DefaultThreadService: let running tasks finish

We wait up to 5 seconds for them to terminate.

I don't really have a good idea whether this is a good amount of time,
but it should be more than enough for common scenarios.

At some point, the ThreadService interface could gain methods to
override this value, but for now, we hardcode it.

Author: ctrueden

src/main/java/org/scijava/thread/DefaultThreadService.java

@@ -39,6 +39,7 @@
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
 import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.TimeUnit;
 
 import org.scijava.log.LogService;
 import org.scijava.plugin.Parameter;
@@ -58,6 +59,8 @@ public final class DefaultThreadService extends AbstractService implements
 
 	private static final String SCIJAVA_THREAD_PREFIX = "SciJava-";
 
+	private static final long SHUTDOWN_TIMEOUT = 5000;
+
 	private static WeakHashMap<Thread, Thread> parents =
 		new WeakHashMap<>();
 
@@ -159,11 +162,23 @@ public synchronized void dispose() {
 		disposed = true;
 		if (executor != null) {
 			executor.shutdown();
+			try {
+				executor.awaitTermination(SHUTDOWN_TIMEOUT, TimeUnit.MILLISECONDS);
+			}
+			catch (final InterruptedException exc) {
+				log.debug(exc);
+			}
 			executor = null;
 		}
 		if (queues != null) {
 			for (final ExecutorService queue : queues.values()) {
 				queue.shutdown();
+				try {
+					queue.awaitTermination(SHUTDOWN_TIMEOUT, TimeUnit.MILLISECONDS);
+				}
+				catch (final InterruptedException exc) {
+					log.debug(exc);
+				}
 			}
 		}
 	}