[Haskell-cafe] haskell and releasing resources

Donald Bruce Stewart dons at cse.unsw.edu.au
Tue Feb 6 08:58:50 EST 2007

> I am just coming to haskell, and I wrote a simple command to get some  
> input from a pdf file
> I just wanted the output of the command so I did something like
> import System.Process (runInteractiveCommand)
> import IO (hGetContents)
> -- | returns the text of the first page of the pdf at the given path,  
> needs pdftotext
> getTextOfPdf :: String -> IO String
> getTextOfPdf pdfPath = do
>     (inp,out,err,pid) <- runInteractiveCommand ("pdftotext -l 1 "+ 
> +pdfPath++" -")
>     return (hGetContents out)
> I don't care about error handling, if something goes wrong it is ok  
> to hang or crash, but knowing unix I wondered if this would do the  
> right thing or if it would create a zombi process.
> I was about to ask, but then I thought "let's test it", and sure  
> enough the zombi stays there.
> I tried to even to allocate more than one, wait, I even managed to  
> exhaust the resources of my machine...
> So here is what I would have liked to happen: when the pid gets  
> garbage collected it tries to wait for the process, and if that fails  
> the pid stays around longer and will try to wait later.

Wait for the process to terminate, using 

    waitForProcess pid

I've a sketch for a nice wrapper for the low level process code here,



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