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    }