Short Trick Of Process Synchronization ( Solve any question in few minutes).

Lui Kreyszig

3 weeks ago

https://www.gyanodhan.com/video/7B7.%20GATE%20CSEIT/Operating%20System/633.%20Short%20Trick%20Of%20Process%20Synchronization%20%28%20Solve%20any%20question%20in%20few%20minutes%29.mp4

Here’s a short trick guide to help you quickly solve any Process Synchronization question in GATE (or similar competitive exams) in a few minutes:

Contents

1 Topic: Process Synchronization

Topic: Process Synchronization

Goal: Identify Mutual Exclusion, Progress, Bounded Waiting in code
Target: GATE-level MCQs or code analysis

TRICK 1: Look for the 3 Magic Words

Always check if the algorithm/code satisfies:

Mutual Exclusion – Only 1 process in the Critical Section
Progress – No unnecessary blocking
Bounded Waiting – Every process eventually gets a turn

Tip: If even one of these is violated, it’s not a correct solution.

TRICK 2: Remember the CORE ALGORITHMS

Algo No.	Name	Processes	Hardware Needed	Notes
1	Simple Lock	2+	No	Violates progress
2	Dekker’s Algo	2	No	Software-only
3	Peterson’s Algo	2	No	Easy to simulate
4	Test-and-Set Lock	2+	Yes (Atomic op)	Uses hardware instruction
5	Semaphore	2+	No	`wait()` and `signal()`
6	Monitor	2+	No	High-level abstraction

Peterson’s = Most Common in GATE Questions!

TRICK 3: Identify the Entry & Exit Sections

Quickly scan the code for these patterns:

Entry Section (wants to enter CS):

flag[i] = true; → intention to enter
turn = 1 - i; → gives other process a chance
while(...) → busy wait / condition checking

Exit Section (leaves CS):

flag[i] = false;
turn = ...; → resets turn for the other process

TRICK 4: Use This YES/NO Table

Condition to Check	Look for in Code	Shortcut Decision
Mutual Exclusion?	Only one process allowed in CS	if `while(flag[] && turn)` pattern exists
Progress?	No unnecessary delay if CS is free	if `turn` changes appropriately
Bounded Waiting?	Process won’t wait forever	if `turn` is assigned fairly

TRICK 5: Look for Common MCQ Keywords

Watch for these question patterns:

“Which condition is violated?”
→ Use the YES/NO table above
“How many processes can be in CS?”
→ If more than one, Mutual Exclusion is violated
“What is the purpose of turn or flag[]?”
→ flag[] = intent, turn = fairness
“Identify correct algorithm from options”
→ Match pattern to Peterson, Dekker, etc.

Super Short Summary

flag[] = true → process wants to enter
while (flag[other] && turn == other) → wait
Critical Section
Reset flag[i] = false, set turn = other

Example (Peterson’s):

This ensures:
Mutual Exclusion
Progress
Bounded Waiting

Would you like:

A printable cheat sheet?
Practice MCQs with answers?
Visual flowcharts for each algorithm?

Let me know!

Short Trick Of Process Synchronization ( Solve any question in few minutes).