多线程设置模式 -- Read-Write Lock Pattern

//读写锁

public final class ReadWriteLock {
    private int readingReaders = 0; // (A)...实际正在读取的执行绪数量
    private int waitingWriters = 0; // (B)...正在等待写入的执行绪数量
    private int writingWriters = 0; // (C)...实际正在写入的执行绪数量
    private boolean preferWriter = true; // 写入优先的话，值为true

    public synchronized void readLock() throws InterruptedException {
        //当有实际写入和当优先写入时有等待写入时等待写入线程
        while (writingWriters > 0 || (preferWriter && waitingWriters > 0)) {
            wait();
        }
        readingReaders++;                       //  (A)实际正在读取的线程数量加1
    }

    public synchronized void readUnlock() {
        readingReaders--;                       //  (A)实际正在读取的线程数量减1
        preferWriter = true;
        //唤醒写线线程
        notifyAll();
    }

    public synchronized void writeLock() throws InterruptedException {
        waitingWriters++;                       // (B)正在等待写入的线程数量加1
        try {
          //当读线程大于或都写线程等待
          while (readingReaders > 0 || writingWriters > 0) {
                wait();
            }
        } finally {
          waitingWriters--;                   // (B)正在等待写入的线程数量减1
        }
        writingWriters++;                       //  (C)实际正在写入的线程数量加1
    }

    public synchronized void writeUnlock() {
        writingWriters--;                       // (C)实际正在写入的线程数量减
        preferWriter = false;
       //唤醒读写线程
       notifyAll();
    }
}

读线程

public class ReaderThread extends Thread {
    private final Data data;
    public ReaderThread(Data data) {
        this.data = data;
    }
    public void run() {
        try {
            while (true) {
                char[] readbuf = data.read();
                System.out.println(Thread.currentThread().getName() + " reads " + String.valueOf(readbuf));
            }
        } catch (InterruptedException e) {
        }
    }
}

写线程

public class WriterThread extends Thread {
    private static final Random random = new Random();
    private final Data data;
    private final String filler;
    private int index = 0;
    public WriterThread(Data data, String filler) {
        this.data = data;
        this.filler = filler;
    }
    public void run() {
        try {
            while (true) {
                char c = nextchar();
                data.write(c);
                Thread.sleep(random.nextInt(3000));
            }
        } catch (InterruptedException e) {
        }
    }
    private char nextchar() {
        char c = filler.charAt(index);
        index++;
        if (index >= filler.length()) {
            index = 0;
        }
        return c;
    }
}

数据

public class Data {
    private final char[] buffer;
    private final ReadWriteLock lock = new ReadWriteLock();
    public Data(int size) {
        this.buffer = new char[size];
        for (int i = 0; i < buffer.length; i++) {
            buffer[i] = '*';
        }
    }
    public char[] read() throws InterruptedException {
        lock.readLock();
        try {
            return doRead();
        } finally {
            lock.readUnlock();
        }
    }
    public void write(char c) throws InterruptedException {
        lock.writeLock();
        try {
            doWrite(c);
        } finally {
            lock.writeUnlock();
        }
    }
    private char[] doRead() {
        char[] newbuf = new char[buffer.length];
        for (int i = 0; i < buffer.length; i++) {
            newbuf[i] = buffer[i];
        }
        slowly();
        return newbuf;
    }
    private void doWrite(char c) {
        for (int i = 0; i < buffer.length; i++) {
            buffer[i] = c;
            slowly();
        }
    }
    private void slowly() {
        try {
            Thread.sleep(50);
        } catch (InterruptedException e) {
        }
    }
}

测试类

public class Main {
    public static void main(String[] args) {
        Data data = new Data(10);
        new ReaderThread(data).start();
        new ReaderThread(data).start();
        new ReaderThread(data).start();
        new ReaderThread(data).start();
        new ReaderThread(data).start();
        new ReaderThread(data).start();
        new WriterThread(data, "ABCDEFGHIJKLMNOPQRSTUVWXYZ").start();
        new WriterThread(data, "abcdefghijklmnopqrstuvwxyz").start();
    }
}

jdk1.5新特性读写锁

public class Data {
	private final char[] buffer;
	//private final ReadWriteLock lock = new ReadWriteLock();
	//读写锁
         private ReadWriteLock lock = new ReentrantReadWriteLock();

         //生成读锁
	private Lock readLock = lock.readLock();
         //生成写锁
	private Lock writeLock = lock.writeLock();

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

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

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

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

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

	private void slowly() {
		try {
			Thread.sleep(50);
		} catch (InterruptedException e) {
		}
	}
}