ReadWriteLock(二)

readLock()用于获得读锁，readUnlock()释放读锁，writeLock()和writeUnlock()一样。由于锁用完必须释放，因此，必须保证lock和unlock匹配。我们修改DataHandler，加入ReadWriteLock：

package com.crackj2ee.thread;
public class DataHandler {
    // store data:
    private char[] buffer = "AAAAAAAAAA".toCharArray();
    // lock:
    private ReadWriteLock lock = new ReadWriteLock();

    public char[] read(String name) throws InterruptedException {
        System.out.println(name + " waiting for read...");
        lock.readLock();
        try {
            char[] data = doRead();
            System.out.println(name + " reads data: " + new String(data));
            return data;
        }
        finally {
            lock.readUnlock();
        }
    }

    public void write(String name, char[] data) throws InterruptedException {
        System.out.println(name + " waiting for write...");
        lock.writeLock();
        try {
            System.out.println(name + " wrote data: " + new String(data));
            doWrite(data);
        }
        finally {
            lock.writeUnlock();
        }
    }

    private char[] doRead() {
        char[] ret = new char[buffer.length];
        for(int i=0; i<buffer.length; i++) {
            ret[i] = buffer[i];
            sleep(3);
        }
        return ret;
    }
    private void doWrite(char[] data) {
        if(data!=null) {
            buffer = new char[data.length];
            for(int i=0; i<buffer.length; i++) {
                buffer[i] = data[i];
                sleep(10);
            }
        }
    }
    private void sleep(int ms) {
        try {
            Thread.sleep(ms);
        }
        catch(InterruptedException ie) {}
    }
}

public方法read()和write()完全封装了底层的ReadWriteLock，因此，多线程可以安全地调用这两个方法：

// ReadingThread不断读取数据：
package com.crackj2ee.thread;
public class ReadingThread extends Thread {
    private DataHandler handler;
    public ReadingThread(DataHandler handler) {
        this.handler = handler;
    }
    public void run() {
        for(;;) {
            try {
                char[] data = handler.read(getName());
                Thread.sleep((long)(Math.random()*1000+100));
            }
            catch(InterruptedException ie) {
                break;
            }
        }
    }
}

// WritingThread不断写入数据，每次写入的都是10个相同的字符：
package com.crackj2ee.thread;
public class WritingThread extends Thread {
    private DataHandler handler;
    public WritingThread(DataHandler handler) {
        this.handler = handler;
    }
    public void run() {
        char[] data = new char[10];
        for(;;) {
            try {
                fill(data);
                handler.write(getName(), data);
                Thread.sleep((long)(Math.random()*1000+100));
            }
            catch(InterruptedException ie) {
                break;
            }
        }
    }
    // 产生一个A-Z随机字符，填入char[10]:
    private void fill(char[] data) {
        char c = (char)(Math.random()*26+'A');
        for(int i=0; i<data.length; i++)
            data[i] = c;
    }
}