[Haskell-cafe] Space leaks in function that uses Data.Vector.Mutable
yankin013 at gmail.com
Wed Jan 23 22:08:28 CET 2013
I have a "low-level" function for insertion element into mutable vector. It
looks like this:
place :: (PrimMonad m) =>
MV.MVector (PrimState m) (Int, t) -> (Int, t) -> Int -> m ()
place v max@(val1,_) i = place' i
place' i = do
let j = i - 1
if j < 0
then return ()
curr@(val2, _) <- MV.unsafeRead v j -- <<<<<
if val2 > val1
MV.unsafeWrite v j max
MV.unsafeWrite v i curr
else return ()
It searches a right place for the i-th element, moving it towards beginning
. Surprisingly, it works, but is slow.
Time profiling says this:
COST CENTRE MODULE %time %alloc ticks bytes
place.place' Main 40.1 77.1 9167 12169223232
And heap profiling says that most of allocations are for Int and (,).
I think, binding of unsafeRead to curr and val might allocate my Precious
memory more than, maybe, it is needed.
Am I right? Is it some strictness that I need? Is there anything I can do
in this situation? Or should I look outside of this function?
PS Emergence of this piece of code is a long story. Originally I was trying
to solve Project Euler's problem 411. But now it is a different issue.
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