Bug#684344: Fwd: Bug#684344: openmp problematic

[Julian Taylor]

sorry for duplicate, webmail fail.

On Wed, Feb 12, 2014 at 5:41 PM, Sébastien Villemot <sebastien at debian.org>wrote:

> Le mardi 04 février 2014 à 23:17 +0100, Julian Taylor a écrit :
> > There are well known issues with the gnu openmp variant of openblas in
> > respect to forks of applications.
>
> Please find attached an example of such a breakage, using
> parallelisation in R. The example is run simply with:
>
>   R --vanilla < foo.R
>
> On sid, with openblas 0.2.8-3 (OpenMP), the program runs and reports 8
> condition numbers.
>
> On sid but with openblas 0.2.8-2 (pthreads), the program hangs.
>
>

thanks, it hangs because R forks:
strace -e clone ...

> mclapply(z, f, mc.cores = num.cores)
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0x7f6df0cd9a50) = 28886
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0x7f6df0cd9a50) = 28887
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0x7f6df0cd9a50) = 28888
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0x7f6df0cd9a50) = 28889


this is the same issue that plagues python and that can be fixed with
pthreads but not gnu openmp.

As I'm not familiar with R, can you construct a testcase where openblas is
used in both the parent and the child of the fork?
It should also hang with openmp.
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