Comments on: Fork/exec in Haskell

By: Emmelaich

Emmelaich — Tue, 15 Sep 2009 03:52:13 +0000

Set ‘close on exec’ on the descriptors. http://en.wikipedia.org/wiki/Fork-exec

By: Magnus

Magnus — Sat, 22 Aug 2009 07:05:22 +0000

@bbb, It seems rather silly to iterate over all valid file descriptors, it'd be much nicer to only iterate over all open file descriptors. I'll have to take a look at the bash code though, for educational purposes.

@ifp5, Yes, that sounds like a good way to go.

By: ifp5

ifp5 — Sat, 22 Aug 2009 00:54:40 +0000

I'd better use /dev/fd/* instead of /proc/self/*, it's much more portable.

By: Magnus

Magnus — Fri, 21 Aug 2009 22:22:42 +0000

@Twan, For this example there isn't much reason, but in many cases it is nice to separate fork and exec.

@ephemient, Yes, it was getdtablesize() I was looking for, but couldn't find.

@Blame, Huh?

By: Blame

Blame — Fri, 21 Aug 2009 20:20:55 +0000

finally

By: ephemient

ephemient — Fri, 21 Aug 2009 18:23:10 +0000

a. Just try to close all FDs up to getdtablesize() or sysconf(_SC_OPEN_MAX). Slow but mostly portable.

b. Look at /proc/self/fd/. Faster but not as portable.

By: Twan van Laarhoven

Twan van Laarhoven — Fri, 21 Aug 2009 16:59:43 +0000

Why are you using fork/exec as opposed to System.Process?

By: bbb

bbb — Fri, 21 Aug 2009 16:44:23 +0000

The classic Unix way to do this is to find out the maximum valid file descriptor and then close all of them in a for loop (e.g., see bash). Looking over System.Posix.IO, it seems that it is lacking a function of the sort

unsafeMakeFd :: Int -> Fd

to replicate that strategy.