【笔记】高并发编程第二阶段18讲、多线程读写锁分离设计模式讲解

1.ReadWriteLock

package com.wangwenjun.concurrent.chapter6;

/***************************************
 * @author:Alex Wang
 * @Date:2017/3/19 QQ:532500648
 * QQ交流群:286081824
 ***************************************/
public class ReadWriteLock {
    private int readingReaders = 0;
    private int waitingReaders = 0;
    private int writingWriters = 0;
    private int waitingWriters = 0;
    private boolean preferWriter = true;

    public ReadWriteLock() {
        this(true);
    }

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

    public synchronized void readLock() throws InterruptedException {
        this.waitingReaders++;
        try {
            while (writingWriters > 0 || (preferWriter && waitingWriters > 0)) {
                this.wait();
            }
            this.readingReaders++;
        } finally {
            this.waitingReaders--;
        }
    }

    public synchronized void readUnlock() {
        this.readingReaders--;
        this.notifyAll();
    }

    public synchronized void writeLock() throws InterruptedException {
        this.waitingWriters++;
        try {
            while (readingReaders > 0 || writingWriters > 0) {
                this.wait();
            }
            this.writingWriters++;
        } finally {
            this.waitingWriters--;
        }
    }

    public synchronized void writeUnlock() {
        this.writingWriters--;
        this.notifyAll();
    }
}

2.SharedData

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 < size; 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) {
        }
    }
}

3.ReaderWorker

public class ReaderWorker extends Thread {

    private final SharedData data;

    public ReaderWorker(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();
        }
    }
}

4.WriterWorker

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(1000));
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

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

5.ReadWritLockClient

public class ReadWritLockClient {
    public static void main(String[] args) {
        final SharedData sharedData = new SharedData(10);
        new ReaderWorker(sharedData).start();
        new ReaderWorker(sharedData).start();
        new ReaderWorker(sharedData).start();
        new ReaderWorker(sharedData).start();
        new ReaderWorker(sharedData).start();
        new WriterWorker(sharedData, "qwertyuiopasdfg").start();
        new WriterWorker(sharedData, "QWERTYUIOPASDFG").start();
    }
}

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