Concurrent Fetch&Adds
•When
multiple Fetch&Adds are executed simultaneously, they are serializable
•Assume Fetch&Add(V, e1) and Fetch&Add(V,
e2) are execute simultaneously
•Assuming
an initial value of e0
•Final
value is e0+e1+e2
•The 1st process receives either e0 or e0+e2, implying it was first (e0)
or second (e0+e2)
•The
2nd process receives either e0 or e0+e1, implying it was second
(e0+e1) or first (e0)
Suppose both execute
Fetch&Add(I,1), then one
gets I back, the other I+1, and final is I+2