java读写锁代码实现

读写锁适用读多写少的场景，读写锁需求必须知足条件：

1.一个线程对共享数据read时，同时容许另一个线程能够并行read操做

2.一个线程对共享数据read时，不容许同时另一个线程进行write操做

3.一个线程对共享数据write时，不容许同时另一个线程进行write操做

 

第一步：

建立一个读写锁，优先写操做进行，为了在读多写少的场景下，能更多执行写操做。

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 {
        try {
            this.waitingReaders++;
            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 {
        try {
            this.waitingWriters++;
            while(writingWriters > 0 || readingReaders > 0) {
                this.wait();
            }
            this.writingWriters++;
        }finally {
            this.waitingWriters--;
        }
    }

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

 

第二步：

建立一个共享数据对象，用于读写操做

public class ShareData {
    private final char[] buffer;

    private final ReadWriteLock lock = new ReadWriteLock();

    public ShareData(int size) {
        this.buffer = new char[size];
        for (int i = 0; i < buffer.length; i++) {
            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(500);
        return newBuf;
    }

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

 

第三步：

建立一个写线程，对共享对象进行写操做

public class WriterWorker extends Thread{
    private static final Random random = new Random(System.currentTimeMillis());

    private final ShareData data;

    private final String filler;

    private int index;

    public WriterWorker(ShareData 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();
        }
    }

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

 

第四步：

建立一个读线程，对共享对象进行读操做，并输出读数据内容

ublic class ReaderWorker extends Thread{
    private final ShareData data;

    public ReaderWorker(ShareData data) {
        this.data = data;
    }

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

 

第五步：

建立一个读多写少的测试类

public class ReadWriteLockClient {
    public static void main(String[] args) {
        final ShareData shareData = new ShareData(10);
        new ReaderWorker(shareData).start();
        new ReaderWorker(shareData).start();
        new ReaderWorker(shareData).start();
        new ReaderWorker(shareData).start();
        new ReaderWorker(shareData).start();

        new WriterWorker(shareData, "ddjifjsidjfisd").start();
        new WriterWorker(shareData, "DDJIFJSIDJFISD").start();
    }
}

 

第六步：

查看打印结果

Thread-0 reads **********
Thread-1 reads **********
Thread-2 reads **********
Thread-4 reads **********
Thread-3 reads **********
Thread-0 reads DDDDDDDDDD
Thread-1 reads DDDDDDDDDD
Thread-2 reads DDDDDDDDDD
Thread-4 reads DDDDDDDDDD
Thread-3 reads DDDDDDDDDD
Thread-3 reads dddddddddd
Thread-1 reads dddddddddd
Thread-0 reads dddddddddd
Thread-2 reads dddddddddd
Thread-4 reads dddddddddd
Thread-4 reads JJJJJJJJJJ
Thread-3 reads JJJJJJJJJJ
Thread-0 reads JJJJJJJJJJ
Thread-1 reads JJJJJJJJJJ
Thread-2 reads JJJJJJJJJJ
Thread-2 reads IIIIIIIIII
Thread-3 reads IIIIIIIIII
Thread-1 reads IIIIIIIIII
Thread-0 reads IIIIIIIIII
Thread-4 reads IIIIIIIIII