Mailing List Archive: CleanupHandler not always running

CleanupHandler not always running

Dec 26, 2015, 11:37 AM

Post #1 of 4 (2199 views)

Hello Mod_perl-ers,

I've got an app that increments a counter in redis in a
PostReadRequestHandler and decrements it in a CleanupHandler. I'm noticing
a small amount of cases where the counter doesn't get decremented. There
are no segfaults but there are a small number of "Apache2::Filter internal
flush: (-3) Unknown error 4294967293 at -e line 0" messages. Looking at
the source code, I believe a modperl_croak is getting called in this case.
Would this cause the CleanupHandler to not run? What exactly happens when
modperl_croak is called?

Thanks,

Paul

Re: CleanupHandler not always running [ In reply to ]

gozer at ectoplasm

Dec 26, 2015, 4:33 PM

Post #2 of 4 (2136 views)

Permalink

Could be the result of shutdown or graceful restarts. CleanupHandlers are synthetic to mod_perl and are not specifically supported/guaranteed by httpd

See https://perl.apache.org/docs/2.0/user/handlers/http.html#Possible_Caveats

Sent from my iPhone

> On Dec 26, 2015, at 14:37, Paul Silevitch <paul@silevitch.com> wrote:
>
> Hello Mod_perl-ers,
>
> I've got an app that increments a counter in redis in a PostReadRequestHandler and decrements it in a CleanupHandler. I'm noticing a small amount of cases where the counter doesn't get decremented. There are no segfaults but there are a small number of "Apache2::Filter internal flush: (-3) Unknown error 4294967293 at -e line 0" messages. Looking at the source code, I believe a modperl_croak is getting called in this case. Would this cause the CleanupHandler to not run? What exactly happens when modperl_croak is called?
>
> Thanks,
>
> Paul
>

Re: CleanupHandler not always running [ In reply to ]

paul at silevitch

Dec 27, 2015, 7:41 AM

Post #3 of 4 (2128 views)

Permalink

Philippe,

I think you are on to something. We use graceful-stops and we reset the
counters during a subsequent start. It looks like the counters sometimes
come out of the graceful-stop / start with an elevated number which
supports your theory. Do you recommend using a LogHandler instead of a
CleanupHandler?

Thanks!

Paul

On Sat, Dec 26, 2015 at 7:33 PM, Philippe Chiasson <gozer@ectoplasm.org>
wrote:

> Could be the result of shutdown or graceful restarts. CleanupHandlers are
> synthetic to mod_perl and are not specifically supported/guaranteed by httpd
>
> See
> https://perl.apache.org/docs/2.0/user/handlers/http.html#Possible_Caveats
>
> Sent from my iPhone
>
> On Dec 26, 2015, at 14:37, Paul Silevitch <paul@silevitch.com> wrote:
>
> Hello Mod_perl-ers,
>
> I've got an app that increments a counter in redis in a
> PostReadRequestHandler and decrements it in a CleanupHandler. I'm noticing
> a small amount of cases where the counter doesn't get decremented. There
> are no segfaults but there are a small number of "Apache2::Filter
> internal flush: (-3) Unknown error 4294967293 at -e line 0" messages.
> Looking at the source code, I believe a modperl_croak is getting called in
> this case. Would this cause the CleanupHandler to not run? What exactly
> happens when modperl_croak is called?
>
> Thanks,
>
> Paul
>
>

Re: CleanupHandler not always running [ In reply to ]

paul at silevitch

Jan 25, 2016, 7:08 PM

Post #4 of 4 (2080 views)

Permalink

I figured this out. We use mod_proxy and in the case where there's a proxy
error, PostReadRequestHandler is executed twice (once for the original
request before proxying and once for the 50x error generated by
mod_proxy). By checking $r->status, I can make sure that the code that
increments in PostReadRequestHandler is only called once.

Paul

On Sun, Dec 27, 2015 at 10:41 AM, Paul Silevitch <paul@silevitch.com> wrote:

> Philippe,
>
> I think you are on to something. We use graceful-stops and we reset the
> counters during a subsequent start. It looks like the counters sometimes
> come out of the graceful-stop / start with an elevated number which
> supports your theory. Do you recommend using a LogHandler instead of a
> CleanupHandler?
>
> Thanks!
>
> Paul
>
> On Sat, Dec 26, 2015 at 7:33 PM, Philippe Chiasson <gozer@ectoplasm.org>
> wrote:
>
>> Could be the result of shutdown or graceful restarts. CleanupHandlers are
>> synthetic to mod_perl and are not specifically supported/guaranteed by httpd
>>
>> See
>> https://perl.apache.org/docs/2.0/user/handlers/http.html#Possible_Caveats
>>
>> Sent from my iPhone
>>
>> On Dec 26, 2015, at 14:37, Paul Silevitch <paul@silevitch.com> wrote:
>>
>> Hello Mod_perl-ers,
>>
>> I've got an app that increments a counter in redis in a
>> PostReadRequestHandler and decrements it in a CleanupHandler. I'm noticing
>> a small amount of cases where the counter doesn't get decremented. There
>> are no segfaults but there are a small number of "Apache2::Filter
>> internal flush: (-3) Unknown error 4294967293 at -e line 0" messages.
>> Looking at the source code, I believe a modperl_croak is getting called in
>> this case. Would this cause the CleanupHandler to not run? What exactly
>> happens when modperl_croak is called?
>>
>> Thanks,
>>
>> Paul
>>
>>
>