Producer-Consumer Synchronization

CSC-264 · Semester IV · Operating Systems

intermediate30 minAvailable

Producer–Consumer with Semaphores

Bounded buffer, empty/full counters and a mutex protect the shared queue.

Shared buffer (size 4)

emptyslot 0

emptyslot 1

emptyslot 2

emptyslot 3

Semaphores

empty

blocks producers when full

full

blocks consumers when empty

mutex

1 = unlocked, 0 = locked

Operation trace

Press Produce or Consume to see the semaphore operations step by step.

The empty/full semaphores enforce capacity, while mutex keeps the buffer update atomic. If a process blocks, try alternating producers and consumers to unblock it.

Lab brief

Objective

Synchronize a producer and a consumer sharing a bounded buffer using semaphores, and observe the race condition when synchronization is removed.

Theory & concepts

The bounded buffer problem has a producer adding items and a consumer removing them from a fixed-size buffer. Three semaphores keep it correct: empty counts free slots, full counts filled slots, and mutex protects the buffer's contents.

Rendering diagram…

Producer-consumer synchronization with counting semaphores

semaphore full = 0, empty = N, mutex = 1;

producer:                    consumer:
  wait(empty)                  wait(full)
  wait(mutex)                  wait(mutex)
  put item                     take item
  signal(mutex)                signal(mutex)
  signal(full)                 signal(empty)

Without synchronization

Without mutex, two concurrent updates can interleave and corrupt the buffer index. Without empty/full, the producer overflows or the consumer underflows the buffer.

Prerequisites

Lesson: Process synchronization

Instructions

1Select a buffer size N (e.g., 5).
2Run the simulation with semaphores enabled and watch producer/consumer timing.
3Disable synchronization and run again; observe the buffer corruption.
4Watch the counters to confirm no item is produced into a full buffer or removed from an empty one.

Tasks

Correct run
Run with semaphores for 20 operations and confirm buffer bounds hold.
Broken run
Remove the semaphores and describe the failure you observe.
Vary N
Repeat with N = 1 and N = 10; explain how throughput changes.

Self-check

The buffer never overflows or underflows when synchronized.
The student identifies the race condition when synchronization is removed.
The role of each semaphore (empty, full, mutex) is explained.

Environment

producer/consumer controlsbuffer visualizersemaphore toggleoperation log