Resource Graphs

Given the four preconditions, some schedules may lead to circular waits.

• Deadlock is easily seen with a resource graph or wait-for graph.
  The graph has a vertex for each process and each resource.
  
  If process A holds resource R, add an arc from R to A.
  If process A is waiting for resource R, add an arc from A to R.

The system is deadlocked iff the wait-for graph has at least one cycle.

2

1

B

A

A grabs fork 1 and

waits for fork 2.

B grabs fork 2 and

waits for fork 1.

Sn

assign

request

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