Ken wrote:
- The "complex" case, where the sequence file could
potentially be changed from the time that it's first
read until the sequence file needs to be manipulated.
"inc" is an example; "pick" is another.
Is sortm in the same category as folder -pack?
The basic issue there is if you add a new message to a
folder, the long-running command wouldn't necessarily know
the new message existed and thus when it wrote the new
sequence file out it wouldn't write out any sequences that
these new messages are in.
I'm worried about something else: concurrent read/write of
the sequences file. If two or more processes read it and
write it concurrently, the last one to write will destroy
everything that the other processes wrote. Locked-read-
write will detect that, but I'm not sure we can always
correct it. I don't have a concrete example of where we
can't, but it feels analogous to a merge conflict.
adding new messages to a folder that you're currently
inc'ing into is already not safe (messages could get
overwritten).
How so? It depends what "adding" means, but I would limit
that to just nmh commands that can add a new message. I
think that's inc, refile, rcvstore, burst, and thing that
fcc's (comp, dist, forw, repl, mhmail). And I don't think
they'll overwrite a message that any other, even non-nmh,
program had created.
David
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