Python工程师Java之路（e）多线程、单例设计模式、生产者消费者模式

于 2021-03-10 21:33:07 发布
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本文链接：https://blog.youkuaiyun.com/Yellow_python/article/details/114624305
本文深入探讨Java多线程的基础知识，包括线程创建、线程安全、生命周期、线程间通信等内容，并通过实例讲解如何避免死锁及实现高效的线程通信。

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文章目录

  • 并行（parallel）：多个事件在同一时刻发生。指在同一时刻，有多条指令在多个处理器上同时执行。
  • 并发（concurrency）：多个事件在同一个时间段内发生。指在同一个时刻只能有一条指令执行，但多个进程的指令被快速轮换执行，使得在宏观上具有多个进程同时执行的效果。

并发示例：
晚上你和妹子网聊，妹子一直秒回，你就以为妹子只在和你聊天。其实妹子在和很多人聊天，但是切换很快，你感觉不出来。

1、Java多线程入门代码

1.1、Thread

  1. 继承Thread类
  2. 重写public void run()，写入业务逻辑
  3. 创建对象，对象.start()来启动线程
class MySleep {
    public static void sleep() {
        try {
            Thread.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

class MyThread extends Thread {
    @Override
    public void run() {
        for (int i = 0; i < 9; i++) {
            System.out.print(i);
            MySleep.sleep();
        }
    }
}

public class Hello {
    public static void main(String[] args) {
        (new MyThread()).start();
        for (int i = 0; i < 9; i++) {
            System.out.print(i);
            MySleep.sleep();
        }
    }
}

打印结果

001122334455667788

1.2、Runnable

  1. 实现Runnable接口
  2. 实现public void run()，写入业务逻辑
  3. 借助Thread对象来start
class MySleep {
    static void sleep() {
        try {
            Thread.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

class MyThread implements Runnable {
    @Override
    public void run() {
        for (int i = 0; i < 9; i++) {
            System.out.print(i);
            MySleep.sleep();
        }
    }
}

public class Hello {
    public static void main(String[] args) {
        Thread t = new Thread(new MyThread());
        t.start();
        for (int i = 0; i < 9; i++) {
            System.out.print(i);
            MySleep.sleep();
        }
    }
}

打印结果

001122334455667788

2、源码截取

2.1、Runnable

  • 只包含一个抽象方法的接口
public interface Runnable {
    public abstract void run();
}

2.2、Thread

  • 实现Runnable接口
  • 可使用静态方法sleep
  • 构造时可传入Runnable实现类的对象
  • 实现了Runnable的抽象方法：调用Runnable实现类对象的run方法
  • start方法开启一个新线程来执行run方法
public class Thread implements Runnable {
    // 静态方法：睡眠（单位：毫秒）
    public static native void sleep(long millis) throws InterruptedException;

    // 其中1个构造器，可传入Runnable实现类的对象
    private Runnable target;
    public Thread(Runnable target) {
        this.target = target;
    }

    // 重写Runnable的run方法
    @Override
    public void run() {
        // 执行Runnable实现类对象的run方法
        if (target != null) {
            target.run();
        }
    }

    // 使线程开始执行
    public synchronized void start() {
        // 两个线程并发运行：
        // 当前线程从start方法的调用返回
        // 另一个线程执行其run方法
    }
}

3、Thread常用API

Thread t = new Thread();
// toString
System.out.println(t); // Thread[Thread-0,5,main]
// 线程的优先级
System.out.println(t.getPriority()); // 5
// 线程的名字
System.out.println(t.getName()); // Thread-0
// 线程组
System.out.println(t.getThreadGroup()); // java.lang.ThreadGroup[name=main,maxpri=10]
// 线程的标识符
System.out.println(t.getId()); // 12

3.1、sleep

自写sleep，复制用

class Sleep {
    public static void sleep(long millisecond) {
        try {
            Thread.sleep(millisecond);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

随机睡眠

import java.util.Random;

class Sleep {
    static void sleep(long millisecond) {
        try {
            Thread.sleep(millisecond);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    static void sleep() {
        sleep(10);
    }

    static void sleepRandomly(int bound) {
        Random random = new Random();
        try {
            Thread.sleep(random.nextInt(bound));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    static void sleepRandomly() {
        sleepRandomly(100);
    }
}

3.2、join

  • 设置最大等待时间，等待当前线程，直至线程死亡或者等待时间结束
  • 等待时间设为0则永久等待
class Thread1 extends Thread {
    @Override
    public void run() {
        for (int i = 0; i < 10; i++) {
            try {
                sleep(100L);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(i);
        }
    }
}

public class Hello {
    public static void main(String[] args) throws InterruptedException {
        Thread1 t = new Thread1();
        t.start();
        t.join(500L);
        //t.join(99999L);
        for (int i = 0; i < 10; i++) {
            Thread.sleep(100);
            System.out.println("----" + i);
        }
    }
}

4、线程安全

线程锁：使用synchronized来锁定某个公共对象

class Cook extends Thread {
    private static int apples = 10;  // 苹果总数
    private static final Object lock = new Object(); // 锁

    private void box(long millis) {
        if (millis > 0) {
            try {
                //System.out.println("准备礼盒，需要一定时间");
                sleep(millis);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    @Override
    public void run() {
        while (true) {
            box(1000L);
            //box(0L);
            synchronized (lock) {
                if (apples > 0) {
                    System.out.print(getName() + "出售1个盒装苹果；");
                    System.out.println("剩余苹果数：" + --apples);
                } else {
                    break;
                }
            }
        }
    }
}

public class Hello {
    public static void main(String[] args) {
        Cook c1 = new Cook();
        Cook c2 = new Cook();
        Cook c3 = new Cook();
        c1.start();
        c2.start();
        c3.start();
    }
}

class Cook implements Runnable {
    private static int apples = 10;  // 苹果总数

    private void box(long millis) {
        if (millis > 0) {
            try {
                //System.out.println("准备礼盒，需要一定时间");
                Thread.sleep(millis);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    @Override
    public void run() {
        while (true) {
            box(1000L);
            //box(0L);
            synchronized (this) {
                if (apples > 0) {
                    System.out.print("出售1个盒装苹果；");
                    System.out.println("剩余苹果数：" + --apples);
                } else {
                    break;
                }
            }
        }
    }
}

public class Hello {
    public static void main(String[] args) {
        Cook c = new Cook();
        Thread t1 = new Thread(c);
        Thread t2 = new Thread(c);
        Thread t3 = new Thread(c);
        t1.start();
        t2.start();
        t3.start();
    }
}

synchronized可以写到方法名的前面
非静态方法被锁的是this
静态方法被锁的是当前类.class

class Cook implements Runnable {
    private static int apples = 10;  // 苹果总数

    private void box(long millis) {
        if (millis > 0) {
            try {
                Thread.sleep(millis);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    @Override
    public void run() {
        while (apples > 0) {
            box(1000L);
            //box(0L);
            sell();
        }
    }

    private synchronized void sell() {
        if (apples > 0) {
            String name = Thread.currentThread().toString();
            System.out.print(name + "出售1个盒装苹果；");
            System.out.println("剩余苹果数：" + --apples);
        }
    }
}

public class Hello {
    public static void main(String[] args) {
        Cook c = new Cook();
        Thread t1 = new Thread(c);
        Thread t2 = new Thread(c);
        Thread t3 = new Thread(c);
        t1.start();
        t2.start();
        t3.start();
    }
}

5、单例设计模式

1、事先创建好一个单例对象

class Singleton {
    public static final Singleton SINGLETON = new Singleton();
    private Singleton() {}
}

2、需要时才创建单例对象

class Singleton {
    private static Singleton instance;

    private Singleton() {}

    public static Singleton getInstance() {
        if (instance == null) {
            instance = new Singleton();
        }
        return instance;
    }
}

3、多线程情况下，会有安全问题

class Sleep {
    public static void sleep(long millisecond) {
        try {
            Thread.sleep(millisecond);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

class Singleton {
    private static Singleton instance;

    private Singleton() {
    }

    public static Singleton getInstance() {
        if (instance == null) {
            Sleep.sleep(1000);
            instance = new Singleton();
        }
        return instance;
    }
}

public class Hello {
    private static Singleton s1;
    private static Singleton s2;

    public static void main(String[] args) throws InterruptedException {
        // 内部类
        Thread t1 = new Thread(() -> s1 = Singleton.getInstance());
        Thread t2 = new Thread(() -> s2 = Singleton.getInstance());
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println(s1 == s2); // false
    }
}

4、加上synchronized

class Sleep {
    public static void sleep(long millisecond) {
        try {
            Thread.sleep(millisecond);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

class Singleton {
    private static Singleton instance;

    private Singleton() {
    }

    synchronized public static Singleton getInstance() {
        Sleep.sleep(5000); // 假设需要一系列准备工作
        if (instance == null) {
            Sleep.sleep(1000); // 假设造一个实例出来要较长时间
            instance = new Singleton();
        }
        return instance;
    }
}

public class Hello {
    private static Singleton s1;
    private static Singleton s2;

    public static void main(String[] args) throws InterruptedException {
        // 内部类
        Thread t1 = new Thread(() -> s1 = Singleton.getInstance());
        Thread t2 = new Thread(() -> s2 = Singleton.getInstance());
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println(s1 == s2); // true（跑了12秒）
    }
}

5、缩小线程锁范围，提高效率

class Sleep {
    public static void sleep(long millisecond) {
        try {
            Thread.sleep(millisecond);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

class Singleton {
    private static Singleton instance;

    private Singleton() {
    }

    public static Singleton getInstance() {
        Sleep.sleep(5000); // 假设需要一系列准备工作
        if (instance == null) {
            synchronized (Singleton.class) {
                if (instance == null) {
                    Sleep.sleep(1000); // 假设造一个实例出来要较长时间
                    instance = new Singleton();
                }
            }
        }
        return instance;
    }
}

public class Hello {
    private static Singleton s1;
    private static Singleton s2;

    public static void main(String[] args) throws InterruptedException {
        // 内部类
        Thread t1 = new Thread(() -> s1 = Singleton.getInstance());
        Thread t2 = new Thread(() -> s2 = Singleton.getInstance());
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println(s1 == s2); // true（跑了6秒）
    }
}

6、使用内部类

class Singleton {
    private Singleton() {}

    private static class Inner {
        public static final Singleton INSTANCE = new Singleton();
    }

    public static Singleton getInstance() {
        return Inner.INSTANCE;
    }
}

6、死锁

至少2个锁

class Merchant implements Runnable {
    private Object goods;
    private Object money;

    Merchant(Object goods, Object money) {
        this.goods = goods;
        this.money = money;
    }

    @Override
    public void run() {
        synchronized (goods) {
            System.out.println("商家说：先给钱");
            synchronized (money) {
                System.out.println("商家发货");
            }
        }
    }
}

class Customer implements Runnable {
    private Object goods;
    private Object money;

    Customer(Object goods, Object money) {
        this.goods = goods;
        this.money = money;
    }

    @Override
    public void run() {
        synchronized (money) {
            System.out.println("顾客说：先发货");
            synchronized (goods) {
                System.out.println("顾客给钱");
            }
        }
    }
}

public class Hello {
    public static void main(String[] args) {
        Object g = new Object();
        Object m = new Object();
        Merchant s = new Merchant(g, m);
        Customer c = new Customer(g, m);
        new Thread(s).start();
        new Thread(c).start();
    }
}

7、Java线程声明周期

public enum State {
    NEW,
    RUNNABLE,
    BLOCKED,
    WAITING,
    TIMED_WAITING,
    TERMINATED;
}

java.lang.Thread.State

8、线程间通信（wait和notify）：生产者和消费者

单个生产者和单个消费者

import java.util.Random;

class Sleep {
    static void sleepRandomly() {
        Random random = new Random();
        try {
            Thread.sleep(random.nextInt(100));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

// 消息队列
class MessageQueue {
    // 容量
    private int capacity = 10;

    // 出队
    synchronized void dequeue() {
        // wait和notify要写在同步代码块中，其调用的对象是锁对象
        if (capacity <= 0) {
            System.out.println("====队列空了，等入队====");
            try {
                // 当前线程进入等待状态，等待其它线程唤醒
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println("出队，剩余量：" + --capacity);
        // 随机唤醒一个线程
        this.notify();
    }

    // 入队
    synchronized void enqueue() {
        if (capacity >= 10) {
            System.out.println("----队列满了，等出队----");
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println("入队，剩余量：" + ++capacity);
        this.notify();
    }
}

class Producer extends Thread {
    private MessageQueue mq;

    Producer(MessageQueue mq) {
        this.mq = mq;
    }

    @Override
    public void run() {
        while (true) {
            Sleep.sleepRandomly();
            mq.enqueue();
        }
    }
}

class Consumer extends Thread {
    private MessageQueue mq;

    Consumer(MessageQueue mq) {
        this.mq = mq;
    }

    @Override
    public void run() {
        while (true) {
            Sleep.sleepRandomly();
            mq.dequeue();
        }
    }
}

public class Hello {
    public static void main(String[] args) {
        MessageQueue mq = new MessageQueue();
        Producer producer = new Producer(mq);
        Consumer consumer = new Consumer(mq);
        producer.start();
        consumer.start();
    }
}

多个生产者和多个消费者：notifyAll

import java.util.Random;

class Sleep {
    static void sleep(long millisecond) {
        try {
            Thread.sleep(millisecond);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    static void sleepRandomly(int bound) {
        Random random = new Random();
        try {
            Thread.sleep(random.nextInt(bound));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    static void sleepRandomly() {
        sleepRandomly(200);
    }
}

// 消息队列
class MessageQueue {
    // 容量
    private int capacity;
    private int maxCapacity;

    MessageQueue(int capacity, int maxCapacity) {
        this.capacity = capacity;
        this.maxCapacity = maxCapacity;
    }

    // 出队
    synchronized void dequeue(String name) {
        while (capacity <= 0) {
            System.out.println("========队列空了，等生产========");
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println(name + "消费1个，剩余量：" + --capacity);
        // 唤醒其它所有线程
        this.notifyAll();
    }

    // 入队
    synchronized void enqueue(String name) {
        while (capacity >= maxCapacity) {
            System.out.println("--------队列满了，等消费--------");
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println(name + "生产1个，剩余量：" + ++capacity);
        this.notifyAll();
    }
}

class Producer extends Thread {
    private MessageQueue mq;

    Producer(MessageQueue mq) {
        System.out.println("生产者名称：" + getName());
        this.mq = mq;
    }

    @Override
    public void run() {
        while (true) {
            Sleep.sleepRandomly();
            mq.enqueue(getName());
        }
    }
}

class Consumer extends Thread {
    private MessageQueue mq;

    Consumer(MessageQueue mq) {
        System.out.println("消费者名称：" + getName());
        this.mq = mq;
    }

    @Override
    public void run() {
        while (true) {
            Sleep.sleepRandomly();
            mq.dequeue(getName());
        }
    }
}

public class Hello {
    public static void main(String[] args) {
        MessageQueue mq = new MessageQueue(2, 4);
        new Producer(mq).start();
        new Producer(mq).start();
        new Consumer(mq).start();
        new Consumer(mq).start();
    }
}
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