On 03/16/2011 12:54 PM, mark florisson wrote:
On 16 March 2011 11:58, Dag Sverre Seljebotn<d.s.seljeb...@astro.uio.no> wrote:
On 03/16/2011 11:28 AM, mark florisson wrote:
I implemented the 'with gil:' statement, and have added error checking
for nested 'with gil' or 'with nogil' statements. For instance, with
the patch applied Cython wil issue an error when you have e.g.
with nogil:
with nogil:
...
(or the same thing for 'with gil:'). This because nested 'nogil' or
'gil' blocks, without intermediate GIL-acquiring/releasing, will abort
the Python interpreter. However, if people are acquiring the GIL
manually in nogil blocks and then want to release the GIL with a
'nogil' block, it will incorrectly issue an error. I do think this
kind of code is uncommon, but perhaps we want to issue a warning
instead?
I think we should make nested nogil-s noops, i.e.
with nogil:
with nogil: # => if True:
This is because one may want to change "with nogil" to "with gil" for
debugging purposes (allow printing debug information).
Interesting, that does sound convenient, but I'm not if mere
convenience should move us to simply ignore what is technically most
likely incorrect code (unless there is intermediate manual locking).
I'm not sure if I understand what you mean here. How does simply
ignoring redundant "with [no]gil" statements cause incorrect code? Or do
you mean this is a
I'm just trying to minimize the "language getting in your way" factor.
It is pretty useless to write
if x:
if x:
...
as well, but Python does allow it.
Warnings on nested "with nogil" is more the role of a "cylint" in my
opinion.
In any case, I wouldn't really be against that. If you simply want to
allow this for debugging, we could also allow print statements in
nogil sections, by either rewriting it using 'with gil:', or by
inserting a simple printf (in which case you probably want to place a
few restrictions).
It's not only print statements. I.e., if I think something is wrong with
an array, I'll stick in code like
print np.std(x), np.mean(x), np.any(np.isnan(x))
or something more complex that may require temporaries. Or even plot the
vector:
plt.plot(x)
plt.show() # blocks until I close plot window
Or, launch a debugger:
if np.any(np.isnan(x)):
import pdb; pdb.set_trace()
so I guess I should stop saying this is only about printing. In general,
it's nice to use Python during debugging. I find myself replacing "with
nogil" with "if True" in such situations, to avoid reindenting.
I guess I can soon start using "with gil" around the debug code though.
Again, the restriction on nested nogil/gil is not a big problem, just an
instance of "the language getting in your way".
Dag
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