Pierre De Rop | afe1295 | 2013-10-25 18:38:24 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Licensed to the Apache Software Foundation (ASF) under one |
| 3 | * or more contributor license agreements. See the NOTICE file |
| 4 | * distributed with this work for additional information |
| 5 | * regarding copyright ownership. The ASF licenses this file |
| 6 | * to you under the Apache License, Version 2.0 (the |
| 7 | * "License"); you may not use this file except in compliance |
| 8 | * with the License. You may obtain a copy of the License at |
| 9 | * |
| 10 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 11 | * |
| 12 | * Unless required by applicable law or agreed to in writing, |
| 13 | * software distributed under the License is distributed on an |
| 14 | * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| 15 | * KIND, either express or implied. See the License for the |
| 16 | * specific language governing permissions and limitations |
| 17 | * under the License. |
| 18 | */ |
| 19 | package org.apache.felix.dm.impl; |
| 20 | |
| 21 | import java.util.LinkedList; |
| 22 | |
| 23 | /** |
| 24 | * This class allows to serialize the execution of tasks on one single/unique thread. |
| 25 | * Other threads are blocked until they are elected for execution. |
| 26 | * |
| 27 | * <p>note I: when one leader thread executes a task, it does not hold any locks |
| 28 | * while executing the task, and does not execute tasks scheduled by other threads. |
| 29 | * |
| 30 | * <p>note II: this executor is reentrant: when one task executed by a leader thread |
| 31 | * reschedule another task, then the task is run immediately. |
| 32 | * |
| 33 | * @author <a href="mailto:dev@felix.apache.org">Felix Project Team</a> |
| 34 | */ |
| 35 | public class BlockingSerialExecutor { |
| 36 | private final LinkedList m_tasksQueue = new LinkedList(); |
| 37 | private Thread m_executingThread = null; |
| 38 | |
| 39 | /** |
| 40 | * Executes a task exclusively without holding any locks (other concurrent tasks are blocked until the current task is executed). |
| 41 | * @param task a task to be executed serially, without holding any locks. |
| 42 | */ |
| 43 | public void execute(Runnable task) { |
| 44 | boolean releaseLock = false; |
| 45 | synchronized (this) { |
| 46 | if (m_executingThread != Thread.currentThread()) { |
| 47 | m_tasksQueue.addLast(task); |
| 48 | while (m_tasksQueue.size() > 0 && m_tasksQueue.get(0) != task) { |
| 49 | try { |
| 50 | // TODO it might make sense to use a maxwait time and throw an exception on timeouts. |
| 51 | wait(); |
| 52 | } catch (InterruptedException e) { |
| 53 | } |
| 54 | } |
| 55 | m_executingThread = Thread.currentThread(); |
| 56 | releaseLock = true; |
| 57 | } |
| 58 | } |
| 59 | try { |
| 60 | task.run(); |
| 61 | } finally { |
| 62 | if (releaseLock) { |
| 63 | synchronized (this) { |
| 64 | m_tasksQueue.remove(task); |
| 65 | notifyAll(); |
| 66 | m_executingThread = null; |
| 67 | } |
| 68 | } |
| 69 | } |
| 70 | } |
| 71 | } |