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NAME
Devel::MAT::Dumper - write a heap dump file for later analysis
SYNOPSIS
use Devel::MAT::Dumper;
Devel::MAT::Dumper::dump( "path/to/the/file.pmat" );
DESCRIPTION
This module provides the memory-dumping function that creates a heap
dump file which can later be read by Devel::MAT::Dumpfile. 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
Devel::MAT::Dumpfile.
This module used to be part of the main Devel::MAT 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.
IMPORT OPTIONS
The following import options control the behaviour of the module. They
may primarily be useful when used in the -M perl option:
-dump_at_DIE
Installs a handler for the special __DIE__ signal to write a dump file
when die() is about to cause a fatal signal. This is more reliable at
catching the callstack and memory state than using an END block.
$ perl -MDevel::MAT::Dumper=-dump_at_DIE ...
-dump_at_WARN
Installs a handler for the special __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 NNN numbering feature of
the -file argument, to ensure that later warnings don't overwrite a
particular file.
-dump_at_END
Installs an END block which writes a dump file at END time, just before
the interpreter exits.
$ perl -MDevel::MAT::Dumper=-dump_at_END ...
-dump_at_SIGQUIT
Installs a handler for SIGQUIT 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 <Ctrl-\> key combination on a terminal
to send this signal to a foreground process, because if it has fork()ed
any background workers or similar, the signal will also be delivered to
those as well.
-dump_at_SIGNAME
Installs a handler for the named signal (e.g. SIGABRT, SIGINT) 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 SIGABRT 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.
-file $PATH
Sets the name of the file which is automatically dumped; defaults to
basename $0.pmat if not supplied.
$ perl -MDevel::MAT::Dumper=-file,foo.pmat ...
In the special case that $0 is exactly the string -e or -E, the
filename will be prefixed with perl 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 NNN, this will be replaced by a unique serial
number per written file, starting from 0. This may be helpful in the
case of DIE, WARN or SIGQUIT handlers, which could be invoked multiple
times.
The file name is converted to an absolute path immediately, so if the
running program later calls chdir(), it will still be generated in the
directory the program started from rather than the one it happens to be
in at the time.
-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.
-eager_open
Opens the dump file immediately at import 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.
FUNCTIONS
These functions are not exported, they must be called fully-qualified.
dump
dump( $path );
Writes a heap dump to the named file
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).
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
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