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Module 4: Deadlocks

201914m

Define deadlock. List four necessary conditions for occurrence of deadlock.

A system contains six units of resource, and n processes that use the resource. What is the maximum value of n for which the system will be deadlock free if the maximum requirement of each process is 3?

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Deadlock Definition & Conditions

Deadlock = set of processes blocked each waiting for resource held by another, circular wait.
Four Coffman conditions: Mutual Exclusion, Hold-and-Wait, No Preemption, Circular Wait.
Max n for 6 units, need 3 per process: For deadlock-free, n*(need-1)+1 ≤6 → n*2+1≤6 → n≤2 (integer). So n=2 deadlock-free, n=3 may deadlock. Some texts give n=2.

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