import edu.mit.media.hive.support.Debug;
import java.io.*;

public class WorkerPool {
    static QueryServer[] pool;
    int lastIdle = -1;

    public WorkerPool(int size) {
        pool = new QueryServer[size];
    }

    public void createWorkers(NTPSpider spider) {
        for (int i = 0; i < pool.length; i++) {
            QueryServer qs = new QueryServer(this, spider);
            Thread t = new Thread(qs);
            t.setDaemon(true);
            t.start();
            addWorker(qs);
        }
    }

    /** Schedule a job. Block if the whole pool is busy. **/
    public void doJob(String host) {
        QueryServer qs = getWorker();
        qs.processHost(host);
    }

    /** Are all threads busy? **/
    private synchronized boolean allBusy() {
        // All threads busy of there are no idles.
        return lastIdle < 0;
    }

    /** Wait until all threads done **/
    public synchronized void waitForAllDone() {
        while (lastIdle < pool.length - 1) {
            try {
                wait();
            } catch (InterruptedException ex) { }
        }
    }

    /** Call this to add a worker to the pool. Typically called by
     ** the worker itself when it finishes its job.
     **/
    public synchronized void addWorker(QueryServer qs) {
        // put this worker back on the pool
        pool[lastIdle+1] = qs;
        lastIdle++;
        // tell anyone waiting on the pool to fill
        notify();
    }

    /** Get a worker from the thread. Block if all are busy. **/
    private synchronized QueryServer getWorker() {
        while (allBusy()) {
            try {
                wait();
            } catch (InterruptedException ex) { }
        }

        QueryServer qs = pool[lastIdle];
        lastIdle--;
        return qs;
    }

    public static void main(String args[]) {
        if (args.length < 2) {
            System.out.println("Usage: WorkerPool NumThreads CommandFile");
            System.exit(1);
        }
                     
        int poolSize = 1;
        BufferedReader br = null;
        try {
            poolSize = Integer.parseInt(args[0]);
            br = new BufferedReader(new FileReader(args[1]));
        } catch (Exception ex) {
            Debug.error(ex);
        }

        WorkerPool wp = new WorkerPool(poolSize);
        String job;
        try {
            while ((job = br.readLine()) != null)
                wp.doJob(job);
        } catch (IOException ex) {
            Debug.error(ex);
        }

        wp.waitForAllDone();
        Debug.notice("All jobs finished.");
    }    
}