Semaphore initialization for mutual exclusion: What initial value should a semaphore have so that only one of many processes can enter its critical section at a time?

Introduction / Context:
Mutual exclusion ensures that concurrent processes do not simultaneously execute a critical section that accesses shared data. A binary semaphore is commonly used to enforce this policy. The correct initial value allows the first entrant and blocks the rest until release.

Given Data / Assumptions:

• Semaphore supports atomic wait (P) and signal (V) operations.
• We want exactly one process at a time in the critical section.
• No process should start blocked unnecessarily once the system begins.

Concept / Approach:

A binary semaphore initialized to 1 indicates the resource is free. The first P makes it 0, entering the critical section. Any subsequent P calls block (since value is 0) until the current process performs V, restoring the semaphore to 1 and allowing the next process to proceed.

Step-by-Step Solution:

Verification / Alternative check:

Textbook mutex examples and POSIX semaphores mirror this pattern: initial value 1 for a lock-like behavior. Initial value 0 is used for ordering/barrier patterns, not initial entry.

Why Other Options Are Wrong:

• 8 or 16: Counting semaphore allowing many concurrent entrants, violating mutual exclusion.
• 0: Blocks all processes at start until a V occurs from outside the section.
• None of the above: Incorrect because 1 is the standard initial value.

Common Pitfalls:

Forgetting to release (signal) causing starvation; mixing multiple locks inconsistently causing deadlock; using a counting semaphore inadvertently when exclusivity is required.

Final Answer:

1