'import ccall unsafe' and parallelism

[Johan Tibell]

Hi!

On Thu, Aug 14, 2014 at 5:54 PM, Christian Höner zu Siederdissen <
choener at tbi.univie.ac.at> wrote:
>
> However, due to the way ghc handles unsafe imports, namely block
> everything else whenever 'cfun' is called, I happen to have only one
> active 'go'. Lets assume 'cfun' is cheap and would suffer from 'ccall
> safe' more than I'd be willing to pay.
>

Calls to unsafe functions do not block everything! Other Haskell threads
can continue running on other capabilities (make sure you run your program
with +RTS -N). However, make sure that the C function itself never blocks,
or it might deadlock your program.
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