Java线程之间通讯（三）

使用wait和notify方法实现了线程间的通讯，都是Object 类的方法，java所有的对象都提供了这两个方法

1.wait和notify必须配合synchronized使用

2.wait方法释放锁，notify方法不释放锁

import java.util.ArrayList;

import java.util.List;

public class ListAdd1 {

    private volatile static List list = new ArrayList();

    public void add(){

        list.add("laoshi");

    }

    public int size(){

        return list.size();

    }

    public static void main(String[] args) {

        final ListAdd1 list1 = new ListAdd1();

        Thread t1 = new Thread(new Runnable() {

            @Override

            public void run() {

                try {

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

                        list1.add();

                        System.out.println("当前线程：" + Thread.currentThread().getName() + "添加了一个元素..");

                        Thread.sleep(500);

                    }

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

            }

        }, "t1");

        Thread t2 = new Thread(new Runnable() {

            @Override

            public void run() {

                while(true){

                    if(list1.size() == 5){

                        System.out.println("当前线程收到通知：" + Thread.currentThread().getName() + " list size = 5 线程停止..");

                        throw new RuntimeException();

                    }

                }

            }

        }, "t2");

        t1.start();

        t2.start();

    }

}

import java.util.ArrayList;

import java.util.List;

import java.util.concurrent.CountDownLatch;

/**

 * wait notfiy 方法，wait释放锁，notfiy不释放锁

 */

public class ListAdd2 {

    private volatile static List list = new ArrayList();

    public void add(){

        list.add("laoshi");

    }

    public int size(){

        return list.size();

    }

    public static void main(String[] args) {

        final ListAdd2 list2 = new ListAdd2();

        // 1 实例化出来一个 lock

        // 当使用wait 和 notify 的时候 ， 一定要配合着synchronized关键字去使用

        final Object lock = new Object();

        final CountDownLatch countDownLatch = new CountDownLatch(1);

        Thread t1 = new Thread(new Runnable() {

            @Override

            public void run() {

                try {

                    synchronized (lock) {

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

                            list2.add();

                            System.out.println("当前线程：" + Thread.currentThread().getName() + "添加了一个元素..");

                            Thread.sleep(500);

                            if(list2.size() == 5){

                                System.out.println("已经发出通知..");

                                countDownLatch.countDown();

                                lock.notify();

                            }

                        }

                    }

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

            }

        }, "t1");

        Thread t2 = new Thread(new Runnable() {

            @Override

            public void run() {

                synchronized (lock) {

                    if(list2.size() != 5){

                        try {

                            System.out.println("t2进入...");

                             lock.wait();

                            countDownLatch.await();

                        } catch (InterruptedException e) {

                            e.printStackTrace();

                        }

                    }

                    System.out.println("当前线程：" + Thread.currentThread().getName() + "收到通知线程停止..");

                    throw new RuntimeException();

                }

            }

        }, "t2");

        t2.start();

        t1.start();

    }

}

import java.util.LinkedList;

import java.util.concurrent.TimeUnit;

import java.util.concurrent.atomic.AtomicInteger;

public class MyQueue {

    //1 需要一个承装元素的集合

    private LinkedList<Object> list=new LinkedList<Object>();

    //2 需要一个计数器

    private AtomicInteger count=new AtomicInteger(0);

    //3 需要制定上限和下限

    private final int minSize=0;

    private final int maxSize ;

    //4 构造方法

    public MyQueue(int size){

        this.maxSize = size;

    }

    //5 初始化一个对象 用于加锁

    private final Object lock=new Object();

    //put(anObject): 把anObject加到BlockingQueue里,如果BlockQueue没有空间,则调用此方法的线程被阻断，

    // 直到BlockingQueue里面有空间再继续.

    public void put(Object obj){

        synchronized (lock){

            while (count.get()==this.maxSize){

                try {

                    lock.wait();

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

            }

            //1 加入元素

            list.add(obj);

            //2.计数器累加

            count.incrementAndGet();

            //3 通知另外一个线程（唤醒）

            lock.notify();

            System.out.println("新加入的元素为:" + obj);

        }

    }

    //take: 取走BlockingQueue里排在首位的对象,若BlockingQueue为空,

    // 阻断进入等待状态直到BlockingQueue有新的数据被加入.

    public Object take(){

        Object ret=null;

        synchronized (lock){

            while (count.get()==this.minSize){

                try {

                    lock.wait();

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

            }

            //1 做移除元素操作

            ret=list.removeFirst();

            //2 计数器递减

            count.decrementAndGet();

            //3 唤醒另外一个线程

            lock.notify();

        }

        return ret;

    }

    public int getSize(){

        return this.count.get();

    }

    public static void main(String[] args) {

        final MyQueue mq = new MyQueue(5);

        mq.put("a");

        mq.put("b");

        mq.put("c");

        mq.put("d");

        mq.put("e");

        System.out.println("当前容器的长度:" + mq.getSize());

        Thread t1 = new Thread(new Runnable() {

            @Override

            public void run() {

                mq.put("f");

                mq.put("g");

            }

        },"t1");

        t1.start();

        Thread t2 = new Thread(new Runnable() {

            @Override

            public void run() {

                Object o1 = mq.take();

                System.out.println("移除的元素为:" + o1);

                Object o2 = mq.take();

                System.out.println("移除的元素为:" + o2);

            }

        },"t2");

        try {

            TimeUnit.SECONDS.sleep(2);

        } catch (InterruptedException e) {

            e.printStackTrace();

        }

        t2.start();

    }

}

　　ThreadLocal：线程局部变量，是一种多线程间并发访问变量的解决方案，与synchronized枷锁的方式不同，ThreadLocal完全不提供锁，使用以空间换时间的手段，为每个线程提供变量的独立副本，以保证线程安全。

在高并发量或者竞争激烈的场景，使用ThreadLoacal可以一定程度少减少锁竞争。

public class ConnThreadLocal {

    public static  ThreadLocal<String> th=new ThreadLocal<String>();

    public void setTh(String value){

        th.set(value);

    }

    public void getTh(){

        System.out.println(Thread.currentThread().getName() + ":" + this.th.get());

    }

    public static void main(String[] args) throws InterruptedException {

        final ConnThreadLocal ct = new ConnThreadLocal();

        Thread t1 = new Thread(new Runnable() {

            @Override

            public void run() {

                ct.setTh("张三");

                ct.getTh();

            }

        }, "t1");

        Thread t2 = new Thread(new Runnable() {

            @Override

            public void run() {

                try {

                    Thread.sleep(1000);

                    ct.getTh();

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

            }

        }, "t2");

        t1.start();

        t2.start();

    }

}

单例模式：最常见的饥饿模式（直接实力化对象），懒汉模式（在调用方法时进行实例化对象）

在多线程中考虑性能和线程安全问题使用

dubble check instance

static inner class

public class DubbleSingleton {

    private static  DubbleSingleton ds;

    public static  DubbleSingleton getDs(){

        if(ds == null){

            try {

                //模拟初始化对象的准备时间...

                Thread.sleep(3000);

            } catch (InterruptedException e) {

                e.printStackTrace();

            }

            synchronized (DubbleSingleton.class) {

                if(ds == null){

                    ds = new DubbleSingleton();

                }

            }

        }

        return ds;

    }

    public static void main(String[] args) {

        Thread t1 = new Thread(new Runnable() {

            @Override

            public void run() {

                System.out.println(DubbleSingleton.getDs().hashCode());

            }

        },"t1");

        Thread t2 = new Thread(new Runnable() {

            @Override

            public void run() {

                System.out.println(DubbleSingleton.getDs().hashCode());

            }

        },"t2");

        Thread t3 = new Thread(new Runnable() {

            @Override

            public void run() {

                System.out.println(DubbleSingleton.getDs().hashCode());

            }

        },"t3");

        t1.start();

        t2.start();

        t3.start();

    }

}

　　这种方法用的多

public class Singletion {

    private static class InnerSingletion {

        private static Singletion single = new Singletion();

    }

    public static Singletion getInstance(){

        return InnerSingletion.single;

    }

}

import java.util.concurrent.TimeUnit;

public class Demo3 {

	private volatile int signal;

    public synchronized void set(int value){

    	signal=1;

    	notifyAll(); //notifyAll叫醒所有的处于wait线程，争夺到时间片的线程只有一个

    	notify(); //notify方法会随机叫醒一个处于wait状态的线程

    	//notify 拿到锁

    	//this.signal=value;

    }

    public synchronized int get(){

    	System.out.println(Thread.currentThread().getName()+"方法执行了。。。");

    	if(signal!=1){

    		try {

				wait(); //释放锁

			} catch (InterruptedException e) {

				e.printStackTrace();

			}

    	}

    	System.out.println(Thread.currentThread().getName()+"方法执行完毕。。。");

    	return signal;

    }

    public static void main(String[] args) {

		Demo3 demo=new Demo3();

		Target t1=new Target(demo);

		Target t2=new Target(demo);

		new Thread(t2).start();

		new Thread(t2).start();

		new Thread(t2).start();

		new Thread(t2).start();

		try {

			TimeUnit.SECONDS.sleep(1);

		} catch (InterruptedException e) {

			e.printStackTrace();

		}

		new Thread(t1).start();

	}

}

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Java线程之间通讯（三）

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