On 5 April 2011 22:29, Dag Sverre Seljebotn <d.s.seljeb...@astro.uio.no> wrote: > I've done a pretty major revision to the prange CEP, bringing in a lot of > the feedback. > > Thread-private variables are now split in two cases: > > i) The safe cases, which really require very little technical knowledge -> > automatically inferred > > ii) As an advanced feature, unsafe cases that requires some knowledge of > threading -> must be explicitly declared > > I think this split simplifies things a great deal. > > I'm rather excited over this now; this could turn out to be a really > user-friendly and safe feature that would not only allow us to support > OpenMP-like threading, but be more convenient to use in a range of common > cases. > > http://wiki.cython.org/enhancements/prange > > Dag Sverre > > _______________________________________________ > cython-devel mailing list > cython-devel@python.org > http://mail.python.org/mailman/listinfo/cython-devel > >
If we want to support cython.parallel.threadsavailable outside of parallel regions (which does not depend on the schedule used for worksharing constructs!), then we have to disable dynamic scheduling. For instance, if OpenMP sees some OpenMP threads are already busy, then with dynamic scheduling it dynamically establishes how many threads to use for any parallel region. So basically, if you put omp_get_num_threads() in a parallel region, you have a race when you depend on that result in a subsequent parallel region, because the number of busy OpenMP threads may have changed. So basically, to make threadsavailable() work outside parallel regions, we'd have to disable dynamic scheduling (omp_set_dynamic(0)). Of course, when OpenMP cannot request the amount of threads desired (because they are bounded by a configurable thread limit (and the OS of course)), the behaviour will be implementation defined. So then we could just put a warning in the docs for that, and users can check for this in the parallel region using threadsavailable() if it's really important. Does that sound like a good idea? And should I update the CEP? _______________________________________________ cython-devel mailing list cython-devel@python.org http://mail.python.org/mailman/listinfo/cython-devel
