| /* |
| * 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.ode.bpel.engine; |
| |
| import org.apache.commons.logging.Log; |
| import org.apache.commons.logging.LogFactory; |
| |
| import java.util.concurrent.locks.Condition; |
| import java.util.concurrent.locks.Lock; |
| import java.util.concurrent.locks.ReentrantLock; |
| |
| /** |
| * An N state synchronization latch useful for implementing hydration/dehydration. The |
| * latch functions as follows. At any time, the latch is in one of N states and has a |
| * count. Clients can "latch" and "release" the latch, which increments/decrements the |
| * count; however, when latching, a state must be specified. If the state does not match |
| * the current state, the latch blocks until the count is zero. Essentially, the latch |
| * can change state only when the count is zero. Every time the latch changes state an |
| * optional {@link Runnable} corresponding to the new state is executed. |
| * |
| * @author Maciej Szefler ( m s z e f l e r @ g m a i l . c o m ) |
| */ |
| public class NStateLatch { |
| static final Log __log = LogFactory.getLog(NStateLatch.class); |
| |
| /** Current state. */ |
| private int _state = -1; |
| |
| /** Current depth (i.e. number of enter() calls) */ |
| private int _depth = 0; |
| |
| /** Action for state transition ?-->i */ |
| protected Runnable _transitions[]; |
| |
| /** Synchronization lock .*/ |
| private Lock _lock; |
| |
| /** _depth == 0 condition. */ |
| private Condition _depth0; |
| |
| private boolean _transitioning = false; |
| |
| /** |
| * Constructor, the array of {@link Runnable}s defines the number of states and the transition |
| * actions. |
| * @param transitions action to perform when entering state x. |
| */ |
| public NStateLatch(Runnable [] transitions) { |
| _transitions = transitions; |
| _lock = new ReentrantLock(); |
| _depth0 = _lock.newCondition(); |
| } |
| |
| public void latch(int state) { |
| if (state >= _transitions.length || state < 0) |
| throw new IllegalArgumentException("Invalid state."); |
| |
| _lock.lock(); |
| try { |
| if (_transitioning ) |
| throw new IllegalStateException("Manipulating latch from transition. "); |
| |
| if (_state != state) { |
| // wait for the depth to become 0 |
| while (_depth != 0) |
| _depth0.awaitUninterruptibly(); |
| |
| if (_state != state) { |
| if (_transitions[state] != null) |
| try { |
| _transitioning = true; |
| _transitions[state].run(); |
| } finally { |
| _transitioning = false; |
| } |
| _state = state; |
| } |
| } |
| } finally { |
| _depth ++; |
| _lock.unlock(); |
| } |
| } |
| |
| public void release(int state) { |
| _lock.lock(); |
| try { |
| |
| if (_transitioning ) |
| throw new IllegalStateException("Manipulating latch from transition. "); |
| |
| if (_state != state) |
| __log.error("Latch error, was releasing for state " + state + " but actually in " + _state); |
| if (_depth <= 0) |
| throw new IllegalStateException("Too many release() calls."); |
| |
| _depth --; |
| |
| if (_depth == 0) |
| _depth0.signal(); |
| } finally { |
| _lock.unlock(); |
| } |
| } |
| } |