Fun with Executor

Main.java

package in.thefourtheye;

import java.util.concurrent.*;

public class Main {

    public static void main(String[] args) {
        final int CORE_POOL_SIZE = 1;
        final int MAX_POOL_SIZE = 5;
        final long KEEP_ALIVE_TIME_IN_MS = 1000;
        final int MAX_CAPACITY = 100;
        final ThreadPoolExecutor executor = new ThreadPoolExecutor(
                CORE_POOL_SIZE,
                MAX_POOL_SIZE,
                KEEP_ALIVE_TIME_IN_MS, TimeUnit.MILLISECONDS,
                new LinkedBlockingQueue<>(MAX_CAPACITY)
        );
        final CountDownLatch latch = new CountDownLatch(1);
        executor.execute(new ParentTask(latch, executor));
        await(latch);
        executor.shutdownNow();
    }

    static class ChildTask implements Runnable {
        private final CountDownLatch latch;

        public ChildTask(final CountDownLatch latch) {
            this.latch = latch;
        }

        @Override
        public void run() {
            latch.countDown();
            print("ChildTask");
        }
    }

    static class ParentTask implements Runnable {
        private final CountDownLatch latch;
        private final Executor executor;

        ParentTask(final CountDownLatch latch, final Executor executor) {
            this.latch = latch;
            this.executor = executor;
        }

        @Override
        public void run() {
            print("ParentTask");
            final CountDownLatch childTaskLatch = new CountDownLatch(1);
            executor.execute(new ChildTask(childTaskLatch));
            await(childTaskLatch);
            latch.countDown();
        }
    }

    static void print(final String msg) {
        System.out.printf("[%s] [%s]\n", Thread.currentThread().getName(), msg);
    }

    static void await(final CountDownLatch latch) {
        try {
            latch.await();
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }
}