Mailing-List: contact tomcat-dev-help@jakarta.apache.org; run by ezmlm
Date: 29 Feb 2000 13:43:26 -0000
Message-ID: <20000229134326.54520.qmail@locus.apache.org>
From: shachor@locus.apache.org
To: jakarta-tomcat-cvs@apache.org
Subject: cvs commit: jakarta-tomcat/src/share/org/apache/tomcat/util
 ThreadPool.java

shachor     00/02/29 05:43:26

  Modified:    src/share/org/apache/tomcat/util ThreadPool.java
  Log:
  Fix the thread-lock problem on Linux/SUN-JDK1.2.2
  
  Revision  Changes    Path
  1.4       +159 -49   jakarta-tomcat/src/share/org/apache/tomcat/util/ThreadPool.java
  
  Index: ThreadPool.java
  ===================================================================
  RCS file: /home/cvs/jakarta-tomcat/src/share/org/apache/tomcat/util/ThreadPool.java,v
  retrieving revision 1.3
  retrieving revision 1.4
  diff -u -r1.3 -r1.4
  --- ThreadPool.java	2000/02/27 02:01:24	1.3
  +++ ThreadPool.java	2000/02/29 13:43:26	1.4
  @@ -1,7 +1,7 @@
   /*
  - * $Header: /home/cvs/jakarta-tomcat/src/share/org/apache/tomcat/util/ThreadPool.java,v 1.3 2000/02/27 02:01:24 rubys Exp $
  - * $Revision: 1.3 $
  - * $Date: 2000/02/27 02:01:24 $
  + * $Header: /home/cvs/jakarta-tomcat/src/share/org/apache/tomcat/util/ThreadPool.java,v 1.4 2000/02/29 13:43:26 shachor Exp $
  + * $Revision: 1.4 $
  + * $Date: 2000/02/29 13:43:26 $
    *
    * ====================================================================
    *
  @@ -75,32 +75,69 @@
    */
   public class ThreadPool  {
   
  +    /*
  +     * Default values ...
  +     */
       public static final int MAX_THREADS = 50;
       public static final int MAX_SPARE_THREADS = 25;
       public static final int MIN_SPARE_THREADS = 10;
       public static final int WORK_WAIT_TIMEOUT = 60*1000;
   
  +    /*
  +     * Where the threads are held.
  +     */
       protected Vector pool;
   
  +    /*
  +     * 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;
  -    protected int currentThreadsUsed;
   
  +    /*
  +     * Number of busy threads in the pool.
  +     */
  +    protected int currentThreadsBusy;
  +
  +    /*
  +     * Flag that the pool should terminate all the threads and stop.
  +     */
  +    protected boolean stopThePool;
  +
       public ThreadPool() {
           maxThreads      = MAX_THREADS;
           maxSpareThreads = MAX_SPARE_THREADS;
           minSpareThreads = MIN_SPARE_THREADS;
           currentThreadCount  = 0;
  -        currentThreadsUsed  = 0;
  +        currentThreadsBusy  = 0;
  +        stopThePool = false;
       }
   
       public synchronized void start() {
           adjustLimits();
   
           openThreads(minSpareThreads);
  +        monitor = new MonitorRunnable(this);
       }
   
       public void setMaxThreads(int maxThreads) {
  @@ -127,60 +164,90 @@
           return maxSpareThreads;
       }
   
  -    public synchronized void runIt(Runnable 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(Runnable r) {
   
           if(null == r) {
               throw new NullPointerException();
           }
   
  -        if(0 == currentThreadCount) {
  +        if(0 == currentThreadCount || stopThePool) {
               throw new IllegalStateException();
           }
  -	//	System.out.print("K");
  -        if(currentThreadsUsed == currentThreadCount) {
  -            if(currentThreadCount < maxThreads) {
  -                int toOpen = currentThreadCount + minSpareThreads;
  -                openThreads(toOpen);
  -            } else {
  -                while(currentThreadsUsed == currentThreadCount) {
  -                    try {
  -                        wait();
  -                    } catch(Throwable t) {
  -                        t.printStackTrace();
  -                    }
  -                    if(0 == currentThreadCount) {
  -                        throw new IllegalStateException();
  +
  +        ControlRunnable c = null;
  +
  +        // Obtain a free thread from the pool.
  +        synchronized(this) {
  +            if(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 {
  +                    // Wait for a thread to become idel.
  +                    while(currentThreadsBusy == currentThreadCount) {
  +                        try {
  +                            this.wait();
  +                        } catch(Throwable t) {
  +                            t.printStackTrace();
  +                        }
  +
  +                        // Pool was stopped. Get away of the pool.
  +                        if(0 == currentThreadCount || stopThePool) {
  +                            throw new IllegalStateException();
  +                        }
                       }
                   }
               }
  -        }
  -	//System.out.print("L");
   
  -        ControlRunnable c = (ControlRunnable)pool.lastElement();
  -        pool.removeElement(c);
  -        currentThreadsUsed++;
  +            // If we are here it means that there is a free thred. Take it.
  +            c = (ControlRunnable)pool.lastElement();
  +            pool.removeElement(c);
  +            currentThreadsBusy++;
  +        }
           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.
  +    /**
  +     * Stop the thread pool
        */
       public synchronized void shutdown() {
  -        for(int i = 0 ; i < currentThreadCount ; i++) {
  -            ((ControlRunnable)(pool.elementAt(i))).terminate();
  +        if(!stopThePool) {
  +            stopThePool = true;
  +            monitor.terminate();
  +            monitor = null;
  +            for(int i = 0 ; i < currentThreadCount ; i++) {
  +                ((ControlRunnable)(pool.elementAt(i))).terminate();
  +            }
  +            currentThreadsBusy = currentThreadCount = 0;
  +            pool = null;
  +            notifyAll();
           }
  -        currentThreadsUsed = currentThreadCount = 0;
  -        pool = null;
  -        notifyAll();
       }
   
  +    /**
  +     * Called by the monitor thread to harvest idel threads.
  +     */
       protected synchronized void checkSpareControllers() {
  -        if((currentThreadCount - currentThreadsUsed) > maxSpareThreads) {
  +
  +        if(stopThePool) {
  +            return;
  +        }
  +        if((currentThreadCount - currentThreadsBusy) > maxSpareThreads) {
               int toFree = currentThreadCount -
  -                         currentThreadsUsed -
  +                         currentThreadsBusy -
                            maxSpareThreads;
   
               for(int i = 0 ; i < toFree ; i++) {
  @@ -192,14 +259,18 @@
           }
       }
   
  +    /**
  +     * Returns the thread to the pool.
  +     * Called by threads as they are becoming idel.
  +     */
       protected synchronized void returnController(ControlRunnable c) {
   
  -        if(0 == currentThreadCount) {
  +        if(0 == currentThreadCount || stopThePool) {
               c.terminate();
               return;
           }
   
  -        currentThreadsUsed--;
  +        currentThreadsBusy--;
           pool.addElement(c);
           notify();
       }
  @@ -240,7 +311,47 @@
           currentThreadCount = toOpen;
       }
   
  +    class MonitorRunnable implements Runnable {
  +        ThreadPool p;
  +        Thread     t;
  +        boolean    shouldTerminate;
   
  +        MonitorRunnable(ThreadPool p) {
  +            shouldTerminate = false;
  +            this.p = p;
  +            t = new Thread(this);
  +            t.start();
  +        }
  +
  +        public void run() {
  +            while(true) {
  +                try {
  +                    // Sleep for a while.
  +                    synchronized(this) {
  +                        this.wait(WORK_WAIT_TIMEOUT);
  +                    }
  +
  +                    // Check if should terminate.
  +                    // termination happens when the pool is shutting down.
  +                    if(shouldTerminate) {
  +                        break;
  +                    }
  +
  +                    // Harvest idel threads.
  +                    p.checkSpareControllers();
  +
  +                } catch(Throwable t) {
  +                    t.printStackTrace();
  +                }
  +            }
  +        }
  +
  +        public synchronized void terminate() {
  +            shouldTerminate = true;
  +            this.notify();
  +        }
  +    }
  +
       class ControlRunnable implements Runnable {
           ThreadPool p;
           Thread     t;
  @@ -260,16 +371,14 @@
           public void run() {
               while(true) {
                   try {
  -                    boolean checkSpare = false;
  +                    // Wait for work.
                       synchronized(this) {
  -                        if(!shouldRun && !shouldTerminate) {
  -                            this.wait(WORK_WAIT_TIMEOUT);
  -                        }
                           if(!shouldRun && !shouldTerminate) {
  -                            checkSpare = true;
  +                            this.wait();
                           }
                       }
   
  +                    // Check if should execute a runnable.
                       try {
                           if(shouldRun) {
                               toRun.run();
  @@ -277,18 +386,18 @@
                       } finally {
                           if(shouldRun) {
                               shouldRun = false;
  +
  +                            // Notify the pool that the thread is now idel.
                               p.returnController(this);
                           }
                       }
   
  +                    // Check if should terminate.
  +                    // termination happens when the pool is shutting down.
                       if(shouldTerminate) {
                           break;
                       }
   
  -                    if(checkSpare) {
  -                        p.checkSpareControllers();
  -                    }
  -
                   } catch(Throwable t) {
                       t.printStackTrace();
                   }
  @@ -303,6 +412,7 @@
   
           public synchronized void terminate() {
               shouldTerminate = true;
  +            this.notify();
           }
       }
   }