Aucb.568
fa.editor-p
utcsrgv!utzoo!decvax!ucbvax!C70:editor-people
Mon Mar  1 20:31:13 1982
interlocking
>From ADMIN.MRC@SU-SCORE Mon Mar  1 20:12:19 1982
    On TOPS-20, if you are interested in merely interlocking between
cooperating processs, there are the ENQ% and DEQ% system calls.  This
lock and unlock a monitor resource independent of the file.  The MM
mailsystem uses this to great success.  In addition, file clobberage
due to that file being mapped during a system crash can be avoided by
not allowing dribbling of updates from the swapper to the filesystem
copy, then forcing the updates at graceful points (another feature that
isn't in Tenex).

    If you insist upon interlocking the file but allowing appends to
it (as in a mail file), I don't know of any system offhand which allows
this.  On SAIL, a file is interlocked once you try to change it, and
once that it done no changes (including appends) may be made by any
other process.
-- Mark --
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