what is deadlock ,methods for handling deadlocks and how to prevent deadlock

2. {
Deadlocks
 Definition
 System model
 Deadlock characterization
• Deadlock with mutex locks
• Necessary conditions
• Resource-allocation graph
 Methods for handling deadlocks
 Deadlock prevention
• Mutual Exclusion
• Hold and Wait
• No pre-emption
• Circular wait
 Conclusion

3.  A process requests resources; if the resources are not available at that
time, the process enters a waiting state. Sometimes, a waiting process is
never again able to change state, because the resources it has requested
are held by other waiting processes. This situation is called a deadlock.
Definition
Deadlock

4. System model

5. Deadlock characterization

7. Mutual
exclusion
Hold and
Wait
No Pre-
emption
Circular
Wait
Necessary conditions

8.  Deadlocks can be described more precisely in terms of a directed graph
called a system resource-allocation graph.
 Request edge
 Assignment edge.
Resource Allocation Graph

10. Methods
• We can use a protocol to prevent or avoid deadlocks, ensuring that the
system will never enter a deadlocked state.
• We can allow the system to enter a deadlocked state, detect it , and
recover.
• We can ignore the problem altogether and pretend that deadlocks never
occur in the system
 Deadlock prevention
 Deadlock avoidance

11.  Mutual exclusion
 Hold and Wait
 No pre-emption
 Circular Wait
Deadlock prevention
Preventing deadlocks by constraining how requests for resources can be made
in the system and how they are handled (system design).
The goal is to ensure that at least one of the necessary conditions for deadlock
can never hold.

12. Mutual Exclusion

13. Hold and Wait

14. No pre-emption

15. Circular Wait

16. Conclusion
Avoiding any one of the condition you can
prevent deadlock!!!