//Listing 7-1. Achieving Synchronization in Terms of Reentrant Locks

import java.util.concurrent.Executors;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.TimeUnit;

import java.util.concurrent.locks.ReentrantLock;

public class A {

    public static void main(String[] args) {

        ExecutorService executor = Executors.newFixedThreadPool();

        final ReentrantLock lock = new ReentrantLock();

        class Worker implements Runnable {

            private final String name;

            Worker(String name) {

                this.name = name;

            }

            @Override

            public void run() {

                lock.lock();

                try {

                    if (lock.isHeldByCurrentThread())

                        System.out.printf(

                                "Thread %s entered critical section.%n", name);

                    System.out.printf("Thread %s performing work.%n", name);

                    try {

                        Thread.sleep();

                    } catch (InterruptedException ie) {

                        ie.printStackTrace();

                    }

                    System.out.printf("Thread %s finished working.%n", name);

                } finally {

                    lock.unlock();

                }

            }

        }

        executor.execute(new Worker("ThdA"));

        executor.execute(new Worker("ThdB"));

        try {

            executor.awaitTermination(, TimeUnit.SECONDS);

        } catch (InterruptedException ie) {

            ie.printStackTrace();

        }

        executor.shutdownNow();

    }

}