| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, |
| * software distributed under the License is distributed on an |
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| * KIND, either express or implied. See the License for the |
| * specific language governing permissions and limitations |
| * under the License. |
| */ |
| package org.apache.felix.dm.impl; |
| |
| import java.util.LinkedList; |
| import java.util.NoSuchElementException; |
| |
| /** |
| * Allows you to enqueue tasks from multiple threads and then execute |
| * them on one thread sequentially. It assumes more than one thread will |
| * try to execute the tasks and it will make an effort to pick the first |
| * task that comes along whilst making sure subsequent tasks return |
| * without waiting. |
| * |
| * @author <a href="mailto:dev@felix.apache.org">Felix Project Team</a> |
| */ |
| public final class SerialExecutor { |
| private final LinkedList m_workQueue = new LinkedList(); |
| private Runnable m_active; |
| |
| /** |
| * Enqueue a new task for later execution. This method is |
| * thread-safe, so multiple threads can contribute tasks. |
| * |
| * @param runnable the runnable containing the actual task |
| */ |
| public synchronized void enqueue(final Runnable runnable) { |
| m_workQueue.addLast(new Runnable() { |
| public void run() { |
| try { |
| runnable.run(); |
| } |
| finally { |
| scheduleNext(); |
| } |
| } |
| }); |
| } |
| |
| /** |
| * Execute any pending tasks. This method is thread safe, |
| * so multiple threads can try to execute the pending |
| * tasks, but only the first will be used to actually do |
| * so. Other threads will return immediately. |
| */ |
| public void execute() { |
| Runnable active; |
| synchronized (this) { |
| active = m_active; |
| } |
| if (active == null) { |
| scheduleNext(); |
| } |
| } |
| |
| private void scheduleNext() { |
| Runnable active; |
| synchronized (this) { |
| try { |
| m_active = (Runnable) m_workQueue.removeFirst(); |
| } |
| catch (NoSuchElementException e) { |
| m_active = null; |
| } |
| active = m_active; |
| } |
| if (active != null) { |
| active.run(); |
| } |
| } |
| } |