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From Toralf Lund <toralf.l...@pgs.com>
Subject Re: QPid 0.22 C++ client threading
Date Mon, 03 Nov 2014 14:52:41 GMT
On 31/10/14 16:13, Gordon Sim wrote:
> On 10/30/2014 01:30 PM, Toralf Lund wrote:
>> Hi,
>> We have encountered a problem with an application using QPid 0.22/APQP
>> 0.10 with the C++ messaging API, which could be caused by creation of an
>> excessive number of threads. This might not be related to QPid, and the
>> issue may not even be threading in this application (the problem occurs
>> once every blue moon, so it's a bit hard to test theories), but in order
>> to get a clear picture of the situation, it would be good to know what
>> threads QPid creates, and if there are any issues with threading. Some
>> questions:
>>   * When exactly does QPid create a new thread?
> There is a shared thread pool for all 0-10 connections, used for IO. 
> The maximum size is controlled by the max-iothreads option. This is by 
> default set to be the number of available cores (or 1 if that cannot 
> be determined), but can be overidden  e.g. by setting 
> QPID_MAX_IOTHREADS). The pool starts out empty and the size is 
> increased as connections are added, up to the configured limit. At 
> present there is nothing that will kill off threads once created however.
> In addition there is a single timer thread that is used for heartbeat 
> related time activities.
OK. Thanks.

>>   * Are there any known situations where one might end up with lots of
>>     runaway threads?
> Nothing known, no.

>>   * Do I have to do anything specific e.g. after a communication error
>>     in order to make sure old threads go away?
> No.
> [...]
>> The actual problem I'm talking about is that a pthread_create() call
>> used for something unrelated will sometimes fail with EAGAIN.
> Could you perhaps have a cron job that does a ptrace on the process in 
> question periodically, and stores it in a file somewhere, so that you 
> can see what threads were present if and when the problem occurs again?
Yes, that's probably a good idea.

So far I've focused on looking for memory leaks (which I'm assuming may 
also cause this kind of problem), but I haven't found anything.


- Toralf

>> An information anyone might have about the threading behaviour of QPid
>> would be helpful.
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