lock.java

package me.lihongjie;

import org.junit.Before;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

public class LockTest {

//    private static Logger logger = LoggerFactory.getLogger(LockTest.class);

    private boolean aNotDone = true;
    private Condition aDoneCnd;
    private ReentrantLock lock;
    private boolean firstRun = true;
    private boolean cNotDone = true;
    private Condition cDoneCnd;
    private Condition bDoneCnd;
    private boolean bNotDone = true;

    @Before
    public void setUp() throws Exception {
        lock = new ReentrantLock();

        aDoneCnd = lock.newCondition();
        bDoneCnd = lock.newCondition();
        cDoneCnd = lock.newCondition();
    }

    @Test
    public void test() throws Exception {


        ExecutorService threadPool = Executors.newFixedThreadPool(3);

        threadPool.submit(() -> {


            for (int i = 0; i < 10; i++) {


                lock.lock();
//                logger.info("a get lock");
                if (firstRun) {
                    System.out.println("A");

                    firstRun = false;

                }else{


                    while (cNotDone) {

                        try {
                            cDoneCnd.await();
                        } catch (InterruptedException e) {
                            Thread.currentThread()
                                    .interrupt();
                        }


                    }

                    System.out.println("A");


                }
                aNotDone = false;
                cNotDone = true;
                aDoneCnd.signal();
                lock.unlock();
//                logger.info("a release lock");
            }
        });


        threadPool.submit(() -> {


            for (int i = 0; i < 10; i++) {

                lock.lock();
//                logger.info("b get lock");
                while (aNotDone) {


                    try {
                        aDoneCnd.await();
                    } catch (InterruptedException e) {
                        Thread.currentThread()
                                .interrupt();
                    }
                }

                System.out.println("B");
                aNotDone = true;
                bNotDone = false;
                bDoneCnd.signal();
                lock.unlock();
//                logger.info("b release lock");
            }
        });


        threadPool.submit(() -> {


            for (int i = 0; i < 10; i++) {

                lock.lock();
//                logger.info("c get lock");

                while (bNotDone) {


                    try {
                        bDoneCnd.await();
                    } catch (InterruptedException e) {
                        Thread.currentThread()
                                .interrupt();
                    }
                }

                System.out.println("C");
                bNotDone = true;
                cNotDone = false;
                cDoneCnd.signal();
                lock.unlock();
//                logger.info("c release lock");
            }
        });


        threadPool.awaitTermination(1, TimeUnit.HOURS);

    }

}