多线程设计模式-多线程读写锁分离模式

多线程读写锁分离模式

定义共享数据缓存区buffer，有线程往缓存区写数据，有线程从缓存区读取数据,读写锁分离

读写锁：为了更高效的读写数据，将锁分为两种，读数据是读锁，可以并行化多线程执行，写数据是写锁，只能串行化。

读写锁ReadWriteLock

/**
 * @ClassName:ReadWriteLock
 * @Author:linianest
 * @CreateTime:2020/3/24 11:06
 * @version:1.0
 * @Description TODO: 读写锁
 */

/**
 * 可以并行多线读，如果是写线程操作，写的线程每次只允许一个
 */
public class ReadWriteLock {
    // 正在读
    private int readingReaders = 0;
    // 等待读
    private int waitingReaders = 0;
    // 正在写
    private int writingwriters = 0;
    // 等待写
    private int waitingwriters = 0;

    private boolean preferWriter = true;

    public ReadWriteLock() {
        this(true);
    }

    public ReadWriteLock(boolean preferWriter) {
        this.preferWriter = preferWriter;
    }

    /**
     * 读锁：如果有线程正在写，那么就wait
     *
     * @throws InterruptedException
     */
    public synchronized void readLock() throws InterruptedException {
        // 有线程在准备读
        this.waitingReaders++;
        try {
            // 有线程正在写
            while (writingwriters > 0 || (preferWriter && waitingwriters > 0)) {
                this.wait();
            }
            // 现在正在读
            this.readingReaders++;
        } finally {
            // 线程读完了
            this.waitingReaders--;
        }
    }

    /**
     * 释放读锁
     */
    public synchronized void readUnlock() {
        this.readingReaders--;
        this.notifyAll();
    }

    /**
     * 写锁：如果有线程在读或者在写，那么就wait
     *
     * @throws InterruptedException
     */
    public synchronized void writeLock() throws InterruptedException {
        this.waitingwriters++;
        try {
            while (readingReaders > 0 || writingwriters > 0) {
                this.wait();
            }
            this.writingwriters++;
        } finally {
            this.waitingwriters--;
        }
    }

    /**
     * 释放写锁
     */
    public synchronized void writeUnlock() {
        this.writingwriters--;
        this.notifyAll();
    }

}

读写缓冲区:共享资源

package com.ln.concurrent.chapter6;
/**
 * @ProjectName: java-concurrency
 * @Package: com.ln.concurrent.chapter6
 * @version: 1.0
 */

/**
 * @ClassName:SharedData
 * @Author:linianest
 * @CreateTime:2020/3/24 11:35
 * @version:1.0
 * @Description TODO: 定义共享数据缓存区buffer，有线程往缓存区写数据，有线程从缓存区读取数据
 */
public class SharedData {
    private final char[] buffer;
    private final ReadWriteLock lock = new ReadWriteLock();

    public SharedData(int size) {
        this.buffer = new char[size];
        for (int i = 0; i < buffer.length; i++) {
            this.buffer[i] = '*';
        }
    }

    public char[] read() throws InterruptedException {
        try {
            lock.readLock();
            return this.doRead();
        } finally {
            lock.readUnlock();
        }
    }

    public void write(char c) throws InterruptedException {
        try {
            lock.writeLock();
            this.doWrite(c);
        } finally {
            lock.writeUnlock();
        }
    }

    private void doWrite(char c) {
        for (int i = 0; i < buffer.length; i++) {
            buffer[i] = c;
            slowly(10);
        }
    }

    private char[] doRead() {
        char[] newBuf = new char[buffer.length];
        for (int i = 0; i < buffer.length; i++) {
            newBuf[i] = buffer[i];
        }
        slowly(50);
        return newBuf;
    }

    private void slowly(int ms) {
        try {
            Thread.sleep(ms);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

多线程写数据

/**
 * @ClassName:WriterWorker
 * @Author:linianest
 * @CreateTime:2020/3/24 16:29
 * @version:1.0
 * @Description TODO: 多线程读数据
 */
public class WriterWorker extends Thread {

    private static final Random random = new Random(System.currentTimeMillis());

    private final SharedData data;
    private final String filler;
    private int index = 0;

    public WriterWorker(SharedData data, String filler) {
        this.data = data;
        this.filler = filler;
    }

    @Override
    public void run() {
        try {
            while (true){
                char c = nextChar();
                data.write(c);
                Thread.sleep(random.nextInt(1_000));
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private char nextChar() {
        char c = filler.charAt(index);
        index++;
        if (index >= filler.length())
            index = 0;
        return c;
    }
}

多线程写数据

package com.ln.concurrent.chapter6;
/**
 * @ProjectName: java-concurrency
 * @Package: com.ln.concurrent.chapter6
 * @version: 1.0
 */

import java.util.Random;

/**
 * @ClassName:ReadWorker
 * @Author:linianest
 * @CreateTime:2020/3/24 17:18
 * @version:1.0
 * @Description TODO: 多线程写数据
 */
public class ReadWorker extends Thread {


    private final SharedData data;

    public ReadWorker(SharedData data) {
        this.data = data;
    }

    @Override
    public void run() {
        try {
            while (true) {
                char[] readBuf = data.read();
                System.out.println(Thread.currentThread().getName() + " reads " + String.valueOf(readBuf));
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

多线程读写客户端

package com.ln.concurrent.chapter6;
/**
 * @ProjectName: java-concurrency
 * @Package: com.ln.concurrent.chapter6
 * @version: 1.0
 * @ClassName:ReadWritLockClient
 * @Author:linianest
 * @CreateTime:2020/3/24 17:24
 * @version:1.0
 * @Description TODO: 读写锁
 */

/**
 *@ClassName:ReadWritLockClient
 *@Author:linianest
 *@CreateTime:2020/3/24 17:24
 *@version:1.0
 *@Description TODO: 读写锁设计模式
 */

/**
 * ReadWriteLock design pattern
 * Reader-Writer design pattern
 */
public class ReadWritLockClient {
    public static void main(String[] args) {
        final SharedData sharedData = new SharedData(10);
        new ReadWorker(sharedData).start();
        new ReadWorker(sharedData).start();
        new ReadWorker(sharedData).start();
        new ReadWorker(sharedData).start();
        new ReadWorker(sharedData).start();
        new WriterWorker(sharedData, "sdfaSDFWEFASewd").start();
        new WriterWorker(sharedData, "werewkjSDFSDFWflksd").start();

    }
}

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