[Pkg-haskell-maintainers] Bug#624389: Bug#624389: System.Cmd.Utils.pipeBoth subject to pipeline stalls with ghc 7

[Giovanni Mascellani]

tag 624389 + confirmed
thanks

Hi.

Cc:-ing, John Goerzen, the upstream maintainer, and full-quoting for his
convenience. John, do you have anything to comment here?

I can confirm this bug (on amd64), but I don't know how to work on it.

Giovanni.

On 28/04/2011 04:50, Joey Hess wrote:
> Package: ghc
> Version: 7.0.3-1
> Severity: normal
> 
> For quite a while I have been using missingh's pipeBoth with success; but as
> soon as my program was rebuilt with ghc 7, it started stalling when large
> quantities of data needed to be passed through the pipe.
> 
> Here is a simple test case. It needs to run in a git repository.
> 
> import System.Cmd.Utils
> 
> main = do
>         as <- checkAttr "blah" $ map show [1..100000]
>         sequence $ map (putStrLn . show) as
> 
> checkAttr attr files = do
>         (_, s) <- pipeBoth "git" params $ unlines files
>         return $ lines s
>         where
>                 params = ["check-attr", attr, "--stdin"]
> 
> It queries git for attribute values for 100000 files. With ghc 6, it
> should run to completion. With ghc 7, it stalls, deadlocked, after
> a varying number of files, under 1000:
> 
> select(2, [], [1], NULL, {0, 0})        = 1 (out [1], left {0, 0})
> write(1, "\"701: blah: unspecified\"\n", 25"701: blah: unspecified") = 25
> select(2, [], [1], NULL, {0, 0})        = 1 (out [1], left {0, 0})
> write(1, "\"702: blah: unspecified\"\n", 25"702: blah: unspecified") = 25
> select(2, [], [1], NULL, {0, 0})        = 1 (out [1], left {0, 0})
> write(1, "\"703: blah: unspecified\"\n", 25"703: blah: unspecified") = 25
> select(2, [], [1], NULL, {0, 0})        = 1 (out [1], left {0, 0})
> write(1, "\"704: blah: unspecified\"\n", 25"704: blah: unspecified") = 25
> --- SIGVTALRM (Virtual timer expired) @ 0 (0) ---
> sigreturn()                             = ? (mask now [])
> gettimeofday({1303958431, 174266}, NULL) = 0
> select(7, [], [6], NULL, {0, 0})        = 1 (out [6], left {0, 0})
> write(6, "345\n15346\n15347\n15348\n15349\n1535"..., 8096
> 
> The program is blocked trying to write to git-check-attr, and
> git-check-attr is in turn blocked waiting for its output to be read.
> 
> I've skipping over missingh and filing this bug directly on ghc because
> I think it's unlikely missingh is at fault. IIRC, pipeBoth works by
> sparking off a helper thread, which is used to write input to a command.
> Unless it made a bad assumption about that being a safe thing to do,
> this must be a bug in GHC?
> 
> FWIW, I have worked around this in my code by forking a process, not a
> thread, to do the writing. Which works fine, just a little more
> heavyweight than needed. I'm concerned about all the other potential
> callers of pipeBoth out there, however.
> 
> -- System Information:
> Debian Release: wheezy/sid
>   APT prefers unstable
>   APT policy: (500, 'unstable')
> Architecture: i386 (i686)
> 
> Kernel: Linux 2.6.32-5-686 (SMP w/2 CPU cores)
> Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
> Shell: /bin/sh linked to /bin/dash
> 
> Versions of packages ghc depends on:
> ii  gcc                       4:4.5.2-5      The GNU C compiler
> ii  libbsd-dev                0.2.0-1        utility functions from BSD systems
> ii  libc6                     2.11.2-11      Embedded GNU C Library: Shared lib
> ii  libc6-dev                 2.11.2-11      Embedded GNU C Library: Developmen
> ii  libffi-dev                3.0.9-4        Foreign Function Interface library
> ii  libffi5                   3.0.9-4        Foreign Function Interface library
> ii  libgmp-dev                2:5.0.1+dfsg-7 Multiprecision arithmetic library 
> ii  libgmp10                  2:5.0.1+dfsg-7 Multiprecision arithmetic library
> ii  libncurses5               5.9-1          shared libraries for terminal hand
> 
> ghc recommends no packages.
> 
> Versions of packages ghc suggests:
> ii  ghc-doc                       7.0.3-1    Documentation for the Glasgow Hask
> ii  ghc-prof                      7.0.3-1    Profiling libraries for the Glasgo
> pn  haskell-doc                   <none>     (no description available)
> ii  perl                          5.10.1-20  Larry Wall's Practical Extraction 
> 
> -- no debconf information


-- 
Giovanni Mascellani <mascellani at poisson.phc.unipi.it>
Pisa, Italy

Web: http://poisson.phc.unipi.it/~mascellani
Jabber: g.mascellani at jabber.org / giovanni at elabor.homelinux.org

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