Deadlock Prevention vs Deadlock Avoidance in OS

Deadlock prevention ensures that at least one of the four necessary conditions for a deadlock (Coffman conditions) never holds true.

1. Mutual Exclusion: Allow resources to be shareable (e.g., read-only files). However, some resources like printers cannot be shared.
2. Hold and Wait: Require processes to request all needed resources at once before starting execution.
3. No Preemption: If a process holding some resources requests another resource that cannot be immediately allocated to it, all resources currently being held are preempted (released).
4. Circular Wait: Impose a total ordering of all resource types and require that each process requests resources in an increasing order of enumeration.

Deadlock avoidance does not strictly prevent the four conditions. Instead, the OS dynamically checks the resource allocation state before granting a resource request to ensure that the system never enters an 'unsafe state'.

• The OS needs prior information about how many resources a process will need over its lifetime.
• If granting a request leads to a state where a deadlock could happen (unsafe state), the request is delayed.
• Banker's Algorithm is the most famous algorithm used for deadlock avoidance.