Consider a system employing a deadlock-avoidance scheme based on pre-
declaration of resource needs for various processes. In particular, the resource needs
of the processes are represented by claim arcs in the resource-allocation graph.
Whenever a resource request by a process is issued, it is rejected by the system if
the newly formed allocation arc (from the resource vertex to the process vertex)
replacing the corresponding claim arc (from the process vertex to the resource
vertex) closes a cycle in the resource-allocation graph. Otherwise, the system grants
the request and converts the claim arc to the allocation arc in the resource-allocation
graph.
Let P1, P2 and P3 be three processes in the system. Let P1 declare that it may
request resources W, X and Y; P2 declare that it may request resources X, Y and Z;
P3 declare that it may request resources W, Y and Z. Construct the resource-
allocation graph with the appropriate claim arcs.
Consider each of the following pairs of resource requests. Based on the resource-
allocation graph constructed above, identify the pair of requests among the
following that can be granted without a deadlock possibility?
\begin{itemize}
\item P1 requesting Y and P3 requesting W
\item P1 requesting X and P2 requesting Z
\item P1 requesting W and P3 requesting Y
\item P1 requesting X and P2 requesting Y
\end{itemize}
