Deadlock Prevention and Deadlock Avoidance are strategies in operating systems to handle deadlocks, but they differ in approach. Deadlock Prevention ensures that at least one of the necessary conditions for a deadlock cannot hold, such as by limiting resource allocation or enforcing a strict order, thus proactively preventing deadlocks from occurring. Deadlock Avoidance, however, dynamically analyzes resource allocation requests to ensure that granting them will not lead to a deadlock, using algorithms like the Banker’s Algorithm.

What is Deadlock Prevention?

Deadlock prevention involves designing the system in such a way that the conditions necessary for a deadlock cannot occur. This proactive approach ensures that the system is always in a safe state, thereby avoiding situations where resources are held indefinitely, leading to a deadlock.

Techniques for Deadlock Prevention:

1. Resource Allocation Graph: Use of a resource allocation graph to detect and prevent potential deadlocks.
2. Mutual Exclusion: Ensuring that resources are held in such a way that only one process can hold them at a time.
3. Hold and Wait: Preventing processes from holding resources while waiting for additional ones.
4. No Preemption: Ensuring that resources cannot be forcibly taken away from a process holding them.

Examples:

1. In a database system, locking strategies that ensure a process cannot hold a lock while requesting additional locks.
2. In an operating system, using strict protocols to allocate resources to prevent circular wait conditions.

What is Deadlock Avoidance?

Deadlock avoidance is a more dynamic approach that ensures the system never enters an unsafe state by carefully analyzing each resource request and allocation. Unlike prevention, which is more static, avoidance involves making real-time decisions based on the current state of the system to avoid potential deadlock scenarios.

Techniques for Deadlock Avoidance:

1. Banker's Algorithm: A method that checks whether a resource request can be safely granted without leading to a deadlock.
2. Safe State Verification: Continuously verifying the system's state to ensure it remains safe and does not lead to deadlock.

Examples:

1. An online transaction processing system using the Banker's Algorithm to decide whether to grant a transaction's resource request.
2. An operating system dynamically analyzing current resource allocation to ensure that granting a new request won’t result in an unsafe state.

Difference Between Deadlock Prevention and Deadlock Avoidance

Basis	Deadlock Prevention	Deadlock Avoidance
Definition	Ensures that the system never enters a state where deadlock can occur by preventing the conditions necessary for deadlock.	Ensures that the system remains in a safe state by dynamically analyzing resource requests and allocations.
Approach	Proactive, static measures to prevent deadlock conditions.	Reactive, dynamic measures to avoid entering unsafe states.
Methodology	Uses techniques like resource allocation graphs, mutual exclusion, and hold and wait prevention.	Uses algorithms like the Banker's Algorithm and safe state verification.
Implementation	May involve design changes and strict protocols.	Requires real-time decision-making and continuous monitoring.
Flexibility	Less flexible as it imposes restrictions to prevent deadlock.	More flexible, adapting to current system state and resource requests.
Example	A system that denies requests for additional resources if it would lead to a potential deadlock.	An online transaction system evaluating if granting a request will maintain system safety.