Re: [Haskell-cafe] trying to understand out of memory exceptions
unfortunately read file tries to get the file size
readFile :: FilePath -> IO ByteStringreadFile f = bracket (openFile f
ReadMode) hClose (\h -> hFileSize h >>= hGet h . fromIntegral)
which wont work on a special file, like a socket. which is what i am
trying to simulate here.
On Tue, Apr 16, 2013 at 11:28 AM, Clark Gaebel
See the comment for hGetContents:
half of available memory, this may lead to memory exhaustion. Consider using readFilehttp://hackage.haskell.org/packages/archive/bytestring/0.9.2.1/doc/html/Data... in
"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 this case."
http://hackage.haskell.org/packages/archive/bytestring/0.9.2.1/doc/html/Data...
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 chars 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?
Have you tried the lazy bytestring version? http://hackage.haskell.org/packages/archive/bytestring/0.10.2.0/doc/html/Dat... - Clark On Tuesday, April 16, 2013, Anatoly Yakovenko wrote:
unfortunately read file tries to get the file size
readFile :: FilePath -> IO ByteStringreadFile f = bracket (openFile f ReadMode) hClose (\h -> hFileSize h >>= hGet h . fromIntegral)
which wont work on a special file, like a socket. which is what i am trying to simulate here.
On Tue, Apr 16, 2013 at 11:28 AM, Clark Gaebel
wrote:
See the comment for hGetContents:
half of available memory, this may lead to memory exhaustion. Consider using readFilehttp://hackage.haskell.org/packages/archive/bytestring/0.9.2.1/doc/html/Data... in
"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 this case."
http://hackage.haskell.org/packages/archive/bytestring/0.9.2.1/doc/html/Data...
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 chars 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?
participants (2)
-
Anatoly Yakovenko -
Clark Gaebel