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//: concurrency/ReaderWriterList.java

import java.util.concurrent.*;

import java.util.concurrent.locks.*;

import java.util.*;

import static net.mindview.util.Print.*;

public class ReaderWriterList<T> {

private ArrayList<T> lockedList;

// Make the ordering fair:

private ReentrantReadWriteLock lock =

new ReentrantReadWriteLock(true);

public ReaderWriterList(int size, T initialValue) {

lockedList = new ArrayList<T>(

Collections.nCopies(size, initialValue));

}

public T set(int index, T element) {

Lock wlock = lock.writeLock();

wlock.lock();

try {

return lockedList.set(index, element);

} finally {

wlock.unlock();

}

}

public T get(int index) {

Lock rlock = lock.readLock();

rlock.lock();

try {

// Show that multiple readers

// may acquire the read lock:

if(lock.getReadLockCount() > 1)

print(lock.getReadLockCount());

return lockedList.get(index);

} finally {

rlock.unlock();

}

}

public static void main(String[] args) throws Exception {

new ReaderWriterListTest(30, 1);

}

}

class ReaderWriterListTest {

ExecutorService exec = Executors.newCachedThreadPool();

private final static int SIZE = 100;

private static Random rand = new Random(47);

private ReaderWriterList<Integer> list =

new ReaderWriterList<Integer>(SIZE, 0);

private class Writer implements Runnable {

public void run() {

try {

for(int i = 0; i < 20; i++) { // 2 second test

list.set(i, rand.nextInt());

TimeUnit.MILLISECONDS.sleep(100);

}

} catch(InterruptedException e) {

// Acceptable way to exit

}

print("Writer finished, shutting down");

exec.shutdownNow();

}

}

private class Reader implements Runnable {

public void run() {

try {

while(!Thread.interrupted()) {

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

list.get(i);

TimeUnit.MILLISECONDS.sleep(1);

}

}

} catch(InterruptedException e) {

// Acceptable way to exit

}

}

}

public ReaderWriterListTest(int readers, int writers) {

for(int i = 0; i < readers; i++)

exec.execute(new Reader());

for(int i = 0; i < writers; i++)

exec.execute(new Writer());

}

} /* (Execute to see output) *///:~