Applied Gate Full Length Test

Question

Let S be the binary semaphore variable initialized to zero. If no blocked processes exist in the system then consider the execution of the following signal (V), wait (P) operation. The number of blocked processes at the end are _________.

                                         4 P, 6 V, 9 P, 13 V, 14 P

Comments

Here we are making changes on Binary Semaphore so it will acquire either 0 or 1 but when i checked the answer they are treating it as Counting Semaphore so where i am wrong can anybody correct me?

Answer 1

is 13 the answer?

4P means 1 process in cs and 3 blocked

6V unblocks all the blocked process

9P = 8 blocked, 1 in cs

13 V similarly unblocks,

finally 14P means 1 block in cs and rest 13 blocked??

Comments

yes

Answer 2

@Sagar475

Here Semaphore is Binary  ….

So if S=0 and if down or P or wait is performed on S it will remain 0 irrespective of the count of down performed in continous order ….

 

And if S=1 and if up

or

V or signal is perforned on S it will remain 1 irrespective of the count of UP performed in continous order ...

So ,

Here s=0 intitally ....

 

#) 4p i.e 4 down on S , s will remain 0 but 4 process will get blocked …

 

  ##) 6v i.e 6 up on S , s will raise to 1 and all 4 process will get unblock and will execute..

 

###) 9p i.e 9 down on S, s will decement to 0 after 1 down and rest 8 down will cause 8 process to get blocked …

####)13 V i.e 13 up on S , s will increment to 1 and will unblock all the 8 processes ….

 

#####) 14P i.e 14 down on S , it will decrement S to 0 after 1 down and rest all 13 down will cause 13 processes to get blocked....

 

 

1. https://gateoverflow.in/112222/Semaphor-blocked-processes

 

 

Answer 3

Answer will be- 18