Operating Systems · Concurrency and Synchronization
Official IIT answer key · IISc Bangalore · Audited Aug 2026
GATE CSE 2024 Set 1 Q40 · MCQ · 2 marks
a = a + 1;b = b + 1;
T2
b = 2 * b;a = 2 * a;
Which one of the following options lists all the possible combinations of values of a and b after both T1 and T2 finish execution?Key concept
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Topic notes
Concurrency and Synchronization is consistently evaluated through rigorous interleaving analysis, semaphore tracing, and correctness verification of mutual exclusion algorithms. Over the years, GATE tests whether candidates can systematically trace race conditions, identify potential deadlocks from mismatched semaphore wait/signal orders, and compute the bounds or exact sets of possible shared variable values under non-atomic operations. Recent papers heavily favor Multi-Select Questions (MSQs) requiring complete enumeration of all valid execution traces and program outcomes.
Full Concurrency and Synchronization guide →Consider the following two threads T1 and T2 that update two shared variables a and b. Assume that initially a = b = 1. Though context switching between threads can happen at any time, each statement of T1 or T2 is executed atomically without interruption. T1 a = a + 1; b = b + 1; T2 b = 2 * b; a = 2 * a; Which one of the following options lists all the possible combinations of values of a and b after both T1 and T2 finish execution?
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Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.