package concurrency;

import java.util.concurrent.*;

import java.util.*;

/**

* RUN:

* javac concurrency/Pool.java && java concurrency.Pool

*

* OUTPUT:

*

*/

public class Pool<T> {

private int size;

private List<T> items = new ArrayList<T>();

private volatile boolean[] checkedOut;

private Semaphore available;

public Pool(Class<T> classObject, int size) {

this.size = size;

checkedOut = new boolean[size];

available = new Semaphore(size, true);

// filling pool

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

try {

items.add(classObject.newInstance());

}

catch (Exception e) {

throw new RuntimeException(e);

}

}

}

public T checkOut() throws InterruptedException {

available.acquire();

return getItem();

}

public void checkIn(T x) {

if (releaseItem(x)) {

available.release();

}

}

private synchronized T getItem() {

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

if (! checkedOut[i]) {

checkedOut[i] = true;

return items.get(i);

}

}

return null; // semaphore save to execute this line

}

private synchronized boolean releaseItem(T item) {

int index = items.indexOf(item);

if (index == -1) {

return false;

}

if (checkedOut[index]) {

checkedOut[index] = false;

return true;

}

return false;

}

}