Stefan Behnel wrote:
>
> Michael G., 28.12.2009 03:31:
>> Hrm, It seems that any sort of implemintation will be quite an involved
>> job.
>>
>> I have done some editing Nodes.py/toForFromStatNode by adding:
>> code.putln("#pragma omp parallel for")
>>
>> However on compilation openMP starts complaining about:
>> error: invalid exit from OpenMP structured block
>> which occures at every "goto" statement inside the paralleled for.
>>
>> So basically, unless cython can be reworked to not utilize goto
>> statements all over the place, openMP is not a feasible option.
>
> We could do it as for try-finally, where we basically pass through the
> finally block in any case, and re-branch afterwards. I would expect that
> gotos that stay inside of the OpenMP block should be fine.
>
> Is there a way to collectively exit from an OpenMP based loop in case of
> an
> error? (I guess that the semantics of that wouldn't be trivial to fix
> anyway.)
IIRC gotos only occur if you attempt to raise a Python exception, which
require the GIL.
A first implementation of Cython + OpenMP should target only nogil mode,
so one should require that OpenMP primitives are within a "with nogil"
block, which should avoid the issue.
There are ways of having OpenMP threads collectively exit on an exception
(like inserting a barrier) but I think its a waste of time to discuss that
until a no-gil, exception-less version is working.
Dag Sverre
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