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Concurrency in Java: Producer-Consumer Problem

Problem

The producer-consumer problem (bounded buffer problem) describes two processes, the producer and the consumer.

Both Producer and Consumer share a common memory buffer of a certain size.

The producer produces the data in the buffer, and the consumer consumes the data from the buffer.

The task is to make sure that the producer won't try to add data to the buffer if it's full and the consumer won't try to remove data from an empty buffer.

Solution

If the buffer is empty, the consumer is to go to sleep. The next time the producer puts data into the buffer, it wakes up the sleeping consumer.

If the buffer is full, the producer is to either go to sleep or discard data. The next time the consumer consumes (removes) an item from the buffer, it notifies the producer, who starts to fill the buffer again.

Implementation

Producer-consumer problems can be solved using Java concurrency constructs such as wait() and notify().

The idea is to create a "Task" class containing both the "data buffer (LinkedList)" and the "consume() and produce()" methods.

Make sure to mark the consume() and produce() methods with the "synchronized" keyword. This will make sure that only one thread is able to execute either of the two consume() or produce() methods on the same object.

Now, the process is simple: if the buffer is empty, make the "consumer" thread wait, and if the buffer is full, make the "producer" thread wait.

...

Produced: true, Queue size: 6
Produced: true, Queue size: 7
Produced: true, Queue size: 8
Produced: true, Queue size: 9
Produced: true, Queue size: 10
Consumed: Something !!!, Queue size: 9
Consumed: Something !!!, Queue size: 8
Consumed: Something !!!, Queue size: 7
Consumed: Something !!!, Queue size: 6
Consumed: Something !!!, Queue size: 5
Consumed: Something !!!, Queue size: 4
Produced: true, Queue size: 5
Produced: true, Queue size: 6
Produced: true, Queue size: 7
Produced: true, Queue size: 8
Produced: true, Queue size: 9
Produced: true, Queue size: 10
Consumed: Something !!!, Queue size: 9
Consumed: Something !!!, Queue size: 8
Consumed: Something !!!, Queue size: 7
Consumed: Something !!!, Queue size: 6
Consumed: Something !!!, Queue size: 5
Consumed: Something !!!, Queue size: 4
Consumed: Something !!!, Queue size: 3
Consumed: Something !!!, Queue size: 2
Consumed: Something !!!, Queue size: 1
Consumed: Something !!!, Queue size: 0
Produced: true, Queue size: 1
....
....

Related: Producer-consumer problem using BlockingQueue



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