NTA-UGC-NET 2021 Dec & 2022 June Paper-1
October 21, 2023Digital-Logic-Design
October 21, 2023Operating-Systems
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Question 50
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Consider the procedure below for the Producer-Consumer problem which uses semaphores:
semaphore n=0;
semaphore s=1;
void producer() void consumer()
{ {
while(true) while(true)
{ {
produce(); semWait(s);
semWait(s); semWait(n);
addToBuffer(); removeFromBuffer();
semSignal(s); semSignal();
semSignal(n); consume();
} }
} }
Which one of the following is TRUE?
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The producer will be able to add an item to the buffer, but the consumer can never consume it.
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The consumer will remove no more than one item from the buffer.
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Deadlock occurs if the consumer succeeds in acquiring semaphore s when the buffer is empty.
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The starting value for the semaphore n must be 1 and not 0 for deadlock-free operation.
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Question 50 Explanation:
Answer is (C), because when consumer first access the semaphore ‘s’ it will down (s) and make ‘s’=0, but for semaphore(n), it has to wait for producer to make it 1 but as for producer it can’t access the critical section because the value of s=0, so semWait(s) will not work. So there will be deadlock.
Correct Answer: C
Question 50 Explanation:
Answer is (C), because when consumer first access the semaphore ‘s’ it will down (s) and make ‘s’=0, but for semaphore(n), it has to wait for producer to make it 1 but as for producer it can’t access the critical section because the value of s=0, so semWait(s) will not work. So there will be deadlock.