TestTest.java

package xyz.krkw.grpc.demo;

import org.junit.Test;

import java.util.ArrayList;
import java.util.concurrent.Semaphore;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * Copyright © Liu Xiao, 2019
 * Created by alex on 2019/4/7.
 */
public class TestTest {
    static class PrintRunner implements Runnable {

        private final String message;
        private final AtomicInteger globalCounter;
        private final Semaphore semaphore;
        private PrintRunner next;

        public PrintRunner(
                String message,
                AtomicInteger globalCounter
        ) {
            this.message = message;
            this.globalCounter = globalCounter;
            this.semaphore = new Semaphore(0);
        }

        @Override
        public void run() {
            if (next == null) {
                System.err.println("You must initialize `next` before running");
                return;
            }
            while (true) {
                try {
                    semaphore.acquire();
                } catch (InterruptedException e) {
                    System.err.println("interrupted: " + e.toString());
                    e.printStackTrace(System.err);
                    return;
                }

                if (globalCounter.getAndDecrement() > 0) {
                    System.out.println(message);
                    next.notifyRunner();
                } else {
                    next.notifyRunner();
                    return;
                }
            }
        }

        public PrintRunner getNext() {
            return next;
        }

        public PrintRunner setNext(PrintRunner next) {
            this.next = next;
            return this;
        }

        public void notifyRunner() {
            semaphore.release();
        }
    }

    @Test
    public void test() throws InterruptedException {
        int threadCount = 3;
        ArrayList<PrintRunner> list = new ArrayList<>(threadCount);
        AtomicInteger counter = new AtomicInteger(30);
        for (int i = 0; i < threadCount; i++) {
            list.add(new PrintRunner(
                    Character.toString((char) ('A' + i)),
                    counter
            ));
        }

        for (int i = 0; i < threadCount; i++) {
            if (i < threadCount - 1) {
                list.get(i).setNext(list.get(i + 1));
            } else {
                list.get(i).setNext(list.get(0));
            }
        }

        ArrayList<Thread> threads = new ArrayList<>(threadCount);
        for (int i = 0; i < threadCount; i++) {
            Thread thread = new Thread(list.get(i));
            thread.setName("Print thread " + i);
            threads.add(thread);
            thread.start();
        }

        list.get(0).notifyRunner();

        for (Thread thread : threads) {
            thread.join();
        }
    }
}