Question

Explain the resource-allocation graph and wait-for graph for deadlock processing.

Answer 1

Please follow the data and description :

Deadlock :

In the stream of computer science and technology, a deadlock refers to a specific condition when two or more processes are waiting for each another to release a resource, or more than two processes are waiting for resources in a circular chain.

Resource Allocation Graph :

It is a graph of data that tracks which resource is being held by which process and which process is waiting for a resource of a particular type. It is very simple but yet a poweful process to illustrate the user of how can the interacting processes arise or result to a situation of deadlock. The graph can be depicted as if a process is using a resource, an arrow is drawn from the resource node to the process node. If a process is requesting a resource, an arrow is drawn from the process node to the resource node.

If for example, let us consider that if a process 1 that holds the resource A, and that the process 2 holds the resource B and it is likely in turn that the process 1 is waiting for the resource B and that the process 2 is waiting for the resource A, which results in a circular dependency over the resources and the processes, then this situation leads for the processes process 1 and 2 execution will be deadlocked.

Wait-for graph :

It is a directed graph used for the process of deadlock detection in the operating systems and even in the relational database systems. A deadlock detection process uses the algorithm that makes use of a wait-for graph to track which other processes a process is currently blocking on. In a wait-for graph, generally the processes are represented as the nodes, and an edge from process A to B conveys that the process B is holding a resource that A needs and thus A is waiting for the process B to release its lock on that resource. If the process is waiting for more than a single resource to become available, multiple edges may represent a conjunctive (and) or disjunctive (or) set of different resources or a certain number of equivalent resources from a collection. In the conjunctive case, graph cycles imply the possibility of a deadlock, whereas in the disjunctive case knots are indicative of deadlock possibility.

Hope this is helpful.