[Haskell-cafe] trying to understand out of memory exceptions
aeyakovenko at gmail.com
Tue Apr 16 20:33:18 CEST 2013
ah, doh, my mistake. i accidently pulled in Strict version of bytestring.
the Lazy works file :). I have a much more complex program that isn't
working correctly which i was trying to simplify and looks like i added an
On Tue, Apr 16, 2013 at 11:29 AM, Clark Gaebel <cgaebel at uwaterloo.ca> wrote:
> See the comment for hGetContents:
> "This function reads chunks at a time, doubling the chunksize on each
> read. The final buffer is then realloced to the appropriate size. For files
> > half of available memory, this may lead to memory exhaustion. Consider
> using readFile<http://hackage.haskell.org/packages/archive/bytestring/0.9.2.1/doc/html/Data-ByteString.html#v:readFile> in
> this case."
> Maybe try lazy bytestrings?
> - Clark
> On Tuesday, April 16, 2013, Anatoly Yakovenko wrote:
>> -- So why does this code run out of memory?
>> import Control.DeepSeq
>> import System.IO
>> import qualified Data.ByteString.Char8 as BS
>> scanl' :: NFData a => (a -> b -> a) -> a -> [b] -> [a]
>> scanl' f q ls = q : (case ls of
>>  -> 
>> x:xs -> let q' = f q x
>> in q' `deepseq` scanl' f q' xs)
>> main = do
>> file <- openBinaryFile "/dev/zero" ReadMode
>> chars <- BS.hGetContents file
>> let rv = drop 100000000000 $ scanl' (+) 0 $ map fromEnum $ BS.unpack
>> print (head rv)
>> -- my scanl' implementation seems to do the right thing, because
>> main = print $ last $ scanl' (+) (0::Int) [0..]
>> -- runs without blowing up. so am i creating a some thunk here? or is
>> hGetContents storing values? any way to get the exception handler to print
>> a trace of what caused the allocation?
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