JavaSE进阶知识学习----多线程JUC高级知识-4-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_27922023/article/details/79168511

本文介绍了Java中读写锁ReadWriteLock的概念及其应用场景，通过示例代码展示了读写锁如何实现读写分离，提高并发性能。同时，文章还探讨了线程锁的八种常见情况，并解释了非静态与静态同步方法锁的区别。

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9.ReadWriteLock读写锁

说明：写写/读写需要‘互斥’，读读不需要‘互斥’。不能一存在线程问题就加锁，读就不需要锁，所以才有了读写分离的读写锁ReadWriteLock。
是一个接口，位于java.util.concurrent.locks包下。有两个方法

Lock readLock() 返回用于读取操作的锁。

Lock writeLock() 返回用于写入操作的锁。

实例如下：

public class TestReadWriteLock {
    public static void main(String[] args) {
        final ReadWriteLockDemo rw = new ReadWriteLockDemo();
        new Thread(new Runnable() {

            @Override
            public void run() {
                rw.set((int)(Math.random()*10));

            }
        },"写线程").start();
        for(int i = 0; i< 5; i++){
            new Thread(new Runnable() {

                @Override
                public void run() {
                    rw.get();
                }
            },"读操作").start();
        }
    }

}
class ReadWriteLockDemo{
    private int number = 0;
    private ReadWriteLock lock = new ReentrantReadWriteLock();
    //读操作
    public void get(){
        lock.readLock().lock();//上锁
        try{
            System.out.println(Thread.currentThread().getName()+":"+number);
        }finally{
            lock.readLock().unlock();//释放锁
        }

    }
    //写操作
    public void set(int number){
        lock.writeLock().lock();
        try{
            System.out.println(Thread.currentThread().getName());
            this.number = number;
        }finally{
            lock.writeLock().unlock();
        }

    }
}

10.线程八锁

如下实例：

1.两个普通同步方法，两个线程，标准打印，结果：one two

public class TestThread8Monitor {
    public static void main(String[] args) {
        final Number number = new Number();

        new Thread(new Runnable() {
            @Override
            public void run() {
                number.getOne();
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                number.getTwo();
            }
        }).start();
    }
}
class Number{
    public synchronized void getOne(){
        System.out.println("one");
    }
    public synchronized void getTwo(){
        System.out.println("Two");
    }
}

2.新增Thread.sleep()给getOne(),结果：one two

public class TestThread8Monitor {
    public static void main(String[] args) {
        final Number number = new Number();

        new Thread(new Runnable() {
            @Override
            public void run() {
                number.getOne();
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                number.getTwo();
            }
        }).start();
    }
}
class Number{
    public synchronized void getOne(){
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("one");
    }
    public synchronized void getTwo(){
        System.out.println("Two");
    }
}

3.新增普通方法getThree(),结果：three one two

public class TestThread8Monitor {
    public static void main(String[] args) {
        final Number number = new Number();

        new Thread(new Runnable() {
            @Override
            public void run() {
                number.getOne();
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                number.getTwo();
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                number.getThree();
            }
        }).start();
    }
}
class Number{
    public synchronized void getOne(){
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("one");
    }
    public synchronized void getTwo(){
        System.out.println("Two");
    }
    public void getThree(){
        System.out.println("Three");
    }
}

4.两个普通同步方法，两个对象，结果：two one

public class TestThread8Monitor {
    public static void main(String[] args) {
        final Number number1 = new Number();
        final Number number2 = new Number();

        new Thread(new Runnable() {
            @Override
            public void run() {
                number1.getOne();
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                number2.getTwo();
            }
        }).start();

    }
}
class Number{
    public synchronized void getOne(){
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("one");
    }
    public synchronized void getTwo(){
        System.out.println("Two");
    }
}

5.修改getOne()为静态同步方法，结果：two one

public class TestThread8Monitor {
    public static void main(String[] args) {
        final Number number1 = new Number();
        final Number number2 = new Number();

        new Thread(new Runnable() {
            @Override
            public void run() {
                number1.getOne();
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                number2.getTwo();
            }
        }).start();

    }
}
class Number{
    public static synchronized void getOne(){
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("one");
    }
    public synchronized void getTwo(){
        System.out.println("Two");
    }
}

6.修改两个方法均为静态同步方法，一个对象，结果：one two

public class TestThread8Monitor {
    public static void main(String[] args) {
        final Number number1 = new Number();

        new Thread(new Runnable() {
            @Override
            public void run() {
                number1.getOne();
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                number1.getTwo();
            }
        }).start();

    }
}
class Number{
    public static synchronized void getOne(){
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("one");
    }
    public static synchronized void getTwo(){
        System.out.println("Two");
    }
}

7.一个静态同步方法，一个非静态同步方法，两个对象，结果：two one

public class TestThread8Monitor {
    public static void main(String[] args) {
        final Number number1 = new Number();
        final Number number2 = new Number();

        new Thread(new Runnable() {
            @Override
            public void run() {
                number1.getOne();
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                number2.getTwo();
            }
        }).start();

    }
}
class Number{
    public static synchronized void getOne(){
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("one");
    }
    public  synchronized void getTwo(){
        System.out.println("Two");
    }
}

8.两个静态同步方法，两个对象，结果：one two

public class TestThread8Monitor {
    public static void main(String[] args) {
        final Number number1 = new Number();
        final Number number2 = new Number();

        new Thread(new Runnable() {
            @Override
            public void run() {
                number1.getOne();
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                number2.getTwo();
            }
        }).start();

    }
}
class Number{
    public static synchronized void getOne(){
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("one");
    }
    public static synchronized void getTwo(){
        System.out.println("Two");
    }
}

以上就是线程的八种常见的情况，线程八锁的关键在于：
1. 非静态方法的锁默认为this，静态方法的锁为对应的class实例（这里是NUmber.class）
2. 某一个时刻内，只能有一个线程持有锁，无论有几个方法