001// Copyright 2006, 2007, 2008, 2009, 2012 The Apache Software Foundation
002//
003// Licensed under the Apache License, Version 2.0 (the "License");
004// you may not use this file except in compliance with the License.
005// You may obtain a copy of the License at
006//
007//     http://www.apache.org/licenses/LICENSE-2.0
008//
009// Unless required by applicable law or agreed to in writing, software
010// distributed under the License is distributed on an "AS IS" BASIS,
011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012// See the License for the specific language governing permissions and
013// limitations under the License.
014
015package org.apache.tapestry5.ioc.internal.util;
016
017/**
018 * Logic for handling one shot semantics for classes; classes that include a method (or methods) that "locks down" the
019 * instance, to prevent it from being used again in the future.
020 */
021public class OneShotLock extends LockSupport
022{
023    private boolean lock;
024
025    /**
026     * Checks to see if the lock has been set (via {@link #lock()}).
027     *
028     * @throws IllegalStateException
029     *         if the lock is set
030     */
031    public void check()
032    {
033        try
034        {
035            acquireReadLock();
036
037            innerCheck();
038        } finally
039        {
040            releaseReadLock();
041        }
042    }
043
044    private void innerCheck()
045    {
046        if (lock)
047        {
048            // The depth to find the caller of the check() or lock() method varies between JDKs.
049
050            StackTraceElement[] elements = Thread.currentThread().getStackTrace();
051
052            int i = 0;
053            while (!elements[i].getMethodName().equals("innerCheck"))
054            {
055                i++;
056            }
057
058            throw new IllegalStateException(UtilMessages.oneShotLock(elements[i + 2]));
059        }
060    }
061
062    /**
063     * Checks the lock, then sets it.
064     */
065    public void lock()
066    {
067        try
068        {
069            takeWriteLock();
070
071            innerCheck();
072
073            lock = true;
074        } finally
075        {
076            releaseWriteLock();
077        }
078    }
079}