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# Representation of System Model with Resource-Allocation Graph - PowerPoint PPT Presentation

DEADLOCK Date- 12/3/14 By Manoj Kumar (11CS10055). Representation of System Model with Resource-Allocation Graph. A set of edges E and A set of vertices V V is partitioned into two types:

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### DEADLOCKDate- 12/3/14 By Manoj Kumar (11CS10055)

• A set of edges E and A set of vertices V

• V is partitioned into two types:

• P = {P1, P2, …, Pn}, the set consisting of all the processes in the system.

• R = {R1, R2, …, Rm}, the set consisting of all resource types in the system.

• request edge – directed edge P1  Rj

• assignment edge – directed edge Rj Pi

• Process Graph

• Resource Type with 4 instances

• Pirequests instance of Rj

• Pi is holding an instance of Rj

Let Deadlocks occur, detect them and take

action.

By Structurally negating one of the four Required

conditions.

Just ignore the problem

- Allow system to enter Deadlock State

- Detection Algorithm

- Recovery Scheme

• Maintain wait-for graph

• Nodes are processes.

• Pi Pjif Piis waiting forPj.

• Periodically invoke an algorithm that searches for a cycle in the graph. If there is cycle there exists Deadlock.

• An algorithm to detect a cycle in a graph requires an order of n2 operations, where n is the number of vertices in the graph.

• Available: A vector of length m indicates the number of available resources of each type.

• Allocation: An n x m matrix defines the number of resources of each type currently allocated to each process.

• Request: An n x m matrix indicates the current request of each process. If Request [ij] = k, then process Pi is requesting k more instances of resource type Rj.