线程的操作

线程操作

线程停止

package com.state;

//测试stop
//1、建议线程正常停止-->利用次数，不建议死循环
//2、建议使用标志为-->设置一个标志位
//3、不要使用stop或者destroy等过时的方法
public class StateTest01 implements Runnable {

    //1、设置一个标志位
    private boolean flag = true;

    @Override
    public void run() {
        int i = 0;
        while (flag) {
            System.out.println("run...Thread " + i++);
        }

    }

    //2、设置一个公开的方法停止线程，转换标志为
    public void stop() {
        this.flag = false;
    }

    public static void main(String[] args) {
        StateTest01 stateTest01 = new StateTest01();
        new Thread(stateTest01).start();


        for (int i = 0; i < 1000; i++) {
            System.out.println("main " + i);
            if (i == 900) {
                //调用stop方法切换标志位，停止线程
                stateTest01.stop();
                System.out.println("线程该停止了");
            }
        }
    }

}

线程休眠

模拟网络延时

package com.state;


//模拟网络延时:放大问题的发生性
public class SleepTest01 implements Runnable {

    private int ticketNum = 10;


    @Override
    public void run() {
        while (true) {
            if (ticketNum <= 0) {
                break;
            }

            //模拟延时
            try {
                Thread.sleep(800);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + "-->拿到了第 " + ticketNum-- + " 张票");
        }
    }

    public static void main(String[] args) {
        SleepTest01 sleepTest01 = new SleepTest01();

        new Thread(sleepTest01, "小明").start();
        new Thread(sleepTest01, "老师").start();
        new Thread(sleepTest01, "黄牛").start();
    }
}

模拟倒计时

package com.state;

//模拟倒计时
public class SleepTest02 {

    public static void main(String[] args) {
        try {
            tenDown();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }


    public static void tenDown() throws InterruptedException {
        int num = 10;
        while (true) {
            Thread.sleep(1000);
            System.out.println(num--);
            if (num <= 0) break;
        }
    }
}

打印当前系统时间

package com.state;

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

//打印当前系统时间
//每个对象都有一把锁，sleep不会释放锁
public class SleepTest03 {
    public static void main(String[] args) {
        Date startTime = new Date(System.currentTimeMillis());//获取当前系统时间

        while (true) {
            try {
                Thread.sleep(1000);
                System.out.println(new SimpleDateFormat("HH:mm:ss").format(startTime));
                startTime = new Date(System.currentTimeMillis());//变更当前时间
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }


    }


    public static void tenDown() throws InterruptedException {
        int num = 10;
        while (true) {
            Thread.sleep(1000);
            System.out.println(num--);
            if (num <= 0) break;
        }
    }
}

线程礼让

代码：

package com.state;

//测试礼让线程
//礼让不一定能成功，需要看CPU的调度
public class YieldTest01 {

    public static void main(String[] args) {
        MyYield myYield = new MyYield();

        new Thread(myYield,"a").start();
        new Thread(myYield,"b").start();
    }
    
}

class MyYield implements Runnable {
    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName() + "线程开始执行");
        Thread.yield();
        System.out.println(Thread.currentThread().getName() + "线程停止执行");
    }
}

礼让成功：

线程强制执行_join

join合并线程，待此线程执行完成后，再执行其他线程，其他线程阻塞

package com.state;


//测试join方法
public class JoinTest01 implements Runnable {
    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            System.out.println("插队线程来了：" + i);
        }
    }

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


        //启动我们的线程
        JoinTest01 joinTest01 = new JoinTest01();
        Thread thread = new Thread(joinTest01);
        thread.start();


        //主线程
        for (int i = 0; i < 500; i++) {
            if (i == 200) {
                thread.join();//插队
            }
            System.out.println("main:" + i);
        }

    }
}

线程状态

package com.state;

//观察测试线程的状态
public class StateTest02 {
    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(() -> {
            for (int i = 0; i < 5; i++) {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            System.out.println(".....");
        });


        //观察状态
        Thread.State state = thread.getState();
        System.out.println(state);

        //观察启动后
        thread.start();//启动线程
        state=thread.getState();
        System.out.println(state);//Run

        while (state!= Thread.State.TERMINATED){
            Thread.sleep(100);
            state=thread.getState();
            System.out.println(state);
        }

    }
}

线程一旦死亡，就不能再次启动

线程的优先级

Java提供一个线程调度器来监控程序中启动后进入就绪状态的所有线程，线程调度器按照优先级决定应该调度哪个线程
线程的优先级用数字、表示，范围从1~10
- Thread.MIN_PRIORITY = 1;
- Thread.MAX_PRIORITY = 10;
- Thread.NORM_PRIORITY = 5;
使用以下方式改变或获取优先级
- getPriority().setPriority(int xxx)

package com.state;

public class PriorityTest01 {

    public static void main(String[] args) {

        // 主线程默认优先级
        System.out.println(Thread.currentThread().getName() + "-->" + Thread.currentThread().getPriority());

        MyPriority myPriority = new MyPriority();

        Thread t1 = new Thread(myPriority);
        Thread t2 = new Thread(myPriority);
        Thread t3 = new Thread(myPriority);
        Thread t4 = new Thread(myPriority);
        Thread t5 = new Thread(myPriority);
        Thread t6 = new Thread(myPriority);

        //先设置优先级，在再启动
        t1.start();

        t2.setPriority(1);
        t2.start();

        t3.setPriority(3);
        t3.start();

        t4.setPriority(Thread.MAX_PRIORITY);//10
        t4.start();

        t5.setPriority(6);
        t5.start();

        t6.setPriority(8);
        t6.start();

    }

}

class MyPriority implements Runnable {
    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName() + "-->" + Thread.currentThread().getPriority());
    }
}

优先级低并不意味着获得调度的概率低，并不是优先级低就不会被调用了，具体需要看CPU调度

守护线程（daemon）

线程分为守护线程和用户线程
虚拟机必须确保用户线程执行完毕
虚拟机不用等待守护线程执行完毕
守护线程如：后台记录操作日志，监控内存，垃圾回收等待

package com.state;

public class DaemonTest01 {

    public static void main(String[] args) {

        god god = new god();
        You you = new You();

        Thread thread = new Thread(god);
        thread.setDaemon(true);//默认值false表示是用户线程，正常的线程都是用户线程

        thread.start();//上帝守护线程启动

        new Thread(you).start();//用户线程启动--你

    }

}


//上帝
class god implements Runnable {
    @Override
    public void run() {
        while (true) {
            System.out.println("上帝保佑着你！！");
        }
    }
}


//你
class You implements Runnable {

    @Override
    public void run() {
        for (int i = 0; i < 36500; i++) {
            System.out.println("你开心的活着");
        }
        System.out.println("====goodbye, the world!!!====");
    }
}

线程同步机制

并发：多个线程访问同一个对象

线程不安全

1、

package com.syn;

//不安全的买票
public class UnsafeBuyTicket {

    public static void main(String[] args) {
        BuyTicket buyTicket = new BuyTicket();

        new Thread(buyTicket, "小明").start();
        new Thread(buyTicket, "小红").start();
        new Thread(buyTicket, "黄牛").start();

    }

}


class BuyTicket implements Runnable {

    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) {
                e.printStackTrace();
            }
        }
    }

    private void buy() throws InterruptedException {
        //判断是否有票
        if (ticketNums <= 0) {
            return;
        }
        //模拟延时
        Thread.sleep(100);
        //买票
        System.out.println(Thread.currentThread().getName() + "拿到了" + ticketNums--);
    }
}

运行结果：

2、

package com.syn;

//不安全的取钱
public class UnsafeBank {

    public static void main(String[] args) {
        Account account = new Account(100, "结婚基金");

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

        you.start();
        girl.start();
    }

}


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

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

}


//银行
class Drawing extends Thread {

    //账户
    Account account;

    //取钱金额
    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() + "账户余额不足，无法取现！");
            return；
        }

        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        //卡上余额更新
        account.money = account.money - drawingMoney;

        //手上现金更新
        nowMoney = nowMoney + drawingMoney;

        //输出
        System.out.println("卡上余额为：" + account.money);
        //Thread.currentThread().getName() = this.getName()
        System.out.println(this.getName() + "手上的现金为：" + nowMoney);
    }
}

运行结果：

3、

package com.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());
    }
}

运行结果：

同步方法

synchronized同步方法

1、安全买票

package com.syn;

//不安全的买票
public class UnsafeBuyTicket {

    public static void main(String[] args) {
        BuyTicket buyTicket = new BuyTicket();

        new Thread(buyTicket, "小明").start();
        new Thread(buyTicket, "小红").start();
        new Thread(buyTicket, "黄牛").start();

    }

}


class BuyTicket implements Runnable {

    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) {
                e.printStackTrace();
            }
        }
    }

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

运行结果：

2、安全取钱

package com.syn;

//不安全的取钱
public class UnsafeBank {

    public static void main(String[] args) {
        Account account = new Account(100, "结婚基金");

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

        you.start();
        girl.start();
    }

}


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

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

}


//银行
class Drawing extends Thread {

    //账户
    Account account;

    //取钱金额
    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本身
    @Override
    public void run() {

        //锁的对象是变化的量,需要增删改的对象
        synchronized (account) {
            //判断有没有钱
            if (account.money - drawingMoney < 0) {
                System.out.println(Thread.currentThread().getName() + "账户余额不足，无法取现！");
                return;
            }

            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            //卡上余额更新
            account.money = account.money - drawingMoney;

            //手上现金更新
            nowMoney = nowMoney + drawingMoney;

            //输出
            //Thread.currentThread().getName() = this.getName()
            System.out.println(this.getName() + "手上取得的现金为：" + nowMoney);
            System.out.println("卡上余额为：" + account.money);
        }
    }


}

运行结果：

3、锁集合的线程

package com.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());
    }
}

运行结果

CopyOnWriteArrayList

一种线程安全的集合

package com.syn;


import java.util.concurrent.CopyOnWriteArrayList;

//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>();
        for (int i = 0; i < 10000; i++) {
            new Thread(
                    () -> {
                        list.add(Thread.currentThread().getName());
                    }
            ).start();
        }
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list.size());
    }
}

死锁

两个或者多个线程都在等待对方释放资源，都停止执行的情形；

某一个同步块同时拥有“两个以上对象的锁”时，就可能会发生死锁的问题。

死锁代码：

package com.thread;

public class DeadLock {
    public static void main(String[] args) {
        Makeup girl1 = new Makeup(0, "灰姑凉");
        Makeup girl2 = new Makeup(1, "白雪公主");

        girl1.start();
        girl2.start();

    }
}

//口红
class LipStick {

}


//镜子
class Mirror {

}


class Makeup extends Thread {

    //需要的资源自由一份，用static来修饰
    static LipStick lipStick = new LipStick();
    static Mirror mirror = new Mirror();

    int choice;//选择
    String name;//化妆的人

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


    @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) {//获得口红的锁
                System.out.println(this.name + "获得口红的锁");
                Thread.sleep(1000);

                synchronized (mirror) {//一秒钟后获得镜子的锁
                    System.out.println(this.name + "获得镜子的锁");
                }

            }
        } else {
            synchronized (mirror) {//获得镜子的锁
                System.out.println(this.name + "获得镜子的锁");
                Thread.sleep(2000);

                synchronized (lipStick) {//一秒钟后获得口红的锁
                    System.out.println(this.name + "获得口红的锁");
                }

            }

        }
    }
}

可以看见两个对象的锁都卡住了

优化代码:

package com.thread;

public class DeadLock {
    public static void main(String[] args) {
        Makeup girl1 = new Makeup(0, "灰姑凉");
        Makeup girl2 = new Makeup(1, "白雪公主");

        girl1.start();
        girl2.start();

    }
}

//口红
class LipStick {

}


//镜子
class Mirror {

}


class Makeup extends Thread {

    //需要的资源自由一份，用static来修饰
    static LipStick lipStick = new LipStick();
    static Mirror mirror = new Mirror();

    int choice;//选择
    String name;//化妆的人

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


    @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) {//获得口红的锁
                System.out.println(this.name + "获得口红的锁");
                Thread.sleep(1000);
            }
            synchronized (mirror) {//一秒钟后获得镜子的锁
                System.out.println(this.name + "获得镜子的锁");
            }
        } else {
            synchronized (mirror) {//获得镜子的锁
                System.out.println(this.name + "获得镜子的锁");
                Thread.sleep(2000);
            }
            synchronized (lipStick) {//一秒钟后获得口红的锁
                System.out.println(this.name + "获得口红的锁");
            }

        }
    }
}

将包含的锁拿出来，用完了后释放

Lock锁

ReentrantLock锁是可重读锁
Lock是显式锁（手动开启和关闭锁），synchronized是隐式锁，出了作用域自动释放
Lock只有代码块锁，synchronized有代码块锁和方法锁
使用Lock锁，JVM将花费较少的时间来调度线程，性能更好。并且具有更好的扩展性
优先使用顺序：
- Lock > 同步代码块 > 同步方法

实现代码：

package com.syn;

import sun.util.resources.cldr.chr.TimeZoneNames_chr;

import java.security.PrivateKey;
import java.util.concurrent.locks.ReentrantLock;

public class LockTest01 {
    public static void main(String[] args) {
        LockTest02 lockTest02 = new LockTest02();

        new Thread(lockTest02).start();
        new Thread(lockTest02).start();
        new Thread(lockTest02).start();
    }

}


class LockTest02 implements Runnable {
    int ticketNums = 10;

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

    @Override
    public void run() {
        while (true) {
            try {//加锁
                lock.lock();
                if (ticketNums > 0) {
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(ticketNums--);
                } else {
                    break;
                }
            } finally {
                //解锁
                lock.unlock();
            }
        }
    }
}

运行结果：

posted @ 2022-08-03 19:09 每年桃花开的时候阅读(42) 评论(0) 收藏举报

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xiaojian1995

线程的操作

线程操作

线程停止

线程休眠

模拟网络延时

模拟倒计时

打印当前系统时间

线程礼让

线程强制执行_join

线程状态

线程的优先级

守护线程（daemon）

线程同步机制

线程不安全

同步方法

CopyOnWriteArrayList

死锁

Lock锁

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