> On Jun 9, 2021, at 3:00 PM, Andrew C Aitchison <andrew@???> wrote:
>
> On Wed, 9 Jun 2021, Felipe Gasper via Exim-users wrote:
>
>> Hello,
>>
>> Is it possible with Eximâ??s Perl integration to create a reference
>> that will last throughout a messageâ??s delivery and then be reaped?
>>
>> Iâ??d like to explore an flock-based lock for mail delivery that
>> would allow an external process to suspend delivery by holding a
>> lock on a designated path: if Exim/Perl does flock($fh, LOCK_SH)
>> and fails EAGAIN, then Exim will defer acceptance of the message.
>>
>> When the flock() succeeds, ideally that flock()ed Perl $fh will
>> last until delivery is done and then be reaped. Is it safe to
>> store that in a Perl global, then call something else at the end
>> of the routing that deletes/undefs that global? Or is there some
>> cleaner way to give Exim such a reference and have Exim hold onto
>> it for me until routing/delivery is over?
>
> I am reminded of the exim_lock utility, though that is an external process.
>
> I'm a bit confused.
> Are you trying to stop a second message from being accepted *into the
> exim queue* whilst the first is being routed/delivered ?
The idea is more to prevent message delivery during a backup or account reconfiguration.
I specifically want to avoid this:
1. External process suspends user’s mail delivery.
2. External process gets SIGKILL.
3. User gets no more mail until user complains ($$) and someone manually ($$) reenables the user’s mail.
Using flock() for this would cause the mail suspension to go away automatically once whatever holds that lock goes away:
1. External process flock(EX)s user’s special designated file.
2. Exim tries to flock(SH) that same file, gets EAGAIN.
3. Exim tells clients :defer:
4. External process finishes or gets SIGKILL.
5. User can receive mail again, no manual intervention needed.
Alternatively:
1. Exim flock(SH)s the user’s special file.
2. External process tries to flock(EX), gets EAGAIN. Either retries later or just fails.
-FG
