Dmitry Kurochkin wrote:
> On Thu, Aug 14, 2008 at 4:43 AM, Gwern Branwen <[EMAIL PROTECTED]> wrote:
>> Actually, while we're on the topic: why does URL.hs now use forkOS? Darcs
>> uses forkIO, usually, which is the standard Haskell practice. It can't be
>> for performance: I replaced forkOS with forkIO and tested it with 4 darcs
>> gets of the Tahoe repo, and they all clocked in at 24-27 minutes (the same
>> as with forkOS).
>
> That is because we do foreign calls that block. AFAIK if we use
> unbound threads (forkIO) all haskell threads are halt during blocking
> syscalls from foreign functions. And that is not what we want.
This is a common misconception: forkIO vs. forkOS makes no difference with
respect to blocking. forkOS is only necessary if you need to call a C
library that makes use of thread-local state, otherwise it just uses extra
resources and will slow things down: context-switching between a forkOS
thread and another thread constitutes a full OS-thread context switch,
which is much much slower than switching between forkIO threads.
People don't seem to believe me when I say this. In retrospect we
shoulnd't have called it forkOS, we should have called it
forkReallyExpensiveOnlyNecessaryForCallingOpenGL_IO.
Cheers,
Simon
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