[Numpy-discussion] Cython-based OpenMP-accelerated quartic polynomial solver

[Nathaniel Smith]

On Mon, Oct 5, 2015 at 2:52 PM, Sturla Molden <sturla.molden at gmail.com> wrote:
> On 02/10/15 13:05, Daπid wrote:
>
>> Have you tried asking Python-dev for help with this? Hopefully they
>> would have some weight there.
>
> It seems both GCC dev and Apple (for GCD and Accelerate) has taken a similar
> stance on this. There is tiny set of functions the POSIX standard demands
> should work on both sides of a fork without exec, but OpenMP, GCD, BLAS or
> LAPAPCK are not included. As long as there is no bug, it is hard to convince
> them to follow Intel and allow fork-based multiprocessing.

To be clear, the GCC devs are open to supporting fork+OpenMP in
principle, they just aren't willing to do it in a way that risks
breaking strict POSIX or OpenMP compatibility. But that isn't even the
problem -- we have a patch that is strictly compatible with POSIX and
OpenMP. The problem is that with the patch, the cases that would
formerly have deadlocked instead leak some memory. This is not a big
deal IMO for a variety of reasons (mostly that a one time leak per
child process is tiny, esp. compared to the current situation with
deadlocks), but it means the patch needs someone serious in the GCC
community to take a look at it carefully, understand what the
tradeoffs actually are, and make a judgement call. And so far we
haven't convinced anyone to do this.

-n

-- 
Nathaniel J. Smith -- http://vorpus.org