Re: [Haskell-cafe] Re: FFI and callbacks

On Mon, 2005-07-25 at 13:47 +0000, John Goerzen wrote:

On 2005-07-25, Simon Marlow wrote:

...

On 23 July 2005 03:38, Duncan Coutts wrote: Thanks for describing the problem in detail, I understand it better now. I think it comes down to this conflict:

- you want to take advantage of the fact that GHC has lightweight "green" threads in order to do multithreading within a single OS thread, but

- our "bound threads" design does not require the implementation to support lightweight threads, and hence doesn't let the programmer take advantage of them.

In my particular case, the C library isn't aware of threading at all. While it may be safe to call it from any arbitrary Haskell thread, it would not be safe to call it from two threads simultaneously.

That's ok. Without the threaded rts, you get just one OS thread being used to make the foreign calls.

It seems that some sort of global lock -- implemented as a global variable of some sort, I guess -- is necessary. I'm not sure exactly how to accomodate that.

It seems the current model doesn't work all that well in this scenario, unless I'm missing something?

So long as you can arrange for your C lib to call back to Haskell reasonably often you can use the same solution as Gtk2Hs uses. I've outlined the technique here (mostly on page 2 for implementation notes): http://haskell.org/gtk2hs/archives/2005/07/24/writing-multi-threaded-guis/ Duncan