Record locking and future releases of the UNIX system

Provisions have been made for file and record locking in a UNIX system environment. In such an environment the system on which the locking process resides may be remote from the system on which the file and record locks reside. In this way multiple processes on different systems may put locks upon a single file that resides on one of these or yet another system. The record locks for a file reside on the system that maintains the file. It is also important to note that deadlock detection/avoidance is only determined by the record locks being held by and for a single system. Therefore, it is necessary that a process only hold record locks on a single system at any given time for the deadlock mechanism to be effective. If a process needs to maintain locks over several systems, it is suggested that the process avoid the sleep-when-blocked features of fcntl or lockf and that the process maintain its own deadlock detection. If the process uses the sleep-when-blocked feature, then a timeout mechanism should be provided by the process so that it does not hang waiting for a lock to be cleared.