Consumer Producer Problem

January 20, 2023

Producer Consumer Problem using Semaphores in Operating System

The producer-consumer problem is a classic multiprocess synchronization problem. In the Producer-Consumer problem there is a producer, a producer produces some items, and a consumer who consumes the items produced by the producer. Producers and consumers share the same fixed-size memory buffer.

Producer Consumer Problem using Semaphores

Producer consumer problem is one classic example of mutual exclusion, process synchronisation using semaphores. It basically synchronises data production and consumption happening simultaneously in a system where there is fixed amount of storage size. The system has the following –

Producer
Consumer
Storage bound of size n

Priority Scheduling

CPU Scheduling

FCFS Scheduling

Preemptive Scheduling

Process of Producer Consumer

The processes is synchronised via a mutex which provides mutual mutual exclusion in the critical section area. There is unit called as empty which defines the number of empty slots in the storage. There is unit called as full which defines the number of full storage slots in the system.

The number of storage slots are initialised as n, the number of empty slots are initialised as n since all slots are empty at the starting similarly the full unit is initialised as 0 as there is no data initially.

It is important to understand wait and signal first from the image above to understand how the problem works.

Producer Consumer Signal and Wait

wait(Semaphore s)
{
  while(s == 0);
  s = s-1;
}

signal(Semaphore s)
{
  s = s+1;
}

What happened above: semicolon after while , which results in the while loop getting executed again again. Until S value is non-zero.

Producer

do
  {

// produce an item
// the producer can only produce if there is atleast 1 empty slot
// thus empty must be >0 and then it also decrements the value

    wait (empty);

// access to critical section is blocked for consumer section

    wait (mutex);

// place in buffer

// access to critical section is released

    signal (mutex);

// value of full is incremented

    signal (full);

  }
while (true)

Consumer

do
  {

// consumer should wait until there is atleast one item in storage
// full value should be greater than 0 and then decremented

    wait (full);

// access to critical section is blocked for producer section 

    wait (mutex);

// remove item from buffer

// access to critical section is released for producer section 

    signal (mutex);

// value of empty is incremented as item was consumer

    signal (empty);

// consumes item

  }
while (true)

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