Semi-preemptible locks for a distributed file system

Many applications require the ability to obtain exclu-sive access to data, where an application is granted privi-leges to an object that cannot be preempted and limits the actions of other processes. Local file systems support ex-clusive access to files by maintaining information about the access rights of current open file instances, and check-ing subsequent opens for compatibility. Implementing ex-clusive access in this manner for distributed file systems degrades performance by requiring every open file to be registered with a server that maintains global open state. We introduce a distributed lock for managing file ac-cess, called a semi-preemptible lock, that avoids this performance limitation. Clients locally grant open re-quests for files that are consistent with a distributed semi-preemptible lock that they hold. File system clients retain or cache distributed locks, even in the absence of open file instances. When a file access lock is already cached, a client services open requests without a server message, improving performance by exploiting locality, the affinity of files to clients.