /**
+     * The minimum size of the job-queue before monitors should begin to warn the administrator(s).
+     */
+    public static final int WORK_QUEUE_SIZE_WARNING_THRESHOLD = 40;
 
     /**
      * Creates a GerritHandler with all the default values set.
@@ -177,13 +181,28 @@ private void post(Work work) {
         try {
             logger.trace("putting work on queue.");
             workQueue.put(work);
+            checkQueueSize();
         } catch (InterruptedException ex) {
             logger.warn("Interrupted while putting work on queue!", ex);
             //TODO check if shutdown
             //TODO try again since it is important
         }
     }
 
+    /**
+     * Checks queue size.
+     */
+    private void checkQueueSize() {
+        int queueSize = workQueue.size();
+        if (queueSize >= WORK_QUEUE_SIZE_WARNING_THRESHOLD) {
+            logger.warn("The Gerrit-trigger incoming events queue contains {} items!"
+                        + " Something might be stuck, or your system can't process the commands fast enough."
+                        + " Try to increase the number of receiving worker threads on the Gerrit configuration page."
+                        + " Current thread-pool size: {}",
+                    queueSize, workers.size());
+        }
+    }
+
     @Override
     public void addListener(GerritEventListener listener) {
         synchronized (this) {
@@ -372,12 +391,6 @@ public void shutdown(boolean join) {
      */
     @Deprecated
     public void triggerEvent(GerritEvent event) {
-        logger.debug("Internally trigger event: {}", event);
-        try {
-            logger.trace("putting work on queue.");
-            workQueue.put(new GerritEventWork(event));
-        } catch (InterruptedException ex) {
-            logger.error("Interrupted while putting work on queue!", ex);
-        }
+        post(event);
     }
 }