That's interesting. This was using my source code? On mine (also a Linux box), it exited immediately, giving me no opportunity to write to the pipe. On 2010-11-23, Patrick LeBoutillier wrote:

Matthew,

Does it return immediately when you start it or only when you try to write to the pipe with some client?

Here's what I get on my Linux box:

$ rm /tmp/dld.fifo && ./pipe & [1] 8603 $ echo -e "1\n2\n3" > /tmp/dld.fifo 1 2 3 pipe: /tmp/dld.fifo: hGetLine: end of file

Patrick

On Tue, Nov 23, 2010 at 7:55 AM, matthew coolbeth wrote:

...

Hello, all.

Three questions:

1> What, if anything, can I do in a Haskell program to do blocking reads from a Linux FIFO?  For the curious, there is a small program below that doesn't block, but immediately terminates because of an EOF

2> How could I have found the answer to this question on my own? (The documentation that Google found for me was not completely adequate)

3> Is this sort of question generally regarded as too unixy or not haskelly enough to be appropriate for this mailing list?

Thanks.

--BEGIN PROGRAM-- module Main () where

import Control.Monad import System.IO import System.Posix.Files

pipeString = "/tmp/dld.fifo"

main :: IO () main = do        createNamedPipe pipeString $ unionFileModes ownerReadMode ownerWriteMode        pipe <- openFile pipeString ReadMode        forever (hGetLine pipe >>= putStrLn)

-- mac _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

-- ===================== Patrick LeBoutillier Rosemère, Québec, Canada

-- mac

Here's the uname -a output: $ uname -a Linux pc207 2.6.30.10-105.2.23.fc11.x86_64 #1 SMP Thu Feb 11 07:06:34 UTC 2010 x86_64 x86_64 x86_64 GNU/Linux Patrick On Tue, Nov 23, 2010 at 10:36 AM, Patrick LeBoutillier wrote:

On Tue, Nov 23, 2010 at 9:13 AM, matthew coolbeth wrote:

...

That's interesting.  This was using my source code?

Yes, as is. I compiled it with "ghc --make pipe.hs".

I'm running Fedora 10 x64 with: $ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.10.1

Patrick

...

On mine (also a Linux box), it exited immediately, giving me no opportunity to write to the pipe.

On 2010-11-23, Patrick LeBoutillier wrote:

...

Matthew,

Does it return immediately when you start it or only when you try to write to the pipe with some client?

Here's what I get on my Linux box:

$ rm /tmp/dld.fifo && ./pipe & [1] 8603 $ echo -e "1\n2\n3" > /tmp/dld.fifo 1 2 3 pipe: /tmp/dld.fifo: hGetLine: end of file

Patrick

On Tue, Nov 23, 2010 at 7:55 AM, matthew coolbeth wrote:

...

Hello, all.

Three questions:

1> What, if anything, can I do in a Haskell program to do blocking reads from a Linux FIFO?  For the curious, there is a small program below that doesn't block, but immediately terminates because of an EOF

2> How could I have found the answer to this question on my own? (The documentation that Google found for me was not completely adequate)

3> Is this sort of question generally regarded as too unixy or not haskelly enough to be appropriate for this mailing list?

Thanks.

--BEGIN PROGRAM-- module Main () where

import Control.Monad import System.IO import System.Posix.Files

pipeString = "/tmp/dld.fifo"

main :: IO () main = do        createNamedPipe pipeString $ unionFileModes ownerReadMode ownerWriteMode        pipe <- openFile pipeString ReadMode        forever (hGetLine pipe >>= putStrLn)

-- mac _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

-- ===================== Patrick LeBoutillier Rosemère, Québec, Canada

-- mac

-- ===================== Patrick LeBoutillier Rosemère, Québec, Canada

-- ===================== Patrick LeBoutillier Rosemère, Québec, Canada

As Mr Therning suggested, I switched over from System.IO.openFile to openFd in System.Posix. This gives the blocking behavior that I want. The only downside was having to provide my own readLine. Just so everyone knows. thanks, mac On 2010-12-03, Brandon S Allbery KF8NH wrote:

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1

On 11/23/10 10:36 , Patrick LeBoutillier wrote:

...

The Glorious Glasgow Haskell Compilation System, version 6.10.1

IIRC this was in fact broken in 6.10.1; upgrade at least to 6.10.3.

- -- brandon s. allbery [linux,solaris,freebsd,perl] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/

iEYEARECAAYFAkz5THAACgkQIn7hlCsL25VOEQCgp/fPxHTsFb6vAeaO1GGonZDc dh8AmgIy4l0khXTHliySwRSnz804tu0Z =m7l1 -----END PGP SIGNATURE-----

_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

-- mac

On Tuesday 23 November 2010 15:16:59, Magnus Therning wrote:

On Tue, Nov 23, 2010 at 14:09, Patrick LeBoutillier

wrote:

...

Matthew,

Does it return immediately when you start it or only when you try to write to the pipe with some client?

Here's what I get on my Linux box:

$ rm /tmp/dld.fifo && ./pipe & [1] 8603 $ echo -e "1\n2\n3" > /tmp/dld.fifo 1 2 3 pipe: /tmp/dld.fifo: hGetLine: end of file

Would you run 'uname -a' and 'ghc --version'?

I don't see that behaviour here

% uname -a Linux bryma 2.6.35-ARCH #1 SMP PREEMPT Sat Oct 30 21:22:26 CEST 2010 x86_64 Intel(R) Core(TM)2 Quad CPU Q9450 @ 2.66GHz GenuineIntel GNU/Linux % ghc --version The Glorious Glasgow Haskell Compilation System, version 6.12.3

% rm /tmp/dld.fifo && ./pipe& [1] 30762 % pipe: /tmp/dld.fifo: hGetLine: end of file

[1] + exit 1 ./pipe

I get the same with 6.12.3 and 7.0.1. $ uname -a Linux linux-mkk1 2.6.27.54-0.1-pae #1 SMP 2010-10-19 18:40:07 +0200 i686 i686 i386 GNU/Linux

/M