threadpool.java

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            for(int i = 0 ; i < toFree ; i++) {
                ControlRunnable c = (ControlRunnable)pool.firstElement();
                pool.removeElement(c);
                c.terminate();
                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;
        }

        currentThreadsBusy--;
        pool.addElement(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;
        }

        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;
            }
        }
    }

    protected void openThreads(int toOpen) {

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

        if(0 == currentThreadCount) {
            pool = new Vector(toOpen);
        }

        for(int i = currentThreadCount ; i < toOpen ; i++) {
            pool.addElement(new ControlRunnable(this));
        }

        currentThreadCount = toOpen;
    }

    void log( String s ) {
	loghelper.log(s);
    }
    
    /** 
     * Periodically execute an action - cleanup in this case
     */
    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 idle threads.
                    p.checkSpareControllers();

                } catch(Throwable t) {
		    loghelper.log("Unexpected exception", t, Logger.ERROR);
                }
            }
        }

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

    /**
     * A Thread object that executes various actions ( ThreadPoolRunnable )
     *  under control of ThreadPool
     */
    class ControlRunnable implements Runnable {

	/**
	 * ThreadPool where this thread will be returned
	 */
        ThreadPool p;

	/**
	 * The thread that executes the actions
	 */
        Thread     t;

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

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

	/**
	 * Activate the execution of the action
	 */
        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.
	 */
	boolean noThData;
	Object thData[]=null;

	/**
	 * Start a new thread, with no method in it
	 */
        ControlRunnable(ThreadPool p) {
            toRun = null;
            shouldTerminate = false;
            shouldRun = false;
            this.p = p;
            t = new Thread(this);
            t.start();
	    noThData=true;
	    thData=null;
        }

        public void run() {
            
            while(true) {
                try {                     
		            /* Wait for work. */
                    synchronized(this) {
                        if(!shouldRun && !shouldTerminate) {
                            this.wait();
                        }
                    }
		            if(toRun == null ) {
			            if( p.debug>0) p.log( "No toRun ???");
		            }

		            if( shouldTerminate ) {
			            if( p.debug>0) p.log( "Terminate");
			            break;
		            }

                    /* Check if should execute a runnable.  */
                    try {
			            if(noThData) {
			                if(p.debug>0) p.log( "Getting new thread data");
			                thData=toRun.getInitData();
			                noThData = false;
			            }

                        if(shouldRun) {
                            toRun.runIt(thData);
                        }
                    } catch(Throwable t) {
			loghelper.log("Caught exception executing " + toRun.toString() + ", terminating thread", t);
                        /*
                        * 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
		    loghelper.log("Unexpected exception", ie);
                }
            }
        }

        public synchronized void runIt(ThreadPoolRunnable toRun) {
	    if( toRun == null ) {
		throw new NullPointerException("No Runnable");
	    }
            this.toRun = toRun;
            shouldRun = true;
            noThData = true;
            this.notify();
        }

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