Commit | Line | Data |
6e0ac6f5 |
1 | ;# $Id: Storable.pm,v 1.0.1.12 2001/08/28 21:51:51 ram Exp $ |
7a6a85bf |
2 | ;# |
3 | ;# Copyright (c) 1995-2000, Raphael Manfredi |
4 | ;# |
9e21b3d0 |
5 | ;# You may redistribute only under the same terms as Perl 5, as specified |
6 | ;# in the README file that comes with the distribution. |
7a6a85bf |
7 | ;# |
8 | ;# $Log: Storable.pm,v $ |
6e0ac6f5 |
9 | ;# Revision 1.0.1.12 2001/08/28 21:51:51 ram |
10 | ;# patch13: fixed truncation race with lock_retrieve() in lock_store() |
11 | ;# |
e993d95c |
12 | ;# Revision 1.0.1.11 2001/07/01 11:22:14 ram |
13 | ;# patch12: systematically use "=over 4" for POD linters |
14 | ;# patch12: updated version number |
15 | ;# |
8be2b38b |
16 | ;# Revision 1.0.1.10 2001/03/15 00:20:25 ram |
17 | ;# patch11: updated version number |
18 | ;# |
19 | ;# Revision 1.0.1.9 2001/02/17 12:37:32 ram |
20 | ;# patch10: forgot to increase version number at previous patch |
21 | ;# |
b12202d0 |
22 | ;# Revision 1.0.1.8 2001/02/17 12:24:37 ram |
23 | ;# patch8: fixed incorrect error message |
24 | ;# |
862382c7 |
25 | ;# Revision 1.0.1.7 2001/01/03 09:39:02 ram |
26 | ;# patch7: added CAN_FLOCK to determine whether we can flock() or not |
27 | ;# |
90826881 |
28 | ;# Revision 1.0.1.6 2000/11/05 17:20:25 ram |
29 | ;# patch6: increased version number |
30 | ;# |
212e9bde |
31 | ;# Revision 1.0.1.5 2000/10/26 17:10:18 ram |
32 | ;# patch5: documented that store() and retrieve() can return undef |
33 | ;# patch5: added paragraph explaining the auto require for thaw hooks |
34 | ;# |
35 | ;# Revision 1.0.1.4 2000/10/23 18:02:57 ram |
36 | ;# patch4: protected calls to flock() for dos platform |
37 | ;# patch4: added logcarp emulation if they don't have Log::Agent |
38 | ;# |
8be2b38b |
39 | ;# Revision 1.0.1.3 2000/09/29 19:49:01 ram |
40 | ;# patch3: updated version number |
41 | ;# |
42 | ;# Revision 1.0.1.2 2000/09/28 21:42:51 ram |
43 | ;# patch2: added lock_store lock_nstore lock_retrieve |
44 | ;# |
45 | ;# Revision 1.0.1.1 2000/09/17 16:46:21 ram |
46 | ;# patch1: documented that doubles are stringified by nstore() |
47 | ;# patch1: added Salvador Ortiz Garcia in CREDITS section |
48 | ;# |
9e21b3d0 |
49 | ;# Revision 1.0 2000/09/01 19:40:41 ram |
50 | ;# Baseline for first official release. |
7a6a85bf |
51 | ;# |
52 | |
53 | require DynaLoader; |
54 | require Exporter; |
55 | package Storable; @ISA = qw(Exporter DynaLoader); |
56 | |
57 | @EXPORT = qw(store retrieve); |
58 | @EXPORT_OK = qw( |
9e21b3d0 |
59 | nstore store_fd nstore_fd fd_retrieve |
7a6a85bf |
60 | freeze nfreeze thaw |
61 | dclone |
9e21b3d0 |
62 | retrieve_fd |
dd19458b |
63 | lock_store lock_nstore lock_retrieve |
7a6a85bf |
64 | ); |
65 | |
66 | use AutoLoader; |
67 | use vars qw($forgive_me $VERSION); |
68 | |
6e0ac6f5 |
69 | $VERSION = '1.013'; |
7a6a85bf |
70 | *AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr... |
71 | |
72 | # |
73 | # Use of Log::Agent is optional |
74 | # |
75 | |
76 | eval "use Log::Agent"; |
77 | |
78 | unless (defined @Log::Agent::EXPORT) { |
79 | eval q{ |
80 | sub logcroak { |
81 | require Carp; |
82 | Carp::croak(@_); |
83 | } |
b29b780f |
84 | sub logcarp { |
85 | require Carp; |
86 | Carp::carp(@_); |
87 | } |
7a6a85bf |
88 | }; |
89 | } |
90 | |
dd19458b |
91 | # |
92 | # They might miss :flock in Fcntl |
93 | # |
94 | |
95 | BEGIN { |
96 | require Fcntl; |
97 | if (exists $Fcntl::EXPORT_TAGS{'flock'}) { |
98 | Fcntl->import(':flock'); |
99 | } else { |
100 | eval q{ |
101 | sub LOCK_SH () {1} |
102 | sub LOCK_EX () {2} |
103 | }; |
104 | } |
105 | } |
106 | |
7a6a85bf |
107 | sub logcroak; |
b29b780f |
108 | sub logcarp; |
7a6a85bf |
109 | |
9e21b3d0 |
110 | sub retrieve_fd { &fd_retrieve } # Backward compatibility |
cb3d9de5 |
111 | |
862382c7 |
112 | # |
113 | # Determine whether locking is possible, but only when needed. |
114 | # |
115 | |
116 | my $CAN_FLOCK; |
117 | |
118 | sub CAN_FLOCK { |
119 | return $CAN_FLOCK if defined $CAN_FLOCK; |
120 | require Config; import Config; |
121 | return $CAN_FLOCK = |
122 | $Config{'d_flock'} || |
123 | $Config{'d_fcntl_can_lock'} || |
124 | $Config{'d_lockf'}; |
125 | } |
126 | |
7a6a85bf |
127 | bootstrap Storable; |
128 | 1; |
129 | __END__ |
130 | |
131 | # |
132 | # store |
133 | # |
134 | # Store target object hierarchy, identified by a reference to its root. |
135 | # The stored object tree may later be retrieved to memory via retrieve. |
136 | # Returns undef if an I/O error occurred, in which case the file is |
137 | # removed. |
138 | # |
139 | sub store { |
dd19458b |
140 | return _store(\&pstore, @_, 0); |
7a6a85bf |
141 | } |
142 | |
143 | # |
144 | # nstore |
145 | # |
146 | # Same as store, but in network order. |
147 | # |
148 | sub nstore { |
dd19458b |
149 | return _store(\&net_pstore, @_, 0); |
150 | } |
151 | |
152 | # |
153 | # lock_store |
154 | # |
155 | # Same as store, but flock the file first (advisory locking). |
156 | # |
157 | sub lock_store { |
158 | return _store(\&pstore, @_, 1); |
159 | } |
160 | |
161 | # |
162 | # lock_nstore |
163 | # |
164 | # Same as nstore, but flock the file first (advisory locking). |
165 | # |
166 | sub lock_nstore { |
167 | return _store(\&net_pstore, @_, 1); |
7a6a85bf |
168 | } |
169 | |
170 | # Internal store to file routine |
171 | sub _store { |
172 | my $xsptr = shift; |
173 | my $self = shift; |
dd19458b |
174 | my ($file, $use_locking) = @_; |
7a6a85bf |
175 | logcroak "not a reference" unless ref($self); |
b12202d0 |
176 | logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist |
7a6a85bf |
177 | local *FILE; |
dd19458b |
178 | if ($use_locking) { |
6e0ac6f5 |
179 | open(FILE, ">>$file") || logcroak "can't write into $file: $!"; |
862382c7 |
180 | unless (&CAN_FLOCK) { |
b29b780f |
181 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
182 | return undef; |
f567092b |
183 | } |
dd19458b |
184 | flock(FILE, LOCK_EX) || |
185 | logcroak "can't get exclusive lock on $file: $!"; |
186 | truncate FILE, 0; |
187 | # Unlocking will happen when FILE is closed |
6e0ac6f5 |
188 | } else { |
189 | open(FILE, ">$file") || logcroak "can't create $file: $!"; |
dd19458b |
190 | } |
6e0ac6f5 |
191 | binmode FILE; # Archaic systems... |
7a6a85bf |
192 | my $da = $@; # Don't mess if called from exception handler |
193 | my $ret; |
194 | # Call C routine nstore or pstore, depending on network order |
195 | eval { $ret = &$xsptr(*FILE, $self) }; |
196 | close(FILE) or $ret = undef; |
197 | unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret; |
198 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
199 | $@ = $da; |
200 | return $ret ? $ret : undef; |
201 | } |
202 | |
203 | # |
204 | # store_fd |
205 | # |
206 | # Same as store, but perform on an already opened file descriptor instead. |
207 | # Returns undef if an I/O error occurred. |
208 | # |
209 | sub store_fd { |
210 | return _store_fd(\&pstore, @_); |
211 | } |
212 | |
213 | # |
214 | # nstore_fd |
215 | # |
216 | # Same as store_fd, but in network order. |
217 | # |
218 | sub nstore_fd { |
219 | my ($self, $file) = @_; |
220 | return _store_fd(\&net_pstore, @_); |
221 | } |
222 | |
223 | # Internal store routine on opened file descriptor |
224 | sub _store_fd { |
225 | my $xsptr = shift; |
226 | my $self = shift; |
227 | my ($file) = @_; |
228 | logcroak "not a reference" unless ref($self); |
229 | logcroak "too many arguments" unless @_ == 1; # No @foo in arglist |
230 | my $fd = fileno($file); |
231 | logcroak "not a valid file descriptor" unless defined $fd; |
232 | my $da = $@; # Don't mess if called from exception handler |
233 | my $ret; |
234 | # Call C routine nstore or pstore, depending on network order |
235 | eval { $ret = &$xsptr($file, $self) }; |
236 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
237 | $@ = $da; |
238 | return $ret ? $ret : undef; |
239 | } |
240 | |
241 | # |
242 | # freeze |
243 | # |
244 | # Store oject and its hierarchy in memory and return a scalar |
245 | # containing the result. |
246 | # |
247 | sub freeze { |
248 | _freeze(\&mstore, @_); |
249 | } |
250 | |
251 | # |
252 | # nfreeze |
253 | # |
254 | # Same as freeze but in network order. |
255 | # |
256 | sub nfreeze { |
257 | _freeze(\&net_mstore, @_); |
258 | } |
259 | |
260 | # Internal freeze routine |
261 | sub _freeze { |
262 | my $xsptr = shift; |
263 | my $self = shift; |
264 | logcroak "not a reference" unless ref($self); |
265 | logcroak "too many arguments" unless @_ == 0; # No @foo in arglist |
266 | my $da = $@; # Don't mess if called from exception handler |
267 | my $ret; |
268 | # Call C routine mstore or net_mstore, depending on network order |
269 | eval { $ret = &$xsptr($self) }; |
270 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
271 | $@ = $da; |
272 | return $ret ? $ret : undef; |
273 | } |
274 | |
275 | # |
276 | # retrieve |
277 | # |
278 | # Retrieve object hierarchy from disk, returning a reference to the root |
279 | # object of that tree. |
280 | # |
281 | sub retrieve { |
dd19458b |
282 | _retrieve($_[0], 0); |
283 | } |
284 | |
285 | # |
286 | # lock_retrieve |
287 | # |
288 | # Same as retrieve, but with advisory locking. |
289 | # |
290 | sub lock_retrieve { |
291 | _retrieve($_[0], 1); |
292 | } |
293 | |
294 | # Internal retrieve routine |
295 | sub _retrieve { |
296 | my ($file, $use_locking) = @_; |
7a6a85bf |
297 | local *FILE; |
dd19458b |
298 | open(FILE, $file) || logcroak "can't open $file: $!"; |
7a6a85bf |
299 | binmode FILE; # Archaic systems... |
300 | my $self; |
301 | my $da = $@; # Could be from exception handler |
dd19458b |
302 | if ($use_locking) { |
862382c7 |
303 | unless (&CAN_FLOCK) { |
8be2b38b |
304 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
b29b780f |
305 | return undef; |
306 | } |
8be2b38b |
307 | flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!"; |
dd19458b |
308 | # Unlocking will happen when FILE is closed |
309 | } |
7a6a85bf |
310 | eval { $self = pretrieve(*FILE) }; # Call C routine |
311 | close(FILE); |
312 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
313 | $@ = $da; |
314 | return $self; |
315 | } |
316 | |
317 | # |
9e21b3d0 |
318 | # fd_retrieve |
7a6a85bf |
319 | # |
320 | # Same as retrieve, but perform from an already opened file descriptor instead. |
321 | # |
9e21b3d0 |
322 | sub fd_retrieve { |
7a6a85bf |
323 | my ($file) = @_; |
324 | my $fd = fileno($file); |
325 | logcroak "not a valid file descriptor" unless defined $fd; |
326 | my $self; |
327 | my $da = $@; # Could be from exception handler |
328 | eval { $self = pretrieve($file) }; # Call C routine |
329 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
330 | $@ = $da; |
331 | return $self; |
332 | } |
333 | |
334 | # |
335 | # thaw |
336 | # |
337 | # Recreate objects in memory from an existing frozen image created |
338 | # by freeze. If the frozen image passed is undef, return undef. |
339 | # |
340 | sub thaw { |
341 | my ($frozen) = @_; |
342 | return undef unless defined $frozen; |
343 | my $self; |
344 | my $da = $@; # Could be from exception handler |
345 | eval { $self = mretrieve($frozen) }; # Call C routine |
346 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
347 | $@ = $da; |
348 | return $self; |
349 | } |
350 | |
351 | =head1 NAME |
352 | |
353 | Storable - persistency for perl data structures |
354 | |
355 | =head1 SYNOPSIS |
356 | |
357 | use Storable; |
358 | store \%table, 'file'; |
359 | $hashref = retrieve('file'); |
360 | |
361 | use Storable qw(nstore store_fd nstore_fd freeze thaw dclone); |
362 | |
363 | # Network order |
364 | nstore \%table, 'file'; |
365 | $hashref = retrieve('file'); # There is NO nretrieve() |
366 | |
367 | # Storing to and retrieving from an already opened file |
368 | store_fd \@array, \*STDOUT; |
369 | nstore_fd \%table, \*STDOUT; |
9e21b3d0 |
370 | $aryref = fd_retrieve(\*SOCKET); |
371 | $hashref = fd_retrieve(\*SOCKET); |
7a6a85bf |
372 | |
373 | # Serializing to memory |
374 | $serialized = freeze \%table; |
375 | %table_clone = %{ thaw($serialized) }; |
376 | |
377 | # Deep (recursive) cloning |
378 | $cloneref = dclone($ref); |
379 | |
dd19458b |
380 | # Advisory locking |
381 | use Storable qw(lock_store lock_nstore lock_retrieve) |
382 | lock_store \%table, 'file'; |
383 | lock_nstore \%table, 'file'; |
384 | $hashref = lock_retrieve('file'); |
385 | |
7a6a85bf |
386 | =head1 DESCRIPTION |
387 | |
388 | The Storable package brings persistency to your perl data structures |
389 | containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be |
390 | convenientely stored to disk and retrieved at a later time. |
391 | |
392 | It can be used in the regular procedural way by calling C<store> with |
393 | a reference to the object to be stored, along with the file name where |
394 | the image should be written. |
395 | The routine returns C<undef> for I/O problems or other internal error, |
396 | a true value otherwise. Serious errors are propagated as a C<die> exception. |
397 | |
398 | To retrieve data stored to disk, use C<retrieve> with a file name, |
399 | and the objects stored into that file are recreated into memory for you, |
400 | a I<reference> to the root object being returned. In case an I/O error |
401 | occurs while reading, C<undef> is returned instead. Other serious |
402 | errors are propagated via C<die>. |
403 | |
404 | Since storage is performed recursively, you might want to stuff references |
405 | to objects that share a lot of common data into a single array or hash |
406 | table, and then store that object. That way, when you retrieve back the |
407 | whole thing, the objects will continue to share what they originally shared. |
408 | |
409 | At the cost of a slight header overhead, you may store to an already |
410 | opened file descriptor using the C<store_fd> routine, and retrieve |
9e21b3d0 |
411 | from a file via C<fd_retrieve>. Those names aren't imported by default, |
7a6a85bf |
412 | so you will have to do that explicitely if you need those routines. |
413 | The file descriptor you supply must be already opened, for read |
414 | if you're going to retrieve and for write if you wish to store. |
415 | |
416 | store_fd(\%table, *STDOUT) || die "can't store to stdout\n"; |
9e21b3d0 |
417 | $hashref = fd_retrieve(*STDIN); |
7a6a85bf |
418 | |
419 | You can also store data in network order to allow easy sharing across |
420 | multiple platforms, or when storing on a socket known to be remotely |
421 | connected. The routines to call have an initial C<n> prefix for I<network>, |
422 | as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be |
423 | correctly restored so you don't have to know whether you're restoring |
dd19458b |
424 | from native or network ordered data. Double values are stored stringified |
425 | to ensure portability as well, at the slight risk of loosing some precision |
426 | in the last decimals. |
7a6a85bf |
427 | |
9e21b3d0 |
428 | When using C<fd_retrieve>, objects are retrieved in sequence, one |
7a6a85bf |
429 | object (i.e. one recursive tree) per associated C<store_fd>. |
430 | |
431 | If you're more from the object-oriented camp, you can inherit from |
432 | Storable and directly store your objects by invoking C<store> as |
433 | a method. The fact that the root of the to-be-stored tree is a |
434 | blessed reference (i.e. an object) is special-cased so that the |
435 | retrieve does not provide a reference to that object but rather the |
436 | blessed object reference itself. (Otherwise, you'd get a reference |
437 | to that blessed object). |
438 | |
439 | =head1 MEMORY STORE |
440 | |
441 | The Storable engine can also store data into a Perl scalar instead, to |
442 | later retrieve them. This is mainly used to freeze a complex structure in |
443 | some safe compact memory place (where it can possibly be sent to another |
444 | process via some IPC, since freezing the structure also serializes it in |
445 | effect). Later on, and maybe somewhere else, you can thaw the Perl scalar |
446 | out and recreate the original complex structure in memory. |
447 | |
448 | Surprisingly, the routines to be called are named C<freeze> and C<thaw>. |
449 | If you wish to send out the frozen scalar to another machine, use |
450 | C<nfreeze> instead to get a portable image. |
451 | |
452 | Note that freezing an object structure and immediately thawing it |
453 | actually achieves a deep cloning of that structure: |
454 | |
455 | dclone(.) = thaw(freeze(.)) |
456 | |
457 | Storable provides you with a C<dclone> interface which does not create |
458 | that intermediary scalar but instead freezes the structure in some |
459 | internal memory space and then immediatly thaws it out. |
460 | |
dd19458b |
461 | =head1 ADVISORY LOCKING |
462 | |
463 | The C<lock_store> and C<lock_nstore> routine are equivalent to C<store> |
464 | and C<nstore>, only they get an exclusive lock on the file before |
465 | writing. Likewise, C<lock_retrieve> performs as C<retrieve>, but also |
466 | gets a shared lock on the file before reading. |
467 | |
468 | Like with any advisory locking scheme, the protection only works if |
469 | you systematically use C<lock_store> and C<lock_retrieve>. If one |
470 | side of your application uses C<store> whilst the other uses C<lock_retrieve>, |
471 | you will get no protection at all. |
472 | |
473 | The internal advisory locking is implemented using Perl's flock() routine. |
474 | If your system does not support any form of flock(), or if you share |
475 | your files across NFS, you might wish to use other forms of locking by |
476 | using modules like LockFile::Simple which lock a file using a filesystem |
477 | entry, instead of locking the file descriptor. |
478 | |
7a6a85bf |
479 | =head1 SPEED |
480 | |
481 | The heart of Storable is written in C for decent speed. Extra low-level |
482 | optimization have been made when manipulating perl internals, to |
483 | sacrifice encapsulation for the benefit of a greater speed. |
484 | |
485 | =head1 CANONICAL REPRESENTATION |
486 | |
487 | Normally Storable stores elements of hashes in the order they are |
488 | stored internally by Perl, i.e. pseudo-randomly. If you set |
489 | C<$Storable::canonical> to some C<TRUE> value, Storable will store |
490 | hashes with the elements sorted by their key. This allows you to |
491 | compare data structures by comparing their frozen representations (or |
492 | even the compressed frozen representations), which can be useful for |
493 | creating lookup tables for complicated queries. |
494 | |
495 | Canonical order does not imply network order, those are two orthogonal |
496 | settings. |
497 | |
498 | =head1 ERROR REPORTING |
499 | |
500 | Storable uses the "exception" paradigm, in that it does not try to workaround |
501 | failures: if something bad happens, an exception is generated from the |
502 | caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap |
503 | those exceptions. |
504 | |
505 | When Storable croaks, it tries to report the error via the C<logcroak()> |
506 | routine from the C<Log::Agent> package, if it is available. |
507 | |
212e9bde |
508 | Normal errors are reported by having store() or retrieve() return C<undef>. |
509 | Such errors are usually I/O errors (or truncated stream errors at retrieval). |
510 | |
7a6a85bf |
511 | =head1 WIZARDS ONLY |
512 | |
513 | =head2 Hooks |
514 | |
515 | Any class may define hooks that will be called during the serialization |
516 | and deserialization process on objects that are instances of that class. |
517 | Those hooks can redefine the way serialization is performed (and therefore, |
518 | how the symetrical deserialization should be conducted). |
519 | |
520 | Since we said earlier: |
521 | |
522 | dclone(.) = thaw(freeze(.)) |
523 | |
524 | everything we say about hooks should also hold for deep cloning. However, |
525 | hooks get to know whether the operation is a mere serialization, or a cloning. |
526 | |
527 | Therefore, when serializing hooks are involved, |
528 | |
529 | dclone(.) <> thaw(freeze(.)) |
530 | |
531 | Well, you could keep them in sync, but there's no guarantee it will always |
532 | hold on classes somebody else wrote. Besides, there is little to gain in |
533 | doing so: a serializing hook could only keep one attribute of an object, |
534 | which is probably not what should happen during a deep cloning of that |
535 | same object. |
536 | |
537 | Here is the hooking interface: |
538 | |
bbc7dcd2 |
539 | =over 4 |
7a6a85bf |
540 | |
541 | =item C<STORABLE_freeze> I<obj>, I<cloning> |
542 | |
543 | The serializing hook, called on the object during serialization. It can be |
544 | inherited, or defined in the class itself, like any other method. |
545 | |
546 | Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating |
547 | whether we're in a dclone() or a regular serialization via store() or freeze(). |
548 | |
549 | Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized |
550 | is the serialized form to be used, and the optional $ref1, $ref2, etc... are |
551 | extra references that you wish to let the Storable engine serialize. |
552 | |
553 | At deserialization time, you will be given back the same LIST, but all the |
554 | extra references will be pointing into the deserialized structure. |
555 | |
556 | The B<first time> the hook is hit in a serialization flow, you may have it |
557 | return an empty list. That will signal the Storable engine to further |
558 | discard that hook for this class and to therefore revert to the default |
559 | serialization of the underlying Perl data. The hook will again be normally |
560 | processed in the next serialization. |
561 | |
562 | Unless you know better, serializing hook should always say: |
563 | |
564 | sub STORABLE_freeze { |
565 | my ($self, $cloning) = @_; |
566 | return if $cloning; # Regular default serialization |
567 | .... |
568 | } |
569 | |
570 | in order to keep reasonable dclone() semantics. |
571 | |
572 | =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ... |
573 | |
574 | The deserializing hook called on the object during deserialization. |
575 | But wait. If we're deserializing, there's no object yet... right? |
576 | |
577 | Wrong: the Storable engine creates an empty one for you. If you know Eiffel, |
578 | you can view C<STORABLE_thaw> as an alternate creation routine. |
579 | |
580 | This means the hook can be inherited like any other method, and that |
581 | I<obj> is your blessed reference for this particular instance. |
582 | |
583 | The other arguments should look familiar if you know C<STORABLE_freeze>: |
584 | I<cloning> is true when we're part of a deep clone operation, I<serialized> |
585 | is the serialized string you returned to the engine in C<STORABLE_freeze>, |
586 | and there may be an optional list of references, in the same order you gave |
587 | them at serialization time, pointing to the deserialized objects (which |
588 | have been processed courtesy of the Storable engine). |
589 | |
212e9bde |
590 | When the Storable engine does not find any C<STORABLE_thaw> hook routine, |
591 | it tries to load the class by requiring the package dynamically (using |
592 | the blessed package name), and then re-attempts the lookup. If at that |
593 | time the hook cannot be located, the engine croaks. Note that this mechanism |
594 | will fail if you define several classes in the same file, but perlmod(1) |
595 | warned you. |
596 | |
7a6a85bf |
597 | It is up to you to use these information to populate I<obj> the way you want. |
598 | |
599 | Returned value: none. |
600 | |
601 | =back |
602 | |
603 | =head2 Predicates |
604 | |
605 | Predicates are not exportable. They must be called by explicitely prefixing |
606 | them with the Storable package name. |
607 | |
bbc7dcd2 |
608 | =over 4 |
7a6a85bf |
609 | |
610 | =item C<Storable::last_op_in_netorder> |
611 | |
612 | The C<Storable::last_op_in_netorder()> predicate will tell you whether |
613 | network order was used in the last store or retrieve operation. If you |
614 | don't know how to use this, just forget about it. |
615 | |
616 | =item C<Storable::is_storing> |
617 | |
618 | Returns true if within a store operation (via STORABLE_freeze hook). |
619 | |
620 | =item C<Storable::is_retrieving> |
621 | |
622 | Returns true if within a retrieve operation, (via STORABLE_thaw hook). |
623 | |
624 | =back |
625 | |
626 | =head2 Recursion |
627 | |
628 | With hooks comes the ability to recurse back to the Storable engine. Indeed, |
629 | hooks are regular Perl code, and Storable is convenient when it comes to |
630 | serialize and deserialize things, so why not use it to handle the |
631 | serialization string? |
632 | |
633 | There are a few things you need to know however: |
634 | |
bbc7dcd2 |
635 | =over 4 |
7a6a85bf |
636 | |
637 | =item * |
638 | |
639 | You can create endless loops if the things you serialize via freeze() |
640 | (for instance) point back to the object we're trying to serialize in the hook. |
641 | |
642 | =item * |
643 | |
644 | Shared references among objects will not stay shared: if we're serializing |
645 | the list of object [A, C] where both object A and C refer to the SAME object |
646 | B, and if there is a serializing hook in A that says freeze(B), then when |
647 | deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D, |
648 | a deep clone of B'. The topology was not preserved. |
649 | |
650 | =back |
651 | |
652 | That's why C<STORABLE_freeze> lets you provide a list of references |
653 | to serialize. The engine guarantees that those will be serialized in the |
654 | same context as the other objects, and therefore that shared objects will |
655 | stay shared. |
656 | |
657 | In the above [A, C] example, the C<STORABLE_freeze> hook could return: |
658 | |
659 | ("something", $self->{B}) |
660 | |
661 | and the B part would be serialized by the engine. In C<STORABLE_thaw>, you |
662 | would get back the reference to the B' object, deserialized for you. |
663 | |
664 | Therefore, recursion should normally be avoided, but is nonetheless supported. |
665 | |
666 | =head2 Deep Cloning |
667 | |
668 | There is a new Clone module available on CPAN which implements deep cloning |
669 | natively, i.e. without freezing to memory and thawing the result. It is |
670 | aimed to replace Storable's dclone() some day. However, it does not currently |
671 | support Storable hooks to redefine the way deep cloning is performed. |
672 | |
673 | =head1 EXAMPLES |
674 | |
675 | Here are some code samples showing a possible usage of Storable: |
676 | |
677 | use Storable qw(store retrieve freeze thaw dclone); |
678 | |
679 | %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1); |
680 | |
681 | store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n"; |
682 | |
683 | $colref = retrieve('/tmp/colors'); |
684 | die "Unable to retrieve from /tmp/colors!\n" unless defined $colref; |
685 | printf "Blue is still %lf\n", $colref->{'Blue'}; |
686 | |
687 | $colref2 = dclone(\%color); |
688 | |
689 | $str = freeze(\%color); |
690 | printf "Serialization of %%color is %d bytes long.\n", length($str); |
691 | $colref3 = thaw($str); |
692 | |
693 | which prints (on my machine): |
694 | |
695 | Blue is still 0.100000 |
696 | Serialization of %color is 102 bytes long. |
697 | |
698 | =head1 WARNING |
699 | |
700 | If you're using references as keys within your hash tables, you're bound |
701 | to disapointment when retrieving your data. Indeed, Perl stringifies |
702 | references used as hash table keys. If you later wish to access the |
703 | items via another reference stringification (i.e. using the same |
704 | reference that was used for the key originally to record the value into |
705 | the hash table), it will work because both references stringify to the |
706 | same string. |
707 | |
708 | It won't work across a C<store> and C<retrieve> operations however, because |
709 | the addresses in the retrieved objects, which are part of the stringified |
710 | references, will probably differ from the original addresses. The |
711 | topology of your structure is preserved, but not hidden semantics |
712 | like those. |
713 | |
714 | On platforms where it matters, be sure to call C<binmode()> on the |
715 | descriptors that you pass to Storable functions. |
716 | |
717 | Storing data canonically that contains large hashes can be |
718 | significantly slower than storing the same data normally, as |
719 | temprorary arrays to hold the keys for each hash have to be allocated, |
720 | populated, sorted and freed. Some tests have shown a halving of the |
721 | speed of storing -- the exact penalty will depend on the complexity of |
722 | your data. There is no slowdown on retrieval. |
723 | |
724 | =head1 BUGS |
725 | |
726 | You can't store GLOB, CODE, FORMLINE, etc... If you can define |
727 | semantics for those operations, feel free to enhance Storable so that |
728 | it can deal with them. |
729 | |
730 | The store functions will C<croak> if they run into such references |
731 | unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that |
732 | case, the fatal message is turned in a warning and some |
733 | meaningless string is stored instead. |
734 | |
735 | Setting C<$Storable::canonical> may not yield frozen strings that |
736 | compare equal due to possible stringification of numbers. When the |
737 | string version of a scalar exists, it is the form stored, therefore |
738 | if you happen to use your numbers as strings between two freezing |
739 | operations on the same data structures, you will get different |
740 | results. |
741 | |
dd19458b |
742 | When storing doubles in network order, their value is stored as text. |
743 | However, you should also not expect non-numeric floating-point values |
744 | such as infinity and "not a number" to pass successfully through a |
745 | nstore()/retrieve() pair. |
746 | |
747 | As Storable neither knows nor cares about character sets (although it |
748 | does know that characters may be more than eight bits wide), any difference |
749 | in the interpretation of character codes between a host and a target |
750 | system is your problem. In particular, if host and target use different |
751 | code points to represent the characters used in the text representation |
752 | of floating-point numbers, you will not be able be able to exchange |
753 | floating-point data, even with nstore(). |
754 | |
7a6a85bf |
755 | =head1 CREDITS |
756 | |
757 | Thank you to (in chronological order): |
758 | |
759 | Jarkko Hietaniemi <jhi@iki.fi> |
760 | Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de> |
761 | Benjamin A. Holzman <bah@ecnvantage.com> |
762 | Andrew Ford <A.Ford@ford-mason.co.uk> |
763 | Gisle Aas <gisle@aas.no> |
764 | Jeff Gresham <gresham_jeffrey@jpmorgan.com> |
765 | Murray Nesbitt <murray@activestate.com> |
766 | Marc Lehmann <pcg@opengroup.org> |
9e21b3d0 |
767 | Justin Banks <justinb@wamnet.com> |
768 | Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!) |
dd19458b |
769 | Salvador Ortiz Garcia <sog@msg.com.mx> |
770 | Dominic Dunlop <domo@computer.org> |
771 | Erik Haugan <erik@solbors.no> |
7a6a85bf |
772 | |
773 | for their bug reports, suggestions and contributions. |
774 | |
775 | Benjamin Holzman contributed the tied variable support, Andrew Ford |
776 | contributed the canonical order for hashes, and Gisle Aas fixed |
777 | a few misunderstandings of mine regarding the Perl internals, |
778 | and optimized the emission of "tags" in the output streams by |
779 | simply counting the objects instead of tagging them (leading to |
780 | a binary incompatibility for the Storable image starting at version |
781 | 0.6--older images are of course still properly understood). |
782 | Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading |
783 | and reference to tied items support. |
784 | |
785 | =head1 TRANSLATIONS |
786 | |
787 | There is a Japanese translation of this man page available at |
788 | http://member.nifty.ne.jp/hippo2000/perltips/storable.htm , |
789 | courtesy of Kawai, Takanori <kawai@nippon-rad.co.jp>. |
790 | |
791 | =head1 AUTHOR |
792 | |
793 | Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>> |
794 | |
795 | =head1 SEE ALSO |
796 | |
797 | Clone(3). |
798 | |
799 | =cut |
800 | |