Profile: /opt/wise/lib/perl5/5.10.0/x86_64-linux-thread-multi/Storable.pm

File	/opt/wise/lib/perl5/5.10.0/x86_64-linux-thread-multi/Storable.pm
Statements Executed	28
Total Time	0.002016 seconds

Subroutines — ordered by exclusive time
Calls	P	F	Exclusive Time	Inclusive Time	Subroutine
0	0	0	0	0	Storable::	CLONE
0	0	0	0	0	Storable::	retrieve_fd

Line	Stmts.	Exclusive Time	Avg.	Code
1				#
2				# Copyright (c) 1995-2000, Raphael Manfredi
3				#
4				# You may redistribute only under the same terms as Perl 5, as specified
5				# in the README file that comes with the distribution.
6				#
7
8	1	1.0e-6	1.0e-6	require DynaLoader;
9	1	1.0e-6	1.0e-6	require Exporter;
10	1	1.0e-5	1.0e-5	package Storable; @ISA = qw(Exporter DynaLoader);
11
12	1	1.0e-6	1.0e-6	@EXPORT = qw(store retrieve);
13	1	4.0e-6	4.0e-6	@EXPORT_OK = qw(
14				nstore store_fd nstore_fd fd_retrieve
15				freeze nfreeze thaw
16				dclone
17				retrieve_fd
18				lock_store lock_nstore lock_retrieve
19				file_magic read_magic
20				);
21
22	3	3.3e-5	1.1e-5	use AutoLoader; # spent 231µs making 1 call to AutoLoader::import
23	3	3.6e-5	1.2e-5	use FileHandle; # spent 497µs making 1 call to FileHandle::import
24	3	9.4e-5	3.1e-5	use vars qw($canonical $forgive_me $VERSION); # spent 46µs making 1 call to vars::import
25
26	1	1.0e-6	1.0e-6	$VERSION = '2.18';
27	1	2.0e-6	2.0e-6	*AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr...
28
29				#
30				# Use of Log::Agent is optional
31				#
32
33				{
34	2	5.0e-6	2.5e-6	local $SIG{__DIE__};
35	1	0.00169	0.00169	eval "use Log::Agent";
36				}
37
38	1	1.0e-6	1.0e-6	require Carp;
39
40				#
41				# They might miss :flock in Fcntl
42				#
43
44				BEGIN {
45	3	2.3e-5	7.7e-6	if (eval { require Fcntl; 1 } && exists $Fcntl::EXPORT_TAGS{'flock'}) { # spent 154µs making 1 call to Exporter::import
46				Fcntl->import(':flock');
47				} else {
48				eval q{
49				sub LOCK_SH () {1}
50				sub LOCK_EX () {2}
51				};
52				}
53	1	7.9e-5	7.9e-5	}
54
55				sub CLONE {
56				# clone context under threads
57				Storable::init_perinterp();
58				}
59
60				# Can't Autoload cleanly as this clashes 8.3 with &retrieve
61				sub retrieve_fd { &fd_retrieve } # Backward compatibility
62
63				# By default restricted hashes are downgraded on earlier perls.
64
65	1	1.0e-6	1.0e-6	$Storable::downgrade_restricted = 1;
66	1	0	0	$Storable::accept_future_minor = 1;
67	1	1.7e-5	1.7e-5	bootstrap Storable; # spent 533µs making 1 call to DynaLoader::bootstrap
68	1	1.3e-5	1.3e-5	1;
69				__END__
70				#
71				# Use of Log::Agent is optional. If it hasn't imported these subs then
72				# Autoloader will kindly supply our fallback implementation.
73				#
74
75				sub logcroak {
76				Carp::croak(@_);
77				}
78
79				sub logcarp {
80				Carp::carp(@_);
81				}
82
83				#
84				# Determine whether locking is possible, but only when needed.
85				#
86
87				sub CAN_FLOCK; my $CAN_FLOCK; sub CAN_FLOCK {
88				return $CAN_FLOCK if defined $CAN_FLOCK;
89				require Config; import Config;
90				return $CAN_FLOCK =
91				$Config{'d_flock'} \|\|
92				$Config{'d_fcntl_can_lock'} \|\|
93				$Config{'d_lockf'};
94				}
95
96				sub show_file_magic {
97				print <<EOM;
98				#
99				# To recognize the data files of the Perl module Storable,
100				# the following lines need to be added to the local magic(5) file,
101				# usually either /usr/share/misc/magic or /etc/magic.
102				#
103				0 string perl-store perl Storable(v0.6) data
104				>4 byte >0 (net-order %d)
105				>>4 byte &01 (network-ordered)
106				>>4 byte =3 (major 1)
107				>>4 byte =2 (major 1)
108
109				0 string pst0 perl Storable(v0.7) data
110				>4 byte >0
111				>>4 byte &01 (network-ordered)
112				>>4 byte =5 (major 2)
113				>>4 byte =4 (major 2)
114				>>5 byte >0 (minor %d)
115				EOM
116				}
117
118				sub file_magic {
119				my $file = shift;
120				my $fh = new FileHandle;
121				open($fh, "<". $file) \|\| die "Can't open '$file': $!";
122				binmode($fh);
123				defined(sysread($fh, my $buf, 32)) \|\| die "Can't read from '$file': $!";
124				close($fh);
125
126				$file = "./$file" unless $file; # ensure TRUE value
127
128				return read_magic($buf, $file);
129				}
130
131				sub read_magic {
132				my($buf, $file) = @_;
133				my %info;
134
135				my $buflen = length($buf);
136				my $magic;
137				if ($buf =~ s/^(pst0\|perl-store)//) {
138				$magic = $1;
139				$info{file} = $file \|\| 1;
140				}
141				else {
142				return undef if $file;
143				$magic = "";
144				}
145
146				return undef unless length($buf);
147
148				my $net_order;
149				if ($magic eq "perl-store" && ord(substr($buf, 0, 1)) > 1) {
150				$info{version} = -1;
151				$net_order = 0;
152				}
153				else {
154				$net_order = ord(substr($buf, 0, 1, ""));
155				my $major = $net_order >> 1;
156				return undef if $major > 4; # sanity (assuming we never go that high)
157				$info{major} = $major;
158				$net_order &= 0x01;
159				if ($major > 1) {
160				return undef unless length($buf);
161				my $minor = ord(substr($buf, 0, 1, ""));
162				$info{minor} = $minor;
163				$info{version} = "$major.$minor";
164				$info{version_nv} = sprintf "%d.%03d", $major, $minor;
165				}
166				else {
167				$info{version} = $major;
168				}
169				}
170				$info{version_nv} \|\|= $info{version};
171				$info{netorder} = $net_order;
172
173				unless ($net_order) {
174				return undef unless length($buf);
175				my $len = ord(substr($buf, 0, 1, ""));
176				return undef unless length($buf) >= $len;
177				return undef unless $len == 4 \|\| $len == 8; # sanity
178				$info{byteorder} = substr($buf, 0, $len, "");
179				$info{intsize} = ord(substr($buf, 0, 1, ""));
180				$info{longsize} = ord(substr($buf, 0, 1, ""));
181				$info{ptrsize} = ord(substr($buf, 0, 1, ""));
182				if ($info{version_nv} >= 2.002) {
183				return undef unless length($buf);
184				$info{nvsize} = ord(substr($buf, 0, 1, ""));
185				}
186				}
187				$info{hdrsize} = $buflen - length($buf);
188
189				return \%info;
190				}
191
192				sub BIN_VERSION_NV {
193				sprintf "%d.%03d", BIN_MAJOR(), BIN_MINOR();
194				}
195
196				sub BIN_WRITE_VERSION_NV {
197				sprintf "%d.%03d", BIN_MAJOR(), BIN_WRITE_MINOR();
198				}
199
200				#
201				# store
202				#
203				# Store target object hierarchy, identified by a reference to its root.
204				# The stored object tree may later be retrieved to memory via retrieve.
205				# Returns undef if an I/O error occurred, in which case the file is
206				# removed.
207				#
208				sub store {
209				return _store(\&pstore, @_, 0);
210				}
211
212				#
213				# nstore
214				#
215				# Same as store, but in network order.
216				#
217				sub nstore {
218				return _store(\&net_pstore, @_, 0);
219				}
220
221				#
222				# lock_store
223				#
224				# Same as store, but flock the file first (advisory locking).
225				#
226				sub lock_store {
227				return _store(\&pstore, @_, 1);
228				}
229
230				#
231				# lock_nstore
232				#
233				# Same as nstore, but flock the file first (advisory locking).
234				#
235				sub lock_nstore {
236				return _store(\&net_pstore, @_, 1);
237				}
238
239				# Internal store to file routine
240				sub _store {
241				my $xsptr = shift;
242				my $self = shift;
243				my ($file, $use_locking) = @_;
244				logcroak "not a reference" unless ref($self);
245				logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist
246				local *FILE;
247				if ($use_locking) {
248				open(FILE, ">>$file") \|\| logcroak "can't write into $file: $!";
249				unless (&CAN_FLOCK) {
250				logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
251				return undef;
252				}
253				flock(FILE, LOCK_EX) \|\|
254				logcroak "can't get exclusive lock on $file: $!";
255				truncate FILE, 0;
256				# Unlocking will happen when FILE is closed
257				} else {
258				open(FILE, ">$file") \|\| logcroak "can't create $file: $!";
259				}
260				binmode FILE; # Archaic systems...
261				my $da = $@; # Don't mess if called from exception handler
262				my $ret;
263				# Call C routine nstore or pstore, depending on network order
264				eval { $ret = &$xsptr(*FILE, $self) };
265				close(FILE) or $ret = undef;
266				unlink($file) or warn "Can't unlink $file: $!\n" if $@ \|\| !defined $ret;
267				logcroak $@ if $@ =~ s/\.?\n$/,/;
268				$@ = $da;
269				return $ret ? $ret : undef;
270				}
271
272				#
273				# store_fd
274				#
275				# Same as store, but perform on an already opened file descriptor instead.
276				# Returns undef if an I/O error occurred.
277				#
278				sub store_fd {
279				return _store_fd(\&pstore, @_);
280				}
281
282				#
283				# nstore_fd
284				#
285				# Same as store_fd, but in network order.
286				#
287				sub nstore_fd {
288				my ($self, $file) = @_;
289				return _store_fd(\&net_pstore, @_);
290				}
291
292				# Internal store routine on opened file descriptor
293				sub _store_fd {
294				my $xsptr = shift;
295				my $self = shift;
296				my ($file) = @_;
297				logcroak "not a reference" unless ref($self);
298				logcroak "too many arguments" unless @_ == 1; # No @foo in arglist
299				my $fd = fileno($file);
300				logcroak "not a valid file descriptor" unless defined $fd;
301				my $da = $@; # Don't mess if called from exception handler
302				my $ret;
303				# Call C routine nstore or pstore, depending on network order
304				eval { $ret = &$xsptr($file, $self) };
305				logcroak $@ if $@ =~ s/\.?\n$/,/;
306				local $\; print $file ''; # Autoflush the file if wanted
307				$@ = $da;
308				return $ret ? $ret : undef;
309				}
310
311				#
312				# freeze
313				#
314				# Store oject and its hierarchy in memory and return a scalar
315				# containing the result.
316				#
317				sub freeze {
318				_freeze(\&mstore, @_);
319				}
320
321				#
322				# nfreeze
323				#
324				# Same as freeze but in network order.
325				#
326				sub nfreeze {
327				_freeze(\&net_mstore, @_);
328				}
329
330				# Internal freeze routine
331				sub _freeze {
332				my $xsptr = shift;
333				my $self = shift;
334				logcroak "not a reference" unless ref($self);
335				logcroak "too many arguments" unless @_ == 0; # No @foo in arglist
336				my $da = $@; # Don't mess if called from exception handler
337				my $ret;
338				# Call C routine mstore or net_mstore, depending on network order
339				eval { $ret = &$xsptr($self) };
340				logcroak $@ if $@ =~ s/\.?\n$/,/;
341				$@ = $da;
342				return $ret ? $ret : undef;
343				}
344
345				#
346				# retrieve
347				#
348				# Retrieve object hierarchy from disk, returning a reference to the root
349				# object of that tree.
350				#
351				sub retrieve {
352				_retrieve($_[0], 0);
353				}
354
355				#
356				# lock_retrieve
357				#
358				# Same as retrieve, but with advisory locking.
359				#
360				sub lock_retrieve {
361				_retrieve($_[0], 1);
362				}
363
364				# Internal retrieve routine
365				sub _retrieve {
366				my ($file, $use_locking) = @_;
367				local *FILE;
368				open(FILE, $file) \|\| logcroak "can't open $file: $!";
369				binmode FILE; # Archaic systems...
370				my $self;
371				my $da = $@; # Could be from exception handler
372				if ($use_locking) {
373				unless (&CAN_FLOCK) {
374				logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
375				return undef;
376				}
377				flock(FILE, LOCK_SH) \|\| logcroak "can't get shared lock on $file: $!";
378				# Unlocking will happen when FILE is closed
379				}
380				eval { $self = pretrieve(*FILE) }; # Call C routine
381				close(FILE);
382				logcroak $@ if $@ =~ s/\.?\n$/,/;
383				$@ = $da;
384				return $self;
385				}
386
387				#
388				# fd_retrieve
389				#
390				# Same as retrieve, but perform from an already opened file descriptor instead.
391				#
392				sub fd_retrieve {
393				my ($file) = @_;
394				my $fd = fileno($file);
395				logcroak "not a valid file descriptor" unless defined $fd;
396				my $self;
397				my $da = $@; # Could be from exception handler
398				eval { $self = pretrieve($file) }; # Call C routine
399				logcroak $@ if $@ =~ s/\.?\n$/,/;
400				$@ = $da;
401				return $self;
402				}
403
404				#
405				# thaw
406				#
407				# Recreate objects in memory from an existing frozen image created
408				# by freeze. If the frozen image passed is undef, return undef.
409				#
410				sub thaw {
411				my ($frozen) = @_;
412				return undef unless defined $frozen;
413				my $self;
414				my $da = $@; # Could be from exception handler
415				eval { $self = mretrieve($frozen) }; # Call C routine
416				logcroak $@ if $@ =~ s/\.?\n$/,/;
417				$@ = $da;
418				return $self;
419				}
420
421				1;
422				__END__
423
424				=head1 NAME
425
426				Storable - persistence for Perl data structures
427
428				=head1 SYNOPSIS
429
430				use Storable;
431				store \%table, 'file';
432				$hashref = retrieve('file');
433
434				use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);
435
436				# Network order
437				nstore \%table, 'file';
438				$hashref = retrieve('file'); # There is NO nretrieve()
439
440				# Storing to and retrieving from an already opened file
441				store_fd \@array, \*STDOUT;
442				nstore_fd \%table, \*STDOUT;
443				$aryref = fd_retrieve(\*SOCKET);
444				$hashref = fd_retrieve(\*SOCKET);
445
446				# Serializing to memory
447				$serialized = freeze \%table;
448				%table_clone = %{ thaw($serialized) };
449
450				# Deep (recursive) cloning
451				$cloneref = dclone($ref);
452
453				# Advisory locking
454				use Storable qw(lock_store lock_nstore lock_retrieve)
455				lock_store \%table, 'file';
456				lock_nstore \%table, 'file';
457				$hashref = lock_retrieve('file');
458
459				=head1 DESCRIPTION
460
461				The Storable package brings persistence to your Perl data structures
462				containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be
463				conveniently stored to disk and retrieved at a later time.
464
465				It can be used in the regular procedural way by calling C<store> with
466				a reference to the object to be stored, along with the file name where
467				the image should be written.
468
469				The routine returns C<undef> for I/O problems or other internal error,
470				a true value otherwise. Serious errors are propagated as a C<die> exception.
471
472				To retrieve data stored to disk, use C<retrieve> with a file name.
473				The objects stored into that file are recreated into memory for you,
474				and a I<reference> to the root object is returned. In case an I/O error
475				occurs while reading, C<undef> is returned instead. Other serious
476				errors are propagated via C<die>.
477
478				Since storage is performed recursively, you might want to stuff references
479				to objects that share a lot of common data into a single array or hash
480				table, and then store that object. That way, when you retrieve back the
481				whole thing, the objects will continue to share what they originally shared.
482
483				At the cost of a slight header overhead, you may store to an already
484				opened file descriptor using the C<store_fd> routine, and retrieve
485				from a file via C<fd_retrieve>. Those names aren't imported by default,
486				so you will have to do that explicitly if you need those routines.
487				The file descriptor you supply must be already opened, for read
488				if you're going to retrieve and for write if you wish to store.
489
490				store_fd(\%table, *STDOUT) \|\| die "can't store to stdout\n";
491				$hashref = fd_retrieve(*STDIN);
492
493				You can also store data in network order to allow easy sharing across
494				multiple platforms, or when storing on a socket known to be remotely
495				connected. The routines to call have an initial C<n> prefix for I<network>,
496				as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be
497				correctly restored so you don't have to know whether you're restoring
498				from native or network ordered data. Double values are stored stringified
499				to ensure portability as well, at the slight risk of loosing some precision
500				in the last decimals.
501
502				When using C<fd_retrieve>, objects are retrieved in sequence, one
503				object (i.e. one recursive tree) per associated C<store_fd>.
504
505				If you're more from the object-oriented camp, you can inherit from
506				Storable and directly store your objects by invoking C<store> as
507				a method. The fact that the root of the to-be-stored tree is a
508				blessed reference (i.e. an object) is special-cased so that the
509				retrieve does not provide a reference to that object but rather the
510				blessed object reference itself. (Otherwise, you'd get a reference
511				to that blessed object).
512
513				=head1 MEMORY STORE
514
515				The Storable engine can also store data into a Perl scalar instead, to
516				later retrieve them. This is mainly used to freeze a complex structure in
517				some safe compact memory place (where it can possibly be sent to another
518				process via some IPC, since freezing the structure also serializes it in
519				effect). Later on, and maybe somewhere else, you can thaw the Perl scalar
520				out and recreate the original complex structure in memory.
521
522				Surprisingly, the routines to be called are named C<freeze> and C<thaw>.
523				If you wish to send out the frozen scalar to another machine, use
524				C<nfreeze> instead to get a portable image.
525
526				Note that freezing an object structure and immediately thawing it
527				actually achieves a deep cloning of that structure:
528
529				dclone(.) = thaw(freeze(.))
530
531				Storable provides you with a C<dclone> interface which does not create
532				that intermediary scalar but instead freezes the structure in some
533				internal memory space and then immediately thaws it out.
534
535				=head1 ADVISORY LOCKING
536
537				The C<lock_store> and C<lock_nstore> routine are equivalent to
538				C<store> and C<nstore>, except that they get an exclusive lock on
539				the file before writing. Likewise, C<lock_retrieve> does the same
540				as C<retrieve>, but also gets a shared lock on the file before reading.
541
542				As with any advisory locking scheme, the protection only works if you
543				systematically use C<lock_store> and C<lock_retrieve>. If one side of
544				your application uses C<store> whilst the other uses C<lock_retrieve>,
545				you will get no protection at all.
546
547				The internal advisory locking is implemented using Perl's flock()
548				routine. If your system does not support any form of flock(), or if
549				you share your files across NFS, you might wish to use other forms
550				of locking by using modules such as LockFile::Simple which lock a
551				file using a filesystem entry, instead of locking the file descriptor.
552
553				=head1 SPEED
554
555				The heart of Storable is written in C for decent speed. Extra low-level
556				optimizations have been made when manipulating perl internals, to
557				sacrifice encapsulation for the benefit of greater speed.
558
559				=head1 CANONICAL REPRESENTATION
560
561				Normally, Storable stores elements of hashes in the order they are
562				stored internally by Perl, i.e. pseudo-randomly. If you set
563				C<$Storable::canonical> to some C<TRUE> value, Storable will store
564				hashes with the elements sorted by their key. This allows you to
565				compare data structures by comparing their frozen representations (or
566				even the compressed frozen representations), which can be useful for
567				creating lookup tables for complicated queries.
568
569				Canonical order does not imply network order; those are two orthogonal
570				settings.
571
572				=head1 CODE REFERENCES
573
574				Since Storable version 2.05, CODE references may be serialized with
575				the help of L<B::Deparse>. To enable this feature, set
576				C<$Storable::Deparse> to a true value. To enable deserialization,
577				C<$Storable::Eval> should be set to a true value. Be aware that
578				deserialization is done through C<eval>, which is dangerous if the
579				Storable file contains malicious data. You can set C<$Storable::Eval>
580				to a subroutine reference which would be used instead of C<eval>. See
581				below for an example using a L<Safe> compartment for deserialization
582				of CODE references.
583
584				If C<$Storable::Deparse> and/or C<$Storable::Eval> are set to false
585				values, then the value of C<$Storable::forgive_me> (see below) is
586				respected while serializing and deserializing.
587
588				=head1 FORWARD COMPATIBILITY
589
590				This release of Storable can be used on a newer version of Perl to
591				serialize data which is not supported by earlier Perls. By default,
592				Storable will attempt to do the right thing, by C<croak()>ing if it
593				encounters data that it cannot deserialize. However, the defaults
594				can be changed as follows:
595
596				=over 4
597
598				=item utf8 data
599
600				Perl 5.6 added support for Unicode characters with code points > 255,
601				and Perl 5.8 has full support for Unicode characters in hash keys.
602				Perl internally encodes strings with these characters using utf8, and
603				Storable serializes them as utf8. By default, if an older version of
604				Perl encounters a utf8 value it cannot represent, it will C<croak()>.
605				To change this behaviour so that Storable deserializes utf8 encoded
606				values as the string of bytes (effectively dropping the I<is_utf8> flag)
607				set C<$Storable::drop_utf8> to some C<TRUE> value. This is a form of
608				data loss, because with C<$drop_utf8> true, it becomes impossible to tell
609				whether the original data was the Unicode string, or a series of bytes
610				that happen to be valid utf8.
611
612				=item restricted hashes
613
614				Perl 5.8 adds support for restricted hashes, which have keys
615				restricted to a given set, and can have values locked to be read only.
616				By default, when Storable encounters a restricted hash on a perl
617				that doesn't support them, it will deserialize it as a normal hash,
618				silently discarding any placeholder keys and leaving the keys and
619				all values unlocked. To make Storable C<croak()> instead, set
620				C<$Storable::downgrade_restricted> to a C<FALSE> value. To restore
621				the default set it back to some C<TRUE> value.
622
623				=item files from future versions of Storable
624
625				Earlier versions of Storable would immediately croak if they encountered
626				a file with a higher internal version number than the reading Storable
627				knew about. Internal version numbers are increased each time new data
628				types (such as restricted hashes) are added to the vocabulary of the file
629				format. This meant that a newer Storable module had no way of writing a
630				file readable by an older Storable, even if the writer didn't store newer
631				data types.
632
633				This version of Storable will defer croaking until it encounters a data
634				type in the file that it does not recognize. This means that it will
635				continue to read files generated by newer Storable modules which are careful
636				in what they write out, making it easier to upgrade Storable modules in a
637				mixed environment.
638
639				The old behaviour of immediate croaking can be re-instated by setting
640				C<$Storable::accept_future_minor> to some C<FALSE> value.
641
642				=back
643
644				All these variables have no effect on a newer Perl which supports the
645				relevant feature.
646
647				=head1 ERROR REPORTING
648
649				Storable uses the "exception" paradigm, in that it does not try to workaround
650				failures: if something bad happens, an exception is generated from the
651				caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap
652				those exceptions.
653
654				When Storable croaks, it tries to report the error via the C<logcroak()>
655				routine from the C<Log::Agent> package, if it is available.
656
657				Normal errors are reported by having store() or retrieve() return C<undef>.
658				Such errors are usually I/O errors (or truncated stream errors at retrieval).
659
660				=head1 WIZARDS ONLY
661
662				=head2 Hooks
663
664				Any class may define hooks that will be called during the serialization
665				and deserialization process on objects that are instances of that class.
666				Those hooks can redefine the way serialization is performed (and therefore,
667				how the symmetrical deserialization should be conducted).
668
669				Since we said earlier:
670
671				dclone(.) = thaw(freeze(.))
672
673				everything we say about hooks should also hold for deep cloning. However,
674				hooks get to know whether the operation is a mere serialization, or a cloning.
675
676				Therefore, when serializing hooks are involved,
677
678				dclone(.) <> thaw(freeze(.))
679
680				Well, you could keep them in sync, but there's no guarantee it will always
681				hold on classes somebody else wrote. Besides, there is little to gain in
682				doing so: a serializing hook could keep only one attribute of an object,
683				which is probably not what should happen during a deep cloning of that
684				same object.
685
686				Here is the hooking interface:
687
688				=over 4
689
690				=item C<STORABLE_freeze> I<obj>, I<cloning>
691
692				The serializing hook, called on the object during serialization. It can be
693				inherited, or defined in the class itself, like any other method.
694
695				Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating
696				whether we're in a dclone() or a regular serialization via store() or freeze().
697
698				Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized
699				is the serialized form to be used, and the optional $ref1, $ref2, etc... are
700				extra references that you wish to let the Storable engine serialize.
701
702				At deserialization time, you will be given back the same LIST, but all the
703				extra references will be pointing into the deserialized structure.
704
705				The B<first time> the hook is hit in a serialization flow, you may have it
706				return an empty list. That will signal the Storable engine to further
707				discard that hook for this class and to therefore revert to the default
708				serialization of the underlying Perl data. The hook will again be normally
709				processed in the next serialization.
710
711				Unless you know better, serializing hook should always say:
712
713				sub STORABLE_freeze {
714				my ($self, $cloning) = @_;
715				return if $cloning; # Regular default serialization
716				....
717				}
718
719				in order to keep reasonable dclone() semantics.
720
721				=item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ...
722
723				The deserializing hook called on the object during deserialization.
724				But wait: if we're deserializing, there's no object yet... right?
725
726				Wrong: the Storable engine creates an empty one for you. If you know Eiffel,
727				you can view C<STORABLE_thaw> as an alternate creation routine.
728
729				This means the hook can be inherited like any other method, and that
730				I<obj> is your blessed reference for this particular instance.
731
732				The other arguments should look familiar if you know C<STORABLE_freeze>:
733				I<cloning> is true when we're part of a deep clone operation, I<serialized>
734				is the serialized string you returned to the engine in C<STORABLE_freeze>,
735				and there may be an optional list of references, in the same order you gave
736				them at serialization time, pointing to the deserialized objects (which
737				have been processed courtesy of the Storable engine).
738
739				When the Storable engine does not find any C<STORABLE_thaw> hook routine,
740				it tries to load the class by requiring the package dynamically (using
741				the blessed package name), and then re-attempts the lookup. If at that
742				time the hook cannot be located, the engine croaks. Note that this mechanism
743				will fail if you define several classes in the same file, but L<perlmod>
744				warned you.
745
746				It is up to you to use this information to populate I<obj> the way you want.
747
748				Returned value: none.
749
750				=item C<STORABLE_attach> I<class>, I<cloning>, I<serialized>
751
752				While C<STORABLE_freeze> and C<STORABLE_thaw> are useful for classes where
753				each instance is independent, this mechanism has difficulty (or is
754				incompatible) with objects that exist as common process-level or
755				system-level resources, such as singleton objects, database pools, caches
756				or memoized objects.
757
758				The alternative C<STORABLE_attach> method provides a solution for these
759				shared objects. Instead of C<STORABLE_freeze> --E<gt> C<STORABLE_thaw>,
760				you implement C<STORABLE_freeze> --E<gt> C<STORABLE_attach> instead.
761
762				Arguments: I<class> is the class we are attaching to, I<cloning> is a flag
763				indicating whether we're in a dclone() or a regular de-serialization via
764				thaw(), and I<serialized> is the stored string for the resource object.
765
766				Because these resource objects are considered to be owned by the entire
767				process/system, and not the "property" of whatever is being serialized,
768				no references underneath the object should be included in the serialized
769				string. Thus, in any class that implements C<STORABLE_attach>, the
770				C<STORABLE_freeze> method cannot return any references, and C<Storable>
771				will throw an error if C<STORABLE_freeze> tries to return references.
772
773				All information required to "attach" back to the shared resource object
774				B<must> be contained B<only> in the C<STORABLE_freeze> return string.
775				Otherwise, C<STORABLE_freeze> behaves as normal for C<STORABLE_attach>
776				classes.
777
778				Because C<STORABLE_attach> is passed the class (rather than an object),
779				it also returns the object directly, rather than modifying the passed
780				object.
781
782				Returned value: object of type C<class>
783
784				=back
785
786				=head2 Predicates
787
788				Predicates are not exportable. They must be called by explicitly prefixing
789				them with the Storable package name.
790
791				=over 4
792
793				=item C<Storable::last_op_in_netorder>
794
795				The C<Storable::last_op_in_netorder()> predicate will tell you whether
796				network order was used in the last store or retrieve operation. If you
797				don't know how to use this, just forget about it.
798
799				=item C<Storable::is_storing>
800
801				Returns true if within a store operation (via STORABLE_freeze hook).
802
803				=item C<Storable::is_retrieving>
804
805				Returns true if within a retrieve operation (via STORABLE_thaw hook).
806
807				=back
808
809				=head2 Recursion
810
811				With hooks comes the ability to recurse back to the Storable engine.
812				Indeed, hooks are regular Perl code, and Storable is convenient when
813				it comes to serializing and deserializing things, so why not use it
814				to handle the serialization string?
815
816				There are a few things you need to know, however:
817
818				=over 4
819
820				=item *
821
822				You can create endless loops if the things you serialize via freeze()
823				(for instance) point back to the object we're trying to serialize in
824				the hook.
825
826				=item *
827
828				Shared references among objects will not stay shared: if we're serializing
829				the list of object [A, C] where both object A and C refer to the SAME object
830				B, and if there is a serializing hook in A that says freeze(B), then when
831				deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D,
832				a deep clone of B'. The topology was not preserved.
833
834				=back
835
836				That's why C<STORABLE_freeze> lets you provide a list of references
837				to serialize. The engine guarantees that those will be serialized in the
838				same context as the other objects, and therefore that shared objects will
839				stay shared.
840
841				In the above [A, C] example, the C<STORABLE_freeze> hook could return:
842
843				("something", $self->{B})
844
845				and the B part would be serialized by the engine. In C<STORABLE_thaw>, you
846				would get back the reference to the B' object, deserialized for you.
847
848				Therefore, recursion should normally be avoided, but is nonetheless supported.
849
850				=head2 Deep Cloning
851
852				There is a Clone module available on CPAN which implements deep cloning
853				natively, i.e. without freezing to memory and thawing the result. It is
854				aimed to replace Storable's dclone() some day. However, it does not currently
855				support Storable hooks to redefine the way deep cloning is performed.
856
857				=head1 Storable magic
858
859				Yes, there's a lot of that :-) But more precisely, in UNIX systems
860				there's a utility called C<file>, which recognizes data files based on
861				their contents (usually their first few bytes). For this to work,
862				a certain file called F<magic> needs to taught about the I<signature>
863				of the data. Where that configuration file lives depends on the UNIX
864				flavour; often it's something like F</usr/share/misc/magic> or
865				F</etc/magic>. Your system administrator needs to do the updating of
866				the F<magic> file. The necessary signature information is output to
867				STDOUT by invoking Storable::show_file_magic(). Note that the GNU
868				implementation of the C<file> utility, version 3.38 or later,
869				is expected to contain support for recognising Storable files
870				out-of-the-box, in addition to other kinds of Perl files.
871
872				You can also use the following functions to extract the file header
873				information from Storable images:
874
875				=over
876
877				=item $info = Storable::file_magic( $filename )
878
879				If the given file is a Storable image return a hash describing it. If
880				the file is readable, but not a Storable image return C<undef>. If
881				the file does not exist or is unreadable then croak.
882
883				The hash returned has the following elements:
884
885				=over
886
887				=item C<version>
888
889				This returns the file format version. It is a string like "2.7".
890
891				Note that this version number is not the same as the version number of
892				the Storable module itself. For instance Storable v0.7 create files
893				in format v2.0 and Storable v2.15 create files in format v2.7. The
894				file format version number only increment when additional features
895				that would confuse older versions of the module are added.
896
897				Files older than v2.0 will have the one of the version numbers "-1",
898				"0" or "1". No minor number was used at that time.
899
900				=item C<version_nv>
901
902				This returns the file format version as number. It is a string like
903				"2.007". This value is suitable for numeric comparisons.
904
905				The constant function C<Storable::BIN_VERSION_NV> returns a comparable
906				number that represent the highest file version number that this
907				version of Storable fully support (but see discussion of
908				C<$Storable::accept_future_minor> above). The constant
909				C<Storable::BIN_WRITE_VERSION_NV> function returns what file version
910				is written and might be less than C<Storable::BIN_VERSION_NV> in some
911				configuations.
912
913				=item C<major>, C<minor>
914
915				This also returns the file format version. If the version is "2.7"
916				then major would be 2 and minor would be 7. The minor element is
917				missing for when major is less than 2.
918
919				=item C<hdrsize>
920
921				The is the number of bytes that the Storable header occupies.
922
923				=item C<netorder>
924
925				This is TRUE if the image store data in network order. This means
926				that it was created with nstore() or similar.
927
928				=item C<byteorder>
929
930				This is only present when C<netorder> is FALSE. It is the
931				$Config{byteorder} string of the perl that created this image. It is
932				a string like "1234" (32 bit little endian) or "87654321" (64 bit big
933				endian). This must match the current perl for the image to be
934				readable by Storable.
935
936				=item C<intsize>, C<longsize>, C<ptrsize>, C<nvsize>
937
938				These are only present when C<netorder> is FALSE. These are the sizes of
939				various C datatypes of the perl that created this image. These must
940				match the current perl for the image to be readable by Storable.
941
942				The C<nvsize> element is only present for file format v2.2 and
943				higher.
944
945				=item C<file>
946
947				The name of the file.
948
949				=back
950
951				=item $info = Storable::read_magic( $buffer )
952
953				=item $info = Storable::read_magic( $buffer, $must_be_file )
954
955				The $buffer should be a Storable image or the first few bytes of it.
956				If $buffer starts with a Storable header, then a hash describing the
957				image is returned, otherwise C<undef> is returned.
958
959				The hash has the same structure as the one returned by
960				Storable::file_magic(). The C<file> element is true if the image is a
961				file image.
962
963				If the $must_be_file argument is provided and is TRUE, then return
964				C<undef> unless the image looks like it belongs to a file dump.
965
966				The maximum size of a Storable header is currently 21 bytes. If the
967				provided $buffer is only the first part of a Storable image it should
968				at least be this long to ensure that read_magic() will recognize it as
969				such.
970
971				=back
972
973				=head1 EXAMPLES
974
975				Here are some code samples showing a possible usage of Storable:
976
977				use Storable qw(store retrieve freeze thaw dclone);
978
979				%color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);
980
981				store(\%color, 'mycolors') or die "Can't store %a in mycolors!\n";
982
983				$colref = retrieve('mycolors');
984				die "Unable to retrieve from mycolors!\n" unless defined $colref;
985				printf "Blue is still %lf\n", $colref->{'Blue'};
986
987				$colref2 = dclone(\%color);
988
989				$str = freeze(\%color);
990				printf "Serialization of %%color is %d bytes long.\n", length($str);
991				$colref3 = thaw($str);
992
993				which prints (on my machine):
994
995				Blue is still 0.100000
996				Serialization of %color is 102 bytes long.
997
998				Serialization of CODE references and deserialization in a safe
999				compartment:
1000
1001				=for example begin
1002
1003				use Storable qw(freeze thaw);
1004				use Safe;
1005				use strict;
1006				my $safe = new Safe;
1007				# because of opcodes used in "use strict":
1008				$safe->permit(qw(:default require));
1009				local $Storable::Deparse = 1;
1010				local $Storable::Eval = sub { $safe->reval($_[0]) };
1011				my $serialized = freeze(sub { 42 });
1012				my $code = thaw($serialized);
1013				$code->() == 42;
1014
1015				=for example end
1016
1017				=for example_testing
1018				is( $code->(), 42 );
1019
1020				=head1 WARNING
1021
1022				If you're using references as keys within your hash tables, you're bound
1023				to be disappointed when retrieving your data. Indeed, Perl stringifies
1024				references used as hash table keys. If you later wish to access the
1025				items via another reference stringification (i.e. using the same
1026				reference that was used for the key originally to record the value into
1027				the hash table), it will work because both references stringify to the
1028				same string.
1029
1030				It won't work across a sequence of C<store> and C<retrieve> operations,
1031				however, because the addresses in the retrieved objects, which are
1032				part of the stringified references, will probably differ from the
1033				original addresses. The topology of your structure is preserved,
1034				but not hidden semantics like those.
1035
1036				On platforms where it matters, be sure to call C<binmode()> on the
1037				descriptors that you pass to Storable functions.
1038
1039				Storing data canonically that contains large hashes can be
1040				significantly slower than storing the same data normally, as
1041				temporary arrays to hold the keys for each hash have to be allocated,
1042				populated, sorted and freed. Some tests have shown a halving of the
1043				speed of storing -- the exact penalty will depend on the complexity of
1044				your data. There is no slowdown on retrieval.
1045
1046				=head1 BUGS
1047
1048				You can't store GLOB, FORMLINE, etc.... If you can define semantics
1049				for those operations, feel free to enhance Storable so that it can
1050				deal with them.
1051
1052				The store functions will C<croak> if they run into such references
1053				unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that
1054				case, the fatal message is turned in a warning and some
1055				meaningless string is stored instead.
1056
1057				Setting C<$Storable::canonical> may not yield frozen strings that
1058				compare equal due to possible stringification of numbers. When the
1059				string version of a scalar exists, it is the form stored; therefore,
1060				if you happen to use your numbers as strings between two freezing
1061				operations on the same data structures, you will get different
1062				results.
1063
1064				When storing doubles in network order, their value is stored as text.
1065				However, you should also not expect non-numeric floating-point values
1066				such as infinity and "not a number" to pass successfully through a
1067				nstore()/retrieve() pair.
1068
1069				As Storable neither knows nor cares about character sets (although it
1070				does know that characters may be more than eight bits wide), any difference
1071				in the interpretation of character codes between a host and a target
1072				system is your problem. In particular, if host and target use different
1073				code points to represent the characters used in the text representation
1074				of floating-point numbers, you will not be able be able to exchange
1075				floating-point data, even with nstore().
1076
1077				C<Storable::drop_utf8> is a blunt tool. There is no facility either to
1078				return B<all> strings as utf8 sequences, or to attempt to convert utf8
1079				data back to 8 bit and C<croak()> if the conversion fails.
1080
1081				Prior to Storable 2.01, no distinction was made between signed and
1082				unsigned integers on storing. By default Storable prefers to store a
1083				scalars string representation (if it has one) so this would only cause
1084				problems when storing large unsigned integers that had never been converted
1085				to string or floating point. In other words values that had been generated
1086				by integer operations such as logic ops and then not used in any string or
1087				arithmetic context before storing.
1088
1089				=head2 64 bit data in perl 5.6.0 and 5.6.1
1090
1091				This section only applies to you if you have existing data written out
1092				by Storable 2.02 or earlier on perl 5.6.0 or 5.6.1 on Unix or Linux which
1093				has been configured with 64 bit integer support (not the default)
1094				If you got a precompiled perl, rather than running Configure to build
1095				your own perl from source, then it almost certainly does not affect you,
1096				and you can stop reading now (unless you're curious). If you're using perl
1097				on Windows it does not affect you.
1098
1099				Storable writes a file header which contains the sizes of various C
1100				language types for the C compiler that built Storable (when not writing in
1101				network order), and will refuse to load files written by a Storable not
1102				on the same (or compatible) architecture. This check and a check on
1103				machine byteorder is needed because the size of various fields in the file
1104				are given by the sizes of the C language types, and so files written on
1105				different architectures are incompatible. This is done for increased speed.
1106				(When writing in network order, all fields are written out as standard
1107				lengths, which allows full interworking, but takes longer to read and write)
1108
1109				Perl 5.6.x introduced the ability to optional configure the perl interpreter
1110				to use C's C<long long> type to allow scalars to store 64 bit integers on 32
1111				bit systems. However, due to the way the Perl configuration system
1112				generated the C configuration files on non-Windows platforms, and the way
1113				Storable generates its header, nothing in the Storable file header reflected
1114				whether the perl writing was using 32 or 64 bit integers, despite the fact
1115				that Storable was storing some data differently in the file. Hence Storable
1116				running on perl with 64 bit integers will read the header from a file
1117				written by a 32 bit perl, not realise that the data is actually in a subtly
1118				incompatible format, and then go horribly wrong (possibly crashing) if it
1119				encountered a stored integer. This is a design failure.
1120
1121				Storable has now been changed to write out and read in a file header with
1122				information about the size of integers. It's impossible to detect whether
1123				an old file being read in was written with 32 or 64 bit integers (they have
1124				the same header) so it's impossible to automatically switch to a correct
1125				backwards compatibility mode. Hence this Storable defaults to the new,
1126				correct behaviour.
1127
1128				What this means is that if you have data written by Storable 1.x running
1129				on perl 5.6.0 or 5.6.1 configured with 64 bit integers on Unix or Linux
1130				then by default this Storable will refuse to read it, giving the error
1131				I<Byte order is not compatible>. If you have such data then you you
1132				should set C<$Storable::interwork_56_64bit> to a true value to make this
1133				Storable read and write files with the old header. You should also
1134				migrate your data, or any older perl you are communicating with, to this
1135				current version of Storable.
1136
1137				If you don't have data written with specific configuration of perl described
1138				above, then you do not and should not do anything. Don't set the flag -
1139				not only will Storable on an identically configured perl refuse to load them,
1140				but Storable a differently configured perl will load them believing them
1141				to be correct for it, and then may well fail or crash part way through
1142				reading them.
1143
1144				=head1 CREDITS
1145
1146				Thank you to (in chronological order):
1147
1148				Jarkko Hietaniemi <jhi@iki.fi>
1149				Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de>
1150				Benjamin A. Holzman <bah@ecnvantage.com>
1151				Andrew Ford <A.Ford@ford-mason.co.uk>
1152				Gisle Aas <gisle@aas.no>
1153				Jeff Gresham <gresham_jeffrey@jpmorgan.com>
1154				Murray Nesbitt <murray@activestate.com>
1155				Marc Lehmann <pcg@opengroup.org>
1156				Justin Banks <justinb@wamnet.com>
1157				Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
1158				Salvador Ortiz Garcia <sog@msg.com.mx>
1159				Dominic Dunlop <domo@computer.org>
1160				Erik Haugan <erik@solbors.no>
1161
1162				for their bug reports, suggestions and contributions.
1163
1164				Benjamin Holzman contributed the tied variable support, Andrew Ford
1165				contributed the canonical order for hashes, and Gisle Aas fixed
1166				a few misunderstandings of mine regarding the perl internals,
1167				and optimized the emission of "tags" in the output streams by
1168				simply counting the objects instead of tagging them (leading to
1169				a binary incompatibility for the Storable image starting at version
1170				0.6--older images are, of course, still properly understood).
1171				Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading
1172				and references to tied items support.
1173
1174				=head1 AUTHOR
1175
1176				Storable was written by Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>>
1177				Maintenance is now done by the perl5-porters F<E<lt>perl5-porters@perl.orgE<gt>>
1178
1179				Please e-mail us with problems, bug fixes, comments and complaints,
1180				although if you have complements you should send them to Raphael.
1181				Please don't e-mail Raphael with problems, as he no longer works on
1182				Storable, and your message will be delayed while he forwards it to us.
1183
1184				=head1 SEE ALSO
1185
1186				L<Clone>.
1187
1188				=cut