(threadDelay (-1)) hangs

[dancor]

threadDelay silently hangs forever given a negative delay interval. It seems like this should at least be documented, but further is probably suboptimal magical behavior that leads to harder-to-find bugs; instead this should be an error. Conceivably threadDelay could take Maybe Int but that seems kind of out there.

Here is some discussion from #haskell:

06:39 < dancor> do other ppl agree that (threadDelay (-1)) hanging silently is 
                bug?
06:39 < dancor> i guess you might want infinite hang, hm
06:39 < Cale> dancor: I think I might agree with that, though now that you 
              mention it, it's very handy.
06:39 < Cale> dancor: A lot of things which would cause a thread to block 
              forever will throw an exception and kill the thread.
06:40 < Cale> (an exception which you'd often wish were silent)
06:40 < Cale> But threadDelay is the wrong place for that
06:40 < b_jonas> dancor: yeah, the thread should just be garbage-collected
06:42  * quicksilver uses "forever (threadDelay maxBound)"

I'm on Debian lenny:

~ uname -a
Linux pima 2.6.26-1-686-bigmem #1 SMP Sat Nov 8 19:46:36 UTC 2008 i686 GNU/Linux
~ ghc --version
The Glorious Glasgow Haskell Compilation System, version 6.10.1
~ cat threadHang.hs
import Control.Concurrent
main = threadDelay (-1)

[dancor]

Very sorry, here is the description with proper formatting:

threadDelay silently hangs forever given a negative delay interval. It seems like this should at least be documented, but further is probably suboptimal magical behavior that leads to harder-to-find bugs; instead this should be an error. Conceivably threadDelay could take Maybe Int but that seems kind of out there.

Here is some discussion from #haskell:

06:39 < dancor> do other ppl agree that (threadDelay (-1)) hanging silently is 
                bug?
06:39 < dancor> i guess you might want infinite hang, hm
06:39 < Cale> dancor: I think I might agree with that, though now that you 
              mention it, it's very handy.
06:39 < Cale> dancor: A lot of things which would cause a thread to block 
              forever will throw an exception and kill the thread.
06:40 < Cale> (an exception which you'd often wish were silent)
06:40 < Cale> But threadDelay is the wrong place for that
06:40 < b_jonas> dancor: yeah, the thread should just be garbage-collected
06:42  * quicksilver uses "forever (threadDelay maxBound)"

I'm on Debian lenny:

~ uname -a
Linux pima 2.6.26-1-686-bigmem #1 SMP Sat Nov 8 19:46:36 UTC 2008 i686 GNU/Linux
~ ghc --version
The Glorious Glasgow Haskell Compilation System, version 6.10.1
~ cat threadHang.hs
import Control.Concurrent
main = threadDelay (-1)

[dancor]

these days (in ghc 7.0.3 anyway), threadDelay on a negative value immediately returns, so i consider this bug closed