On Thu, 2010-03-25 at 21:38 +0000, Simon Marlow wrote: > On 25/03/10 17:07, Jason Dagit wrote: > > On Thu, 2010-03-25 at 16:13 +0000, Simon Marlow wrote: > >> On 25/03/2010 15:40, Jason Dagit wrote: > >>> Hello, > >>> > >>> I was trying to figure out if hGetLine is safe to use inside of > >>> withFile. Specifically, I want to return the line I read and use it > >>> later, without inspecting it before withFile calls hClose. > >>> > >>> If you want to understand the concern I have, look here: > >>> http://www.haskell.org/haskellwiki/Maintaining_laziness#Input_and_Output > >>> > >>> There is a bit of explanation showing that hGetContents can be > >>> problematic with withFile. > >>> > >>> I can tell from reading the source of hGetContents that it uses > >>> unsafeInterleaveIO so this make sense to me why that wiki page talks > >>> about hGetContents: > >>> http://www.haskell.org/ghc/docs/latest/html/libraries/base/src/GHC-IO-Handle-Text.html#hGetContents > >>> > >>> When I read the source of hGetLine, it is less clear to me if I need to > >>> be concerned. I believe it is not lazy in the sense of lazy IO above. > >>> Could someone else please comment? > >>> http://www.haskell.org/ghc/docs/latest/html/libraries/base/src/GHC-IO-Handle-Text.html#hGetLine > >> > >> Correct: it is not lazy, and it is safe to use inside withFile. > > > > Great! I did a few simple tests in GHCi and it seemed safe, but I > > wanted to be extra prudent. Thanks. > > > >> > >>> Then I notice this 'todo' item in the description: > >>> -- ToDo: the unbuffered case is wrong: it doesn't lock the handle for > >>> -- the duration. > >>> > >>> The code itself looks to me like it only handles the buffered case. > >>> Perhaps this todo is obsolete and needs to be removed? If it's not > >>> obsolete, do we need to create a ticket for this? > >> > >> Well spotted, that comment is out of date and wrong. There used to be a > >> version of hGetLine written in terms of hGetChar which was used when the > >> Handle was unbuffered, but I think I removed it in the recent rewrite. > > > > What is the next step for getting rid of the obsolete comment? Did you > > already nuke it? If not, I could try to get a copy of the ghc repo and > > see if I can figure out the right protocol for submitting a patch. > > Already nuked in my working tree, it'll filter through into the repo in > due course. The library submission process would be way overkill for that!
I received your email about 5 minutes too late :) Feel free to delete my library submission ticket. Thanks, Jason
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