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Re: Multiple Routers Processing A Single Message (patch enclosed)
> As we have discussed recently, one can enforce single-threadedness of
> renaming of the message files in $POSTOFFICE/router by using link() and
> unlink() and checking the return from unlink(). Participants seemed to be of
> the opinion that unlink() should always be an atomic operation, whereas
> rename() is apparently not always atomic.
> I've implemented this change after testing the theory using file locks for
> several days. The duplicate messages ceased.
There were dupes even with file-locks ?
> The diff below changes lib/esyslib.c to never use rename(), but to use link()
> and unlink() instead and check the outcome of the unlink(). If the unlink()
> of "from" fails, then "to" is also unlink()ed and we return -1 to indicate
> failure - either due to an error or because another router process link()ed
> and unlink()ed the file before we could. This should enforce single-threaded
> renaming in the routers.
I accepted it in a bit different form. For erename() the rename(2)
is ok, but for eqrename() that is used for acquiring locking, it
will now always use link(2)/unlink(2).
The rename(2) is nice with NFS, I think. One message instead of
a slew of them...
It looks like ZMailer can never be put on top of Andrew-FS, which
allows only one link to any file... (Not that I have any reason
to want to do that, for that matter.)
> I submit the following diff (against v2.99.46) for your consideration. I
> have placed the resultant router into production use on several IRIX 5.3
/Matti Aarnio <email@example.com>