    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
    017import org.apache.tapestry5.commons.internal.util.LockSupport;
    018
    019/**
    020 * Logic for handling one shot semantics for classes; classes that include a method (or methods) that "locks down" the
    021 * instance, to prevent it from being used again in the future.
    022 */
    023public class OneShotLock extends LockSupport
    024{
    025    private boolean lock;
    026
    027    /**
    028     * Checks to see if the lock has been set (via {@link #lock()}).
    029     *
    030     * @throws IllegalStateException
    031     *         if the lock is set
    032     */
    033    public void check()
    034    {
    035        try
    036        {
    037            acquireReadLock();
    038
    039            innerCheck();
    040        } finally
    041        {
    042            releaseReadLock();
    043        }
    044    }
    045
    046    private void innerCheck()
    047    {
    048        if (lock)
    049        {
    050            // The depth to find the caller of the check() or lock() method varies between JDKs.
    051
    052            StackTraceElement[] elements = Thread.currentThread().getStackTrace();
    053
    054            int i = 0;
    055            while (!elements[i].getMethodName().equals("innerCheck"))
    056            {
    057                i++;
    058            }
    059
    060            throw new IllegalStateException(UtilMessages.oneShotLock(elements[i + 2]));
    061        }
    062    }
    063
    064    /**
    065     * Checks the lock, then sets it.
    066     */
    067    public void lock()
    068    {
    069        try
    070        {
    071            takeWriteLock();
    072
    073            innerCheck();
    074
    075            lock = true;
    076        } finally
    077        {
    078            releaseWriteLock();
    079        }
    080    }
    081}