The Deadlock Problem

---

A set of blocked processes each holding a resource and waiting to acquire a resource held by another process in the set.

Example
• System has 2 disk drives.
• P1 and P2 each hold one disk drive and each needs another one.

Example
• semaphores A and B, initialized to 1

P0	P1
wait (A);	wait(B)
wait (B);	wait(A)

Bridge Crossing Example

---

Traffic only in one direction.

Each section of a bridge can be viewed as a resource.

If a deadlock occurs, it can be resolved if one car backs up (preempt resources and rollback).

Several cars may have to be backed up if a deadlock occurs.

Starvation is possible.

---