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:


๐ŸŽ“ CSE/IT โ€“ GATE 2025

๐Ÿ“˜ Subject: Operating System

๐Ÿ“Œ Topic: Process Synchronization (Based on Algo-3 โ€“ Petersonโ€™s Algorithm)


๐Ÿง  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).


๐Ÿ” Algo-3: Petersonโ€™s Algorithm

๐Ÿ“Œ Used for: Synchronization between 2 processes (P0 and P1)
๐Ÿ“Œ Type: Software-based solution
๐Ÿ“Œ Key Features:

  • Guarantees mutual exclusion

  • Ensures progress and bounded waiting

  • No need for hardware-level atomic instructions


โš™๏ธ Shared Variables:

c
boolean flag[2] = {false, false}; // Indicates interest in entering CS
int turn = 0; // Whose turn is it?

๐Ÿ‘จโ€๐Ÿ’ป Code for Process Pi (i = 0 or 1):

c
// Entry Section
flag[i] = true; // Express interest in entering CS
turn = 1 - i; // Give turn to the other process
while (flag[1 - i] && turn == 1 - i)
; // Busy wait

// ---- Critical Section ----

// Exit Section
flag[i] = false; // Exit CS


โœ… 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 itโ€™s its turn, the current process waits.

  • This guarantees mutual exclusion.


๐Ÿ“Œ Satisfies the 3 Conditions of Critical Section Problem:

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

๐Ÿงช GATE-Style Example Question:

Q: In Petersonโ€™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

โœ… Correct Answer: C โ€“ Both flag[] and turn are essential for mutual exclusion.


๐Ÿ“– Summary:

  • Petersonโ€™s Algorithm is simple but powerful.

  • Itโ€™s a frequent topic in GATE questions.

  • Best understood by writing and simulating the code.


Would you like:

  • A flowchart of the algorithm?

  • A PDF of this explanation?

  • More practice questions or MCQs?

Let me know how you’d like to prepare!

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

OPERATING SYSTEMS PROCESS SYNCHRONIZATION

Computer Science & Engineering Second Year

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