Resource Allocation Graphs

The set of vertices in this graph contains both the set $R$ and $P$.

A Request edge forms $P_i\to R_j$, and an Assignment edge forms $R_j\to P_i$.

A deadlock can be observed in such a graph through cycles. If a cycle is in the graph, and all resources involved have only one instance, then a deadlock occurs, if each resource has several instances, then there is a possibility of a deadlock.