Operating Systems · Concurrency and Synchronization
Official IIT answer key · IIT Delhi · Audited Aug 2026
GATE CSE 2020 Q34 · MCQ · 2 marks
a and b initialized to 1 and 0, respectively. Assume that count is a shared variable initialized to 0 and not used in CODE SECTION P.
CODE SECTION P
wait(a); count=count+1;
if (count==n) signal(b);
signal(a); wait(b); signal(b);
CODE SECTION Q
What does the code achieve?Key concept
No account needed
Sit 5 related Concurrency and SynchronizationPYQs as a guest. We'll score the set and show which traps cost marks — sign in only if you want to save the run.
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 →Each of a set of n processes executes the following code using two semaphores a and b initialized to 1 and 0, respectively. Assume that count is a shared variable initialized to 0 and not used in CODE SECTION P. CODE SECTION P wait(a); count=count+1; if (count==n) signal(b); signal(a); wait(b); signal(b); CODE SECTION Q What does the code achieve?
Topic-wise GATE CS PYQs with verified steps
Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.