RSS reader causes Trac to crash

[PBruin]

My Trac web site crashes 9 out of 10 times when starting my RSS Reader

• Using RSS Owl as rss reader
• Apache 2.0.52 mod_python 3.1.4 python 2.3.5 on Windows XP
• Other websites on the same server will still work as per normal
• Using Trac [1864]
• When restarting Apache Windows XP comes with a crash message in libhttpd.dll or ntdll.dll
• Apache log file does not contain much usefull info
  • [notice] Child 6708: Terminating 5 threads that failed to exit.

Is anybody else experiencing the same problem?

[PBruin]

Some more info. I am actually getting three RSS streams:
​https://trac.myserver.com/trac/timeline?changeset=on&ticket=on&milestone=on&max=50&daysback=90&format=rss
​https://trac.myserver.com/trac/timeline?changeset=on&ticket=on&ticket_details=on&milestone=on&wiki=on&max=100&daysback=7&format=rss
​https://trac.myserver.com/trac/report/9?format=rss&USER=PBruin
It will cause trac to stop responding, the only way to continue is to restart Apache. Is there maybe some additional info that you would like me to provide?

[Christian Boos]

You should also enable logging for Trac (see TracLogging) and look there for a stack trace.

Your problem is likely related to multithreaded issues… (see #1721)

In the meantime, you can setup a tracd server (with rev ≥ r1875, which has the multithreading disabled) and see if this still happens, with your RSS reader starting 3 simultaneous requests.

[PBruin]

I used this configuration for logging

[logging]
log_file = trac.log
log_level = DEBUG
log_type = file

All I got was this debug info.

10:16:41 Trac[formatter] DEBUG: Executing Wiki macro TOC by provider <trac.wiki.macros.UserMacroProvider object at 0x04A0B3F0>
10:16:48 Trac[svn_fs] DEBUG: Opening subversion file-system at /repos/sw with scope /
10:16:48 Trac[cache] DEBUG: Checking whether sync with repository is needed
10:16:48 Trac[svn_fs] DEBUG: Closing subversion file-system at /repos/sw
10:16:52 Trac[svn_fs] DEBUG: Opening subversion file-system at /repos/sw with scope /
10:16:52 Trac[cache] DEBUG: Checking whether sync with repository is needed
10:16:52 Trac[svn_fs] DEBUG: Closing subversion file-system at /repos/sw
10:17:00 Trac[svn_fs] DEBUG: Opening subversion file-system at /repos/sw with scope /
10:17:00 Trac[cache] DEBUG: Checking whether sync with repository is needed
10:17:00 Trac[svn_fs] DEBUG: Opening subversion file-system at /repos/sw with scope /

What I did:

• 10:16:41 Restart Apache
• 10:16:48 Reload rss feed 1
• 10:16:52 Reload rss feed 2
• 10:17:00 Reload both feeds at the same time

[Christian Boos]

This problem is related to #1401 for the cause (crash in SVN bindings) and to #1811 for the context (Apache server (2.0.54, worker)).

From your log:

...
10:17:00 Trac[svn_fs] DEBUG: Opening subversion file-system at /repos/sw with scope /
10:17:00 Trac[cache] DEBUG: Checking whether sync with repository is needed
10:17:00 Trac[svn_fs] DEBUG: Opening subversion file-system at /repos/sw with scope /

it seems that two subversion filesystem objects are opened at the same time, therefore by two different threads.

While theoretically this shouldn't be a problem since each call to the SVN API should be done with the GIL held, I suspect that this is not implemented in a very robust way in the bindings…

In the meantime, you should try to setup a server which doesn't make use of threads. As I don't use apache myself, I'm not sure the prefork model is available on Windows, but if so, you could try to use this model instead of mpm_winnt one, as it is probably the case.

[PBruin]

Thanks for the tip. I have not used the prefork module as I cann't find much on it for Windows but after your tip have reduced the number of Threads per child from 250 to 1. This prevents the crashes and I will stick with this for the moment.

<IfModule mpm_winnt.c>
ThreadsPerChild 1
MaxRequestsPerChild  0
</IfModule>

[Christian Boos]

Can you please try out the patch cmlenz wrote for #1811? (with ThreadsPerChild set higher than 1, of course)

[PBruin]

Bingo,

Tried the patch with the ThreadsPerChild set back to 250 and it seems to work fine. I can hit the reload favarites button many times without a problem.

Thanks

[Christopher Lenz]

Thanks for testing the patch.

[Christopher Lenz]

This has hopefully been fixed in [2013]. Please reopen if you still encounter an error related to this.