Deadlocks

• Deadlocks

A deadlock situation can arise if the following four conditions hold simultaneously in a system:

*Mutual exclusion. At least one resource must be held in a nonsharable mode;
That is, only one process at a time can use the resource.
If another process requests that resource, the requesting process must be delayed until the resource has been released.

*Hold and wait. A process must be holding at least one resource and waiting to acquire additional resources that are currently being held by other processes.


*No preemption. Resources cannot be preempted; that is, a resource can be released only voluntarily by the process holding it, after that process has completed its task.


*Circular wait. A set $ \{P_0,P_1,\ldots,P_n\}$ of waiting processes must exist such that

http://siber.cankaya.edu.tr/ozdogan/OperatingSystems/ceng328/node155.html

• Deadlock

A deadlock is a situation in which two or more competing actions are each waiting for the other to finish, and thus neither ever does
http://en.wikipedia.org/wiki/Deadlock