Re-Occurrence of bug #199 in code based on gr_bin_statistics_f

Hello all,

It looks as though I have uncovered GNU Radio bug #199 in one of my
programs. I used gr_bin_statistics_f as a template and designed a new
block
which uses the same method to callback to Python code and retune the
USRP.

http://gnuradio.org/redmine/issues/show/199

Now, I could get into more details of my specific program, however it
seems
like this bug could be hard to replicate on different hardware. I am not
sure to the extent of the issue, but I know where the problem is.


The problem occurs in the callback code in gr_feval.i. As described in
the
bug report, Py_GILState_Ensure() is called before calleval(), and then
Py_GILState_Release() is called after returning from Python land. It is
at
this point that I get a segmentation fault.

For a gdb stacktrace similar to that on the bug report, please refer to
my
blog post:

After googling around for a while I read about similar issues which were
solved by adding a call to PyEval_InitThreads() right before
Py_GILState_Ensure() is called (hinted at in the bug report). This did
the
trick for me! Calling PyEval_InitThreads() acquires and initializes the
GIL,
and calling it multiple times is a NOOP. More details can be found in
Python
documentation. I am not sure if this is the correct solution, but it
worked
for me. Others have suggested to me that the module using the
multi-threaded
Python extension should ‘import threading’ early to ensure that
PyEval_InitThreads is called.

Finally, here is the system I tested on:
Fedora 14 64-bit
Linux tjadesktop 2.6.35.10-72.fc14.x86_64 #1 SMP Mon Dec 20 21:14:22 UTC
2010 x86_64 x86_64 x86_64 GNU/Linux
Intel i5 760
USRP 1 w/ WBX d’board

I have attached a small patch file which includes my fix. I could submit
a
formal fix if that would help, but I would really just like to get some
feedback on the issue. What do you guys think?

Thanks!
-Tom

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