On Thu, Oct 28, 2010 at 2:16 AM, Kazu Yamamoto <kazu@iij.ad.jp> wrote:
When I compiled a network server with GHC 7 without the "-threaded"
option and ran it, I got the following error.

       file descriptor 5496824 out of range for select (0--1024).

I have read the paper "Scalable Event Handling for GHC" and understand
that this new IO manger assumes the "-threaded" option.

The unthreaded runtime has a completely different I/O manager from the threaded one. We didn't touch the unthreaded runtime. Does your app work under earlier versions of GHC without -threaded?
 
Does this mean that we need the "-threaded" option to GHC 7 for
networking programming and GHC 7 does not maintain backward
compatibility?

No.