Re: [Caml-list] External C functions

[Jacques Garrigue <garrigue@kurims.kyoto-u.ac.jp>]

From: Ravi Chamarty <ravi@ittc.ukans.edu>

>  I would like to use a C library which has a number of Pthread operations
> used in it. What would be the limitations of the Caml system if I write a
> wrapper around it's API ? These wrappers would be using the API provided
> by  the C library. The C library threads interact among one another. Are
> there any special concerns I should be aware of ?
> 
>  Specifically, I would be interested in knowing if I could run and
> schedule two or more threads within the C system. 

Having multiple threads within the C system is not a problem at all.
For instance we linked the mozilla widget inside a Caml program,
itself using native threads, and this worked OK.  The only constraint
proper to Caml is that no more than one Caml thread can be running at
once, but this does not affect pure C threads.

However, one has to be careful about callbacks: if a Caml callback is
called from a C thread, and this C thread is not the thread which was
called from Caml, then the callback will only run after the original
thread gives the control back to Caml. This is then very easy to
deadlock. Worse, if your Caml program isn't compiled with threads,
there is no locking involved, and you end up running two Caml thread
simultaneously, for an happy crash.

Cheers,

---------------------------------------------------------------------------
Jacques Garrigue      Kyoto University     garrigue at kurims.kyoto-u.ac.jp
		<A HREF=http://wwwfun.kurims.kyoto-u.ac.jp/~garrigue/>JG</A>

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