[Numpy-discussion] Fast threading solution thoughts

Dag Sverre Seljebotn dagss@student.matnat.uio...
Thu Feb 12 14:26:17 CST 2009

Brian Granger wrote:
> And a question:
> With the new Numpy support in Cython, does Cython release the GIL if
> it can when running through through loops over numpy arrays?  Does
> Cython call into the C API during these sections?

You know, I thought of the exact same thing when reading your post. No,
you need the GIL currently, but that's something I'd like to fix.

Ideally, it would be something like this:

cdef int i, s = 0, n = ...
cdef np.ndarray[int] arr = ... # will require the GIL
with nogil:
    for i in range(n):
        s += arr[i] # does not require GIL

The only Python operation needed on the last line is throwing an exception
if one is out of bounds; but I can always insert code to reacquire the GIL
in that exceptional case. (And in most cases like this the user will turn
off bounds-checking anyway.)

http://trac.cython.org/cython_trac/ticket/210 will contain progress on this.

Dag Sverre

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