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Tomcat example source code file (ThreadPool.java)

This example Tomcat source code file (ThreadPool.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 - Tomcat tags/keywords

controlrunnable, controlrunnable, integer, max_threads, monitorrunnable, string, string, thread, thread, threadpool, threadpool, threadpoollistener, threadwithattributes, unexpected, util

The Tomcat ThreadPool.java 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.
 */

package org.apache.tomcat.util.threads;

import java.util.*;

import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;
import org.apache.tomcat.util.res.StringManager;

/**
 * A thread pool that is trying to copy the apache process management.
 *
 * Should we remove this in favor of Doug Lea's thread package?
 *
 * @author Gal Shachor
 * @author Yoav Shapira <yoavs@apache.org>
 */
public class ThreadPool  {

    private static Log log = LogFactory.getLog(ThreadPool.class);

    private static StringManager sm =
        StringManager.getManager("org.apache.tomcat.util.threads.res");

    private static boolean logfull=true;

    /*
     * Default values ...
     */
    public static final int MAX_THREADS = 200;
    public static final int MAX_THREADS_MIN = 10;
    public static final int MAX_SPARE_THREADS = 50;
    public static final int MIN_SPARE_THREADS = 4;
    public static final int WORK_WAIT_TIMEOUT = 60*1000;

    /*
     * Where the threads are held.
     */
    protected ControlRunnable[] pool = null;

    /*
     * A monitor thread that monitors the pool for idel threads.
     */
    protected MonitorRunnable monitor;


    /*
     * Max number of threads that you can open in the pool.
     */
    protected int maxThreads;

    /*
     * Min number of idel threads that you can leave in the pool.
     */
    protected int minSpareThreads;

    /*
     * Max number of idel threads that you can leave in the pool.
     */
    protected int maxSpareThreads;

    /*
     * Number of threads in the pool.
     */
    protected int currentThreadCount;

    /*
     * Number of busy threads in the pool.
     */
    protected int currentThreadsBusy;

    /*
     * Flag that the pool should terminate all the threads and stop.
     */
    protected boolean stopThePool;

    /* Flag to control if the main thread is 'daemon' */
    protected boolean isDaemon=true;

    /** The threads that are part of the pool.
     * Key is Thread, value is the ControlRunnable
     */
    protected Hashtable threads=new Hashtable();

    protected Vector listeners=new Vector();

    /** Name of the threadpool
     */
    protected String name = "TP";

    /**
     * Sequence.
     */
    protected int sequence = 1;

    /**
     * Thread priority.
     */
    protected int threadPriority = Thread.NORM_PRIORITY;


    /**
     * Constructor.
     */    
    public ThreadPool() {
        maxThreads = MAX_THREADS;
        maxSpareThreads = MAX_SPARE_THREADS;
        minSpareThreads = MIN_SPARE_THREADS;
        currentThreadCount = 0;
        currentThreadsBusy = 0;
        stopThePool = false;
    }


    /** Create a ThreadPool instance.
     *
     * @param jmx UNUSED 
     * @return ThreadPool instance. If JMX support is requested, you need to
     *   call register() in order to set a name.
     */
    public static ThreadPool createThreadPool(boolean jmx) {
        return new ThreadPool();
    }

    public synchronized void start() {
	stopThePool=false;
        currentThreadCount  = 0;
        currentThreadsBusy  = 0;

        adjustLimits();

        pool = new ControlRunnable[maxThreads];

        openThreads(minSpareThreads);
        if (maxSpareThreads < maxThreads) {
            monitor = new MonitorRunnable(this);
        }
    }

    public MonitorRunnable getMonitor() {
        return monitor;
    }
  
    /**
     * Sets the thread priority for current
     * and future threads in this pool.
     *
     * @param threadPriority The new priority
     * @throws IllegalArgumentException If the specified
     *  priority is less than Thread.MIN_PRIORITY or
     *  more than Thread.MAX_PRIORITY 
     */
    public synchronized void setThreadPriority(int threadPriority) {
        if(log.isDebugEnabled())
            log.debug(getClass().getName() +
                      ": setPriority(" + threadPriority + "): here.");

      if (threadPriority < Thread.MIN_PRIORITY) {
        throw new IllegalArgumentException("new priority < MIN_PRIORITY");
      } else if (threadPriority > Thread.MAX_PRIORITY) {
        throw new IllegalArgumentException("new priority > MAX_PRIORITY");
      }

      // Set for future threads
      this.threadPriority = threadPriority;

      Enumeration currentThreads = getThreads();
      Thread t = null;
      while(currentThreads.hasMoreElements()) {
        t = (Thread) currentThreads.nextElement();
        t.setPriority(threadPriority);
      } 
    }

    /**
     * Returns the priority level of current and
     * future threads in this pool.
     *
     * @return The priority
     */
    public int getThreadPriority() {
      return threadPriority;
    }   
     

    public void setMaxThreads(int maxThreads) {
        this.maxThreads = maxThreads;
    }

    public int getMaxThreads() {
        return maxThreads;
    }

    public void setMinSpareThreads(int minSpareThreads) {
        this.minSpareThreads = minSpareThreads;
    }

    public int getMinSpareThreads() {
        return minSpareThreads;
    }

    public void setMaxSpareThreads(int maxSpareThreads) {
        this.maxSpareThreads = maxSpareThreads;
    }

    public int getMaxSpareThreads() {
        return maxSpareThreads;
    }

    public int getCurrentThreadCount() {
        return currentThreadCount;
    }

    public int getCurrentThreadsBusy() {
        return currentThreadsBusy;
    }

    public boolean isDaemon() {
        return isDaemon;
    }

    public static int getDebug() {
        return 0;
    }

    /** The default is true - the created threads will be
     *  in daemon mode. If set to false, the control thread
     *  will not be daemon - and will keep the process alive.
     */
    public void setDaemon( boolean b ) {
        isDaemon=b;
    }
    
    public boolean getDaemon() {
        return isDaemon;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public int getSequence() {
        return sequence;
    }

    public int incSequence() {
        return sequence++;
    }

    public void addThread( Thread t, ControlRunnable cr ) {
        threads.put( t, cr );
        for( int i=0; i<listeners.size(); i++ ) {
            ThreadPoolListener tpl=(ThreadPoolListener)listeners.elementAt(i);
            tpl.threadStart(this, t);
        }
    }

    public void removeThread( Thread t ) {
        threads.remove(t);
        for( int i=0; i<listeners.size(); i++ ) {
            ThreadPoolListener tpl=(ThreadPoolListener)listeners.elementAt(i);
            tpl.threadEnd(this, t);
        }
    }

    public void addThreadPoolListener( ThreadPoolListener tpl ) {
        listeners.addElement( tpl );
    }

    public Enumeration getThreads(){
        return threads.keys();
    }

    public void run(Runnable r) {
        ControlRunnable c = findControlRunnable();
        c.runIt(r);
    }    
    
    //
    // You may wonder what you see here ... basically I am trying
    // to maintain a stack of threads. This way locality in time
    // is kept and there is a better chance to find residues of the
    // thread in memory next time it runs.
    //

    /**
     * Executes a given Runnable on a thread in the pool, block if needed.
     */
    public void runIt(ThreadPoolRunnable r) {
        if(null == r) {
            throw new NullPointerException();
        }

        ControlRunnable c = findControlRunnable();
        c.runIt(r);
    }

    private ControlRunnable findControlRunnable() {
        ControlRunnable c=null;

        if ( stopThePool ) {
            throw new IllegalStateException();
        }

        // Obtain a free thread from the pool.
        synchronized(this) {

            while (currentThreadsBusy == currentThreadCount) {
                 // All threads are busy
                if (currentThreadCount < maxThreads) {
                    // Not all threads were open,
                    // Open new threads up to the max number of idel threads
                    int toOpen = currentThreadCount + minSpareThreads;
                    openThreads(toOpen);
                } else {
                    logFull(log, currentThreadCount, maxThreads);
                    // Wait for a thread to become idel.
                    try {
                        this.wait();
                    }
                    // was just catch Throwable -- but no other
                    // exceptions can be thrown by wait, right?
                    // So we catch and ignore this one, since
                    // it'll never actually happen, since nowhere
                    // do we say pool.interrupt().
                    catch(InterruptedException e) {
                        log.error("Unexpected exception", e);
                    }
		    if( log.isDebugEnabled() ) {
			log.debug("Finished waiting: CTC="+currentThreadCount +
				  ", CTB=" + currentThreadsBusy);
                    }
                    // Pool was stopped. Get away of the pool.
                    if( stopThePool) {
                        break;
                    }
                }
            }
            // Pool was stopped. Get away of the pool.
            if(0 == currentThreadCount || stopThePool) {
                throw new IllegalStateException();
            }
                    
            // If we are here it means that there is a free thread. Take it.
            int pos = currentThreadCount - currentThreadsBusy - 1;
            c = pool[pos];
            pool[pos] = null;
            currentThreadsBusy++;

        }
        return c;
    }

    private static void logFull(Log loghelper, int currentThreadCount,
                                int maxThreads) {
	if( logfull ) {
            log.error(sm.getString("threadpool.busy",
                                   new Integer(currentThreadCount),
                                   new Integer(maxThreads)));
            logfull=false;
        } else if( log.isDebugEnabled() ) {
            log.debug("All threads are busy " + currentThreadCount + " " +
                      maxThreads );
        }
    }

    /**
     * Stop the thread pool
     */
    public synchronized void shutdown() {
        if(!stopThePool) {
            stopThePool = true;
            if (monitor != null) {
                monitor.terminate();
                monitor = null;
            }
            for(int i = 0; i < currentThreadCount - currentThreadsBusy; i++) {
                try {
                    pool[i].terminate();
                } catch(Throwable t) {
                    /*
		     * Do nothing... The show must go on, we are shutting
		     * down the pool and nothing should stop that.
		     */
		    log.error("Ignored exception while shutting down thread pool", t);
                }
            }
            currentThreadsBusy = currentThreadCount = 0;
            pool = null;
            notifyAll();
        }
    }

    /**
     * Called by the monitor thread to harvest idle threads.
     */
    protected synchronized void checkSpareControllers() {

        if(stopThePool) {
            return;
        }

        if((currentThreadCount - currentThreadsBusy) > maxSpareThreads) {
            int toFree = currentThreadCount -
                         currentThreadsBusy -
                         maxSpareThreads;

            for(int i = 0 ; i < toFree ; i++) {
                ControlRunnable c = pool[currentThreadCount - currentThreadsBusy - 1];
                c.terminate();
                pool[currentThreadCount - currentThreadsBusy - 1] = null;
                currentThreadCount --;
            }

        }

    }

    /**
     * Returns the thread to the pool.
     * Called by threads as they are becoming idel.
     */
    protected synchronized void returnController(ControlRunnable c) {

        if(0 == currentThreadCount || stopThePool) {
            c.terminate();
            return;
        }

        // atomic
        currentThreadsBusy--;

        pool[currentThreadCount - currentThreadsBusy - 1] = c;
        notify();
    }

    /**
     * Inform the pool that the specific thread finish.
     *
     * Called by the ControlRunnable.run() when the runnable
     * throws an exception.
     */
    protected synchronized void notifyThreadEnd(ControlRunnable c) {
        currentThreadsBusy--;
        currentThreadCount --;
        notify();
    }


    /*
     * Checks for problematic configuration and fix it.
     * The fix provides reasonable settings for a single CPU
     * with medium load.
     */
    protected void adjustLimits() {
        if(maxThreads <= 0) {
            maxThreads = MAX_THREADS;
        } else if (maxThreads < MAX_THREADS_MIN) {
            log.warn(sm.getString("threadpool.max_threads_too_low",
                                  new Integer(maxThreads),
                                  new Integer(MAX_THREADS_MIN)));
            maxThreads = MAX_THREADS_MIN;
        }

        if(maxSpareThreads >= maxThreads) {
            maxSpareThreads = maxThreads;
        }

        if(maxSpareThreads <= 0) {
            if(1 == maxThreads) {
                maxSpareThreads = 1;
            } else {
                maxSpareThreads = maxThreads/2;
            }
        }

        if(minSpareThreads >  maxSpareThreads) {
            minSpareThreads =  maxSpareThreads;
        }

        if(minSpareThreads <= 0) {
            if(1 == maxSpareThreads) {
                minSpareThreads = 1;
            } else {
                minSpareThreads = maxSpareThreads/2;
            }
        }
    }

    /** Create missing threads.
     *
     * @param toOpen Total number of threads we'll have open
     */
    protected void openThreads(int toOpen) {

        if(toOpen > maxThreads) {
            toOpen = maxThreads;
        }

        for(int i = currentThreadCount ; i < toOpen ; i++) {
            pool[i - currentThreadsBusy] = new ControlRunnable(this);
        }

        currentThreadCount = toOpen;
    }

    /** @deprecated */
    void log( String s ) {
	log.info(s);
	//loghelper.flush();
    }
    
    /** 
     * Periodically execute an action - cleanup in this case
     */
    public static class MonitorRunnable implements Runnable {
        ThreadPool p;
        Thread     t;
        int interval=WORK_WAIT_TIMEOUT;
        boolean    shouldTerminate;

        MonitorRunnable(ThreadPool p) {
            this.p=p;
            this.start();
        }

        public void start() {
            shouldTerminate = false;
            t = new Thread(this);
            t.setDaemon(p.getDaemon() );
	    t.setName(p.getName() + "-Monitor");
            t.start();
        }

        public void setInterval(int i ) {
            this.interval=i;
        }

        public void run() {
            while(true) {
                try {

                    // Sleep for a while.
                    synchronized(this) {
                        this.wait(interval);
                    }

                    // Check if should terminate.
                    // termination happens when the pool is shutting down.
                    if(shouldTerminate) {
                        break;
                    }

                    // Harvest idle threads.
                    p.checkSpareControllers();

                } catch(Throwable t) {
		    ThreadPool.log.error("Unexpected exception", t);
                }
            }
        }

        public void stop() {
            this.terminate();
        }

	/** Stop the monitor
	 */
        public synchronized void terminate() {
            shouldTerminate = true;
            this.notify();
        }
    }

    /**
     * A Thread object that executes various actions ( ThreadPoolRunnable )
     *  under control of ThreadPool
     */
    public static class ControlRunnable implements Runnable {
        /**
	 * ThreadPool where this thread will be returned
	 */
        private ThreadPool p;

	/**
	 * The thread that executes the actions
	 */
        private ThreadWithAttributes     t;

	/**
	 * The method that is executed in this thread
	 */
        
        private ThreadPoolRunnable   toRun;
        private Runnable toRunRunnable;

	/**
	 * Stop this thread
	 */
	private boolean    shouldTerminate;

	/**
	 * Activate the execution of the action
	 */
        private boolean    shouldRun;

	/**
	 * Per thread data - can be used only if all actions are
	 *  of the same type.
	 *  A better mechanism is possible ( that would allow association of
	 *  thread data with action type ), but right now it's enough.
	 */
	private boolean noThData;

	/**
	 * Start a new thread, with no method in it
	 */
        ControlRunnable(ThreadPool p) {
            toRun = null;
            shouldTerminate = false;
            shouldRun = false;
            this.p = p;
            t = new ThreadWithAttributes(p, this);
            t.setDaemon(true);
            t.setName(p.getName() + "-Processor" + p.incSequence());
            t.setPriority(p.getThreadPriority());
            p.addThread( t, this );
	    noThData=true;
            t.start();
        }

        public void run() {
            boolean _shouldRun = false;
            boolean _shouldTerminate = false;
            ThreadPoolRunnable _toRun = null;
            try {
                while (true) {
                    try {
                        /* Wait for work. */
                        synchronized (this) {
                            while (!shouldRun && !shouldTerminate) {
                                this.wait();
                            }
                            _shouldRun = shouldRun;
                            _shouldTerminate = shouldTerminate;
                            _toRun = toRun;
                        }

                        if (_shouldTerminate) {
                            if (ThreadPool.log.isDebugEnabled())
                                ThreadPool.log.debug("Terminate");
                            break;
                        }

                        /* Check if should execute a runnable.  */
                        try {
                            if (noThData) {
                                if (_toRun != null) {
                                    Object thData[] = _toRun.getInitData();
                                    t.setThreadData(p, thData);
                                    if (ThreadPool.log.isDebugEnabled())
                                        ThreadPool.log.debug(
                                            "Getting new thread data");
                                }
                                noThData = false;
                            }

                            if (_shouldRun) {
                                if (_toRun != null) {
                                    _toRun.runIt(t.getThreadData(p));
                                } else if (toRunRunnable != null) {
                                    toRunRunnable.run();
                                } else {
                                    if (ThreadPool.log.isDebugEnabled())
                                    ThreadPool.log.debug("No toRun ???");
                                }
                            }
                        } catch (Throwable t) {
                            ThreadPool.log.error(sm.getString
                                ("threadpool.thread_error", t, toRun.toString()));
                            /*
                             * The runnable throw an exception (can be even a ThreadDeath),
                             * signalling that the thread die.
                             *
                            * The meaning is that we should release the thread from
                            * the pool.
                            */
                            _shouldTerminate = true;
                            _shouldRun = false;
                            p.notifyThreadEnd(this);
                        } finally {
                            if (_shouldRun) {
                                shouldRun = false;
                                /*
                                * Notify the pool that the thread is now idle.
                                 */
                                p.returnController(this);
                            }
                        }

                        /*
                        * Check if should terminate.
                        * termination happens when the pool is shutting down.
                        */
                        if (_shouldTerminate) {
                            break;
                        }
                    } catch (InterruptedException ie) { /* for the wait operation */
                        // can never happen, since we don't call interrupt
                        ThreadPool.log.error("Unexpected exception", ie);
                    }
                }
            } finally {
                p.removeThread(Thread.currentThread());
            }
        }
        /** Run a task
         *
         * @param toRun
         */
        public synchronized void runIt(Runnable toRun) {
	    this.toRunRunnable = toRun;
	    // Do not re-init, the whole idea is to run init only once per
	    // thread - the pool is supposed to run a single task, that is
	    // initialized once.
            // noThData = true;
            shouldRun = true;
            this.notify();
        }

        /** Run a task
         *
         * @param toRun
         */
        public synchronized void runIt(ThreadPoolRunnable toRun) {
	    this.toRun = toRun;
	    // Do not re-init, the whole idea is to run init only once per
	    // thread - the pool is supposed to run a single task, that is
	    // initialized once.
            // noThData = true;
            shouldRun = true;
            this.notify();
        }

        public void stop() {
            this.terminate();
        }

        public void kill() {
            t.stop();
        }

        public synchronized void terminate() {
            shouldTerminate = true;
            this.notify();
        }
    }

    /** 
     * Debug display of the stage of each thread. The return is html style,
     * for display in the console ( it can be easily parsed too ).
     *
     * @return The thread status display
     */
    public String threadStatusString() {
        StringBuffer sb=new StringBuffer();
        Iterator it=threads.keySet().iterator();
        sb.append("<ul>");
        while( it.hasNext()) {
            sb.append("<li>");
            ThreadWithAttributes twa=(ThreadWithAttributes)
                    it.next();
            sb.append(twa.getCurrentStage(this) ).append(" ");
            sb.append( twa.getParam(this));
            sb.append( "</li>\n");
        }
        sb.append("</ul>");
        return sb.toString();
    }

    /** Return an array with the status of each thread. The status
     * indicates the current request processing stage ( for tomcat ) or
     * whatever the thread is doing ( if the application using TP provide
     * this info )
     *
     * @return The status of all threads
     */
    public String[] getThreadStatus() {
        String status[]=new String[ threads.size()];
        Iterator it=threads.keySet().iterator();
        for( int i=0; ( i<status.length && it.hasNext()); i++ ) {
            ThreadWithAttributes twa=(ThreadWithAttributes)
                    it.next();
            status[i]=twa.getCurrentStage(this);
        }
        return status;
    }

    /** Return an array with the current "param" ( XXX better name ? )
     * of each thread. This is typically the last request.
     *
     * @return The params of all threads
     */
    public String[] getThreadParam() {
        String status[]=new String[ threads.size()];
        Iterator it=threads.keySet().iterator();
        for( int i=0; ( i<status.length && it.hasNext()); i++ ) {
            ThreadWithAttributes twa=(ThreadWithAttributes)
                    it.next();
            Object o=twa.getParam(this);
            status[i]=(o==null)? null : o.toString();
        }
        return status;
    }
    
    /** Interface to allow applications to be notified when
     * a threads are created and stopped.
     */
    public static interface ThreadPoolListener {
        public void threadStart( ThreadPool tp, Thread t);

        public void threadEnd( ThreadPool tp, Thread t);
    }
}

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