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}