How and why dead lock occur in operating system. Briefly explain in this presentation.

1. Topic
Deadlock
Presented by
Ali Haider

2. What is Deadlock?
• A dead-lock is a situation in which two devices or computer programs
sharing the same resource are affectively stopping each other from
accessing the resource.
• Final result in both programs closing to function.

3. Four conditions for Deadlocks?
1. Mutual Exclusion condition
2. Hold & wait condition
3. No preemption condition
4. Circular wait condition

4. Deadlock Modeling?

5. How Deadlock Occur?

6. How to Handle deadlocks?
• Four major areas of interest in deadlock research
1) Deadlock prevention
2) Deadlock Avoidance
3) Deadlock detection
4) Deadlock Recovery

7. Deadlock prevention?
• Prevention eliminates one of four conditions
1. Elimination of Mutual Exclusion
2. Elimination of Hold & wait condition
3. Elimination of No preemption condition
4. Elimination Of Circular Wait Condition

8. How deadlock can be avoided?
• We can avoid the situation of
deadlocked by:
1. Safe state
2. Banker’s Algorithm
3. Resource Allocation Graph

9. Safe state
• State is safe because OS can definitely avoid deadlock by
blocking any new requests until safe order is executed.
 This avoids circular wait condition.
 Process waits until safe state is guaranteed.

10. Banker’s Algorithm

11. Resource Allocation Graph
• If we have a resource allocation system with only one instance of each
process, a variant of the resource allocation graph can be used for
deadlock avoidance.

12. Deadlock Detection?
• Determines if deadlock has occurred.
• Identifies those processes & resources involved in the
deadlock.

13. Any Question!

14. Thanks