Re: Flakey behavior

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Stas Bekman <stas@xxxxxx.xxx> writes:

> David Dyer-Bennet wrote:
>> David Dyer-Bennet <dd-b@xxxx.xxx> writes:
>>
>>>I'm running into flakoid behavior in a script that uses Image::EXIF to
>>>read file information under mod_perl (via Apache::Registry).
>>>Sometimes, without throwing any error or setting the internal error
>>>variable, Image::EXIF reads nothing from the file.  I can't correlate
>>>it with anything; a random string of reloads will start producing
>>> different results at a random point.
>> Not solved yet; but setting the same script up as a CGI instead
>> (i.e. copying into /cgi-bin/), it works fine; whatever the problem is
>> it's definitely caused by running under mod_perl.  And now that I'm
>> not changing the script so often, I see that it seems
>> to always (nearly always?) run correctly the first time after I change
>> it, and after that it mostly finds null EXIF data.  I see a very
>> *very* rare case where it comes up with the right data, so it's not
>> 100.00% failure on reload, but it's close. Still looking for clues!
>
> David, take a look at:
> http://perl.apache.org/docs/1.0/guide/debug.html#Debugging_your_code_in_Single_Server_Mode
> to avoid guessing. If you have a problem in your code, you will see it
> immediately on the second request.
>
> Most likely it's the fault of the module that you are using. Perhaps
> it wasn't written in mind to run under mod_perl. I'd look there
> first. Look for globals first. Then see if there are initialized on
> each request. My guess is that this is your problem. Under mod_cgi you
> can't see that since there is no interpreter persistance. Take some
> time to read:
> http://perl.apache.org/docs/1.0/guide/porting.html#Global_Variables_Persistence

Thanks for the pointers.  I've looked at the module code, and the perl
part of it doesn't seem to use global variables or anything nasty.
However, it's just a wrapper around some C code.  I'm not sure I want
to start debugging this at that level tonight; I just wanted to drain
the swamp! 

I'm now looking at Image::ExifTool, which has a much more recent date
and a higher version number :-); maybe it works!
        -- 
        David Dyer-Bennet, <mailto:dd-b@xxxx.xxx>;, <http://www.dd-b.net/dd-b/>;
RKBA: <http://noguns-nomoney.com/>; <http://www.dd-b.net/carry/>;
Pics: <http://dd-b.lighthunters.net/>; <http://www.dd-b.net/dd-b/SnapshotAlbum/>;
Dragaera/Steven Brust: <http://dragaera.info/>;

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