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1. Methods for Handling Deadlocks

2. Methods for Handling Deadlocks
• Deadlock Prevention
• Deadlock Avoidance
• Deadlock Detection
• Recovery from Deadlock

3. Deadlock Prevention
• Necessary Conditions for Deadlock
• Mutual Exclusion
• Hold and Wait
• No Preemption
• Circular Wait
• We can prevent a Deadlock by eliminating any of
the above four conditions.

4. Deadlock Avoidance
• Deadlock prevention algorithm may lead to
low device utilization and reduces system
throughput.
• Avoiding deadlocks requires additional
information about how resources are to be
requested.

5. States
• Safe state( No deadlock)
It is a state where the operating system can avoid
unsafe and deadlocked states.
• Unsafe state (Deadlock)
It is a state where the operating system cannot
prevent processes from requesting resources in
such a way that any deadlock occurs.
• Deadlock state is a state where two or more
processes are blocked and waiting for each other
to release the resources they need to proceed.

7. Banker’s Algorithm
• Banker’s algorithm is a deadlock avoidance and
Detection algorithm.
• It is named so because this algorithm is
Banker’s Algorithm used in banking systems to
determine whether a loan can be granted or
not.
• Bankers’ Algorithm is a resource allocation and
deadlock avoidance algorithm that tests all
resource requests made by processes.

8. Banker’s Algorithm
• It checks for the safe state, and if granting a
request keeps the system in safe state, the
request is allowed.
• However, if no safe state exists, the request is
denied.
• The Banker’s Algorithm is a smart way for
computer systems to manage how programs
use resources, like memory or CPU time.

9. Components of the Banker’s Algorithm
1. Available
2. Max
3. Allocation
4. Need

10. Need [i, j] = Max [i, j] – Allocation [i, j]
So, the content of Need Matrix is:

17. Deadlock Detection
• When the system is in deadlock then one method is to
inform the operator and then operator deal with
deadlock manually.
• A Resource Allocation Graph (RAG) is used to detect
deadlocks by analyzing the relationships between
processes and resources in a system. It visually
represents how resources are allocated and requested.
• If graph contains no cycles → no deadlock.
• If graph contains a cycle → if only one instance per
resource type, then deadlock.
if several instances per resource type, possibility of
deadlock

18. Recovery from Deadlock
• Process termination:
One way to recover from a deadlock is to
terminate one or more of the processes involved in
the deadlock.
• By releasing the resources held by these
terminated processes, the remaining processes
may be able to continue executing.
• Resources preemption:
Resources can be forcibly taken away from one or
more processes and allocated to the waiting
processes.