On Thu, 2009-01-29 at 17:37 +0100, Juraj Hercek wrote:
Duncan Coutts wrote:
On Wed, 2009-01-28 at 16:56 +0100, Juraj Hercek wrote:
Prelude> a <- readFile "/sys/devices/system/cpu/online" Prelude> length a `seq` a "^CInterrupted.
http://hackage.haskell.org/trac/ghc/ticket/2971
Files in /proc and /sys are not select()able which messes up ghc's IO system. It's not entirely clear what changed between 6.8 and 6.10 that means we hit this now. (I'd have expected it never to have worked given that ghc has always used non-blocking IO.
Interesting. It looks like it works when I use non-lazy interface for file reading (withFile "/sys/devices/system/cpu/online" ReadMode hGetLine). Does this non-lazy interface use select too? In other words, is it only a good luck that it works?
Ah but that's doing something quite different. You're only asking for the first line of input (in a file which presumably is only one line long). If you did hGetLine in a loop until there was no more input then you would get the same problem. So it's not to do with strict/lazy it's checking to see if there is more data available that is the problem (I think). Clearly we're not sure exactly what is going on, after all it worked in 6.8 and now doesn't in 6.10 and both use essentially the same strategy for non-blocking IO. Duncan