ThreadPoolMain.java Source code

Introduction

Here is the source code for ThreadPoolMain.java

Source

public class ThreadPoolMain extends Object {

    public static Runnable makeRunnable(final String name, final long firstDelay) {

        return new Runnable() {
            public void run() {
                try {
                    System.out.println(name + ": starting up");
                    Thread.sleep(firstDelay);
                    System.out.println(name + ": doing some stuff");
                    Thread.sleep(2000);
                    System.out.println(name + ": leaving");
                } catch (InterruptedException ix) {
                    System.out.println(name + ": got interrupted!");
                    return;
                } catch (Exception x) {
                    x.printStackTrace();
                }
            }

            public String toString() {
                return name;
            }
        };
    }

    public static void main(String[] args) {
        try {
            ThreadPool pool = new ThreadPool(3);

            Runnable ra = makeRunnable("RA", 3000);
            pool.execute(ra);

            Runnable rb = makeRunnable("RB", 1000);
            pool.execute(rb);

            Runnable rc = makeRunnable("RC", 2000);
            pool.execute(rc);

            Runnable rd = makeRunnable("RD", 60000);
            pool.execute(rd);

            Runnable re = makeRunnable("RE", 1000);
            pool.execute(re);

            pool.stopRequestIdleWorkers();
            Thread.sleep(2000);
            pool.stopRequestIdleWorkers();

            Thread.sleep(5000);
            pool.stopRequestAllWorkers();
        } catch (InterruptedException ix) {
            ix.printStackTrace();
        }
    }
}

class ThreadPool extends Object {
    private ObjectFIFO idleWorkers;

    private ThreadPoolWorker[] workerList;

    public ThreadPool(int numberOfThreads) {
        // make sure that it's at least one
        numberOfThreads = Math.max(1, numberOfThreads);

        idleWorkers = new ObjectFIFO(numberOfThreads);
        workerList = new ThreadPoolWorker[numberOfThreads];

        for (int i = 0; i < workerList.length; i++) {
            workerList[i] = new ThreadPoolWorker(idleWorkers);
        }
    }

    public void execute(Runnable target) throws InterruptedException {
        // block (forever) until a worker is available
        ThreadPoolWorker worker = (ThreadPoolWorker) idleWorkers.remove();
        worker.process(target);
    }

    public void stopRequestIdleWorkers() {
        try {
            Object[] idle = idleWorkers.removeAll();
            for (int i = 0; i < idle.length; i++) {
                ((ThreadPoolWorker) idle[i]).stopRequest();
            }
        } catch (InterruptedException x) {
            Thread.currentThread().interrupt(); // re-assert
        }
    }

    public void stopRequestAllWorkers() {
        stopRequestIdleWorkers();

        try {
            Thread.sleep(250);
        } catch (InterruptedException x) {
        }

        for (int i = 0; i < workerList.length; i++) {
            if (workerList[i].isAlive()) {
                workerList[i].stopRequest();
            }
        }
    }
}

class ThreadPoolWorker extends Object {
    private static int nextWorkerID = 0;

    private ObjectFIFO idleWorkers;

    private int workerID;

    private ObjectFIFO handoffBox;

    private Thread internalThread;

    private volatile boolean noStopRequested;

    public ThreadPoolWorker(ObjectFIFO idleWorkers) {
        this.idleWorkers = idleWorkers;

        workerID = getNextWorkerID();
        handoffBox = new ObjectFIFO(1); // only one slot

        // just before returning, the thread should be created and started.
        noStopRequested = true;

        Runnable r = new Runnable() {
            public void run() {
                try {
                    runWork();
                } catch (Exception x) {
                    // in case ANY exception slips through
                    x.printStackTrace();
                }
            }
        };

        internalThread = new Thread(r);
        internalThread.start();
    }

    public static synchronized int getNextWorkerID() {
        // notice: synchronized at the class level to ensure uniqueness
        int id = nextWorkerID;
        nextWorkerID++;
        return id;
    }

    public void process(Runnable target) throws InterruptedException {
        handoffBox.add(target);
    }

    private void runWork() {
        while (noStopRequested) {
            try {
                System.out.println("workerID=" + workerID + ", ready for work");

                idleWorkers.add(this);

                Runnable r = (Runnable) handoffBox.remove();

                System.out.println("workerID=" + workerID + ", starting execution of new Runnable: " + r);
                runIt(r);
            } catch (InterruptedException x) {
                Thread.currentThread().interrupt(); // re-assert
            }
        }
    }

    private void runIt(Runnable r) {
        try {
            r.run();
        } catch (Exception runex) {
            System.err.println("Uncaught exception fell through from run()");
            runex.printStackTrace();
        } finally {
            Thread.interrupted();
        }
    }

    public void stopRequest() {
        System.out.println("workerID=" + workerID + ", stopRequest() received.");
        noStopRequested = false;
        internalThread.interrupt();
    }

    public boolean isAlive() {
        return internalThread.isAlive();
    }
}

class ObjectFIFO extends Object {
    private Object[] queue;

    private int capacity;

    private int size;

    private int head;

    private int tail;

    public ObjectFIFO(int cap) {
        capacity = (cap > 0) ? cap : 1; // at least 1
        queue = new Object[capacity];
        head = 0;
        tail = 0;
        size = 0;
    }

    public int getCapacity() {
        return capacity;
    }

    public synchronized int getSize() {
        return size;
    }

    public synchronized boolean isEmpty() {
        return (size == 0);
    }

    public synchronized boolean isFull() {
        return (size == capacity);
    }

    public synchronized void add(Object obj) throws InterruptedException {

        waitWhileFull();

        queue[head] = obj;
        head = (head + 1) % capacity;
        size++;

        notifyAll();
    }

    public synchronized void addEach(Object[] list) throws InterruptedException {

        for (int i = 0; i < list.length; i++) {
            add(list[i]);
        }
    }

    public synchronized Object remove() throws InterruptedException {

        waitWhileEmpty();

        Object obj = queue[tail];

        queue[tail] = null;

        tail = (tail + 1) % capacity;
        size--;

        notifyAll();

        return obj;
    }

    public synchronized Object[] removeAll() throws InterruptedException {

        Object[] list = new Object[size];

        for (int i = 0; i < list.length; i++) {
            list[i] = remove();
        }

        return list;
    }

    public synchronized Object[] removeAtLeastOne() throws InterruptedException {

        waitWhileEmpty();
        return removeAll();
    }

    public synchronized boolean waitUntilEmpty(long msTimeout) throws InterruptedException {

        if (msTimeout == 0L) {
            waitUntilEmpty();
            return true;
        }

        long endTime = System.currentTimeMillis() + msTimeout;
        long msRemaining = msTimeout;

        while (!isEmpty() && (msRemaining > 0L)) {
            wait(msRemaining);
            msRemaining = endTime - System.currentTimeMillis();
        }

        return isEmpty();
    }

    public synchronized void waitUntilEmpty() throws InterruptedException {

        while (!isEmpty()) {
            wait();
        }
    }

    public synchronized void waitWhileEmpty() throws InterruptedException {

        while (isEmpty()) {
            wait();
        }
    }

    public synchronized void waitUntilFull() throws InterruptedException {

        while (!isFull()) {
            wait();
        }
    }

    public synchronized void waitWhileFull() throws InterruptedException {

        while (isFull()) {
            wait();
        }
    }
}