ghci and ghc -threaded broken with pipes & forking

[Simon Marlow]

John Goerzen wrote:
> Brian B wrote:
>> Hi Bulat,
>>
>> My contribution to the survey: I've used forkProcess to daemonize
>> a ghc program inside the haskell fuse bindings:
>> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HFuse
>> http://code.haskell.org/hfuse/System/Fuse.hsc
>>
>> If removing the non-threaded RTS would break forkProcess entirely,
>> these bindings would have to do something different. The issue: users
>> of the FUSE C api will get daemonized using daemon(2); it'd be
>> nice if GHC fuse programs could behave similarly.
> 
> I also use forkProcess extensively: in HSH, for instance, which is used
> by hpodder, twidge, and a host of other tools.  Removing the ability to
> use forkProcess removes the ability to write a Unix shell in Haskell, or
> to do anything shell-like, or anything even mildly advanced involving
> piping, file descriptors, and the like.  I would see it as a significant
> regression.

Have you tried those apps with the threaded RTS?  I'd be interested to 
know whether they work as expected.

I'm not suggesting we remove the non-threaded RTS, however perhaps 
there's an argument for making -threaded the default.  After all, that's 
what you get with GHCi by default right now.

Maintaining both versions of the RTS is certainly a burden, but I think 
it's one we have to carry, since there are still reasons to want both.

> The System.Process calls, last I checked (in 6.8.x) were both too buggy
> to use for complex tasks, and too inadequate for some (though the
> adequacy has been improving.)

If there's bugginess we need to get it fixed - please report those bugs!

Cheers,
	Simon