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596596d5 1;# $Id: Storable.pm,v 1.0.1.13 2001/12/01 13:34:49 ram Exp $
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2;#
3;# Copyright (c) 1995-2000, Raphael Manfredi
4;#
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5;# You may redistribute only under the same terms as Perl 5, as specified
6;# in the README file that comes with the distribution.
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7;#
8;# $Log: Storable.pm,v $
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9;# Revision 1.0.1.13 2001/12/01 13:34:49 ram
10;# patch14: avoid requiring Fcntl upfront, useful to embedded runtimes
11;# patch14: store_fd() will now correctly autoflush file if needed
12;#
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13;# Revision 1.0.1.12 2001/08/28 21:51:51 ram
14;# patch13: fixed truncation race with lock_retrieve() in lock_store()
15;#
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16;# Revision 1.0.1.11 2001/07/01 11:22:14 ram
17;# patch12: systematically use "=over 4" for POD linters
18;# patch12: updated version number
19;#
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20;# Revision 1.0.1.10 2001/03/15 00:20:25 ram
21;# patch11: updated version number
22;#
23;# Revision 1.0.1.9 2001/02/17 12:37:32 ram
24;# patch10: forgot to increase version number at previous patch
25;#
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26;# Revision 1.0.1.8 2001/02/17 12:24:37 ram
27;# patch8: fixed incorrect error message
28;#
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29;# Revision 1.0.1.7 2001/01/03 09:39:02 ram
30;# patch7: added CAN_FLOCK to determine whether we can flock() or not
31;#
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32;# Revision 1.0.1.6 2000/11/05 17:20:25 ram
33;# patch6: increased version number
34;#
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35;# Revision 1.0.1.5 2000/10/26 17:10:18 ram
36;# patch5: documented that store() and retrieve() can return undef
37;# patch5: added paragraph explaining the auto require for thaw hooks
38;#
39;# Revision 1.0.1.4 2000/10/23 18:02:57 ram
40;# patch4: protected calls to flock() for dos platform
41;# patch4: added logcarp emulation if they don't have Log::Agent
42;#
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43;# Revision 1.0.1.3 2000/09/29 19:49:01 ram
44;# patch3: updated version number
45;#
46;# Revision 1.0.1.2 2000/09/28 21:42:51 ram
47;# patch2: added lock_store lock_nstore lock_retrieve
48;#
49;# Revision 1.0.1.1 2000/09/17 16:46:21 ram
50;# patch1: documented that doubles are stringified by nstore()
51;# patch1: added Salvador Ortiz Garcia in CREDITS section
52;#
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53;# Revision 1.0 2000/09/01 19:40:41 ram
54;# Baseline for first official release.
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55;#
56
57require DynaLoader;
58require Exporter;
59package Storable; @ISA = qw(Exporter DynaLoader);
60
61@EXPORT = qw(store retrieve);
62@EXPORT_OK = qw(
9e21b3d0 63 nstore store_fd nstore_fd fd_retrieve
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64 freeze nfreeze thaw
65 dclone
9e21b3d0 66 retrieve_fd
dd19458b 67 lock_store lock_nstore lock_retrieve
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68);
69
70use AutoLoader;
71use vars qw($forgive_me $VERSION);
72
0a0da639 73$VERSION = '1.015';
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74*AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr...
75
76#
77# Use of Log::Agent is optional
78#
79
80eval "use Log::Agent";
81
82unless (defined @Log::Agent::EXPORT) {
83 eval q{
84 sub logcroak {
85 require Carp;
86 Carp::croak(@_);
87 }
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88 sub logcarp {
89 require Carp;
90 Carp::carp(@_);
91 }
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92 };
93}
94
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95#
96# They might miss :flock in Fcntl
97#
98
99BEGIN {
596596d5 100 if (eval { require Fcntl; 1 } && exists $Fcntl::EXPORT_TAGS{'flock'}) {
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101 Fcntl->import(':flock');
102 } else {
103 eval q{
104 sub LOCK_SH () {1}
105 sub LOCK_EX () {2}
106 };
107 }
108}
109
7a6a85bf 110sub logcroak;
b29b780f 111sub logcarp;
7a6a85bf 112
9e21b3d0 113sub retrieve_fd { &fd_retrieve } # Backward compatibility
cb3d9de5 114
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115#
116# Determine whether locking is possible, but only when needed.
117#
118
119my $CAN_FLOCK;
120
121sub CAN_FLOCK {
122 return $CAN_FLOCK if defined $CAN_FLOCK;
123 require Config; import Config;
124 return $CAN_FLOCK =
125 $Config{'d_flock'} ||
126 $Config{'d_fcntl_can_lock'} ||
127 $Config{'d_lockf'};
128}
129
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130sub show_file_magic {
131 print <<EOM;
132#
133# To recognize the data files of the Perl module Storable,
134# the following lines need to be added to the local magic(5) file,
135# usually either /usr/share/misc/magic or /etc/magic.
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136#
1370 string perl-store perl Storable(v0.6) data
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138>4 byte >0 (net-order %d)
139>>4 byte &01 (network-ordered)
140>>4 byte =3 (major 1)
141>>4 byte =2 (major 1)
142
0a0da639 1430 string pst0 perl Storable(v0.7) data
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144>4 byte >0
145>>4 byte &01 (network-ordered)
146>>4 byte =5 (major 2)
147>>4 byte =4 (major 2)
148>>5 byte >0 (minor %d)
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149EOM
150}
151
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152bootstrap Storable;
1531;
154__END__
155
156#
157# store
158#
159# Store target object hierarchy, identified by a reference to its root.
160# The stored object tree may later be retrieved to memory via retrieve.
161# Returns undef if an I/O error occurred, in which case the file is
162# removed.
163#
164sub store {
dd19458b 165 return _store(\&pstore, @_, 0);
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166}
167
168#
169# nstore
170#
171# Same as store, but in network order.
172#
173sub nstore {
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174 return _store(\&net_pstore, @_, 0);
175}
176
177#
178# lock_store
179#
180# Same as store, but flock the file first (advisory locking).
181#
182sub lock_store {
183 return _store(\&pstore, @_, 1);
184}
185
186#
187# lock_nstore
188#
189# Same as nstore, but flock the file first (advisory locking).
190#
191sub lock_nstore {
192 return _store(\&net_pstore, @_, 1);
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193}
194
195# Internal store to file routine
196sub _store {
197 my $xsptr = shift;
198 my $self = shift;
dd19458b 199 my ($file, $use_locking) = @_;
7a6a85bf 200 logcroak "not a reference" unless ref($self);
b12202d0 201 logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist
7a6a85bf 202 local *FILE;
dd19458b 203 if ($use_locking) {
6e0ac6f5 204 open(FILE, ">>$file") || logcroak "can't write into $file: $!";
862382c7 205 unless (&CAN_FLOCK) {
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206 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
207 return undef;
f567092b 208 }
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209 flock(FILE, LOCK_EX) ||
210 logcroak "can't get exclusive lock on $file: $!";
211 truncate FILE, 0;
212 # Unlocking will happen when FILE is closed
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213 } else {
214 open(FILE, ">$file") || logcroak "can't create $file: $!";
dd19458b 215 }
6e0ac6f5 216 binmode FILE; # Archaic systems...
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217 my $da = $@; # Don't mess if called from exception handler
218 my $ret;
219 # Call C routine nstore or pstore, depending on network order
220 eval { $ret = &$xsptr(*FILE, $self) };
221 close(FILE) or $ret = undef;
222 unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret;
223 logcroak $@ if $@ =~ s/\.?\n$/,/;
224 $@ = $da;
225 return $ret ? $ret : undef;
226}
227
228#
229# store_fd
230#
231# Same as store, but perform on an already opened file descriptor instead.
232# Returns undef if an I/O error occurred.
233#
234sub store_fd {
235 return _store_fd(\&pstore, @_);
236}
237
238#
239# nstore_fd
240#
241# Same as store_fd, but in network order.
242#
243sub nstore_fd {
244 my ($self, $file) = @_;
245 return _store_fd(\&net_pstore, @_);
246}
247
248# Internal store routine on opened file descriptor
249sub _store_fd {
250 my $xsptr = shift;
251 my $self = shift;
252 my ($file) = @_;
253 logcroak "not a reference" unless ref($self);
254 logcroak "too many arguments" unless @_ == 1; # No @foo in arglist
255 my $fd = fileno($file);
256 logcroak "not a valid file descriptor" unless defined $fd;
257 my $da = $@; # Don't mess if called from exception handler
258 my $ret;
259 # Call C routine nstore or pstore, depending on network order
260 eval { $ret = &$xsptr($file, $self) };
261 logcroak $@ if $@ =~ s/\.?\n$/,/;
596596d5 262 local $\; print $file ''; # Autoflush the file if wanted
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263 $@ = $da;
264 return $ret ? $ret : undef;
265}
266
267#
268# freeze
269#
270# Store oject and its hierarchy in memory and return a scalar
271# containing the result.
272#
273sub freeze {
274 _freeze(\&mstore, @_);
275}
276
277#
278# nfreeze
279#
280# Same as freeze but in network order.
281#
282sub nfreeze {
283 _freeze(\&net_mstore, @_);
284}
285
286# Internal freeze routine
287sub _freeze {
288 my $xsptr = shift;
289 my $self = shift;
290 logcroak "not a reference" unless ref($self);
291 logcroak "too many arguments" unless @_ == 0; # No @foo in arglist
292 my $da = $@; # Don't mess if called from exception handler
293 my $ret;
294 # Call C routine mstore or net_mstore, depending on network order
295 eval { $ret = &$xsptr($self) };
296 logcroak $@ if $@ =~ s/\.?\n$/,/;
297 $@ = $da;
298 return $ret ? $ret : undef;
299}
300
301#
302# retrieve
303#
304# Retrieve object hierarchy from disk, returning a reference to the root
305# object of that tree.
306#
307sub retrieve {
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308 _retrieve($_[0], 0);
309}
310
311#
312# lock_retrieve
313#
314# Same as retrieve, but with advisory locking.
315#
316sub lock_retrieve {
317 _retrieve($_[0], 1);
318}
319
320# Internal retrieve routine
321sub _retrieve {
322 my ($file, $use_locking) = @_;
7a6a85bf 323 local *FILE;
dd19458b 324 open(FILE, $file) || logcroak "can't open $file: $!";
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325 binmode FILE; # Archaic systems...
326 my $self;
327 my $da = $@; # Could be from exception handler
dd19458b 328 if ($use_locking) {
862382c7 329 unless (&CAN_FLOCK) {
8be2b38b 330 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
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331 return undef;
332 }
8be2b38b 333 flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!";
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334 # Unlocking will happen when FILE is closed
335 }
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336 eval { $self = pretrieve(*FILE) }; # Call C routine
337 close(FILE);
338 logcroak $@ if $@ =~ s/\.?\n$/,/;
339 $@ = $da;
340 return $self;
341}
342
343#
9e21b3d0 344# fd_retrieve
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345#
346# Same as retrieve, but perform from an already opened file descriptor instead.
347#
9e21b3d0 348sub fd_retrieve {
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349 my ($file) = @_;
350 my $fd = fileno($file);
351 logcroak "not a valid file descriptor" unless defined $fd;
352 my $self;
353 my $da = $@; # Could be from exception handler
354 eval { $self = pretrieve($file) }; # Call C routine
355 logcroak $@ if $@ =~ s/\.?\n$/,/;
356 $@ = $da;
357 return $self;
358}
359
360#
361# thaw
362#
363# Recreate objects in memory from an existing frozen image created
364# by freeze. If the frozen image passed is undef, return undef.
365#
366sub thaw {
367 my ($frozen) = @_;
368 return undef unless defined $frozen;
369 my $self;
370 my $da = $@; # Could be from exception handler
371 eval { $self = mretrieve($frozen) }; # Call C routine
372 logcroak $@ if $@ =~ s/\.?\n$/,/;
373 $@ = $da;
374 return $self;
375}
376
377=head1 NAME
378
379Storable - persistency for perl data structures
380
381=head1 SYNOPSIS
382
383 use Storable;
384 store \%table, 'file';
385 $hashref = retrieve('file');
386
387 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);
388
389 # Network order
390 nstore \%table, 'file';
391 $hashref = retrieve('file'); # There is NO nretrieve()
392
393 # Storing to and retrieving from an already opened file
394 store_fd \@array, \*STDOUT;
395 nstore_fd \%table, \*STDOUT;
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396 $aryref = fd_retrieve(\*SOCKET);
397 $hashref = fd_retrieve(\*SOCKET);
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398
399 # Serializing to memory
400 $serialized = freeze \%table;
401 %table_clone = %{ thaw($serialized) };
402
403 # Deep (recursive) cloning
404 $cloneref = dclone($ref);
405
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406 # Advisory locking
407 use Storable qw(lock_store lock_nstore lock_retrieve)
408 lock_store \%table, 'file';
409 lock_nstore \%table, 'file';
410 $hashref = lock_retrieve('file');
411
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412=head1 DESCRIPTION
413
414The Storable package brings persistency to your perl data structures
415containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be
416convenientely stored to disk and retrieved at a later time.
417
418It can be used in the regular procedural way by calling C<store> with
419a reference to the object to be stored, along with the file name where
420the image should be written.
421The routine returns C<undef> for I/O problems or other internal error,
422a true value otherwise. Serious errors are propagated as a C<die> exception.
423
424To retrieve data stored to disk, use C<retrieve> with a file name,
425and the objects stored into that file are recreated into memory for you,
426a I<reference> to the root object being returned. In case an I/O error
427occurs while reading, C<undef> is returned instead. Other serious
428errors are propagated via C<die>.
429
430Since storage is performed recursively, you might want to stuff references
431to objects that share a lot of common data into a single array or hash
432table, and then store that object. That way, when you retrieve back the
433whole thing, the objects will continue to share what they originally shared.
434
435At the cost of a slight header overhead, you may store to an already
436opened file descriptor using the C<store_fd> routine, and retrieve
9e21b3d0 437from a file via C<fd_retrieve>. Those names aren't imported by default,
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438so you will have to do that explicitely if you need those routines.
439The file descriptor you supply must be already opened, for read
440if you're going to retrieve and for write if you wish to store.
441
442 store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
9e21b3d0 443 $hashref = fd_retrieve(*STDIN);
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444
445You can also store data in network order to allow easy sharing across
446multiple platforms, or when storing on a socket known to be remotely
447connected. The routines to call have an initial C<n> prefix for I<network>,
448as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be
449correctly restored so you don't have to know whether you're restoring
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450from native or network ordered data. Double values are stored stringified
451to ensure portability as well, at the slight risk of loosing some precision
452in the last decimals.
7a6a85bf 453
9e21b3d0 454When using C<fd_retrieve>, objects are retrieved in sequence, one
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455object (i.e. one recursive tree) per associated C<store_fd>.
456
457If you're more from the object-oriented camp, you can inherit from
458Storable and directly store your objects by invoking C<store> as
459a method. The fact that the root of the to-be-stored tree is a
460blessed reference (i.e. an object) is special-cased so that the
461retrieve does not provide a reference to that object but rather the
462blessed object reference itself. (Otherwise, you'd get a reference
463to that blessed object).
464
465=head1 MEMORY STORE
466
467The Storable engine can also store data into a Perl scalar instead, to
468later retrieve them. This is mainly used to freeze a complex structure in
469some safe compact memory place (where it can possibly be sent to another
470process via some IPC, since freezing the structure also serializes it in
471effect). Later on, and maybe somewhere else, you can thaw the Perl scalar
472out and recreate the original complex structure in memory.
473
474Surprisingly, the routines to be called are named C<freeze> and C<thaw>.
475If you wish to send out the frozen scalar to another machine, use
476C<nfreeze> instead to get a portable image.
477
478Note that freezing an object structure and immediately thawing it
479actually achieves a deep cloning of that structure:
480
481 dclone(.) = thaw(freeze(.))
482
483Storable provides you with a C<dclone> interface which does not create
484that intermediary scalar but instead freezes the structure in some
485internal memory space and then immediatly thaws it out.
486
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487=head1 ADVISORY LOCKING
488
489The C<lock_store> and C<lock_nstore> routine are equivalent to C<store>
490and C<nstore>, only they get an exclusive lock on the file before
491writing. Likewise, C<lock_retrieve> performs as C<retrieve>, but also
492gets a shared lock on the file before reading.
493
494Like with any advisory locking scheme, the protection only works if
495you systematically use C<lock_store> and C<lock_retrieve>. If one
496side of your application uses C<store> whilst the other uses C<lock_retrieve>,
497you will get no protection at all.
498
499The internal advisory locking is implemented using Perl's flock() routine.
500If your system does not support any form of flock(), or if you share
501your files across NFS, you might wish to use other forms of locking by
502using modules like LockFile::Simple which lock a file using a filesystem
503entry, instead of locking the file descriptor.
504
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505=head1 SPEED
506
507The heart of Storable is written in C for decent speed. Extra low-level
508optimization have been made when manipulating perl internals, to
509sacrifice encapsulation for the benefit of a greater speed.
510
511=head1 CANONICAL REPRESENTATION
512
513Normally Storable stores elements of hashes in the order they are
514stored internally by Perl, i.e. pseudo-randomly. If you set
515C<$Storable::canonical> to some C<TRUE> value, Storable will store
516hashes with the elements sorted by their key. This allows you to
517compare data structures by comparing their frozen representations (or
518even the compressed frozen representations), which can be useful for
519creating lookup tables for complicated queries.
520
521Canonical order does not imply network order, those are two orthogonal
522settings.
523
524=head1 ERROR REPORTING
525
526Storable uses the "exception" paradigm, in that it does not try to workaround
527failures: if something bad happens, an exception is generated from the
528caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap
529those exceptions.
530
531When Storable croaks, it tries to report the error via the C<logcroak()>
532routine from the C<Log::Agent> package, if it is available.
533
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534Normal errors are reported by having store() or retrieve() return C<undef>.
535Such errors are usually I/O errors (or truncated stream errors at retrieval).
536
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537=head1 WIZARDS ONLY
538
539=head2 Hooks
540
541Any class may define hooks that will be called during the serialization
542and deserialization process on objects that are instances of that class.
543Those hooks can redefine the way serialization is performed (and therefore,
544how the symetrical deserialization should be conducted).
545
546Since we said earlier:
547
548 dclone(.) = thaw(freeze(.))
549
550everything we say about hooks should also hold for deep cloning. However,
551hooks get to know whether the operation is a mere serialization, or a cloning.
552
553Therefore, when serializing hooks are involved,
554
555 dclone(.) <> thaw(freeze(.))
556
557Well, you could keep them in sync, but there's no guarantee it will always
558hold on classes somebody else wrote. Besides, there is little to gain in
559doing so: a serializing hook could only keep one attribute of an object,
560which is probably not what should happen during a deep cloning of that
561same object.
562
563Here is the hooking interface:
564
bbc7dcd2 565=over 4
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566
567=item C<STORABLE_freeze> I<obj>, I<cloning>
568
569The serializing hook, called on the object during serialization. It can be
570inherited, or defined in the class itself, like any other method.
571
572Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating
573whether we're in a dclone() or a regular serialization via store() or freeze().
574
575Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized
576is the serialized form to be used, and the optional $ref1, $ref2, etc... are
577extra references that you wish to let the Storable engine serialize.
578
579At deserialization time, you will be given back the same LIST, but all the
580extra references will be pointing into the deserialized structure.
581
582The B<first time> the hook is hit in a serialization flow, you may have it
583return an empty list. That will signal the Storable engine to further
584discard that hook for this class and to therefore revert to the default
585serialization of the underlying Perl data. The hook will again be normally
586processed in the next serialization.
587
588Unless you know better, serializing hook should always say:
589
590 sub STORABLE_freeze {
591 my ($self, $cloning) = @_;
592 return if $cloning; # Regular default serialization
593 ....
594 }
595
596in order to keep reasonable dclone() semantics.
597
598=item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ...
599
600The deserializing hook called on the object during deserialization.
601But wait. If we're deserializing, there's no object yet... right?
602
603Wrong: the Storable engine creates an empty one for you. If you know Eiffel,
604you can view C<STORABLE_thaw> as an alternate creation routine.
605
606This means the hook can be inherited like any other method, and that
607I<obj> is your blessed reference for this particular instance.
608
609The other arguments should look familiar if you know C<STORABLE_freeze>:
610I<cloning> is true when we're part of a deep clone operation, I<serialized>
611is the serialized string you returned to the engine in C<STORABLE_freeze>,
612and there may be an optional list of references, in the same order you gave
613them at serialization time, pointing to the deserialized objects (which
614have been processed courtesy of the Storable engine).
615
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616When the Storable engine does not find any C<STORABLE_thaw> hook routine,
617it tries to load the class by requiring the package dynamically (using
618the blessed package name), and then re-attempts the lookup. If at that
619time the hook cannot be located, the engine croaks. Note that this mechanism
620will fail if you define several classes in the same file, but perlmod(1)
621warned you.
622
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623It is up to you to use these information to populate I<obj> the way you want.
624
625Returned value: none.
626
627=back
628
629=head2 Predicates
630
631Predicates are not exportable. They must be called by explicitely prefixing
632them with the Storable package name.
633
bbc7dcd2 634=over 4
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635
636=item C<Storable::last_op_in_netorder>
637
638The C<Storable::last_op_in_netorder()> predicate will tell you whether
639network order was used in the last store or retrieve operation. If you
640don't know how to use this, just forget about it.
641
642=item C<Storable::is_storing>
643
644Returns true if within a store operation (via STORABLE_freeze hook).
645
646=item C<Storable::is_retrieving>
647
648Returns true if within a retrieve operation, (via STORABLE_thaw hook).
649
650=back
651
652=head2 Recursion
653
654With hooks comes the ability to recurse back to the Storable engine. Indeed,
655hooks are regular Perl code, and Storable is convenient when it comes to
656serialize and deserialize things, so why not use it to handle the
657serialization string?
658
659There are a few things you need to know however:
660
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662
663=item *
664
665You can create endless loops if the things you serialize via freeze()
666(for instance) point back to the object we're trying to serialize in the hook.
667
668=item *
669
670Shared references among objects will not stay shared: if we're serializing
671the list of object [A, C] where both object A and C refer to the SAME object
672B, and if there is a serializing hook in A that says freeze(B), then when
673deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D,
674a deep clone of B'. The topology was not preserved.
675
676=back
677
678That's why C<STORABLE_freeze> lets you provide a list of references
679to serialize. The engine guarantees that those will be serialized in the
680same context as the other objects, and therefore that shared objects will
681stay shared.
682
683In the above [A, C] example, the C<STORABLE_freeze> hook could return:
684
685 ("something", $self->{B})
686
687and the B part would be serialized by the engine. In C<STORABLE_thaw>, you
688would get back the reference to the B' object, deserialized for you.
689
690Therefore, recursion should normally be avoided, but is nonetheless supported.
691
692=head2 Deep Cloning
693
694There is a new Clone module available on CPAN which implements deep cloning
695natively, i.e. without freezing to memory and thawing the result. It is
696aimed to replace Storable's dclone() some day. However, it does not currently
697support Storable hooks to redefine the way deep cloning is performed.
698
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699=head1 Storable magic
700
701Yes, there's a lot of that :-) But more precisely, in UNIX systems
702there's a utility called C<file>, which recognizes data files based on
703their contents (usually their first few bytes). For this to work,
8b793558 704a certain file called F<magic> needs to taught about the I<signature>
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705of the data. Where that configuration file lives depends on the UNIX
706flavour, often it's something like F</usr/share/misc/magic> or
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707F</etc/magic>. Your system administrator needs to do the updating of
708the F<magic> file. The necessary signature information is output to
709stdout by invoking Storable::show_file_magic(). Note that the open
710source implementation of the C<file> utility 3.38 (or later)
711is expected to contain the support for recognising Storable files,
712in addition to other kinds of Perl files.
0a0da639 713
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714=head1 EXAMPLES
715
716Here are some code samples showing a possible usage of Storable:
717
718 use Storable qw(store retrieve freeze thaw dclone);
719
720 %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);
721
722 store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n";
723
724 $colref = retrieve('/tmp/colors');
725 die "Unable to retrieve from /tmp/colors!\n" unless defined $colref;
726 printf "Blue is still %lf\n", $colref->{'Blue'};
727
728 $colref2 = dclone(\%color);
729
730 $str = freeze(\%color);
731 printf "Serialization of %%color is %d bytes long.\n", length($str);
732 $colref3 = thaw($str);
733
734which prints (on my machine):
735
736 Blue is still 0.100000
737 Serialization of %color is 102 bytes long.
738
739=head1 WARNING
740
741If you're using references as keys within your hash tables, you're bound
742to disapointment when retrieving your data. Indeed, Perl stringifies
743references used as hash table keys. If you later wish to access the
744items via another reference stringification (i.e. using the same
745reference that was used for the key originally to record the value into
746the hash table), it will work because both references stringify to the
747same string.
748
749It won't work across a C<store> and C<retrieve> operations however, because
750the addresses in the retrieved objects, which are part of the stringified
751references, will probably differ from the original addresses. The
752topology of your structure is preserved, but not hidden semantics
753like those.
754
755On platforms where it matters, be sure to call C<binmode()> on the
756descriptors that you pass to Storable functions.
757
758Storing data canonically that contains large hashes can be
759significantly slower than storing the same data normally, as
760temprorary arrays to hold the keys for each hash have to be allocated,
761populated, sorted and freed. Some tests have shown a halving of the
762speed of storing -- the exact penalty will depend on the complexity of
763your data. There is no slowdown on retrieval.
764
765=head1 BUGS
766
767You can't store GLOB, CODE, FORMLINE, etc... If you can define
768semantics for those operations, feel free to enhance Storable so that
769it can deal with them.
770
771The store functions will C<croak> if they run into such references
772unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that
773case, the fatal message is turned in a warning and some
774meaningless string is stored instead.
775
776Setting C<$Storable::canonical> may not yield frozen strings that
777compare equal due to possible stringification of numbers. When the
778string version of a scalar exists, it is the form stored, therefore
779if you happen to use your numbers as strings between two freezing
780operations on the same data structures, you will get different
781results.
782
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783When storing doubles in network order, their value is stored as text.
784However, you should also not expect non-numeric floating-point values
785such as infinity and "not a number" to pass successfully through a
786nstore()/retrieve() pair.
787
788As Storable neither knows nor cares about character sets (although it
789does know that characters may be more than eight bits wide), any difference
790in the interpretation of character codes between a host and a target
791system is your problem. In particular, if host and target use different
792code points to represent the characters used in the text representation
793of floating-point numbers, you will not be able be able to exchange
794floating-point data, even with nstore().
795
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796=head1 CREDITS
797
798Thank you to (in chronological order):
799
800 Jarkko Hietaniemi <jhi@iki.fi>
801 Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de>
802 Benjamin A. Holzman <bah@ecnvantage.com>
803 Andrew Ford <A.Ford@ford-mason.co.uk>
804 Gisle Aas <gisle@aas.no>
805 Jeff Gresham <gresham_jeffrey@jpmorgan.com>
806 Murray Nesbitt <murray@activestate.com>
807 Marc Lehmann <pcg@opengroup.org>
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808 Justin Banks <justinb@wamnet.com>
809 Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
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810 Salvador Ortiz Garcia <sog@msg.com.mx>
811 Dominic Dunlop <domo@computer.org>
812 Erik Haugan <erik@solbors.no>
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813
814for their bug reports, suggestions and contributions.
815
816Benjamin Holzman contributed the tied variable support, Andrew Ford
817contributed the canonical order for hashes, and Gisle Aas fixed
818a few misunderstandings of mine regarding the Perl internals,
819and optimized the emission of "tags" in the output streams by
820simply counting the objects instead of tagging them (leading to
821a binary incompatibility for the Storable image starting at version
8220.6--older images are of course still properly understood).
823Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading
824and reference to tied items support.
825
826=head1 TRANSLATIONS
827
828There is a Japanese translation of this man page available at
829http://member.nifty.ne.jp/hippo2000/perltips/storable.htm ,
830courtesy of Kawai, Takanori <kawai@nippon-rad.co.jp>.
831
832=head1 AUTHOR
833
834Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>>
835
836=head1 SEE ALSO
837
838Clone(3).
839
840=cut
841