Path: utzoo!attcan!uunet!mcsun!hp4nl!nikhefh!e07
From: e07@nikhefh.nikhef.nl (Eric Wassenaar)
Newsgroups: comp.sys.apollo
Subject: Unix file locking problems
Message-ID: <948@nikhefh.nikhef.nl>
Date: 11 Jul 90 15:12:21 GMT
Sender: e07@nikhef.nl (Eric Wassenaar)
Organization: Nikhef-H, Amsterdam (the Netherlands).
Lines: 29


A Unix application that requires regulated access from several
processes to one and the same file, may not run safely on Apollo.
A usual method to grant exclusive access is to follow an open()
by a flock() but this does not work on Apollo because

1. flock() only works when used from processes running on the
   same node.
2. you cannot open() a file (not even readonly) that is currently
   opened for write on another node. The open() fails with ETXTBSY.

This makes it difficult to port such applications to Apollo without
major re-writes. An obvious example is the electronic mail, which
suffers from the above behaviour, and cannot be trusted to work
reliably on Apollo. You have to adapt all mail utilities such as
/usr/lib/sendmail, /bin/mail, /usr/ucb/mail, /usr/ucb/from, mush, etc.
(Another example is the usenet news facility, with multiple access
to the active file. This package was adapted by Jim Rees, I believe.)

Does someone know a solution to solve this problem in general (without
replacing unix system calls with aegis system calls everywhere) ?
Or is this a fundamental portability difficulty ?

Eric Wassenaar
-- 
Organization: NIKHEF-H, National Institute for Nuclear and High-Energy Physics
Address: Kruislaan 409, P.O. Box 41882, 1009 DB Amsterdam, the Netherlands
Phone: +31 20 592 0412, Home: +31 20 909449, Telefax: +31 20 592 5155
Internet: e07@nikhef.nl