On 03/03/2010 08:43, Neil Davies wrote:
On 2 Mar 2010, at 21:38, Simon Marlow wrote:
On 02/03/10 20:37, Luke Palmer wrote:
On Tue, Mar 2, 2010 at 7:17 AM, Simon Marlow<marlo...@gmail.com> wrote:
For games,
though, we have a very good point that occurs regularly where we know
that all/most short-lived objects will no longer be referenced - at
the
start of a fresh frame.
System.Mem.performGC is your friend, but if you're unlucky it might
do a
major GC and then you'll get more pause than you bargained for.
Some fine-grained control might be nice here. Eg. I could do a major
GC as a player is opening a menu, on a loading screen, when the game
is paused, or some other key points, and it might still be annoying,
but at least it wouldn't interfere with gameplay. There is of course
the question of what happens if one of these key points doesn't happen
when we need to do an allocation, but... oh well. Perhaps that could
be mitigated by saying "I would rather you allocate than major GC
right now". Are any of these options impossible, or be unreasonably
difficult to implement (I don't suspect so)?
Actually that's one thing we can do relatively easily, i.e. defer
major GC for a while. Due to the way GHC has a two-layer memory
manager, the heap is a list of discontiguous blocks, so we can always
allocate some more memory.
So it would be pretty easy to provide something like
disableMajorGC, enableMajorGC :: IO ()
Of course leaving it disabled too long could be bad, but that's your
responsibility.
Oh, I just checked and System.Mem.performGC actually performs a major
GC, here's its implementation:
foreign import ccall {-safe-} "performMajorGC" performGC :: IO ()
to perform a minor GC (or possibly a major GC if one is due), you want
this:
foreign import ccall {-safe-} "performGC" performMinorGC :: IO ()
Cheers,
Simon
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Is there a similar set of runes to be able to see how much mutation has
occurred, how much was live last GC, etc?
No, but there could be - the information is collected by the RTS, it
just isn't made available via a public API right now.
Cheers,
Simon
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