Java多线程顺序打印abc的多种写法

Java多线程顺序打印abc的多种写法

问题描述：

有三个线程顺序打印abc十次，请用线程同步实现。

问题分析：

这个问题是一个线程同步的问题，一共打印十轮每一轮都要保证a，b，c三个线程顺序执行。本文给出以下几个常用方法。

CAS实现

package com.shu.yzy.thread;

import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * 三个线程按次序轮流打印a,b,c AtomicInteger 实现
 * @author yzy
 */
public class ThreadDemo implements Runnable{
    private static  AtomicInteger currentCount = new AtomicInteger(0);

    private static final Integer MAX_COUNT = 30;

    private static String [] chars = {"a", "b", "c"};

    private String name;

    public ThreadDemo(String name) {
        this.name =  name;
    }

    @Override
    public void run() {
        while(currentCount.get()if(this.name.equals(chars[currentCount.get()%3])){
                printAndPlusOne(this.name + "\t" + currentCount);
            }
        }
    }

    public void printAndPlusOne(String content){
        System.out.println(content);
        currentCount.getAndIncrement();
    }

    public static void main(String [] args){
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(3, 3, 20, TimeUnit.MINUTES, new LinkedBlockingQueue());
        threadPoolExecutor.execute(new ThreadDemo("a"));
        threadPoolExecutor.execute(new ThreadDemo("b"));
        threadPoolExecutor.execute(new ThreadDemo("c"));
        threadPoolExecutor.shutdown();
    }
}

synchronized实现

package com.shu.yzy.thread;

import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

/**
 * 三个线程按次序轮流打印a,b,c synchronized + wait() + notifyAll() 实现
 * Integer 对象不能作为synchronized锁的对象，因为修改Integer对象的值会改变对象引用
 * @author yzy
 */
public class ThreadDemo2 implements Runnable {

    private static String[] chars = {"a", "b", "c"};

    private static final OperateInteger operateInteger = new OperateInteger(0, 30);

    private String name;

    public ThreadDemo2(String name) {
        this.name = name;
    }

    @Override
    public void run() {
        while (operateInteger.getCurrentCount() < operateInteger.getMaxCount()) {
            synchronized (operateInteger) {
                if (operateInteger.getCurrentCount() < operateInteger.getMaxCount()) {
                    if (this.name.equals(chars[operateInteger.getCurrentCount() % 3])) {
                        operateInteger.printAndPlusOne();
                        operateInteger.notifyAll();
                    } else {
                        try {
                            operateInteger.wait();
                        } catch (Exception e1) {
                            e1.printStackTrace();
                        }
                    }
                }
            }
        }

    }


    public static void main(String[] args) {
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(3, 3, 20, TimeUnit.MINUTES, new LinkedBlockingQueue());
        threadPoolExecutor.execute(new ThreadDemo2("a"));
        threadPoolExecutor.execute(new ThreadDemo2("b"));
        threadPoolExecutor.execute(new ThreadDemo2("c"));
        threadPoolExecutor.shutdown();
    }

    private static class OperateInteger{
        private int currentCount;

        private int maxCount;

        private void printAndPlusOne() {
            System.out.println(chars[currentCount%3] + "\t" + currentCount);
            currentCount++;
        }

        public OperateInteger(int currentCount, int maxCount) {
            this.currentCount = currentCount;
            this.maxCount = maxCount;
        }

        public int getCurrentCount() {
            return currentCount;
        }

        public int getMaxCount() {
            return maxCount;
        }
    }
}

Lock实现

package com.shu.yzy.thread;

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

/**
 * 三个线程按次序轮流打印a,b,c Lock实现
 * @author yzy
 */
public class ThreadDemo3 implements Runnable{
    private static Lock lock = new ReentrantLock();

    private static Integer currentCount = 0;

    private static final Integer MAX_COUNT = 30;

    private static String [] chars = {"a", "b", "c"};

    private String name;

    public ThreadDemo3(String name) {
        this.name =  name;
    }

    @Override
    public void run() {
        while(currentCount//lock() 与 unlock() 必须和 try...finally 配套使用 避免出现异常不解锁
            try{
                lock.lock();
                while(this.name.equals(chars[currentCount%3])&¤tCountthis.name);
                }
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                lock.unlock();
            }
        }
    }

    public void printAndPlusOne(String name){
        System.out.println(name + "\t" + currentCount);
        currentCount ++;
    }

    public static void main(String [] args){
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(3, 3, 20, TimeUnit.MINUTES, new LinkedBlockingQueue());
        threadPoolExecutor.execute(new ThreadDemo3("a"));
        threadPoolExecutor.execute(new ThreadDemo3("b"));
        threadPoolExecutor.execute(new ThreadDemo3("c"));
        threadPoolExecutor.shutdown();
    }
}

JUC 包同步工具实现(以CylicBarrier为例)

package com.shu.yzy.thread;

import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class ThreadDemo4 implements Runnable{
    private static CyclicBarrier cyclicBarrier = new CyclicBarrier(3);

    private static Integer currentCount = 0;

    private static final Integer MAX_COUNT = 30;

    private static String [] chars = {"a", "b", "c"};

    private String name;

    public ThreadDemo4(String name) {
        this.name =  name;
    }

    @Override
    public void run() {
        while(currentCountwhile(this.name.equals(chars[currentCount%3]))
                printAndPlusOne(this.name + "\t" + currentCount);
            try {
                cyclicBarrier.await();
            }catch (Exception e){
                e.printStackTrace();
            }
        }
    }

    public void printAndPlusOne(String name){
        System.out.println(name);
        currentCount ++;
    }

    public static void main(String [] args){
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(3, 3, 20, TimeUnit.MINUTES, new LinkedBlockingQueue());
        threadPoolExecutor.execute(new ThreadDemo4("a"));
        threadPoolExecutor.execute(new ThreadDemo4("b"));
        threadPoolExecutor.execute(new ThreadDemo4("c"));
        threadPoolExecutor.shutdown();
    }
}