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Re: [gpsd-dev] Hang on Linux/Ubuntu

From: Eric S. Raymond
Subject: Re: [gpsd-dev] Hang on Linux/Ubuntu
Date: Wed, 11 Feb 2015 04:27:00 -0500
User-agent: Mutt/1.5.23 (2014-03-12)

Hal Murray <address@hidden>:
> I setup several Fedora systems to loop running scons check and my extra batch 
> of 100 tests that were good at finding the timing bugs.  They ran for hours 
> without problems.
> So I added another system to the collection, and bingo.  It hangs on the 
> first try.
> Anything else I should look at before I kill it and try again?

Yes.  git pull and try again.  I just fixed a problem that caused a repeatable 
hang on Frank Nicholas's Mac OS X machine.

Annoyingly, I still don't understand exactly why the problem was a
problem.  The test frame used to write "# EOF\n" to gpsd when it
detected that the last sentence of the test load had been sent, but
for some unknown reason doing this did not unstick the select(2) call
in gpsd's main loop under Mac OS X.

I had a feeling that might cause some sort of timing issue and changed
it to append "# EOF\n" to the test load when it's first built (if the
-1 option is on)  That made the tests all work, and I think it likely
to do the same thing for other *BSDs, but... 

...I don't know why.  There's some wacky interaction between select(2), 
delays, and input timing that I don't grok, and it's variable by OS.
                <a href="";>Eric S. Raymond</a>

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