Binary semaphore


#1

Two concurrent processes P1 and P2use four shared resources R1, R2, R3 and R4 as shown below:

P1: Compute; P2: Compute;
Use R1; Use R1;
Use R2; Use R2;
Use R3; Use R3;
Use R4; Use R4;

Both processes are started at the same time, and each resource can be accessed by only one process at a time. The following scheduling constraints exist between the accesses of resources by the processes:

P2 must complete use of R1 before P1 gets access to R1
P1 must complete use of R2 before P2 gets access to R2
P2 must complete use of R3 before P1 gets access to R3
P1 must complete use of R4 before P2 gets access to R4

There are no other scheduling constraints between the processes above scheduling constraints, what is the minimum no. of binary semaphores needed?
(a) 1 (b) 2 © 3 (d) 4


#2

Answer must be B.