Java Language Concurrent Programming (Threads) Multiple producer/consumer example with shared global queue
Example
Below code showcases multiple Producer/Consumer program. Both Producer and Consumer threads share same global queue.
import java.util.concurrent.*;
import java.util.Random;
public class ProducerConsumerWithES {
public static void main(String args[]) {
BlockingQueue<Integer> sharedQueue = new LinkedBlockingQueue<Integer>();
ExecutorService pes = Executors.newFixedThreadPool(2);
ExecutorService ces = Executors.newFixedThreadPool(2);
pes.submit(new Producer(sharedQueue, 1));
pes.submit(new Producer(sharedQueue, 2));
ces.submit(new Consumer(sharedQueue, 1));
ces.submit(new Consumer(sharedQueue, 2));
pes.shutdown();
ces.shutdown();
}
}
/* Different producers produces a stream of integers continuously to a shared queue,
which is shared between all Producers and consumers */
class Producer implements Runnable {
private final BlockingQueue<Integer> sharedQueue;
private int threadNo;
private Random random = new Random();
public Producer(BlockingQueue<Integer> sharedQueue,int threadNo) {
this.threadNo = threadNo;
this.sharedQueue = sharedQueue;
}
@Override
public void run() {
// Producer produces a continuous stream of numbers for every 200 milli seconds
while (true) {
try {
int number = random.nextInt(1000);
System.out.println("Produced:" + number + ":by thread:"+ threadNo);
sharedQueue.put(number);
Thread.sleep(200);
} catch (Exception err) {
err.printStackTrace();
}
}
}
}
/* Different consumers consume data from shared queue, which is shared by both producer and consumer threads */
class Consumer implements Runnable {
private final BlockingQueue<Integer> sharedQueue;
private int threadNo;
public Consumer (BlockingQueue<Integer> sharedQueue,int threadNo) {
this.sharedQueue = sharedQueue;
this.threadNo = threadNo;
}
@Override
public void run() {
// Consumer consumes numbers generated from Producer threads continuously
while(true){
try {
int num = sharedQueue.take();
System.out.println("Consumed: "+ num + ":by thread:"+threadNo);
} catch (Exception err) {
err.printStackTrace();
}
}
}
}
output:
Produced:69:by thread:2
Produced:553:by thread:1
Consumed: 69:by thread:1
Consumed: 553:by thread:2
Produced:41:by thread:2
Produced:796:by thread:1
Consumed: 41:by thread:1
Consumed: 796:by thread:2
Produced:728:by thread:2
Consumed: 728:by thread:1
and so on ................
Explanation:
sharedQueue, which is aLinkedBlockingQueueis shared among all Producer and Consumer threads.- Producer threads produces one integer for every 200 milli seconds continuously and append it to
sharedQueue Consumerthread consumes integer fromsharedQueuecontinuously.- This program is implemented with-out explicit
synchronizedorLockconstructs. BlockingQueue is the key to achieve it.
BlockingQueue implementations are designed to be used primarily for producer-consumer queues.
BlockingQueue implementations are thread-safe. All queuing methods achieve their effects atomically using internal locks or other forms of concurrency control.
