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From Mark Thomas <ma...@apache.org>
Subject Re: Bug that spans tomcat and tomcat-native
Date Mon, 27 Jun 2016 21:19:03 GMT
On 27/06/2016 19:59, Nate Clark wrote:
> On Mon, Jun 27, 2016 at 2:13 PM, Rainer Jung <rainer.jung@kippdata.de> wrote:

<snip/>

>> I wouldn't care too much about portability right now. If you can prove
>> Mark's analysis by using gettid() on Linux and checking that this fixes the
>> performance issue, that would very useful feedback. If it doesn't help, we
>> can go down the path of using the hash statistics to get more info about
>> what's happening. If it helps, we can think further about how to reduce hash
>> collisions fo every platform.

I went down the hash statistics route any way. The short version is with
11 threads and 8 buckets every thread ends up in the same bucket. This
was on OSX. I'm pretty sure Linux will be the same.

> I can try that, but unfortunately will not be able to run the test
> right away. The machine I was using is a shared resource, which
> somebody else needs for the next few days.

Next up is trying to figure out a patch to fix the bucket distribution.

> Even if that does help the performance and makes it so the hash map
> has better distribution. It won't help with long term bloat. If a
> system is running long enough and threads are started and stopped the
> hash map could grow to include up to almost max pid entries, 32768 by
> default on Linux. With the size of the ERR_STATE struct that will be
> roughly 12MB of memory, not horrible but not ideal. I still think
> ERR_remove_thread_state() should probably be invoked prior to a thread
> exiting. The only way I can think of doing that and keeping everything
> in native and not call it for every request would be to call
> pthread_cleanup_push(ERR_remove_thread_state, NULL) the first time a
> thread is used to perform any ssl operation. That would then require
> you to track per thread if the cleanup function had been registered.

That is definitely a secondary consideration at the moment.

> Also, any solution which make the thread id random and not a bounded
> set of values would cause the max memory foot print of the hash map to
> be virtually unbounded and require that ERR_remove_thread_state be
> invoked to clean up the error states.

The function that generated the 'random' ID from the thread ID would
have to be deterministic so the total number of values should remain
bounded. Shouldn't it?

Mark

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