The three cooperating processes all read data from the same input device. Each process, when it gets the input device, must read two consecutive data. I want to use mutual exclusion to do this. The declaration and initialization that I think would work here are:

semaphore s=1

sa1 = 0, sa2 = 0, sb1 = 0, sb2 = 0, sc1 = 0, sc2 = 0

I'd like to use semaphores to synchronize the following processes:

P1:                     P2:                     P3:
input(a1,a2)            input (b1,b2)           input(c1,c2)
Y=a1+c1                 W=b2+c2                 Z=a2+b1
Print (X)               X=Z-Y+W

I'm wondering how to use the minimum number of semaphores to solve this.

Diagram of cooperating Processes and one input device:

It seems like P1 and P2 would start something like:

wait(s)

input (a1/b1, a2/b2)

signal(s)