[Haskell-cafe] createProcess shutting file handles

[Neil Mitchell]

Hi

>> > However the createProcess command structure has the close_fds flag,
>> > which seems like it should override that behaviour, and therefore this
>> > seems like a bug in createProcess.
>>
>>         close_fds :: Bool
>>
>>         Close all file descriptors except stdin, stdout and stderr in
>>         the new process
>>
>> This refers to inheriting open unix file descriptors (or Win32 HANDLEs)
>> in the child process. It's not the same as closing the Haskell98 Handles
>> in the parent process that you pass to the child process.
>
> So lets not talk about if the current behaviour is a bug or not. It's
> reasonably clear (if not brilliantly well documented) that it's the
> intended behaviour.
>
> The thing we want to talk about is what reason is there for the current
> behaviour, if that's necessary and if it is the sensible default
> behaviour. As I said before I don't know why it is the way it is. I'm
> cc'ing the ghc users list in the hope that someone there might know.

One guiding principle of resource management is that whoever
opens/allocates something should release/free it. i.e. if you did the
malloc you do the free. For that reason it seems weird that I call
openFile but someone else calls hClose on my behalf.

Plus, in my particular application, the above behaviour is necessary
or I'm going to have to write to a file, open that file, and copy it
over to my intended file (which is what I will end up doing, no
doubt!)

Thanks

Neil