When and under what conditions can resource deadlock occur in a system?

Mutual exclusion (deadlock) of resources occurs when multiple processes or threads simultaneously hold resources and wait for the release of resources occupied by each other, creating a cyclic dependency.

Conditions for deadlock:

1. Mutual exclusion — resources can only be held by one process at a time.
2. Hold and wait — a process holds one resource and waits for another.
3. No preemption — resources cannot be forcibly taken away from a process.
4. Circular wait — there exists a cycle of processes, each waiting for a resource held by the next in the cycle.

Example: Process A has acquired resource 1 and is waiting for resource 2, while process B has acquired resource 2 and is waiting for resource 1 — a deadlock occurs.