/*** free software* from apusic* by www.cn-java.com 2001*/import java.util.LinkedList;public class ThreadPool{   static final long IDLE_TIMEOUT = 60000L;   private String name;   private int minsize;   private int maxsize;   private int nextWorkerId = 0;   private LinkedList pool = new LinkedList();   public ThreadPool() {       this("PooledThread");   }   public ThreadPool(String name) {       this(name, 0, 20);   }   public ThreadPool(String name, int minsize, int maxsize) {       this.name = name;       this.minsize = minsize;       this.maxsize = maxsize;   }   public synchronized void run(Runnable runner) {       Worker worker;       if (runner == null) {           throw new NullPointerException();       }       // get a worker from free list...       if (!pool.isEmpty()) {           worker = (Worker) pool.removeFirst();       } else {           // ...no free worker available, create new one...           worker = new Worker(name + "-" + ++nextWorkerId);           worker.start();       }       // ...and wake up worker to service incoming runner       worker.wakeup(runner);   }   // Notified when a worker has idled timeout   // @return true if worker should die, false otherwise   synchronized boolean notifyTimeout(Worker worker) {       if (worker.runner != null) {           return false;       }       if (pool.size() > minsize) {           // Remove from free list           pool.remove(worker);           return true; // die       }       return false; // continue   }   // Notified when a worker has finished his work and   // free to service next runner   // @return true if worker should die, false otherwise   synchronized boolean notifyFree(Worker worker) {       if (pool.size() < maxsize) {           // Add to free list           pool.addLast(worker);           return false; // continue       }       return true; // die   }   // The inner class that implement worker thread   class Worker extends Thread {       Runnable runner = null;       public Worker(String name) {           super(name);       }       synchronized void wakeup(Runnable runner) {           this.runner = runner;           notify();       }       public void run() {           for (;;) {               synchronized (this) {                   if (runner == null) {                       try {                           wait(IDLE_TIMEOUT);                       } catch (InterruptedException e) {}                   }               }               // idle timed out, die or put into free list               if (runner == null) {                    if (notifyTimeout(this))                        return;                    else                        continue;               }               try {                   runner.run();               } finally {                   runner = null;                   if (notifyFree(this))                       return;               }           }       }   }}