what is Producer Consumer Problem and Solution

Producer-Consumer solution using threads in Java

In 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.

• The producer’s job is to generate data, put it into the buffer, and start again.
• At the same time, the consumer is consuming the data (i.e. removing it from the buffer), one piece at a time.

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.

Producer Consumer Problem is a classical concurrency problem. In fact it is one of the concurrency design pattern.  It is also known as the bounded-buffer problem.

The problem describes two processes, the producer and the consumer, who share a common, fixed-size buffer used as a queue.

The producer's job is to generate data and put it into the buffer. At the same time, the consumer consumes the data (i.e., by removing it from the buffer), one piece at a time.

The problem is 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.

The solution for 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.

Real Life Example

Lets say in our Example, The producer is Mr Simpson whose job is to bake Pizza and consumer is Joey Tribbiani who consumes Pizza at the same time. Both of them share common Pizza counter to interact with each other.

The problem is to make sure that the Simpson won't try to add more pizza on Pizza counter if it's full. He needs to wait until Joey consumes Pizza.

Similarly Joey can't consume pizza from an empty counter. He needs to wait until Mr Simpson adds Pizza on counter.

You can understand it better by watching this video.

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Uses
 

In Java library, Executor framework implements Producer Consumer design pattern to separate responsibility of addition and execution of task.

Benefits 

1. It simplifies developement process. you can Code Producer and Consumer independently and Concurrently, they just need to know shared object.
2. Producer doesn't need to know about who is consumer or how many consumers are there. Same is true with Consumer.
3. Producer and Consumer can work with different speed. In fact by monitoring consumer speed, one can introduce more consumer for better utilization.

Java Program Implementation

Producer Consumer Design Patter can be implemented using following two approaches.

1. By using wait(), notify() and notifyAll() methods
2. By using BlockingQueue