Close all open file descriptors

bschmer has asked for the wisdom of the Perl Monks concerning the following question:

Good day monks. I have a bit of a head-scratcher that I haven't had much luck with so I hope that the collective mind of the monks can be of some help.

The problem is this, I have a script that starts with some filehandles already open which seem to be inherited via fork and/or exec and these file handles point to files not on the local filesystem which causes some pain when the remote file system goes out to lunch or the local system is rebooted. The annoyance is that I don't use these files in my script at all, so I'd just like to close all files other than STDIN, STDOUT and STDERR. Here's the code that was my attempt:

  opendir(DH, "/proc/$$/fd");
  while (my $item = readdir DH){
    next if ($item =~ /\.\.?/);
    my @sinfo = stat("/proc/$/fd/" . $item);
    my $mode = $sinfo[2];
    printf("Item is $item: %o\n", $mode);
    my $fh = FileHandle::fdopen($item, O_RDWR) || warn "Could not dup 
+$item";
    print Dumper($fh);
    close($fh);
  }
  closedir(DH);

  opendir(DH, "/proc/$$/fd");
  while (my $item = readdir DH){
    next if ($item =~ /\.\.?/);
    print "Item is $item\n";
  }
  closedir(DH);
[download]

This doesn't do the jobs since the 2nd opendir set prints out all of the same file descriptor numbers that exist at the beginning.

I'd be grateful for any suggestions.

Comment on Close all open file descriptors Download Code

Replies are listed 'Best First'.
Re: Close all open file descriptors by ysth (Canon) on Jul 28, 2004 at 13:49 UTC
Not an answer to your question, but you should make that regex `/^\.\.?\z/` or you'll skip any item name with a period anywhere in it. Update: if the stuff in /proc/.../fd are file designators, the above obviously doesn't apply, but you should skip the fdopen and just close them with POSIX::close($item) instead.	[reply] [d/l]
Re^2: Close all open file descriptors by bschmer (Friar) on Jul 28, 2004 at 15:22 UTC
That did the trick. Thanks!	[reply]
Re: Close all open file descriptors by mifflin (Curate) on Jul 28, 2004 at 14:45 UTC
The module Proc::Daemon closes all file handles before it forks. Here's the code snippet from its Init function... `## Close open file descriptors foreach $i (0 .. OpenMax) { POSIX::close($i); }` [download]	[reply] [d/l]
Re^2: Close all open file descriptors by belg4mit (Prior) on Jul 28, 2004 at 14:47 UTC
Ewww! Okay so it works, and I have to admit I thought of that general idea too, but iterating over all possible descriptors? That's just inelegant. And POSIX is still so like, heavy, man. `-- I'm not belgian but I play one on TV.`	[reply]
Re: Close all open file descriptors by BrowserUk (Patriarch) on Jul 28, 2004 at 14:55 UTC
How about `use POSIX qw[ close ]; POSIX::close( $_ ) for 3 .. 1024; ## Arbitrary upper bound` [download] This seems to work ok on win32 which isn't the most posix-complient beast in the world. Examine what is said, not who speaks. "Efficiency is intelligent laziness." -David Dunham "Think for yourself!" - Abigail "Memory, processor, disk in that order on the hardware side. Algorithm, algoritm, algorithm on the code side." - tachyon	[reply] [d/l]
Re^2: Close all open file descriptors by Fletch (Bishop) on Jul 28, 2004 at 15:34 UTC
Then again you can use `POSIX::sysconf( &POSIX::_POSIX_OPEN_MAX )` instead of an arbitrary bound. :) Update: Ooh, missed the Win32 there. Yeah, All hope abandon, ye who program here.	[reply] [d/l]
Re^3: Close all open file descriptors by BrowserUk (Patriarch) on Jul 28, 2004 at 15:38 UTC
I said that Win32 was the most posix compliant beast in the world :) `print POSIX::sysconf( &POSIX::_POSIX_OPEN_MAX );; POSIX::sysconf not implemented on this architecture at ...` [download] Examine what is said, not who speaks. "Efficiency is intelligent laziness." -David Dunham "Think for yourself!" - Abigail "Memory, processor, disk in that order on the hardware side. Algorithm, algoritm, algorithm on the code side." - tachyon	[reply] [d/l]
Re^4: Close all open file descriptors by edan (Curate) on Jul 29, 2004 at 08:19 UTC
Re^5: Close all open file descriptors by ysth (Canon) on Jul 29, 2004 at 08:41 UTC
Some notes below your chosen depth have not been shown here
Re: Close all open file descriptors by belg4mit (Prior) on Jul 28, 2004 at 14:24 UTC
Unfortunately, unlike open close has little magic and only accepts real filehandles. After quickly perusing the dox and experimenting I see nothing too promising other than a fork (with no dup or pipe) and exit. UPDATE: Okay so here's a possibiliy, the details I'll leave to you, but it's not pretty. If you look at the symbol table (`%main::` for package main) entries with value /`*::`.+/ seem to correspond to filehandles, this gets you a list of things to close. `-- I'm not belgian but I play one on TV.`	[reply]
Re: Close all open file descriptors by zentara (Cardinal) on Jul 28, 2004 at 14:41 UTC
Just a quick thought which may lead you into the right direction. In /proc/$$/fd is a list of the open file desciptors for that process. I havn't thought about how to process the list. I'm not really a human, but I play one on earth. flash japh	[reply]