Extract work queue to allow reusing it

Change-Id: I28f7800030a3b9db48e315061509af0746feffcc
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/lib/BatchingProgressMonitor.java

@@ -43,55 +43,11 @@
 
 package org.eclipse.jgit.lib;
 
-import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
-import java.util.concurrent.ScheduledThreadPoolExecutor;
-import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 
 /** ProgressMonitor that batches update events. */
 public abstract class BatchingProgressMonitor implements ProgressMonitor {
-	private static final ScheduledThreadPoolExecutor alarmQueue;
-
-	static final Object alarmQueueKiller;
-
-	static {
-		// To support garbage collection, start our thread but
-		// swap out the thread factory. When our class is GC'd
-		// the alarmQueueKiller will finalize and ask the executor
-		// to shutdown, ending the worker.
-		//
-		int threads = 1;
-		alarmQueue = new ScheduledThreadPoolExecutor(threads,
-				new ThreadFactory() {
-					private final ThreadFactory baseFactory = Executors
-							.defaultThreadFactory();
-
-					public Thread newThread(Runnable taskBody) {
-						Thread thr = baseFactory.newThread(taskBody);
-						thr.setName("JGit-AlarmQueue"); //$NON-NLS-1$
-						thr.setDaemon(true);
-						return thr;
-					}
-				});
-		alarmQueue.setContinueExistingPeriodicTasksAfterShutdownPolicy(false);
-		alarmQueue.setExecuteExistingDelayedTasksAfterShutdownPolicy(false);
-		alarmQueue.prestartAllCoreThreads();
-
-		// Now that the threads are running, its critical to swap out
-		// our own thread factory for one that isn't in the ClassLoader.
-		// This allows the class to GC.
-		//
-		alarmQueue.setThreadFactory(Executors.defaultThreadFactory());
-
-		alarmQueueKiller = new Object() {
-			@Override
-			protected void finalize() {
-				alarmQueue.shutdownNow();
-			}
-		};
-	}
-
 	private long delayStartTime;
 
 	private TimeUnit delayStartUnit = TimeUnit.MILLISECONDS;
@@ -219,7 +175,7 @@ public abstract class BatchingProgressMonitor implements ProgressMonitor {
 
 		void delay(long time, TimeUnit unit) {
 			display = false;
-			timerFuture = alarmQueue.schedule(this, time, unit);
+			timerFuture = WorkQueue.getExecutor().schedule(this, time, unit);
 		}
 
 		public void run() {
@@ -254,7 +210,8 @@ public abstract class BatchingProgressMonitor implements ProgressMonitor {
 
 		private void restartTimer() {
 			display = false;
-			timerFuture = alarmQueue.schedule(this, 1, TimeUnit.SECONDS);
+			timerFuture = WorkQueue.getExecutor().schedule(this, 1,
+					TimeUnit.SECONDS);
 		}
 
 		void end(BatchingProgressMonitor pm) {

org.eclipse.jgit/src/org/eclipse/jgit/lib/WorkQueue.java

@@ -0,0 +1,99 @@
+/*
+ * Copyright (C) 2008-2016, Google Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.lib;
+
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledThreadPoolExecutor;
+import java.util.concurrent.ThreadFactory;
+
+/**
+ * Simple work queue to run tasks in the background
+ */
+class WorkQueue {
+	private static final ScheduledThreadPoolExecutor executor;
+
+	static final Object executorKiller;
+
+	static {
+		// To support garbage collection, start our thread but
+		// swap out the thread factory. When our class is GC'd
+		// the executorKiller will finalize and ask the executor
+		// to shutdown, ending the worker.
+		//
+		int threads = 1;
+		executor = new ScheduledThreadPoolExecutor(threads,
+				new ThreadFactory() {
+					private final ThreadFactory baseFactory = Executors
+							.defaultThreadFactory();
+
+					public Thread newThread(Runnable taskBody) {
+						Thread thr = baseFactory.newThread(taskBody);
+						thr.setName("JGit-WorkQueue"); //$NON-NLS-1$
+						thr.setDaemon(true);
+						return thr;
+					}
+				});
+		executor.setRemoveOnCancelPolicy(true);
+		executor.setContinueExistingPeriodicTasksAfterShutdownPolicy(false);
+		executor.setExecuteExistingDelayedTasksAfterShutdownPolicy(false);
+		executor.prestartAllCoreThreads();
+
+		// Now that the threads are running, its critical to swap out
+		// our own thread factory for one that isn't in the ClassLoader.
+		// This allows the class to GC.
+		//
+		executor.setThreadFactory(Executors.defaultThreadFactory());
+
+		executorKiller = new Object() {
+			@Override
+			protected void finalize() {
+				executor.shutdownNow();
+			}
+		};
+	}
+
+	static ScheduledThreadPoolExecutor getExecutor() {
+		return executor;
+	}
+}