# Deadlock and Starvation - Operating Systems - Lecture Slides, Slides for Computer Science. All India Institute of Medical Sciences

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These are the Lecture Slides of Operating Systems which includes Sleeping Barber Problem, Waiting Customers, Chair and Sleeps, Barber Is Sleeping, New Customer Arrives, Barber Shop Hints, Customer Threads, Barber Invokes...
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Operating Systems Lecture 14:

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I need quad A and B

I need quad B and C

I need quad C and B

I need quad D and A

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HALT until B is free

HALT until C is free

HALT until D is free

HALT until A is free

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• A set of processes is deadlocked when each process in the set is blocked awaiting an event that can only be triggered by another blocked process in the set – Typically involves processes competing for the

same set of resources

• The bad news: no efficient solution

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Two Processes P and Q

• Two processes P and Q, each needing exclusive access to a resource A and B for a period of time

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Alternative logic

• Suppose that P does not need both resources at the same time so that the two processes have this form

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Diagram of alternative logic

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Resource Allocation Graphs

• Directed graph that depicts a state of the system of resources and processes

• Process == circle, Resource == square

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Resource Allocation Graphs

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Four Conditions for Deadlock 1. Mutual exclusion condition

– Only one process may use a resource at a time 2. Hold-and-wait condition

– A process may hold allocated resources while awaiting assignment of others

3. No preemption condition – No resource can be forcibly removed form a process holding it

4. Circular wait condition – A closed chain of processes exists, such that each process holds

at least one resource needed by the next process in the chain

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Cars in Intersection, again

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