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Re: A way to report open file handles a Perl script has open? -- using ${^LAST_FH} ?

by Discipulus (Monsignor)
on Apr 05, 2017 at 08:39 UTC ( #1187076=note: print w/replies, xml ) Need Help??


in reply to A way to report open file handles a Perl script has open?

Hello nysus,

For sure the best thing to do is to open always lexical filehandles to let Perl close them for you. The habit to close them esplicitally is a sane one anyway.

Extra scope can help if you have many declared into the top scope.

But the strange behaviour you announce (leaking file handles like a sieve)

I'd expand the mr_mischief's solution: take count of what you open.

You can override open builtin function very soon in the program or in a BEGIN block, and you can profit of the ${^LAST_FH} special variable: if I understand the doc correctly it tracks the last open $fh (only read-fh ?) taking a reference to it

You probably need to override close to erase from your tracking variable.

An END block can dump the tracking datastructure.

So given a %fhs in the outher scope you can store there your fh

# TOTALLY UNTESTED!! no warning 'redefine'; my %fhs; BEGIN { *CORE::GLOBAL::open = sub { my ($fh,$mode,$path) = @_; # open the file $fhs{fileno($fh)} = $path.' '.${^LAST_FH}; }; } END{ print "Files already opened:\n", map {"fileno $_ $fhs{$_}\n"} sor +t keys %fhs; }

PS sorry the node was composed on a spare PC where was impossible to test anything..

L*

There are no rules, there are no thumbs..
Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.

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Re^2: A way to report open file handles a Perl script has open? -- using ${^LAST_FH} ?
by shmem (Chancellor) on Apr 05, 2017 at 12:57 UTC

    Nice. A sub wrapping open before overriding is missing... and for close. Combining your and my approach:

    At toplevel:

    use Hash::Util::FieldHash qw(id_2obj); my %fd; BEGIN{ Hash::Util::FieldHash::fieldhash %fd; my $open = sub { @_ > 2 ? open $_[0],$_[1],$_[2] : open $_[0], $_[1]; }; my $close = sub { close $_[0] }; *CORE::GLOBAL::open = sub { my $result = $open->(@_); if ($result) { $fd{$_[0]} = join " ",@_[1,2],caller; } $result; }; *CORE::GLOBAL::close = sub { my $result = $close->(@_); if ($result) { $fd{$_[0]} .= " (closed)"; } else { $fd{$_[0]} .= " (close failed)"; } $result; }; } open my $devnull, '>/dev/null' or die; { open my $fh, '>', "blorfldyick" or die; print $fh "foo!\n" or die; print "(1) ", id_2obj($_), " => $fd{$_}\n" for keys %fd; close $fh; print "after close\n"; print "(2) ", id_2obj($_), " => $fd{$_}\n" for keys %fd; } print "after scope:\n"; print "(3) ", id_2obj($_), " => $fd{$_}\n" for keys %fd; open my $devzero, '<', '/dev/zero' or die; # time passes... print "later:\n"; print "(4) ", id_2obj($_), " => $fd{$_}\n" for keys %fd; __END__ (1) GLOB(0xb22190) => >/dev/null main open.pl 29 (1) GLOB(0xb63780) => > blorfldyick main open.pl 32 after close (2) GLOB(0xb22190) => >/dev/null main open.pl 29 (2) GLOB(0xb63780) => > blorfldyick main open.pl 32 (closed) after scope: (3) GLOB(0xb22190) => >/dev/null main open.pl 29 later: (4) GLOB(0xb363b8) => < /dev/zero main open.pl 42 (4) GLOB(0xb22190) => >/dev/null main open.pl 29

    Combine with Time::HiRes and you can sort the history.

    update: done, made into a package.

    perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'

      That is a neat trick i need to remember

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