On 2008 Oct 30, at 10:08, Johannes Waldmann wrote:
are there any known issues
with file handles/descriptors in ghc-compiled executables?
My program has a lot of calls to System.Process.runInteractiveProcess
and I'm running into unpredictable behaviour (sometimes the program
just silently dies, sometimes it gets stuck)
runInteractiveProcess returns 3 filehandles and a process handle.
Either can cause problems: if you use too many filehandles, the
select()-based mechanism in the Haskell runtime will fail (select()
has a fairly low limit on filehandles as compared to poll(), epoll(),
and other mechanisms); if you spawn too many subprocesses without
reaping them (waitForProcess / getProcessExitCode) you will hit the
child process limit and not be able to create new child processes.
A third problem is that you can deadlock if you write too much data
without reading any back. Your best bet is to forkIO so input and
output are independent.
Or perhaps you see anything that's wrong with my code here
http://dfa.imn.htwk-leipzig.de/cgi-bin/cvsweb/box/src/SMT/Time.hs?rev=1.9
And there's a fourth problem: you hGetContents after blocking
waitForProcess. If the output is larger than the size of a pipe
buffer (often 512 bytes), the subprocess will block waiting for the
pipe to be read, while you're waiting for it to exit before reading
from the pipe.
--
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED]
system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED]
electrical and computer engineering, carnegie mellon university KF8NH
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