DEADLOCK CHARACTERIZATION

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 non-sharable 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� there must exist a process that is holding at least one resource and is waiting to acquire additional resources that are currently being held by other processes.
� No preemption resources cannot be preempted; that is, the process holding it after that process has completed its task can release a resource only voluntarily by the process holding it, after that process has completed its task.
� Circular wait� there must exist a set {Po,P1,�,Pn} 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 held by Pn and Pn is waiting for a resource that is held by Po.