<div class="Gk Jk" dir="ltr" style="color:rgb(34,34,34);line-height:22px;background-color:rgb(255,255,255)">See the comment for hGetContents:<div><br></div><div>"<span style="line-height:18px;font-size:13px;font-family:sans-serif">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 </span><code style="line-height:16px;font-size:13px;margin:0px;padding:0px"><a href="http://hackage.haskell.org/packages/archive/bytestring/0.9.2.1/doc/html/Data-ByteString.html#v:readFile" target="_blank" style="color:rgb(171,105,84);text-decoration:none;margin:0px;padding:0px">readFile</a></code><span style="line-height:18px;font-size:13px;font-family:sans-serif"> in this case."</span></div>
<div><br></div><div><a href="http://hackage.haskell.org/packages/archive/bytestring/0.9.2.1/doc/html/Data-ByteString-Char8.html#g:31" target="_blank" style="color:rgb(17,85,204);text-decoration:none">http://hackage.haskell.org/packages/archive/bytestring/0.9.2.1/doc/html/Data-ByteString-Char8.html#g:31</a></div>
<div><br></div><div>Maybe try lazy bytestrings?</div><div style="clear:both"></div></div><div style="color:rgb(34,34,34);line-height:22px;background-color:rgb(255,255,255);clear:both"></div><div class="Gk Kk" dir="ltr" style="padding-top:1em;color:rgb(0,123,53);line-height:22px;background-color:rgb(255,255,255)">
<div><br></div><div> - Clark</div></div><br>On Tuesday, April 16, 2013, Anatoly Yakovenko wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>
-- So why does this code run out of memory?</div><div><br></div><div>import Control.DeepSeq</div><div>import System.IO</div><div>import qualified Data.ByteString.Char8 as BS</div><div><br></div>
<div>scanl' :: NFData a => (a -> b -> a) -> a -> [b] -> [a]</div><div>scanl' f q ls = q : (case ls of</div><div> [] -> []</div><div> x:xs -> let q' = f q x</div>
<div> in q' `deepseq` scanl' f q' xs)</div><div><br></div><div><br></div><div>main = do</div><div> file <- openBinaryFile "/dev/zero" ReadMode</div><div> chars <- BS.hGetContents file</div>
<div> let rv = drop 100000000000 $ scanl' (+) 0 $ map fromEnum $ BS.unpack chars</div><div> print (head rv)</div><div><br></div><div>-- my scanl' implementation seems to do the right thing, because </div><div>
<br></div><div>main = print $ last $ scanl' (+) (0::Int) [0..]<br></div><div><br></div><div>-- 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?</div>
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