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
--
see shy jo
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