Readロック、Writeロックを使ったサンプルです。

TestReentrant.java

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class TestReentrant implements Runnable {

	Map<String, String> pool = new HashMap<String, String>();
	Lock lockObj;

	/**
	 * メイン
	 * 
	 * @param args
	 */
	public static void main(String[] args) {

		ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
		ExecutorService exec = Executors.newCachedThreadPool();
		exec.execute(new TestReentrant(lock.readLock()));
		exec.execute(new TestReentrant(lock.readLock()));
		exec.execute(new TestReentrant(lock.writeLock()));
		exec.execute(new TestReentrant(lock.readLock()));

		// new Thread(new TestReentrant(lock.readLock())).start();
		// new Thread(new TestReentrant(lock.readLock())).start();
		// new Thread(new TestReentrant(lock.writeLock())).start();
		// new Thread(new TestReentrant(lock.readLock())).start();
	}

	/**
	 * コンストラクタ
	 * 
	 * @param writeFlg
	 */
	public TestReentrant(Lock lockObj) {
		this.lockObj = lockObj;
	}

	public void task() throws InterruptedException {
		String lockName = this.lockObj.getClass().getSimpleName();
		try {
			this.lockObj.lock();
			System.out.printf("[%s] start\r\n", lockName);
			Thread.sleep(3000L);

		} finally {
			System.out.printf("[%s] end\r\n", lockName);
			this.lockObj.unlock();
		}
	}

	@Override
	public void run() {
		try {
			task();
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}