Remove org.bushe:eventbus CleanupEvent logic

We do not need to monitor these events.
Removing it simplifies the codebase and avoids a hack.

Author: ctrueden

src/main/java/org/scijava/event/DefaultEventBus.java

@@ -34,7 +34,6 @@
 import java.util.Arrays;
 import java.util.List;
 
-import org.scijava.event.bushe.CleanupEvent;
 import org.scijava.event.bushe.ThreadSafeEventService;
 import org.scijava.log.LogService;
 import org.scijava.service.Service;
@@ -116,33 +115,6 @@ public void publishLater(final String topicName, final Object eventObj) {
 
 	@Override
 	public void publish(final Object event) {
-		// HACK: Work around a deadlock problem caused by ThreadSafeEventService:
-
-		// 1) The ThreadSafeEventService superclass has a special cleanup thread
-		// that takes care of cleaning up stale references. Every time it runs, it
-		// publishes some CleanupEvents using publish(Object) to announce that this
-		// is occurring. Normally, such publication delegates to
-		// publishNow, which calls ThreadService#invoke, which calls
-		// EventQueue.invokeAndWait, which queues the publication for execution on
-		// the EDT and then blocks until publication is complete.
-
-		// 2) When the ThreadSafeEventService publishes the CleanupEvents, it does
-		// so inside a synchronized block that locks on a "listenerLock" object.
-
-		// 3) Unfortunately, since the CleanupEvent publication is merely *queued*,
-		// any other pending operations on the EDT happen first. If one such
-		// operation meanwhile calls e.g.
-		// ThreadSafeEventService#getSubscribers(Class<T>), it will deadlock because
-		// those getter methods are also synchronized on the listenerLock object.
-
-		// Hence, our hack workaround is to instead use publishLater for the
-		// CleanupEvents, since no one really cares about them anyway. ;-)
-
-		if (event instanceof CleanupEvent) {
-			publishLater(event);
-			return;
-		}
-
 		publishNow(event);
 	}
 

src/main/java/org/scijava/event/bushe/CleanupEvent.java

@@ -122,8 +122,6 @@
  * to <tt>CLEANUP_STOP_THRESHOLD_DEFAULT</tt> (100) by default.  The default is overridable in the constructor or via 
  * #setCleanupStopThreshhold(Integer).  If set to null or 0, cleanup will not stop if it is ever started.  
  * <p/>
- * Cleanup can be monitored by subscribing to the {@link CleanupEvent} class. 
- * <p/>
  * All cleanup parameters are tunable "live" and checked after each subscription and after each cleanup cycle.
  * To make cleanup never run, set cleanupStartThreshhold to Integer.MAX_VALUE and cleanupPeriodMS to null.
  * To get cleanup to run continuously, set set cleanupStartThreshhold to 0 and cleanupPeriodMS to some reasonable value,
@@ -137,7 +135,7 @@
  * @todo (param) a JMS-like selector (can be done in base classes by implements like a commons filter
  * @see EventService for a complete description of the API
  */
-@SuppressWarnings({"unchecked", "ForLoopReplaceableByForEach"})
+@SuppressWarnings({"unchecked"})
 public class ThreadSafeEventService implements EventService {
    public static final Integer CLEANUP_START_THRESHOLD_DEFAULT = 250;
    public static final Integer CLEANUP_STOP_THRESHOLD_DEFAULT = 100;
@@ -2057,17 +2055,14 @@ class CleanupTimerTask extends TimerTask {
       @Override
       public void run() {
          synchronized(listenerLock) {
-            ThreadSafeEventService.this.publish(new CleanupEvent(CleanupEvent.Status.STARTING, weakRefPlusProxySubscriberCount, null));
             if (weakRefPlusProxySubscriberCount <= cleanupStopThreshold) {
                this.cancel();
                cleanupTimer = null;
                cleanupTimerTask = null;
                LOG.debug("Cancelled scheduled weak reference and proxy cleanup.");
-               ThreadSafeEventService.this.publish(new CleanupEvent(CleanupEvent.Status.UNDER_STOP_THRESHOLD_CLEANING_CANCELLED, weakRefPlusProxySubscriberCount, null));
                return;
             }
             LOG.debug("Starting a weak reference and proxy cleanup.");
-            ThreadSafeEventService.this.publish(new CleanupEvent(CleanupEvent.Status.OVER_STOP_THRESHOLD_CLEANING_BEGUN, weakRefPlusProxySubscriberCount, null));               
             List<Map> allSubscriberMaps = new ArrayList<Map>();
             allSubscriberMaps.add(subscribersByEventType);
             allSubscriberMaps.add(subscribersByEventClass);
@@ -2093,7 +2088,6 @@ public void run() {
                   }
                }
             }
-            ThreadSafeEventService.this.publish(new CleanupEvent(CleanupEvent.Status.FINISHED_CLEANING, weakRefPlusProxySubscriberCount, staleCount));
          }         
       }      
    }