Java ReentrantReadWriteLock用法及代碼示例

// Java Program to Illustrate ReentrantReadWriteLock Class
// Importing ReentrantReadWriteLock
// fro java.util package
import java.util.concurrent.locks.ReentrantReadWriteLock;
// Class 1
// Main class
public class ReentrantReadWriteLockExample {
    private static final ReentrantReadWriteLock lock
        = new ReentrantReadWriteLock(true);
    // Initially the string contains only 1 character
    private static String message = "a";
    // Main driver method
    public static void main(String[] args)
        throws InterruptedException
    {
        // Creating threads
        Thread t1 = new Thread(new Read());
        Thread t2 = new Thread(new WriteA());
        Thread t3 = new Thread(new WriteB());
        // Starting threads with help of start() method
        t1.start();
        t2.start();
        t3.start();
        t1.join();
        t2.join();
        t3.join();
    }
    // Class 2
    // Helper class implementing Runnable interface
    static class Read implements Runnable {
        // run() method for thread
        public void run()
        {
            for (int i = 0; i <= 10; i++) {
                if (lock.isWriteLocked()) {
                    System.out.println(
                        "I'll take the lock from Write");
                }
                // operating lock()
                lock.readLock().lock();
                System.out.println(
                    "ReadThread "
                    + Thread.currentThread().getId()
                    + "Message is " + message);
                lock.readLock().unlock();
            }
        }
    }
    // Class 3
    // Helper class implementing Runnable interface
    static class WriteA implements Runnable {
        // run() method for thread
        public void run()
        {
            for (int i = 0; i <= 10; i++) {
                // Try block to check fr exceptions
                try {
                    lock.writeLock().lock();
                    message = message.concat("a");
                }
                finally {
                    lock.writeLock().unlock();
                }
            }
        }
    }
    // Class 4
    // Helper class implementing Runnable interface
    static class WriteB implements Runnable {
        // run() method for thread
        public void run()
        {
            for (int i = 0; i <= 10; i++) {
                // Try block to check for exceptions
                try {
                    lock.writeLock().lock();
                    message = message.concat("b");
                }
                finally {
                    lock.writeLock().unlock();
                }
            }
        }
    }
}