Deadlock and Starvation - Operating Systems - Lecture Slides, Slides of Computer Science

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Operating Systems

Lecture 14:

Deadlock and Starvation

Potential Deadlock

I need quad A and B

I need quad B and C

I need quad C and B

I need quad D and A

Deadlock

• 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

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

Alternative logic

• Suppose that P does not

need both resources at

the same time so that the

two processes have this

form

Diagram of

alternative logic

Resource Allocation Graphs

11

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