Debug openings and closings

[senduran]

I have a complicated script that uses many modules and runs for many minutes before dieing with a 'Too many open files' problem.

I don't want to step through it all with the debugger... Is there some simple way I can just see the stack trace every time something does an open(), and everytime something does a close(), to find the culprit that isn't closing when it should?

[FunkyMonk]

You can override CORE::open and close. The following should get you going:

BEGIN {
    *CORE::GLOBAL::open = \&my_open;

    sub my_open(*;$@) {
        my ( undef, $filename, $line ) = caller;
        print "opening $_[2] in $filename:$line\n";
        CORE::open($_[0], $_[1], $_[2]);
    }
}

open my $fh, "<", "temp~" or die $!;

Googling came up with Testing Legacy Code

[moritz]

On linux and unix based systems you can use the command (not perl function!) strace to watch which files are opened and closed.

On windows you can use filemon for that.

I know that's not exactly what you want, but maybe when you see which files are opened you can guess which module is to blame.

[Fletch]

Actually on Linuxen it's strace, on Solaris (and other SysVs?) it's truss (as Anno mentions below), and on BSDen it's a pair of utilities ktrace and kdump (Free- and OS X for sure, pretty sure about Open-).</pedant>

[bruceb3]

As a suggestion to avoid this kind of problem, if you use a lexical variable as a file handle instead of a bareword, when the variable goes out of scope, Perl will automatically close the file for you. e.g.

open my $file, "<", $filename # use lexical variable

open FILE, "<", $filename # use bareword.


So if you have a subroutine;

sub foo {
  my ($filename) = @_;
  open my $file,  "<", $filename or die "blah :$!\n";
  while (<$file>) {
    # etc
  }
  # explicit call to close not needed.
}

The file will be closed at the end of the foo subroutine. If you want the file handle then return it.
And if you aren't using a lot of subroutines but want this behavior, simply start a new block.

[BrowserUk]

Take a look at Fatal.

[Anno]

On most Unix systems you can trace system calls (that includes open() and close()) using something like strace (truss in other systems).

Anno

[ides]

Definitely find out why you're running out of file handles, but if you find at the end of the day it is necessary, you can up these limits on your Linux/Unix system. Googling around for ulimit and that error message should help you to find how to do that on your particular OS.