[yt-users] Interesting crash when using ("deposit", "all_cic")

[Brian O'Shea]

Hi folks,

I have been trying to make some dark matter density movies using the
"all_cic" field, and have discovered that using "all_cic" can reliably
cause yt to seg fault on the supercomputer I'm using (x86_64 linux cluster
with kernel 2.6.32-504.8.1.el6.x86_64) using the tip of yt-dev (changeset
fa08e386d0da).  The script that causes the crash is here:

http://paste.yt-project.org/show/5774/

After I turned up the log level and started using pdb to debug, I
discovered that the line in the script that causes the seg fault is line 88:

dm_dens_x = my_reg[("deposit", "all_cic")].value

where my_reg is defined as (on line 82):

my_reg = ds.arbitrary_grid(left, right, dims=[1,800, 800])

After stepping through with pdb, it seems that the code dies in this
function:

/mnt/home/oshea/yt-3/lib/python2.7/site-packages/sympy/core/basic.py(83)__new__()

with the traceback shown here:

http://paste.yt-project.org/show/5775/

Based on this traceback, it seems that there are problems with the unit
system.

Interestingly enough, though, this does not happen on every dataset - it
seems to happen occasionally, but predictably.  For example, I can generate
two images using this script, but it will seg fault on the third.  On a
different dataset in the time series, it will produce one image and then
seg fault on the second.  If I run the script over and over, it will
eventually produce quite a few images, until it runs into a situation where
it seg faults on the first image I produce (at which point I went to the
debugger).

I don't have enough experience with the guts of yt - and the units section
of yt in particular - to have a sense of what might be happening here based
on the traceback.  Does anybody have any suggestions?

Thank you!

--Brian
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