Thanks for the responses everyone. More below inline...
On Fri, Mar 27, 2009 at 9:12 AM, John Hunter <jdh2...@gmail.com> wrote:
> On Fri, Mar 27, 2009 at 5:54 AM, Darren Dale <dsdal...@gmail.com> wrote:
>
>>
>> It might not be too much trouble to protect RcParams and its data,
>> although I dont know how disruptive it would be to the mpl codebase and to
>> users for rcParams to begin returning copies of things like font lists.
>>
>
>
> In addition to the rc params, I suspect some of the caching we do at the
> module level, eg in agg
>
>
> class RendererAgg(RendererBase):
>
> texd = maxdict(50) # a cache of tex image rasters
> _fontd = maxdict(50)
>
> might be what is hurting here. Karen, could you try editing
> site-packages/matplotlib/backends/backend_agg.py and moving these two lines
> into the __init__method so they are at the instance level rather than the
> class level. Eg,
>
> def __init__(self, width, height, dpi):
> if __debug__: verbose.report('RendererAgg.__init__',
> 'debug-annoying')
> RendererBase.__init__(self)
> self.texd = maxdict(50) # a cache of tex image rasters
> self._fontd = maxdict(50)
>
> and see if that helps.
Yes, this change appears to fix the problem. I created a standalone script
to recreate the problem. The script starts several threads. Each thread
enters a loop generating a (different) png file. With the original
matplotlib code, the threads seem unable to complete 50 iterations without
the exception being raised. (I tried the script at least a dozen times, it
never finished successfully with 50 iterations. Usually failed before 5,
but once made it as high as 20, so I bumped it up to 50 and that seemed to
ensure it would fail before finishing). With the above change to make the
texd and _fontd caches per-instance, the script has finished successfully 4
times. Seems pretty convincing evidence that it fixes the problem.
>
Also, make sure you have disabled usetex in matplotlibrc, since the use of
> the filesystem for caching the tex datafiles is probably not thread safe.
> My guess is that the font cache on the file system is not thread safe
> either, but this may only affect the first run of mpl after a clean install.
>
Not sure what matplotlibrc is? I found a file
/usr/share/matplotlib/matplotlib.conf that has usetex set to False. Is that
it? If so I guess it's been disabled all along, this is not something I
have fiddled with.
> Also, as Eric suggests, a freestanding script which is thread enabled
> (preferably just using mpl and the standard threading library rather than
> django et al) which uses the agg backend that we could use for debugging
> would be very helpful.
>
Understood, and I did make a standalone script (plus a set of pickle files
for the data to graph) to recreate it. I can zip them up and send them
somewhere, or open a ticket and attach it there, or whatever. Let me know
what would be most convenient/helpful.
Thanks!
Karen
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