[Haskell-cafe] Safe/Unsafe calls with the GHC Foreign Function Interface

[Rob Hoelz]

Stefan O'Rear <stefanor at cox.net> wrote:

> On Thu, May 17, 2007 at 10:32:11PM -0500, Rob Hoelz wrote:
> > More questions from Rob regarding his mysterious bindings...
> > 
> > So I've been reading the docs for the FFI, and it's my understanding
> > that foreign functions imported as "unsafe" are faster, but they've
> > got a problem with callbacks.  From what I read, I believe that I
> > should just make a foreign function safe if it sets up a callback;
> > is this correct?  Normally I wouldn't bother people with questions
> > like this, but I'd rather be absolutely certain and avoid tracking
> > down a strange bug later.
> > 
> > Many thanks as always,
> > Rob
> 
> If it *calls* a callback into haskell.
> 
> Also, for unfathomable reasons, safety has been overloaded to include
> forking OS threads.  If it could block (like getchar), you must make
> it safe. 
> 
> Stefan

Ouch...how bad is the overhead for a safe function?