[Haskell-cafe] Fwd: Will GHC finally support epoll in 2009?

Johann Höchtl johann.hoechtl at gmail.com
Fri Dec 11 13:39:44 EST 2009

Gregory Collins wrote:
> Johann Höchtl <johann.hoechtl at gmail.com> writes:
>> I think the overall goal should be to get rid of
>> http://github.com/gregorycollins/event/blob/master/src/System/Event/EPoll.hsc,
>> as it's in the core.
> I don't follow, could you explain?
I might be wrong, but it's EPoll.hsc where you define the call to the 
Linux kernel function. This would be unneccessary, when poll (and kqueue 
and Windows equivalents) are already in the core. Ok, a bit more than 
EPoll.hsc would be unneccessary ;)

What I mean is that applications like web servers should benefit 
immediately from a change in the exisiting core and not require a (new) 
library. So a change is likely neccessary in Network.Socket and 
and in the IO monad when it comes to files. 
If someone want's to benefit from more functionality, like overlapping 
IO on Windows, the extension may be platform dependent available. 
However, in order to produce portable code which uses non blocking IO 
"the new way", a programer should never have to think about the target 

BTW: Here are also some names and ideas mentioned:

I actually had web applications in mind when I asked my first question 
as many tiny and lightweight requests to the web server will become more 
and more the rule with techniques as comet or Bayeux protocoll or HTML5 
web sockets. I speculate  this will be even more true with per thread 
garbage collection in GHC 6.12.x
>> Any non-blocking call to select should be save to replace by epoll, as the
>> semantics are the same.
> Not exactly the same; but keep in mind we also need to support kqueue &
> Windows I/O completion ports (and select() as a fallback). In an ideal
> world you can provide a unified API that will work across all of the
> platforms, with the I/O multiplexer hidden behind the interface.
Absolutely right, I forgot to mention. I am aware of

epoll - Linux
kqueue - the BSD's and MacOS; does the interface differ, on MacOS, I 
dont't know
IO Completion Port 
<http://msdn.microsoft.com/en-us/library/aa365198%28VS.85%29.aspx> - 
poll - Solaris

>> As epoll is considerably more fine grained than non-blocking select,
>> the architecture must support a run loop which effectively retrieves
>> events faster than non-blocking select would do. Otherwise the effort
>> would be futile.
> It'd be hard to be slower, with select() you have to do O(n) "fdIsSet"
> tests.
> G

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