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From fredk2 <>
Subject Re: Deadlock situation detected/avoided with jk_log_lock
Date Fri, 06 Feb 2009 19:40:34 GMT

Thanks Rainer,

Do I understand you correctly that when Mr. Orton said to never use pthread
nor posixsem mutex ( that
is now obsolete news and that Solaris perfected pthread mutex support since.

You mention that mod_jk uses pthread is that the same as the httpd itself?

Some fellow at Covalent back in the early Apache 2.0 days, posted a white
paper about his various mutex testing, but it does not appear to be
available anymore. Would be interesting to know how it was tested and how it
would playout today.

Rgds - Fred

Rainer Jung-3 wrote:
> On 06.02.2009 18:13, fredk2 wrote:
>> I was doing some stress test (with apache ab, 100 users, 100K requests)
>> to
>> compare an Apache prefork and worker mpm.  The test url is a simple hello
>> servlet on Tomcat 6.0.x via mod_jk. On my Sparc Solaris 10 server with
>> only
>> the Apache set to worker mpm I see following error messages in my jk log:
>> Apache/2.2.11 (Unix) with mod_jk/1.2.26 on Solaris 10.
>> . . .
>> [Thu Jan 08 11:42:28 2009] [error] (45)Deadlock situation
>> detected/avoided:
>> apr_global_mutex_lock(jk_log_lock) failed
>> . . .
>> [Thu Jan 08 11:42:29 2009] [emerg] (45)Deadlock situation
>> detected/avoided:
>> apr_proc_mutex_lock failed. Attempting to shutdown process gracefully.
>> [Thu Jan 08 11:42:29 2009] [error] (45)Deadlock situation
>> detected/avoided:
>> apr_global_mutex_lock(jk_log_lock) failed
>> . . .
>> these errors do not appear to impact the test results and the jk log file
>> seems complete.
>> I can suppress the errors by choosing another Mutex in the Apache
>> directive
>> AcceptMutex, such as sysvsem or pthread.  For Solaris 10 the default
>> mutex
>> for worker MPM is fcntl.  Setting the Mutex sysvsem (also the default on
>> Linux) marginally improves the request time.
>> Can someone explain what exactly these errors means? when does it occur?
>> I would have almost expect a "detected/avoided" to be a [warn] instead of
>> an
>> [error].
>> I have seen the trail but
>> I'd
>> like to hear updated experiences that people have with sysvsem mutexes on
>> Solaris 10 - what is the better mutex?  sysvsme, posixsem, pthread **?
>> any comment will be appreciated.
> I experienced this too a couple of times and once wrote a small C 
> program to reproduce the problem. On Solaris the algorithm to detect a 
> possible deadlock is very careful and returns EDEADLOCK even in 
> situations were you can mathematically prove, that a deadlock is not 
> possible. This happens in a multi-threaded environment when more than 
> one mutex is used.
> Apache httpd and mod_jk use such a mutex and SSL also (so you can 
> observe the same warnings without mod_jk only using SSL with httpd and 
> doing stress tests).
> In older JK versions this could lead to a hang, but we worked around 
> that a couple of versions ago. I generally recommend the pthread mutex 
> for Solaris which doesn't have the problem and seems to be robust 
> despite warnings about pthread mutexes in very old versions of Solaris.
> We even once had a discussion about changing the default httpd mutex on 
> Solaris once, but I think that discussion didn't come to an end.
> Regards,
> Rainer
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