Dead Lock

Deadlocks!
• System Model!
• Deadlock Characterization!
• Methods for Handling Deadlocks!
• Deadlock Prevention!
• Deadlock Avoidance!
• Deadlock Detection !
• Recovery from Deadlock !
• Combined Approach to Deadlock Handling

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.!

Deadlock Characterization!
• Mutual exclusion: only one process at a time can use a resource.!
• Hold and wait: a process holding at least one resource is waiting to acquire additional resources held by other processes.!
• No preemption: a resource can be released only voluntarily by the process holding it, after that process has completed its task.!
• Circular wait: there exists a set {P0, P1, …, P0} of waiting processes such that P0 is waiting for a resource that is held by P1, P1 is waiting for a resource that is held by P2, …, Pn–1 is waiting for a resource that is held by Pn, and P0 is waiting for a resource that is held by P0.!