File Coverage

blib/lib/Devel/MAT/Dumper.pm

Criterion	Covered	Total	%
statement	22	72	30.5
branch	2	34	5.8
condition	0	3	0.0
subroutine	8	12	66.6
pod			n/a
total	32	121	26.4

#  You may distribute under the terms of either the GNU General Public License
#  or the Artistic License (the same terms as Perl itself)
#
#  (C) Paul Evans, 2013-2024 -- [e-mail]

package Devel::MAT::Dumper;

use v5.10;
use strict;
use warnings;

our $VERSION = '0.51';

use File::Basename qw( basename );
use File::Spec;
use POSIX;

require XSLoader;
XSLoader::load( __PACKAGE__, $VERSION );

=head1 NAME

C - write a heap dump file for later analysis

=head1 SYNOPSIS

=for highlighter language=perl

   use Devel::MAT::Dumper;

   Devel::MAT::Dumper::dump( "path/to/the/file.pmat" );

=head1 DESCRIPTION

This module provides the memory-dumping function that creates a heap dump file
which can later be read by L. It provides a single
function which is not exported, which writes a file to the given path.

The dump file will contain a representation of every SV in Perl's arena,
providing information about pointers between them, as well as other
information about the state of the process at the time it was created. It
contains a snapshot of the process at that moment in time, which can later be
loaded and analysed by various tools using C.

This module used to be part of the main L distribution but is now
in its own one so that it can be installed independently on servers or other
locations where perl processes need to inspected but analysis tools can be run
elsewhere.

=cut

=head1 IMPORT OPTIONS

=for highlighter

The following C options control the behaviour of the module. They may
primarily be useful when used in the C<-M> perl option:

=head2 -dump_at_DIE

Installs a handler for the special C<__DIE__> signal to write a dump file when
C is about to cause a fatal signal. This is more reliable at catching
the callstack and memory state than using an C block.

   $ perl -MDevel::MAT::Dumper=-dump_at_DIE ...

=head2 -dump_at_WARN

Installs a handler for the special C<__WARN__> signal to write a dump file
when perl prints a warning.

   $ perl -MDevel::MAT::Dumper=-dump_at_WARN ...

It is likely useful to combine this with the C numbering feature of the
C<-file> argument, to ensure that later warnings don't overwrite a particular
file.

=head2 -dump_at_END

Installs an C block which writes a dump file at C time, just before
the interpreter exits.

   $ perl -MDevel::MAT::Dumper=-dump_at_END ...

=head2 -dump_at_SIGQUIT

Installs a handler for C to write a dump file if the signal is
received. The signal handler will remain in place and can be used several
times.

   $ perl -MDevel::MAT::Dumper=-dump_at_SIGQUIT ...

Take care if you are using the C<<  >> key combination on a terminal
to send this signal to a foreground process, because if it has Ced any
background workers or similar, the signal will also be delivered to those as
well.

=head2 -dump_at_SIGI

Installs a handler for the named signal (e.g. C, C) to write
a dump file if the signal is received. After dumping the file, the signal
handler is removed and the signal re-raised.

   $ perl -MDevel::MAT::Dumper=-dump_at_SIGABRT ...

Note that C uses an "unsafe" signal handler (i.e. not deferred until
the next perl op), so it can capture the full context of any ongoing XS or C
library operations.

=head2 -file $PATH

Sets the name of the file which is automatically dumped; defaults to basename
F<$0.pmat> if not supplied.

   $ perl -MDevel::MAT::Dumper=-file,foo.pmat ...

In the special case that C<$0> is exactly the string C<-e> or C<-E>, the
filename will be prefixed with C so as not to create files whose names
begin with a leading hyphen, as this confuses some commandline parsers.

   $ perl -MDevel::MAT::Dumper=-dump_at_END -E 'say "hello"'
   hello
   Dumping to perl-e.pmat because of END

If the pattern contains C, this will be replaced by a unique serial
number per written file, starting from 0. This may be helpful in the case of
C, C or C handlers, which could be invoked multiple times.

The file name is converted to an absolute path immediately, so if the running
program later calls C, it will still be generated in the directory
the program started from rather than the one it happens to be in at the time.

=head2 -max_string

Sets the maximum length of string buffer to dump from PVs; defaults to 256 if
not supplied. Use a negative size to dump the entire buffer of every PV
regardless of size.

=head2 -eager_open

Opens the dump file immediately at C time, instead of waiting until
the time it actually writes the heap dump. This may be useful if the process
changes user ID, or to debug problems involving too many open filehandles.

=cut

our $MAX_STRING = 256; # used by XS code

my $basename = basename( $0 );
$basename = "perl$basename" if $basename =~ m/^-e$/i; # RT119164
my $dumpfile_name = File::Spec->rel2abs( "$basename.pmat" );

my $dumpfh;
my $next_serial = 0;

my $dump_at_END;
END {
   return unless $dump_at_END;

   if( $dumpfh ) {
      Devel::MAT::Dumper::dumpfh( $dumpfh );
   }
   else {
      ( my $file = $dumpfile_name ) =~ s/NNN/$next_serial++/e;
      print STDERR "Dumping to $file because of END\n";
      Devel::MAT::Dumper::dump( $file );
   }
}

sub import
{
   my $pkg = shift;

   my $eager_open;

   while( @_ ) {
      my $sym = shift;

      if( $sym eq "-dump_at_DIE" ) {
         my $old_DIE = $SIG{__DIE__};
         $SIG{__DIE__} = sub {
            local $SIG{__DIE__} = $old_DIE if defined $old_DIE;
            return if $^S or !defined $^S; # only catch real process-fatal errors

            ( my $file = $dumpfile_name ) =~ s/NNN/$next_serial++/e;
            print STDERR "Dumping to $file because of DIE\n";
            Devel::MAT::Dumper::dump( $file );
            die @_;
         };
      }
      elsif( $sym eq "-dump_at_WARN" ) {
         my $old_WARN = $SIG{__WARN__};
         $SIG{__WARN__} = sub {
            local $SIG{__WARN__} = $old_WARN if defined $old_WARN;

            ( my $file = $dumpfile_name ) =~ s/NNN/$next_serial++/e;
            print STDERR "Dumping to $file because of WARN\n";
            Devel::MAT::Dumper::dump( $file );
            warn @_;
         };
      }
      elsif( $sym eq "-dump_at_END" ) {
         $dump_at_END++;
      }
      elsif( $sym eq "-dump_at_SIGQUIT" ) {
         $SIG{QUIT} = sub {
            ( my $file = $dumpfile_name ) =~ s/NNN/$next_serial++/e;
            print STDERR "Dumping to $file because of SIGQUIT\n";
            Devel::MAT::Dumper::dump( $file );
         };
      }
      elsif( $sym =~ m/^-dump_at_SIG(\S+)$/ ) {
         my $signal = $1;
         exists $SIG{$signal} or die "Unrecognised signal name SIG$signal\n";

         my $handler = sub {
            ( my $file = $dumpfile_name ) =~ s/NNN/$next_serial++/e;
            print STDERR "Dumping to $file because of SIG$signal\n";
            Devel::MAT::Dumper::dump( $file );
            undef $SIG{$signal};
            kill $signal => $$;
         };

         if( $signal eq "ABRT" ) {
            # Install SIGABRT handler using unsafe signal so it can see
            # inner workings of C code properly
            my $sigaction = POSIX::SigAction->new( $handler );
            $sigaction->safe(0);

            POSIX::sigaction( POSIX::SIGABRT, $sigaction );
         }
         else {
            $SIG{$signal} = $handler;
         }
      }
      elsif( $sym eq "-file" ) {
         $dumpfile_name = File::Spec->rel2abs( shift );
      }
      elsif( $sym eq "-max_string" ) {
         $MAX_STRING = shift;
      }
      elsif( $sym eq "-eager_open" ) {
         $eager_open++;
      }
      else {
         die "Unrecognised $pkg import symbol $sym\n";
      }
   }

   if( $eager_open ) {
      open $dumpfh, ">", $dumpfile_name or
         die "Cannot open $dumpfile_name for writing - $!\n";
   }
}

=head1 FUNCTIONS

=for highlighter language=perl

These functions are not exported, they must be called fully-qualified.

=head2 dump

   dump( $path );

Writes a heap dump to the named file

=head2 dumpfh

   dumpfh( $fh );

Writes a heap dump to the given filehandle (which must be a plain OS-level
filehandle, though does not need to be a regular file, or seekable).

=cut

=head1 AUTHOR

Paul Evans

=cut

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