ProducerConsumer solution using Semaphores in Java | Set 2 (original) (raw)

Producer-Consumer solution using Semaphores in Java | Set 2

Last Updated : 23 Jul, 2025

Prerequisites - Semaphore in Java, Inter Process Communication, Producer Consumer Problem using Semaphores | Set 1In computing, the producer–consumer problem (also known as the bounded-buffer problem) is a classic example of a multi-process synchronization problem. The problem describes two processes, the producer and the consumer, which share a common, fixed-size buffer used as a queue.

Problem : To make sure that the producer won’t try to add data into the buffer if it’s full and that the consumer won’t try to remove data from an empty buffer.Solution : The producer is to either go to sleep or discard data if the buffer is full. The next time the consumer removes an item from the buffer, it notifies the producer, who starts to fill the buffer again. In the same way, the consumer can go to sleep if it finds the buffer to be empty. The next time the producer puts data into the buffer, it wakes up the sleeping consumer.An inadequate solution could result in a deadlock where both processes are waiting to be awakened. In the post Producer-Consumer solution using threads in Java, we have discussed above solution by using inter-thread communication(wait(), notify(), sleep()). In this post, we will use Semaphores to implement the same.The below solution consists of four classes:

  1. Q : the queue that you’re trying to synchronize
  2. Producer : the threaded object that is producing queue entries
  3. Consumer : the threaded object that is consuming queue entries
  4. PC : the driver class that creates the single Q, Producer, and Consumer. Java `

// Java implementation of a producer and consumer // that use semaphores to control synchronization.

import java.util.concurrent.Semaphore;

class Q { // an item int item;

// semCon initialized with 0 permits
// to ensure put() executes first
static Semaphore semCon = new Semaphore(0);

static Semaphore semProd = new Semaphore(1);

// to get an item from buffer
void get()
{
    try {
        // Before consumer can consume an item,
        // it must acquire a permit from semCon
        semCon.acquire();
    }
    catch (InterruptedException e) {
        System.out.println("InterruptedException caught");
    }

    // consumer consuming an item
    System.out.println("Consumer consumed item : " + item);

    // After consumer consumes the item,
    // it releases semProd to notify producer
    semProd.release();
}

// to put an item in buffer
void put(int item)
{
    try {
        // Before producer can produce an item,
        // it must acquire a permit from semProd
        semProd.acquire();
    }
    catch (InterruptedException e) {
        System.out.println("InterruptedException caught");
    }

    // producer producing an item
    this.item = item;

    System.out.println("Producer produced item : " + item);

    // After producer produces the item,
    // it releases semCon to notify consumer
    semCon.release();
}

}

// Producer class class Producer implements Runnable { Q q; Producer(Q q) { this.q = q; new Thread(this, "Producer").start(); }

public void run()
{
    for (int i = 0; i < 5; i++)
        // producer put items
        q.put(i);
}

}

// Consumer class class Consumer implements Runnable { Q q; Consumer(Q q) { this.q = q; new Thread(this, "Consumer").start(); }

public void run()
{
    for (int i = 0; i < 5; i++)
        // consumer get items
        q.get();
}

}

// Driver class class PC { public static void main(String args[]) { // creating buffer queue Q q = new Q();

    // starting consumer thread
    new Consumer(q);

    // starting producer thread
    new Producer(q);
}

}

`

Output:

Producer produced item : 0 Consumer consumed item : 0 Producer produced item : 1 Consumer consumed item : 1 Producer produced item : 2 Consumer consumed item : 2 Producer produced item : 3 Consumer consumed item : 3 Producer produced item : 4 Consumer consumed item : 4

Explanation : As you can see, the calls to put() and get( ) are synchronized, i.e. each call to put() is followed by a call to get( ) and no items are missed. Without the semaphores, multiple calls to put() would have occurred without matching calls to get(), resulting in items being missed. (To prove this, remove the semaphore code and observe the results.)The sequencing of put() and get() calls is handled by two semaphores: semProd and semCon.