CSEIT – GATE 2025 Subject – Operating System/Topic – Process Synchronization (based on Algo-3).

CSEIT – GATE 2025 Subject – Operating System/Topic – Process Synchronization (based on Algo-3).

Here is a structured and GATE-focused explanation for:

CSE/IT – GATE 2025

Subject: Operating System

Topic: Process Synchronization (Based on Algo-3 – Peterson’s Algorithm)

What is Process Synchronization?

Process Synchronization is the technique used to coordinate the execution of concurrent processes that share resources. It ensures that:

• Only one process accesses the critical section (CS) at a time (Mutual Exclusion),

• The system makes progress without unnecessary delay,

• Every process eventually gets a chance (Bounded Waiting).

Algo-3: Peterson’s Algorithm

Used for: Synchronization between 2 processes (P0 and P1)
Type: Software-based solution
Key Features:

• Guarantees mutual exclusion

• Ensures progress and bounded waiting

• No need for hardware-level atomic instructions

Shared Variables:

Code for Process Pi (i = 0 or 1):

How It Works:

• Each process sets its flag to true indicating its interest in entering CS.

• It gives the turn to the other process.

• If the other process also wants to enter and it’s its turn, the current process waits.

• This guarantees mutual exclusion.

Satisfies the 3 Conditions of Critical Section Problem:

Condition	Met?	Explanation
Mutual Exclusion		Only one process can enter the CS at a time.
Progress		A process not in CS doesn’t block others.
Bounded Waiting		Each process gets a turn in a finite time.

GATE-Style Example Question:

Q: In Peterson’s algorithm for two processes P0 and P1, what ensures mutual exclusion?

A. Setting turn = 1 - i
B. The flag array
C. The combination of flag[] and turn
D. None of the above

Correct Answer: C – Both flag[] and turn are essential for mutual exclusion.

Summary:

• Peterson’s Algorithm is simple but powerful.

• It’s a frequent topic in GATE questions.

• Best understood by writing and simulating the code.

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• A flowchart of the algorithm?

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CSEIT – GATE 2025 Subject – Operating System/Topic – Process Synchronization (based on Algo-3).

OPERATING SYSTEMS PROCESS SYNCHRONIZATION

Computer Science & Engineering Second Year