On Tue, Apr 11, 2006 at 09:13:00AM +0100, Simon Marlow wrote:
What are the conclusions of this thread?
I think, but correct me if I'm wrong, that the eventual outcome was:
- concurrent reentrant should be supported, because it is not significantly more difficult to implement than just concurrent.
It wasn't a difficulty of implementation issue, it was whether there were unavoidable performance traeoffs. I have no problem with very difficult things if they are well specified and don't require unreasonable concessions elsewhere in the design. in any case, I think the __thread local storage trick makes this fast enough to implement everywhere and there were strong arguments for not having it causing issues for library developers.
- the different varieties of foreign call should all be identifiable, because there are efficiency gains to be had in some implementations.
indeed.
- the default should be... concurrent reentrant, presumably, because that is the safest. (so we need to invert the notation).
well, I like to reserve the word 'safe' for things that might crash the runtime, unsafePerformIO, so making things nonconcurrent isn't so much something unsafe as a decision. I'd prefer nonconcurrent be the default because it is the much more common case and is just as safe in that regard IMHO.
So, can I go ahead and update the wiki? I'll try to record the rationale from the discussion too.
sure.
I'd like to pull out something from the discussion that got a bit lost in the swamp: the primary use case we have for concurrent reentrant is for calling the main loop of a GUI library. The main loop usually never returns (at least, not until the application exits), hence concurrent, and it needs to invoke callbacks, hence reentrant.
this is a pain. (making various libraries main loops play nice together). not that it is a haskell specific problem though I guess we have to deal with it. I was thikning of using something like http://liboop.org/ internally in jhc.. but am not sure and would prefer a pure haskell solution without compelling reason to do otherwise. John -- John Meacham - ⑆repetae.net⑆john⑈