Question

Given the following process/resource information, construct a resource-
allocation graph. Is deadlock possible? Explain.

Resource # of instances Requested by Allocated to

R1 2 P3 P1, P2
R2 1 P4 P3
R3 2 P4 P2, P3
R4 1 P1 P2

Answer 1

P2 is holding R1 and R4.
P2 is waiting for R3 and can’t be released.
R3 is held by P3 and is waited by P4.
P3 is waiting for R1, which is held by P2, so there is a deadlock. P4 doesn’t break the cycle, because it is waiting for R3.