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computer networks
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Deadlock Detection
With one resource of each type• Construct a resource graph– If this graph contains one or more cycles, deadlock
exists– If no cycles exist, system is not deadlocked.
Operating Systems: Deadlock 7
Resource Allocation Modelling using Graphs
Nodes : resource process
Arcs : resource requested :
resource allocated :
Operating Systems: Deadlock 8
• Methods of Detection - single resources– search for loops in resource allocation graph
Operating Systems: Deadlock 9
• Depth-first Graph search– use a list of nodes L and progressively mark arcs
1. For each node N in the graph, perform steps 2-6 with N as starting node
2. Initialise L to empty and designate all arcs as unmarked3. Add current node to L
• check if node appears twice in L• if so, graph contains a cycle - algorithm terminates
4. From given node, if there are any unmarked outgoing arcs, goto 5else goto 6
5. Pick an unmarked outgoing arc and mark it• follow it to new current node and goto 3
6. Have reached a dead end• go back to previous node and goto 4• if this node is the initial node, graph does not contain cycles and
algorithm terminates
Recovery