[executor] Purge the thread pool periodically.

The choice was to launch a purging task periodically.
The period is given by a system property (by default 30 seconds).

see #82

Signed-off-by: Stéphane Galland <galland@arakhne.org>

io.janusproject.kernel/src/main/java/io/janusproject/JanusConfig.java

@@ -163,6 +163,18 @@ public final class JanusConfig {
 	 */
 	public static final String INJECTION_MODULE_NAME_VALUE = StandardJanusPlatformModule.class.getName();
 
+	/** Name of the property that contains the numbers of seconds between two purges of
+	 * the terminated threads by the kernel.
+	 * @see #KERNEL_THREAD_PURGE_DELAY_VALUE
+	 */
+	public static final String KERNEL_THREAD_PURGE_DELAY_NAME = "janus.executors.purgeDelay"; //$NON-NLS-1$
+
+	/** Indicates the numbers of seconds between two purges of
+	 * the terminated threads by the kernel.
+	 * @see #KERNEL_THREAD_PURGE_DELAY_NAME
+	 */
+	public static final int KERNEL_THREAD_PURGE_DELAY_VALUE = 30;
+
 	private JanusConfig() {
 		//
 	}
@@ -185,6 +197,7 @@ public static void getDefaultValues(Properties defaultValues) {
 		defaultValues.put(MAX_NUMBER_OF_THREADS_IN_EXECUTOR_NAME,
 				Integer.toString(MAX_NUMBER_OF_THREADS_IN_EXECUTOR_VALUE));
 		defaultValues.put(KERNEL_THREAD_TIMEOUT_NAME, Integer.toString(KERNEL_THREAD_TIMEOUT_VALUE));
+		defaultValues.put(KERNEL_THREAD_PURGE_DELAY_NAME, Integer.toString(KERNEL_THREAD_PURGE_DELAY_VALUE));
 		defaultValues.put(INJECTION_MODULE_NAME, INJECTION_MODULE_NAME_VALUE);
 		defaultValues.put(JANUS_LOGO_SHOW_NAME, JANUS_LOGO_SHOW.toString());
 	}

io.janusproject.kernel/src/main/java/io/janusproject/kernel/Kernel.java

@@ -234,7 +234,7 @@ public void run() {
 		@Override
 		public Thread newThread(Runnable r) {
 			Thread t = Executors.defaultThreadFactory().newThread(r);
-			t.setName("Janus shutdown"); //$NON-NLS-1$
+			t.setName("Janus kernel shutdown"); //$NON-NLS-1$
 			t.setDaemon(false);
 			t.setUncaughtExceptionHandler(this);
 			return t;

io.janusproject.kernel/src/main/java/io/janusproject/kernel/services/jdk/executors/JdkExecutorService.java

@@ -27,6 +27,7 @@
 import java.util.concurrent.Future;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 
 import com.google.common.util.concurrent.Service;
@@ -45,18 +46,35 @@
 @Singleton
 public class JdkExecutorService extends AbstractDependentService implements io.janusproject.services.executor.ExecutorService {
 
-	@Inject
 	private ScheduledExecutorService schedules;
-
-	@Inject
 	private ExecutorService exec;
 
+	private ScheduledFuture<?> purgeTask;
+
 	/**
 	 */
 	public JdkExecutorService() {
 		//
 	}
 
+	/** Change the JRE service for scheduled tasks.
+	 *
+	 * @param service - the JRE service.
+	 */
+	@Inject
+	void setScheduledExecutorService(ScheduledExecutorService service) {
+		this.schedules = service;
+	}
+
+	/** Change the JRE service for scheduled tasks.
+	 *
+	 * @param service - the JRE service.
+	 */
+	@Inject
+	void setExecutorService(ExecutorService service) {
+		this.exec = service;
+	}
+
 	@Override
 	public final Class<? extends Service> getServiceType() {
 		return io.janusproject.services.executor.ExecutorService.class;
@@ -66,13 +84,29 @@ public final Class<? extends Service> getServiceType() {
 	 */
 	@Override
 	protected void doStart() {
+		assert (this.schedules != null);
+		assert (this.exec != null);
+		// Launch a periodic task that is purging the executor pools.
+		if ((this.schedules instanceof ThreadPoolExecutor)
+				|| (this.exec instanceof ThreadPoolExecutor)) {
+			int delay = JanusConfig.getSystemPropertyAsInteger(
+					JanusConfig.KERNEL_THREAD_PURGE_DELAY_NAME,
+					JanusConfig.KERNEL_THREAD_PURGE_DELAY_VALUE);
+			this.purgeTask = this.schedules.scheduleWithFixedDelay(
+					new Purger(),
+					delay, delay, TimeUnit.SECONDS);
+		}
 		notifyStarted();
 	}
 
 	/** {@inheritDoc}
 	 */
 	@Override
 	protected void doStop() {
+		if (this.purgeTask != null) {
+			this.purgeTask.cancel(true);
+			this.purgeTask = null;
+		}
 		this.exec.shutdown();
 		this.schedules.shutdown();
 		try {
@@ -152,4 +186,74 @@ public ExecutorService getExecutorService() {
 		return this.exec;
 	}
 
+	/** {@inheritDoc}
+	 */
+	@Override
+	public void purge() {
+		if (this.exec instanceof ThreadPoolExecutor) {
+			((ThreadPoolExecutor) this.exec).purge();
+		}
+		if (this.schedules instanceof ThreadPoolExecutor) {
+			((ThreadPoolExecutor) this.schedules).purge();
+		}
+	}
+
+	/** Task that is purging the thread pools.
+	 *
+	 * @author $Author: sgalland$
+	 * @version $FullVersion$
+	 * @mavengroupid $GroupId$
+	 * @mavenartifactid $ArtifactId$
+	 */
+	private class Purger implements Runnable {
+
+		private String oldThreadName;
+
+		/**
+		 */
+		public Purger() {
+			//
+		}
+
+		private boolean setName() {
+			if (this.oldThreadName != null) {
+				return false;
+			}
+			Thread t = Thread.currentThread();
+			this.oldThreadName = t.getName();
+			t.setName(toString());
+			return true;
+		}
+
+		private boolean restoreName() {
+			if (this.oldThreadName == null) {
+				return false;
+			}
+			Thread t = Thread.currentThread();
+			t.setName(this.oldThreadName);
+			this.oldThreadName = null;
+			return true;
+		}
+
+		/** {@inheritDoc}
+		 */
+		@Override
+		public void run() {
+			assert (setName());
+			try {
+				purge();
+			} finally {
+				assert (restoreName());
+			}
+		}
+
+		/** {@inheritDoc}
+		 */
+		@Override
+		public String toString() {
+			return "Janus Thread Purger"; //$NON-NLS-1$
+		}
+
+	}
+
 }

io.janusproject.kernel/src/main/java/io/janusproject/services/executor/ExecutorService.java

@@ -126,4 +126,8 @@ ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
 	ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay,
 			long delay, TimeUnit unit);
 
+	/** Remove any canceled/terminated tasks from the lists of tasks.
+	 */
+	void purge();
+
 }

io.janusproject.kernel/src/test/java/io/janusproject/kernel/services/jdk/executors/JdkExecutorServiceTest.java

@@ -186,5 +186,5 @@ public void doStop() {
 		Mockito.verify(this.scheduledExecutorService, new Times(1)).shutdownNow();
 		Mockito.verify(this.executorService, new Times(1)).shutdownNow();
 	}
-
+	
 }