package concurrency;

import java.util.concurrent.*;

import java.util.*;

/**

* RUN:

* javac concurrency/SemaphoreDemo.java && java concurrency.SemaphoreDemo

*

* OUTPUT:

*

*/

public class SemaphoreDemo {

final static int SIZE = 25;

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

final Pool<Fat> pool = new Pool<Fat>(Fat.class, SIZE);

ExecutorService exec = Executors.newCachedThreadPool();

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

exec.execute(new CheckoutTask<Fat>(pool));

}

System.out.println("All CheckoutTasks created");

List<Fat> list = new ArrayList<Fat>();

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

Fat f = pool.checkOut();

System.out.print(i + " main() thread checked out ");

f.operation();

list.add(f);

}

Future<?> blocked = exec.submit(new Runnable() {

public void run() {

try {

// Semaphore blocking this checkOut() eexecution

pool.checkOut();

}

catch (InterruptedException e) {

System.out.println("checkOut() interrupted");

}

}

});

TimeUnit.SECONDS.sleep(2);

blocked.cancel(true); // return from blocking

System.out.println("Checking in objects in " + list);

for (Fat f : list) {

pool.checkIn(f);

}

for (Fat f : list) {

pool.checkIn(f); // this checkIn() ignored

}

exec.shutdown();

}

}

class CheckoutTask<T> implements Runnable {

private static int counter = 0;

private final int id = counter++;

private Pool<T> pool;

public CheckoutTask(Pool<T> pool) {

this.pool = pool;

}

public void run() {

try {

T item = pool.checkOut();

System.out.println(this + " checked out " + item);

TimeUnit.SECONDS.sleep(1);

System.out.println(this + " checked in " + item);

pool.checkIn(item);

}

catch (InterruptedException e) {

//

}

}

public String toString() {

return String.format("CheckoutTask %1$d ", id);

}

}