opening up the apcu stats file causes FUTEX_WAIT (and subsequent crashes)

[fruitl00p]

Our setup is:
Ubuntu 14.04
Webserver: Apache/2.4.7
PHP 5.5.9-1ubuntu4.3 with OPcache v7.0.3 enabled and loaded via mod_php
APCu 4.0.4

After having the setup run for a while and just accessing the apcu.php script the apache2 processes freeze with a FUTEX_WAIT issue... I've looked at the strace-output but other than the futex_wait i haven't found anything usefull...

Now what? :)

[krakjoe]

Please try to reproduce against latest sources ?

I will need more information to investigate, a backtrace, a way to reproduce or something, possibly access to the machine where it occurs.

[fruitl00p]

Alas, i cant even reproduce it outside of our running production machines in production state... ? After a while just opening up the apcu.php script locks it up... I'll try to reproduce in someother way..

[fruitl00p]

Hmmm...
Upgraded to latest ubuntu php: PHP 5.5.9-1ubuntu4.4 with latest (released apcu: 4.0.6 / $Revision: 328290) And it happened again:
(the master apache2 process)

Process 15563 attached
select(0, NULL, NULL, NULL, {0, 810260}) = 0 (Timeout)
gettimeofday({1410356454, 98973}, NULL) = 0
write(2, "[Wed Sep 10 15:40:54.098973 2014"..., 163) = 163
wait4(-1, 0x7fff32c6d944, WNOHANG|WSTOPPED, NULL) = 0
select(0, NULL, NULL, NULL, {1, 0})     = 0 (Timeout)
wait4(-1, 0x7fff32c6d944, WNOHANG|WSTOPPED, NULL) = 0
select(0, NULL, NULL, NULL, {1, 0})     = 0 (Timeout)
wait4(-1, 0x7fff32c6d944, WNOHANG|WSTOPPED, NULL) = 0
select(0, NULL, NULL, NULL, {1, 0})     = 0 (Timeout)
wait4(-1, 0x7fff32c6d944, WNOHANG|WSTOPPED, NULL) = 0
select(0, NULL, NULL, NULL, {1, 0})     = 0 (Timeout)
wait4(-1, 0x7fff32c6d944, WNOHANG|WSTOPPED, NULL) = 0
select(0, NULL, NULL, NULL, {1, 0})     = 0 (Timeout)
wait4(-1, 0x7fff32c6d944, WNOHANG|WSTOPPED, NULL) = 0
select(0, NULL, NULL, NULL, {1, 0})     = 0 (Timeout)
wait4(-1, 0x7fff32c6d944, WNOHANG|WSTOPPED, NULL) = 0
select(0, NULL, NULL, NULL, {1, 0})     = 0 (Timeout)
wait4(-1, 0x7fff32c6d944, WNOHANG|WSTOPPED, NULL) = 0
....

I still haven't been able to reproduce locally in a separate environment ...

[krakjoe]

I think this to be a bug in APCIterator, while working on PHP7 branch, I noticed a couple of things ... try that ?

[fruitl00p]

@krakjoe Wow, you've had a 'free' weekend? Been working hard, great! And thanks so much for (imho) an extension that should be part of core :) Great job! If only i had some C skills to contribute... :/

Anyway, will have a look and see if there is anything to reproduce with the latest and greatest from the seven branch

[krakjoe]

Please try with the latest release on pecl, and report back ?

[krakjoe]

Bump, can you try with 4.0.10 or 5.1.2 please ?

[krakjoe]

This was recently fixed, it was caused by the retention of a lock after fatal engine error.