[Haskell-cafe] Re: Timeouts that don't cause data growth.
leimy2k at gmail.com
Tue Mar 23 22:42:06 EDT 2010
On Tue, Mar 23, 2010 at 4:04 PM, Bas van Dijk <v.dijk.bas at gmail.com> wrote:
> On Tue, Mar 23, 2010 at 10:20 PM, Simon Marlow <marlowsd at gmail.com> wrote:
> > The leak is caused by the Data.Unique library, and coincidentally it was
> > fixed recently. 6.12.2 will have the fix.
> Oh yes of course, I've reported that bug myself but didn't realize it
> was the problem here :-)
> David, to clarify the problem: newUnqiue is currently implemented as:
> newUnique :: IO Unique
> newUnique = do
> val <- takeMVar uniqSource
> let next = val+1
> putMVar uniqSource next
> return (Unique next)
> You can see that the 'next' value is lazily written to the uniqSource
> MVar. When you repeatedly call newUnique (like in your example) a big
> thunk is build up: 1+1+1+...+1 which causes the space-leak. In the
> recent fix, 'next' is strictly evaluated before it is written to the
> MVar which prevents a big thunk to build up.
Thanks for this excellent description of what's going on. This whole thread
has been a reminder of what makes the Haskell community truly excellent to
work with. I appreciate everything you guys are doing!
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