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Consider the procedure below for the Producer-Consumer problem which uses semaphores: semaphore n = 0; semaphore s = 1;   void producer() { while(true) { produce(); semWait(s); addToBuffer(); semSignal(s); semSignal(n); } }         void consumer() {            while(true)            {             semWait(s);             semWait(n);             removeFromBuffer();             semSignal(s);              consume();              } }   Which one of the following is TRUE?

Consider the procedure below for the Producer-Consumer problem which uses semaphores: semaphore n = 0; semaphore s = 1;   void producer() { while(true) { produce(); semWait(s); addToBuffer(); semSignal(s); semSignal(n); } }         void consumer() {            while(true)            {             semWait(s);             semWait(n);             removeFromBuffer();             semSignal(s);              consume();              } }   Which one of the following is TRUE? Correct Answer <p>Deadlock occurs if the consumer succeeds in acquiring semaphore s when the buffer is empty.</p>

Explanation:

semaphore n = 0;

semaphore s = 1;

 

void producer()

{

        1   while(true)

        2        {

        3     produce();

        4     semWait(s);

        5    addToBuffer();

        6    semSignal(s);

        7    semSignal(n);

}

}

 

 

 

void consumer()

{

      1     while(true)

      2     {

      3     semWait(s);

      4     semWait(n);

      5    removeFromBuffer();

      6     semSignal(s);

      7     consume();

             }

}

 

Method 1

  • If consumer executes first and execute line number 1, 2, 3 and now after 3 it has been pre-empted and now producer start executing line number 1, 2 , 3 after line 3 producer will go into waiting because s is 0 it is decremented by consumer earlier, now we pre-empted producer.
  • Now again consumer start executing from line 4 but it cannot execute further because n=0 and it will for n to become 1, now we pre-empted consumer process.
  • Now we can see that both are waiting for each other, producer it waiting to become s=1 from

Consumer and consumer is waiting to become n=1 from producer.

  • This is nothing but deadlock.


Method 2:

Consumer: 1, 2 3 |producer 1,2, 3,4 (waiting for s to become 1)| consumer : 4 (waiting for n to become 1 )  So both are in waiting state so deadlock .

Hence option 3 is the correct answer.

Related Questions

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