Media access scheduler method and apparatus

Abstract

A media access scheduling system that allows concurrent users to access shared media by having each user decide, as it gets access to the media, whether it is the best candidate for the use of the media: if it is, it proceeds to use the media; if it is not, it does not access the media, but instead releases access reservation and waits for a time when it may be the best candidate. In a preferred embodiment, the determining factor for the best candidate is whether the media needs to be repositioned or setup. If the media is positioned where the candidate wants it to be, no positioning or setup is required, and the user declares itself to be the best choice. If the media must be repositioned or setup, then there is probably another user process which would be a better candidate. To identify when a user is finished with the media and repositioning or setup is warranted, each user program refers to and maintains an access time in a globally visible place. If some period of time has elapsed since the previous access to the volume, it is likely that the previous user program has finished, and a candidate which requires repositioning should proceed. To prevent users from waiting indefinitely, each candidate keeps track of the time it has spent waiting, and upon reaching some predetermined limit of continuous waiting, accesses the media regardless of whether or not it needs to reposition.