GATE CS 2015 Set 3 — Question 31

MCQ+1 / -0.33MediumRace Conditions & Critical SectionProcess SynchronizationOperating SystemDeadlocks

Operating System → Deadlocks → Race Conditions & Critical Section

Last updated 5 September 2026

Question

X

Correct answer (A) The proposed solution prevents deadlock but fails to guarantee mutual exclusion Solution Let's analyze the execution trace: 1. Initially varP = false, varQ = false . 2. Process X executes varP = true . 3. Context switch to Process Y. 4. Process Y executes varQ = true . 5. Process Y checks while(varP == true) . Since varP is true, Y enters the Critical Section (CS). 6. Context switch to Process X. 7. Process X checks while(varQ == true) . Since varQ is true, X enters the Critical Section (CS). Both processes are in the Critical Section simultaneously, so Mutual Exclusion is violated . Regarding Deadlock: Deadlock implies processes are waiting indefinitely for a condition that will never become true. Here, processes do not wait; they enter the CS (incorrectly) or loop. If executed sequentially (e.g., X runs alone), X sets varP=true, checks varQ (false), skips the inner loop (CS), and repeats. While this might be a liveness issue (starvation/livelock), it is not a deadlock in the sense of circular wait preventing any progress. The primary failure is Mutual Exclusion. The option stating it prevents deadlock but fails mutual exclusion is the most appropriate description of the race condition allowing both to enter. Turn this into a strength. Explore AI-powered practice and doubt support with Success Tracker.

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Correct answer (A) The proposed solution prevents deadlock but fails to guarantee mutual exclusion Solution Let's analyze the execution trace: 1. Initially varP = false, varQ = false . 2. Process X executes varP = true . 3. Context switch to Process Y. 4. Process Y executes varQ = true . 5. Process Y checks while(varP == true) . Since varP is true, Y enters the Critical Section (CS). 6. Context switch to Process X. 7. Process X checks while(varQ == true) . Since varQ is true, X enters the Critical Section (CS). Both processes are in the Critical Section simultaneously, so Mutual Exclusion is violated . Regarding Deadlock: Deadlock implies processes are waiting indefinitely for a condition that will never become true. Here, processes do not wait; they enter the CS (incorrectly) or loop. If executed sequentially (e.g., X runs alone), X sets varP=true, checks varQ (false), skips the inner loop (CS), and repeats. While this might be a liveness issue (starvation/livelock), it is not a deadlock in the sense of circular wait preventing any progress. The primary failure is Mutual Exclusion. The option stating it prevents deadlock but fails mutual exclusion is the most appropriate description of the race condition allowing both to enter.

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