001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one 003 * or more contributor license agreements. See the NOTICE file 004 * distributed with this work for additional information 005 * regarding copyright ownership. The ASF licenses this file 006 * to you under the Apache License, Version 2.0 (the 007 * "License"); you may not use this file except in compliance 008 * with the License. You may obtain a copy of the License at 009 * 010 * http://www.apache.org/licenses/LICENSE-2.0 011 * 012 * Unless required by applicable law or agreed to in writing, 013 * software distributed under the License is distributed on an 014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 015 * KIND, either express or implied. See the License for the 016 * specific language governing permissions and limitations 017 * under the License. 018 */ 019 package org.apache.felix.framework.util; 020 021 /** 022 * This class implements a simple one-shot gate for threads. The gate 023 * starts closed and will block any threads that try to wait on it. Once 024 * opened, all waiting threads will be released. The gate cannot be reused. 025 **/ 026 public class ThreadGate 027 { 028 private boolean m_open = false; 029 private Object m_msg = null; 030 private boolean m_initialized = false; 031 032 /** 033 * Open the gate and release any waiting threads. 034 **/ 035 public synchronized void open() 036 { 037 m_open = true; 038 notifyAll(); 039 } 040 041 /** 042 * Returns the message object associated with the gate; the 043 * message is just an arbitrary object used to pass information 044 * to the waiting threads. 045 * @return the message object associated with the gate. 046 **/ 047 public synchronized Object getMessage() 048 { 049 return m_msg; 050 } 051 052 /** 053 * Sets the message object associated with the gate. The message 054 * object can only be set once, subsequent calls to this method 055 * are ignored. 056 * @param msg the message object to associate with this gate. 057 **/ 058 public synchronized void setMessage(Object msg) 059 { 060 if (!m_initialized) 061 { 062 m_msg = msg; 063 m_initialized = true; 064 } 065 } 066 067 /** 068 * Wait for the gate to open. 069 * @return <tt>true</tt> if the gate was opened or <tt>false</tt> if the timeout expired. 070 * @throws java.lang.InterruptedException If the calling thread is interrupted; 071 * the gate still remains closed until opened. 072 **/ 073 public synchronized boolean await(long timeout) throws InterruptedException 074 { 075 long start = System.currentTimeMillis(); 076 long remaining = timeout; 077 while (!m_open) 078 { 079 wait(remaining); 080 if (timeout > 0) 081 { 082 remaining = timeout - (System.currentTimeMillis() - start); 083 if (remaining <= 0) 084 { 085 break; 086 } 087 } 088 } 089 return m_open; 090 } 091 }