    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}