[Haskell-cafe] Strange behavior of executeFile

Krzysztof Kościuszkiewicz k.kosciuszkiewicz at gmail.com
Sun Jul 29 14:41:40 EDT 2007

On Sun, Jul 29, 2007 at 10:34:10AM -0700, Bryan O'Sullivan wrote:

> GHC's file handles are backed by non-blocking file descriptors.  The 
> child process run by executeFile inherits the stdin, stdout and stderr 
> file descriptors of your Haskell process, so they're unexpectedly (from 
> its perspective) in non-blocking mode.
> Due to POSIX sharing semantics, you can't simply switch those file 
> descriptors to blocking in the child, because they'll then become 
> blocking in the parent, too.

Yes, this would explain the behavior I'm seeing. My script neither forks
nor reads stdin, so I could hack around this problem by clearing the

> setFdOption stdInput NonBlockingRead False

Thanks for your help!

Krzysztof Kościuszkiewicz
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"Simplicity is the ultimate sophistication" -- Leonardo da Vinci

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