PausableExecutor.java

import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

public class PausableExecutor extends ThreadPoolExecutor {
    private boolean isPaused;
    private ReentrantLock pauseLock = new ReentrantLock();
    private Condition unPaused = pauseLock.newCondition();

    /**
     * Default constructor for a simple fixed threadpool
     */
    public PausableExecutor(int corePoolSize) {
        super("PausebaleExecutor", corePoolSize, corePoolSize, 1, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());
    }

    /**
     * Executed before a task is assigned to a thread.
     */
    protected void beforeExecute(Thread t, Runnable r) {
        super.beforeExecute(t, r);
        pauseLock.lock();
        try {
            while (isPaused) unPaused.await();
        } catch (InterruptedException ie) {
            t.interrupt();
        } finally {
            pauseLock.unlock();
        }
    }

    /**
     * Pause the threadpool. Running tasks will continue running, but new tasks
     * will not start until the threadpool is resumed.
     */
    public void pause() {
        pauseLock.lock();
        try {
            isPaused = true;
        } finally {
            pauseLock.unlock();
        }
    }

    /**
     * Resume the threadpool.
     */
    public void resume() {
        pauseLock.lock();
        try {
            isPaused = false;
            unPaused.signalAll();
        } finally {
            pauseLock.unlock();
        }
    }
}