I'm trying to understand usage of file.flock(File::LOCK_SH) which
obtains a shared lock. The documentation says it allows other
processes to also obtain a shared lock. What's the point of a lock if
it isn't locking anybody else out? There must be a use case for this
that I'm not seeing.

Also, the documentation for File.flock says that it isn't supported on
all platforms. If you know of platforms that definitely do or do not
support this, I'd like to hear about them. I'm particularly interested
in XP and Fedora Core Linux.

--
R. Mark Volkmann
Partner, Object Computing, Inc.