Multithreaded Nagios Event Loops

Steven D. Morrey smorrey at ldschurch.org
Thu Aug 27 19:42:54 CEST 2009


Hello Everyone,

So after running through it about thousand times I think I have enough data to see what was wrong with my previous approach to multi-threading by splitting the high and low event lists into their own threads.

It turns out there is contention in the macro system, but I think this contention could be better addressed with less granularity rather than more.
My previous approach placed each read and write to the macro system under control of a mutex, this approach didn't work because the layout of the macro system is as such that ANY access needs to be one thread at a time for the entire time the thread needs access to the macro system.
i.e. It was too granular, so what happened is that one thread would go through and setup the macro array, and the other thread would come in and destroy all that.
My new system is much more simplified, but basically each time a function such as grab_host_macros is called, we totally lock out access until the thread is completely done with the macros, and then we release it.
The easiest way to do this would be to utilize a single mutex that is placed right before any thread uses the macro system and released as soon as the thread is completely done with it.
This will require some serious analysis, but will be worth it :) 

A better solution would of course be to rework the entire macro system so each thread is working on it's own copy of the entire macro array, but thats just not practical for me to do at this time.

So anyways, I'm back on track and if anyone is running a 2x branch of nagios I would really appreciate hearing from you if you have any interest at all in this.
Sincerely,
Steve


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