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Java example source code file (WaitingThread.java)

This example source code file (WaitingThread.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java tags/keywords

condition, illegalargumentexception, illegalstateexception, interruptedexception, nobody, notthreadsafe, operation, routespecificpool, util, waitingthread

The WaitingThread.java example source code

/*
 * ====================================================================
 *
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */

package org.apache.http.impl.conn.tsccm;


import java.util.Date;
import java.util.concurrent.locks.Condition;

import org.apache.http.annotation.NotThreadSafe;

/**
 * Represents a thread waiting for a connection.
 * This class implements throwaway objects. It is instantiated whenever
 * a thread needs to wait. Instances are not re-used, except if the
 * waiting thread experiences a spurious wakeup and continues to wait.
 * <br/>
 * All methods assume external synchronization on the condition
 * passed to the constructor.
 * Instances of this class do <i>not synchronize access!
 *
 *
 * @since 4.0
 */
@NotThreadSafe
public class WaitingThread {

    /** The condition on which the thread is waiting. */
    private final Condition cond;

    /** The route specific pool on which the thread is waiting. */
    //@@@ replace with generic pool interface
    private final RouteSpecificPool pool;

    /** The thread that is waiting for an entry. */
    private Thread waiter;
    
    /** True if this was interrupted. */
    private boolean aborted;


    /**
     * Creates a new entry for a waiting thread.
     *
     * @param cond      the condition for which to wait
     * @param pool      the pool on which the thread will be waiting,
     *                  or <code>null
     */
    public WaitingThread(Condition cond, RouteSpecificPool pool) {

        if (cond == null) {
            throw new IllegalArgumentException("Condition must not be null.");
        }

        this.cond = cond;
        this.pool = pool;
    }


    /**
     * Obtains the condition.
     *
     * @return  the condition on which to wait, never <code>null
     */
    public final Condition getCondition() {
        // not synchronized
        return this.cond;
    }


    /**
     * Obtains the pool, if there is one.
     *
     * @return  the pool on which a thread is or was waiting,
     *          or <code>null
     */
    public final RouteSpecificPool getPool() {
        // not synchronized
        return this.pool;
    }


    /**
     * Obtains the thread, if there is one.
     *
     * @return  the thread which is waiting, or <code>null
     */
    public final Thread getThread() {
        // not synchronized
        return this.waiter;
    }


    /**
     * Blocks the calling thread.
     * This method returns when the thread is notified or interrupted,
     * if a timeout occurrs, or if there is a spurious wakeup.
     * <br/>
     * This method assumes external synchronization.
     *
     * @param deadline  when to time out, or <code>null for no timeout
     *
     * @return  <code>true if the condition was satisfied,
     *          <code>false in case of a timeout.
     *          Typically, a call to {@link #wakeup} is used to indicate
     *          that the condition was satisfied. Since the condition is
     *          accessible outside, this cannot be guaranteed though.
     *
     * @throws InterruptedException     if the waiting thread was interrupted
     *
     * @see #wakeup
     */
    public boolean await(Date deadline)
        throws InterruptedException {

        // This is only a sanity check. We cannot synchronize here,
        // the lock would not be released on calling cond.await() below.
        if (this.waiter != null) {
            throw new IllegalStateException
                ("A thread is already waiting on this object." +
                 "\ncaller: " + Thread.currentThread() +
                 "\nwaiter: " + this.waiter);
        }

        if (aborted)
            throw new InterruptedException("Operation interrupted");
        
        this.waiter = Thread.currentThread();

        boolean success = false;
        try {
            if (deadline != null) {
                success = this.cond.awaitUntil(deadline);
            } else {
                this.cond.await();
                success = true;
            }
            if (aborted)
                throw new InterruptedException("Operation interrupted");
        } finally {
            this.waiter = null;
        }
        return success;

    } // await


    /**
     * Wakes up the waiting thread.
     * <br/>
     * This method assumes external synchronization.
     */
    public void wakeup() {

        // If external synchronization and pooling works properly,
        // this cannot happen. Just a sanity check.
        if (this.waiter == null) {
            throw new IllegalStateException
                ("Nobody waiting on this object.");
        }

        // One condition might be shared by several WaitingThread instances.
        // It probably isn't, but just in case: wake all, not just one.
        this.cond.signalAll();
    }
    
    public void interrupt() {
        aborted = true;
        this.cond.signalAll();
    }


} // class WaitingThread

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