A deadlock in an operating system is a situation where a group of processes are unable to proceed because each process is waiting for a resource that is being held by another process in the group. Essentially, it's a situation where processes get stuck, waiting for resources that will never become available.
Key Conditions for Deadlock
Four conditions must be true simultaneously for a deadlock to occur:
1. Mutual Exclusion: At least one resource must be held in a non-shareable mode, meaning only one process can use the resource at a time.
2. Hold and Wait: A process holding at least one resource is waiting to acquire additional resources that are currently being held by other processes.
3. No Preemption: Resources cannot be forcibly taken from processes holding them. The process must release the resource voluntarily.
4. Circular Wait: There exists a set of processes {P1, P2, ..., Pn} such that P1 is waiting for a resource held by P2, P2 is waiting for a resource held by P3, and so on, with Pn waiting for a resource held by P1, forming a circular chain.
