1) Mutex condition : A resource cannot be used by another process for a period of time when it is in use. 2) request and hold condition : means that the process has maintained at least one resource, but a new resource request has been made, and the resource has been occupied by another process, at which time the request process is blocked, but the other resources that you have obtained remain. 3) non-deprivation conditions : Refers to the process has been obtained resources, before the end of use, can not be deprived, can only be released by themselves when the use is complete. 4) cyclic wait condition : Refers to a process-the circular chain of resources, that is, the P0 in the process collection {p0,p1,p2,,pn} is waiting for a resource to be occupied by a P1 in the event of a deadlock P1 is waiting for P2 to occupy the resources, ..., PN is waiting for resources that have been consumed by P0.
Four prerequisites for iOS development----operating system----deadlock
