import java.util.HashMap;

import java.util.Map;

import java.util.concurrent.Executors;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.locks.Lock;

import java.util.concurrent.locks.ReadWriteLock;

import java.util.concurrent.locks.ReentrantReadWriteLock;

public class Dictionary{

public static void main(String[] args){

final String[] words = {"hypocalcemia", "prolixity", "assiduous", "indefatigable", "castellan"};

final String[] definitions = {"a deficiency of calcium in the blood",

"unduly prolonged or drawn out",

"showing great care, attention, and effort",

"able to work or continue for a lengthy time without tiring",

"the govenor or warden of a castle or fort"};

final Map<String, String> dictionary = new HashMap<String, String>();

ReadWriteLock rwl = new ReentrantReadWriteLock(true);

final Lock writeLock = rwl.writeLock();

final Lock readLock = rwl.readLock();

System.out.println("WriteLock: " + writeLock + "; ReadLock: " + readLock);

Runnable writer = new Runnable(){

public void run(){

for(int i=0;i<words.length;i++){

writeLock.lock();

try{

System.out.println();

dictionary.put(words[i], definitions[i]);

System.out.println("writer storing " + words[i] + " entry"+ " from " + Thread.currentThread() + "; owning lock: " + writeLock);

System.out.println("writer doing something...");

System.out.println("writer doing something...");

System.out.println("writer doing something...");

}finally{

System.out.println("writer releasing the write lock" + "\n");

writeLock.unlock();

}

try{

Thread.sleep((int)(Math.random()*2000));

}catch(InterruptedException ie){

ie.printStackTrace();

}

}

}

};

ExecutorService es = Executors.newFixedThreadPool(1);

es.submit(writer);

Runnable reader = new Runnable(){

public void run(){

while(true){

readLock.lock();

try{

int index = (int)(Math.random()*words.length);

System.out.println("reader accessing " + words[index] + ": " + dictionary.get(words[index]) + " entry" + " from " + Thread.currentThread() + "; owning lock: " + readLock);

}finally{

readLock.unlock();

}

try{

Thread.sleep((int)(Math.random()*500));

}catch(InterruptedException ie){

ie.printStackTrace();

}

}

}

};

final int readerAmount = 5;

es = Executors.newFixedThreadPool(readerAmount);

for(int i=0;i<readerAmount; i++){

es.submit(reader);

}

}

}

/* Thread.toString() implementation.

* [ThreadName , ThreadPriority , ThreadGroupName]

*/