Java 并发优化

线程不安全

SimpleDateFormat不是线程安全的

SimpleDateThread

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class SimpleDateThread extends Thread {
    private SimpleDateFormat sdf;
    private String dateString;
    public SimpleDateThread(SimpleDateFormat sdf,String dateString){
        this.sdf=sdf;
        this.dateString=dateString;
    }
    public void run(){
        try {
            Date dateRef=sdf.parse(dateString);
            String newDateString=sdf.format(dateRef).toString();
            if(!newDateString.equals(dateString)){
                System.out.println("ThreadName="+this.getName()+"报错了 日期字符串:"+dateString+"转换成的日期为:"+newDateString);
            }else{
                System.out.println("ThreadName="+this.getName()+"转换正确 日期字符串:"+dateString+"转换成的日期为:"+newDateString);
            }
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
}

SimpleDateDemo

import java.text.SimpleDateFormat;

public class SimpleDateDemo {
    public static void main(String[] args){
        SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
        String[] dateStringArray=new String[]{"2000-01-01","2001-01-01","2002-01-01","2003-01-01","2004-01-01","2005-01-01","2006-01-01","2007-01-01","2008-01-01","2009-01-01"};
        SimpleDateThread[] threadArray=new SimpleDateThread[10];
        for(int i=0;i<10;i++){
            threadArray[i]=new SimpleDateThread(sdf,dateStringArray[i]);
        }
        for(int i=0;i<10;i++){
            threadArray[i].start();
        }
    }
}

运行结果

 新增DateTools 类

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class DateTools {
    public static Date parse(String formatPattern,String dateString)throws ParseException{
        return new SimpleDateFormat(formatPattern).parse(dateString);
    }
    public static String format(String formatPattern,Date date){
        return new SimpleDateFormat(formatPattern).format(date).toString();
    }
}

将SimpleDateThread中的代码替换

Date dateRef=DateTools.parse("yyyy-MM-dd",dateString);
String newDateString=DateTools.format("yyyy-MM-dd",dateRef).toString();

可解决线程不安全问题。

非阻塞队列

ConcurrentLinkedQueue

import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ConcurrentLinkedQueueTest {
    private static ConcurrentLinkedQueue<Integer> queue=new ConcurrentLinkedQueue<Integer>();
    private static int count=2;
    private static CountDownLatch latch=new CountDownLatch(count);

    public static void main(String[] args) throws InterruptedException {
        long timeStart=System.currentTimeMillis();
        ExecutorService es= Executors.newFixedThreadPool(4);
        ConcurrentLinkedQueueTest.offer();
        for(int i=0;i<count;i++){
            es.submit(new Poll());
        }
        latch.await();
        System.out.println("cost time "+(System.currentTimeMillis()-timeStart)+"ms");
        es.shutdown();
    }

    public static void offer(){
        for(int i=0;i<100000;i++){
            queue.offer(i);
        }
    }

    static class Poll implements Runnable{

        @Override
        public void run() {
            while (!queue.isEmpty()){
                System.out.println(queue.poll());
            }
            latch.countDown();
        }
    }
}

阻塞队列

BlockingQueue

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingDeque;

public class BlockingQueueTest {
    public class Basket{
        BlockingQueue<String> basket=new LinkedBlockingDeque<>(3);

        public void produce() throws InterruptedException{
            basket.put("An apple");
        }

        public String consume() throws InterruptedException{
            return basket.take();
        }
    }
    public class Producer implements Runnable{
        private String instance;
        private Basket basket;

        public Producer(String instance, Basket basket) {
            this.instance = instance;
            this.basket = basket;
        }

        @Override
        public void run() {
            try {
                while (true){
                    System.out.println("生产者准备生产苹果: "+instance);
                    basket.produce();
                    System.out.println("!生产者生产苹果完毕: "+instance);
                    Thread.sleep(300);
                }
            } catch (InterruptedException e) {
                System.out.println("Producer Interrupted");
            }
        }
    }

    public class Consumer implements Runnable{
        private String instance;
        private Basket basket;

        public Consumer(String instance, Basket basket) {
            this.instance = instance;
            this.basket = basket;
        }

        @Override
        public void run() {
            try {
                while (true){
                    System.out.println("消费者准备消费苹果: "+instance);
                    System.out.println(basket.consume());
                    System.out.println("!消费者消费苹果完毕: "+instance);
                    Thread.sleep(1000);
                }
            } catch (InterruptedException e) {
                System.out.println("Consumer Interrupted");
            }
        }
    }
    public static void main(String[] args){
        BlockingQueueTest test=new BlockingQueueTest();
        Basket basket=test.new Basket();
        ExecutorService service= Executors.newCachedThreadPool();
        Producer producer=test.new Producer("生产者001",basket);
        Producer producer1=test.new Producer("生产者002",basket);
        Consumer consumer=test.new Consumer("消费者001",basket);
        service.submit(producer);
        service.submit(producer1);
        service.submit(consumer);
    }
}

并发工具类

CyclicBarrier

import java.util.Random;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class CyclicBarrierDemo {
    public static void main(String[] args) throws Exception{
        CyclicBarrier barrier=new CyclicBarrier(3);
        ExecutorService service= Executors.newFixedThreadPool(3);
        service.submit(new Thread(new Runner(barrier, "1号选手")));
        service.submit(new Thread(new Runner(barrier, "2号选手")));
        service.submit(new Thread(new Runner(barrier, "3号选手")));
        service.shutdown();
    }
    static class Runner implements Runnable{
        private CyclicBarrier barrier;
        private String name;

        public Runner(CyclicBarrier barrier, String name) {
            this.barrier = barrier;
            this.name = name;
        }

        @Override
        public void run() {
            try {
                Thread.sleep(1000*(new Random()).nextInt(8));
                System.out.println(name+" 准备好了...");
                barrier.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
            System.out.println(name+" 起跑!");
        }
    }
}

CountDownLatch

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class CountDownLatchDemo {
    private static final int PLAYER_AMOUNT=5;
    public static void main(String[] args){
        CountDownLatchDemo demo=new CountDownLatchDemo();
        demo.exec();
    }

    public void exec(){
        CountDownLatch begin=new CountDownLatch(1);
        CountDownLatch end=new CountDownLatch(PLAYER_AMOUNT);
        Player[] players=new Player[PLAYER_AMOUNT];
        for(int i=0;i<PLAYER_AMOUNT;i++){
            players[i]=new Player(i+1,begin,end);
        }
        ExecutorService service= Executors.newFixedThreadPool(PLAYER_AMOUNT);
        System.out.println("Race begins!");
        begin.countDown();
        for(Player p:players){
            service.execute(p);
        }
        try {
            end.await();
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            System.out.println("Race ends!");
        }
        service.shutdown();
    }
    class Player implements Runnable{
        private  int id;
        private CountDownLatch begin;
        private CountDownLatch end;

        public Player(int id, CountDownLatch begin, CountDownLatch end) {
            this.id = id;
            this.begin = begin;
            this.end = end;
        }

        @Override
        public void run() {
            try {
                begin.await();
                Thread.sleep((long)(Math.random()*100));
                System.out.println("Play"+id+" arrived.");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }finally {
                end.countDown();
            }
        }
    }
}

Semaphore

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

public class SemaphoreDemo {
    public static void main(String[] args){
        ExecutorService service= Executors.newCachedThreadPool();
        final Semaphore semaphore=new Semaphore(5);
        for(int i=0;i<20;i++){
            final int no=i;
            Runnable runnable=new Runnable() {
                @Override
                public void run() {
                    try {
                        semaphore.acquire();
                        System.out.println("Accessing: "+no);
                        Thread.sleep((long)(Math.random()*10000));
                        semaphore.release();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            };
            service.execute(runnable);
        }
        service.shutdown();
    }
}