(Moving discussion from http://markflorisson.wordpress.com/, where Mark
said:)
"""
Started a new branch https://github.com/markflorisson88/cython/tree/openmp .
Now the question is whether sharing attributes should be propagated
outwards. e.g. if you do
for i in prange(m):
for j in prange(n):
sum += i * j
then ‘sum’ is a reduction for the inner parallel loop, but not for the
outer one. So the user would currently have to rewrite this to
for i in prange(m):
for j in prange(n):
sum += i * j
sum += 0
which seems a bit silly . Of course, we could just disable nested
parallelism, or tell the users to use a prange and a ‘for from’ in such
cases.
"""
Dag: Interesting. The first one is definitely the behaviour we want, as
long as it doesn't cause unintended consequences.
I don't really think it will -- the important thing is that that the
order of loop iteration evaluation must be unimportant. And that is
still true (for the outer loop, as well as for the inner) in your first
example.
Question: When you have nested pranges, what will happen is that two
nested OpenMP parallel blocks are used, right? And do you know if there
is complete freedom/"reentrancy" in that variables that are
thread-private in an outer parallel block and be shared in an inner one,
and vice versa?
If so I'd think that this algorithm should work and feel natural:
- In each prange, for the purposes of variable
private/shared/reduction inference, consider all internal "prange" just
as if they had been "range"; no special treatment.
- Recurse to children pranges.
DS
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