Java多线程同步和互斥的方法 java多线程 同步

线程同步

1.发生在多个线程操作同一个资源

2.并发：同一个对象被多个线程同时操作

3.于是，就需要线程同步。线程同步其实就是一种等待机制，多个需要同时访问此对象的线程进入这个对象的等待池形成队列，等待前面线程使用完毕，下一个线程再使用

4.线程同步的形成条件：队列+锁（synchronized）

5.线程同步也存在问题：

• 性能降低：一个线程持有锁会导致其他所有需要此锁的线程挂起；在多线程竞争下，加锁，释放锁会导致比较多的上下文切换和调度延时，引起性能问题。
• 性能倒置：如果一个优先级高的线程等待一个优先级低的线程释放锁，会导致优先级倒置，引起性能问题。

三个不安全的案例

1.不安全的买票

package com.zhang.syn;

//不安全的买票
//线程不安全，有负数
public class UnsafeBuyTicket {
    public static void main(String[] args) {
        BuyTicket station = new BuyTicket();

        new Thread(station,"漂亮的羡羡").start();
        new Thread(station,"可靠的野哥").start();
        new Thread(station,"温柔的魏魏").start();
    }
}

class BuyTicket implements Runnable{
    //票
    private int ticketNums = 10;
    boolean flag = true;//外部停止方式

    @Override
    public void run() {
        //买票
        while (flag){
            try {
                buy();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
    }

    private void buy() throws InterruptedException {
        //判断是否有票
        if (ticketNums <= 0){
            flag = false;
            return;
        }
        //模拟延时，放大问题的发生性
        Thread.sleep(100);
        //买票
        System.out.println(Thread.currentThread().getName() + "拿到" + ticketNums--);
    }
}

2.不安全的取钱

package com.zhang.syn;

//不安全的取钱
//两个人去银行取钱
public class UnsafeBank {
    public static void main(String[] args) {
        //账户
        Account account = new Account(100, "份子钱");

        Drawing you = new Drawing(account,50,"你");
        Drawing teammates = new Drawing(account,100,"姐妹");

        you.start();
        teammates.start();
    }
}

//账户
class Account{
    int money;//余额
    String name;//卡名

    public Account(int money, String name) {
        this.money = money;
        this.name = name;
    }
}

//银行：模拟取款
class Drawing extends Thread{
    Account account;//账户
    //取了多少钱
    int drawingMoney;
    //现在手里有多少钱
    int nowMoney;

    public Drawing(Account account,int drawingMoney,String name){
        super(name);
        this.account = account;
        this.drawingMoney = drawingMoney;
    }

    //取钱

    @Override
    public void run() {
        //判断有没有钱
        if (account.money-drawingMoney < 0){
            System.out.println(Thread.currentThread().getName() + "钱不够，取不了");
            return;
        }

        //sleep可以放大问题的发生性
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        //卡内余额 = 余额 - 你取的钱
        account.money -= drawingMoney;
        //你手里的钱
        nowMoney += drawingMoney;

        System.out.println(account.name+"余额为"+account.money);
        //Thread.currentThread().getName() = this.getName()
        System.out.println(this.getName()+"手里的钱"+nowMoney);
    }
}

3.线程不安全的集合

package com.zhang.syn;

import java.util.ArrayList;
import java.util.List;

//线程不安全的集合
public class UnsafeList {
    public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
        for (int i = 0; i < 10000; i++) {
            new Thread(()->{
                list.add(Thread.currentThread().getName());
            }).start();
        }
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list.size());
    }
}

同步方法及同步块

三个案例重写

1.不安全的买票

（只加了synchronized关键字）

package com.zhang.syn;

//不安全的买票
public class UnsafeBuyTicket {
    public static void main(String[] args) {
        BuyTicket station = new BuyTicket();

        new Thread(station,"漂亮的羡羡").start();
        new Thread(station,"可靠的野哥").start();
        new Thread(station,"温柔的魏魏").start();
    }
}

class BuyTicket implements Runnable{
    //票
    private int ticketNums = 10;
    boolean flag = true;//外部停止方式

    @Override
    public void run() {
        //买票
        while (flag){
            try {
                buy();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
    }

    //synchronized 同步方法，锁的是this
    private synchronized void buy() throws InterruptedException {
        //判断是否有票
        if (ticketNums <= 0){
            flag = false;
            return;
        }
        //模拟延时，放大问题的发生性
        Thread.sleep(100);
        //买票
        System.out.println(Thread.currentThread().getName() + "拿到" + ticketNums--);
    }
}

2.不安全的取钱

（加了synchronized(obj){}方法块）

package com.zhang.syn;

//不安全的取钱
//两个人去银行取钱
public class UnsafeBank {
    public static void main(String[] args) {
        //账户
        Account account = new Account(100, "份子钱");

        Drawing you = new Drawing(account,50,"你");
        Drawing teammates = new Drawing(account,100,"姐妹");

        you.start();
        teammates.start();
    }
}

//账户
class Account{
    int money;//余额
    String name;//卡名

    public Account(int money, String name) {
        this.money = money;
        this.name = name;
    }
}

//银行：模拟取款
class Drawing extends Thread{
    Account account;//账户
    //取了多少钱
    int drawingMoney;
    //现在手里有多少钱
    int nowMoney;

    public Drawing(Account account,int drawingMoney,String name){
        super(name);
        this.account = account;
        this.drawingMoney = drawingMoney;
    }

    //取钱
    //synchronized 默认锁的是this，于是用到同步块
    @Override
    public void run() {

        synchronized (account){//方法丢到方法里面，块丢到块里面
            //判断有没有钱
            if (account.money-drawingMoney < 0){
                System.out.println(Thread.currentThread().getName() + "钱不够，取不了");
                return;
            }

            //sleep可以放大问题的发生性
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            //卡内余额 = 余额 - 你取的钱
            account.money -= drawingMoney;
            //你手里的钱
            nowMoney += drawingMoney;

            System.out.println(account.name+"余额为"+account.money);
            //Thread.currentThread().getName() = this.getName()
            System.out.println(this.getName()+"手里的钱"+nowMoney);
        }
    }
}

3.线程不安全的集合

（用synchronized(obj){}方法块锁了对象）

package com.zhang.syn;

import java.util.ArrayList;
import java.util.List;

//线程不安全的集合
public class UnsafeList {
    public static void main(String[] args) {
        List<String> list = new ArrayList<String>();

        for (int i = 0; i < 10000; i++) {
            new Thread(()->{
                synchronized (list){
                    list.add(Thread.currentThread().getName());
                }
            }).start();
        }
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list.size());
    }
}

安全的类CopyOnWriteArrayList

（JUC包下的）（JUC是并发领域的）

package com.zhang.syn;

import java.util.concurrent.CopyOnWriteArrayList;//JUC并发包，Callable也需导入这个包，Callable是关于并发编程的

//测试JUC安全类型的集合
public class TestJUC {
    public static void main(String[] args) {
        CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<String>();//集合都加泛型约束，注意代码规范！！
        for (int i = 0; i < 10000; i++) {
            new Thread(()->{
                list.add(Thread.currentThread().getName());
            }).start();
        }

        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }

        System.out.println(list.size());
    }
}

死锁

（相互等待对方的资源，于是都停下来了）

package com.zhang.Thread;

//死锁：多个线程互相抱着对方需要的资源，然后形成僵持
public class DeadLock {
    public static void main(String[] args) {
        Makeup lover1 = new Makeup(0,"羡羡");
        Makeup lover2 = new Makeup(1,"染染");

        lover1.start();
        lover2.start();
    }
}

//红发带
class Lipstick{

}

//扇子
class Mirror{

}

class Makeup extends Thread{

    //需要的资源只有一份，用static来保证只有一份
    static Lipstick lipstick = new Lipstick();
    static Mirror mirror = new Mirror();

    int choice;//选择
    String loverName;//使用化妆品的人

    Makeup(int choice, String loverName){
        this.choice = choice;
        this.loverName = loverName;
    }

    @Override
    public void run() {
        //化妆
        try {
            makeup();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    //化妆，互相持有对方的锁，就是需要拿到对方的资源
    private void makeup() throws InterruptedException {
        if (choice == 0){
            synchronized (lipstick){//获得红发带的锁
                System.out.println(this.loverName + "获得红发带的锁");
                Thread.sleep(1000);
            }
            synchronized (mirror){//一秒钟之后想获得扇子
                System.out.println(this.loverName + "获得扇子的锁");
            }
        }else {
            synchronized (mirror){//获得扇子的锁
                System.out.println(this.loverName + "获得扇子的锁");
                Thread.sleep(2000);
            }
            synchronized (lipstick){//一秒钟之后想获得红发带
                System.out.println(this.loverName + "获得红发带的锁");
            }
        }
    }
}

Lock（锁）

package com.zhang.gaoji;

import java.util.concurrent.locks.ReentrantLock;

//测试Lock锁
public class TestLock {
    public static void main(String[] args) {
        TestLock2 testLock2 = new TestLock2();


        new Thread(testLock2).start();
        new Thread(testLock2).start();
        new Thread(testLock2).start();
    }
}

//
class TestLock2 implements Runnable{

    int ticketNums =10;

    //定义Lock锁
    private final ReentrantLock lock = new ReentrantLock();

    @Override
    public void run() {
        while (true){

            try{
                lock.lock();//加锁
                if (ticketNums > 0){
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(ticketNums--);
                }else {
                    break;
                }
            }finally {
                lock.unlock();
            }

        }
    }
}

线程通信（生产者消费者问题）

管程法

package com.zhang.gaoji;

//测试：生产者消费者模型-->利用缓冲区解决：管程法
//生产者，消费者，产品，缓冲区
public class TestPC {
    public static void main(String[] args) {
        SynContainer container = new SynContainer();
        new Productor(container).start();
        new Consumer(container).start();
    }
}

//生产者
class Productor extends Thread{
    SynContainer container;
    public Productor(SynContainer container){//构造器方便创造对象
        this.container = container;
    }

    //生产

    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {//生产100瓶酒
            container.push(new Wine(i));
            System.out.println("生产了" + i +"瓶酒");
        }
    }
}

//消费者
class Consumer extends Thread{
    SynContainer container;
    public Consumer(SynContainer container){//构造器方便创造对象
        this.container = container;
    }

    //消费

    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            System.out.println("消费了-->" + container.pop().id +"瓶酒");

        }


    }
}

//产品
class Wine{
    int id;//产品编号

    public Wine(int id) {
        this.id = id;
    }
}

//缓冲区
class SynContainer{

    //需要一个容器大小
    Wine[] wines = new Wine[10];
    //容器的计数器
    int count = 0;

    //生产者放入产品
    public synchronized void push(Wine wine){
        //如果容器满了，就需要等待消费者消费
        if (count == wines.length){
            //通知消费者消费，生产者等待
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        //如果没有满，我们就需要丢入产品
        wines[count] = wine;
        count++;

        //可以通知消费者消费了
        this.notifyAll();
    }

    //消费者消费产品
    public synchronized Wine pop(){
        //判断能否消费
        if (count == 0){
            //等待生产者生产，消费者等待
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        //如果可以消费
        count--;
        Wine wine = wines[count];
        //喝完了，通知生产者生产
        this.notifyAll();
        return wine;
    }
}

信号灯法

package com.zhang.gaoji;

//测试生产者消费者问题2：信号灯法，标志位解决
public class TestPC2 {
    public static void main(String[] args) {
        Video video = new Video();
        new Actor(video).start();
        new Viewer(video).start();
    }
}

//生产者-->演员
class Actor extends Thread{
    Video video;
    public Actor(Video video){
        this.video = video;
    }

    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            if (i%2 == 0){
                this.video.play("我们的歌");
            }else {
                this.video.play("最美逆行者");
            }
        }
    }
}

//消费者-->观众
class Viewer extends Thread{
    Video video;
    public Viewer(Video video){

        this.video = video;
    }

    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            video.watch();
        }
    }
}

//产品-->节目
class Video{
    //演员表演，观众等待 T
    //观众观看，演员等待 F
    String voice;//表演的节目
    boolean flag = true;

    //表演
    public synchronized void play(String voice){

        if (!flag){
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println("演员潘达表演了：" + voice);
        //通知观众观看
        this.notifyAll();//通知唤醒
        this.voice = voice;//voice更新了
        this.flag = !this.flag;
    }

    //观看
    public synchronized void watch(){
        if (flag){
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println("观众蔡丁观看了：" + voice);
        //通知演员表演
        this.notifyAll();
        this.flag = !this.flag;
    }
}

线程池

package com.zhang.gaoji;

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

//测试线程池
public class TestPool {
    public static void main(String[] args) {
        //1.创建服务，创建线程池
        //newFixedThreadPool 参数为线程池大小
        ExecutorService service = Executors.newFixedThreadPool(10);

        //执行  Runnable接口的一个实现类
        service.execute(new MyThread());
        service.execute(new MyThread());
        service.execute(new MyThread());
        service.execute(new MyThread());

        //关闭连接
        service.shutdown();
    }
}

class MyThread implements Runnable{

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName());
    }
}

线程创建总结

1.继承Thread类

2.实现Runnable接口

3.实现Callable接口

package com.zhang.gaoji;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;

//回顾总结线程的创建
public class ThreadNew {
    public static void main(String[] args) {
        new MyThread1().start();

        new Thread(new MyThread2()).start();//Thread()代理类

        FutureTask<Integer> futureTask = new FutureTask<Integer>(new MyThread3());
        new Thread(futureTask).start();//可以实现Runnable接口  因为FutureTask继承了Runnable接口

        try {
            Integer integer = futureTask.get();
            System.out.println(integer);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
    }
}

//1.继承Thread类
class MyThread1 extends Thread{
    @Override
    public void run() {
        System.out.println("MyThread1");
    }
}

//2.实现Runnable接口
class MyThread2 implements Runnable{

    @Override
    public void run() {
        System.out.println("MyThread2");
    }
}

//实现Callable接口
class MyThread3 implements Callable<Integer>{

    @Override
    public Integer call() throws Exception {
        System.out.println("MyThread3");
        return 100;
    }
}