[Solved] Consider a producer-consumer system using semaphores: when a producer produces an item, what is the correct sequence of semaphore operations to ensure proper synchronization? | Operating Systems

Operating Systems - Producer-Consumer Problem Using Semaphores

Consider a producer-consumer system using semaphores: when a producer produces an item, what is the correct sequence of semaphore operations to ensure proper synchronization?

AWait on 'empty' semaphore, wait on mutex, add item, signal mutex, signal 'full' semaphore

BWait on mutex, wait on 'empty' semaphore, add item, signal 'full' semaphore, signal mutex

CWait on 'full' semaphore, wait on mutex, add item, signal mutex, signal 'empty' semaphore

DSignal 'empty' semaphore, wait on mutex, add item, signal 'full' semaphore, wait on 'full' semaphore

Step-by-Step Solution

Step 1: Understand semaphore roles
'empty' counts available buffer slots; 'full' counts filled slots; mutex protects buffer access.
Step 2: Producer must wait for empty slot
Producer waits (P operation) on 'empty' to ensure space is available before producing.
Step 3: Acquire mutex before modifying buffer
Mutex wait ensures exclusive access to buffer.
Step 4: Add item, then release mutex
After adding, signal (V operation) mutex to release critical section.
Step 5: Signal 'full' to indicate new item
Signaling 'full' wakes consumers waiting for items.
Step 6: Why other options fail
Wait on 'full' semaphore, wait on mutex, add item, signal mutex, signal 'empty' semaphore waits on 'full' which is incorrect; Wait on mutex, wait on 'empty' semaphore, add item, signal 'full' semaphore, signal mutex waits on mutex before 'empty' which can cause deadlock; Signal 'empty' semaphore, wait on mutex, add item, signal 'full' semaphore, wait on 'full' semaphore signals before waiting, breaking synchronization.
Final Answer:
Option A -> Option A
Quick Check:
Wait empty -> wait mutex -> produce -> signal mutex -> signal full [OK]

Quick Trick: Producer waits on empty, consumer waits on full

Common Mistakes:

MISTAKES

Confusing 'full' and 'empty' semaphore roles
Incorrect order of mutex and semaphore waits
Signaling before waiting causing race

Trap Explanation:

PITFALL

Misordering semaphore waits or signaling breaks synchronization and can cause deadlocks or lost wakeups.

Interviewer Note:

CONTEXT

Tests candidate's understanding of the exact semaphore operation sequence in producer-consumer

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More Operating Systems Quizzes

Consider a producer-consumer system using semaphores: when a producer produces an item, what is the correct sequence of semaphore operations to ensure proper synchronization?

Step 1: Understand semaphore roles

Step 2: Producer must wait for empty slot

Step 3: Acquire mutex before modifying buffer

Step 4: Add item, then release mutex

Step 5: Signal 'full' to indicate new item

Step 6: Why other options fail

Final Answer:

Quick Check:

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