Commit | Line | Data |
9e21b3d0 |
1 | ;# $Id: Storable.pm,v 1.0 2000/09/01 19:40:41 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 $ |
9e21b3d0 |
9 | ;# Revision 1.0 2000/09/01 19:40:41 ram |
10 | ;# Baseline for first official release. |
7a6a85bf |
11 | ;# |
12 | |
13 | require DynaLoader; |
14 | require Exporter; |
15 | package Storable; @ISA = qw(Exporter DynaLoader); |
16 | |
17 | @EXPORT = qw(store retrieve); |
18 | @EXPORT_OK = qw( |
9e21b3d0 |
19 | nstore store_fd nstore_fd fd_retrieve |
7a6a85bf |
20 | freeze nfreeze thaw |
21 | dclone |
9e21b3d0 |
22 | retrieve_fd |
dd19458b |
23 | lock_store lock_nstore lock_retrieve |
7a6a85bf |
24 | ); |
25 | |
26 | use AutoLoader; |
27 | use vars qw($forgive_me $VERSION); |
28 | |
b29b780f |
29 | $VERSION = '1.004'; |
7a6a85bf |
30 | *AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr... |
31 | |
32 | # |
33 | # Use of Log::Agent is optional |
34 | # |
35 | |
36 | eval "use Log::Agent"; |
37 | |
38 | unless (defined @Log::Agent::EXPORT) { |
39 | eval q{ |
40 | sub logcroak { |
41 | require Carp; |
42 | Carp::croak(@_); |
43 | } |
b29b780f |
44 | sub logcarp { |
45 | require Carp; |
46 | Carp::carp(@_); |
47 | } |
7a6a85bf |
48 | }; |
49 | } |
50 | |
dd19458b |
51 | # |
52 | # They might miss :flock in Fcntl |
53 | # |
54 | |
55 | BEGIN { |
56 | require Fcntl; |
57 | if (exists $Fcntl::EXPORT_TAGS{'flock'}) { |
58 | Fcntl->import(':flock'); |
59 | } else { |
60 | eval q{ |
61 | sub LOCK_SH () {1} |
62 | sub LOCK_EX () {2} |
63 | }; |
64 | } |
65 | } |
66 | |
7a6a85bf |
67 | sub logcroak; |
b29b780f |
68 | sub logcarp; |
7a6a85bf |
69 | |
9e21b3d0 |
70 | sub retrieve_fd { &fd_retrieve } # Backward compatibility |
cb3d9de5 |
71 | |
7a6a85bf |
72 | bootstrap Storable; |
73 | 1; |
74 | __END__ |
75 | |
76 | # |
77 | # store |
78 | # |
79 | # Store target object hierarchy, identified by a reference to its root. |
80 | # The stored object tree may later be retrieved to memory via retrieve. |
81 | # Returns undef if an I/O error occurred, in which case the file is |
82 | # removed. |
83 | # |
84 | sub store { |
dd19458b |
85 | return _store(\&pstore, @_, 0); |
7a6a85bf |
86 | } |
87 | |
88 | # |
89 | # nstore |
90 | # |
91 | # Same as store, but in network order. |
92 | # |
93 | sub nstore { |
dd19458b |
94 | return _store(\&net_pstore, @_, 0); |
95 | } |
96 | |
97 | # |
98 | # lock_store |
99 | # |
100 | # Same as store, but flock the file first (advisory locking). |
101 | # |
102 | sub lock_store { |
103 | return _store(\&pstore, @_, 1); |
104 | } |
105 | |
106 | # |
107 | # lock_nstore |
108 | # |
109 | # Same as nstore, but flock the file first (advisory locking). |
110 | # |
111 | sub lock_nstore { |
112 | return _store(\&net_pstore, @_, 1); |
7a6a85bf |
113 | } |
114 | |
115 | # Internal store to file routine |
116 | sub _store { |
117 | my $xsptr = shift; |
118 | my $self = shift; |
dd19458b |
119 | my ($file, $use_locking) = @_; |
7a6a85bf |
120 | logcroak "not a reference" unless ref($self); |
dd19458b |
121 | logcroak "too many arguments" unless @_ == 2; # No @foo in arglist |
7a6a85bf |
122 | local *FILE; |
123 | open(FILE, ">$file") || logcroak "can't create $file: $!"; |
124 | binmode FILE; # Archaic systems... |
dd19458b |
125 | if ($use_locking) { |
f567092b |
126 | if ($^O eq 'dos') { |
b29b780f |
127 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
128 | return undef; |
f567092b |
129 | } |
dd19458b |
130 | flock(FILE, LOCK_EX) || |
131 | logcroak "can't get exclusive lock on $file: $!"; |
132 | truncate FILE, 0; |
133 | # Unlocking will happen when FILE is closed |
134 | } |
7a6a85bf |
135 | my $da = $@; # Don't mess if called from exception handler |
136 | my $ret; |
137 | # Call C routine nstore or pstore, depending on network order |
138 | eval { $ret = &$xsptr(*FILE, $self) }; |
139 | close(FILE) or $ret = undef; |
140 | unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret; |
141 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
142 | $@ = $da; |
143 | return $ret ? $ret : undef; |
144 | } |
145 | |
146 | # |
147 | # store_fd |
148 | # |
149 | # Same as store, but perform on an already opened file descriptor instead. |
150 | # Returns undef if an I/O error occurred. |
151 | # |
152 | sub store_fd { |
153 | return _store_fd(\&pstore, @_); |
154 | } |
155 | |
156 | # |
157 | # nstore_fd |
158 | # |
159 | # Same as store_fd, but in network order. |
160 | # |
161 | sub nstore_fd { |
162 | my ($self, $file) = @_; |
163 | return _store_fd(\&net_pstore, @_); |
164 | } |
165 | |
166 | # Internal store routine on opened file descriptor |
167 | sub _store_fd { |
168 | my $xsptr = shift; |
169 | my $self = shift; |
170 | my ($file) = @_; |
171 | logcroak "not a reference" unless ref($self); |
172 | logcroak "too many arguments" unless @_ == 1; # No @foo in arglist |
173 | my $fd = fileno($file); |
174 | logcroak "not a valid file descriptor" unless defined $fd; |
175 | my $da = $@; # Don't mess if called from exception handler |
176 | my $ret; |
177 | # Call C routine nstore or pstore, depending on network order |
178 | eval { $ret = &$xsptr($file, $self) }; |
179 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
180 | $@ = $da; |
181 | return $ret ? $ret : undef; |
182 | } |
183 | |
184 | # |
185 | # freeze |
186 | # |
187 | # Store oject and its hierarchy in memory and return a scalar |
188 | # containing the result. |
189 | # |
190 | sub freeze { |
191 | _freeze(\&mstore, @_); |
192 | } |
193 | |
194 | # |
195 | # nfreeze |
196 | # |
197 | # Same as freeze but in network order. |
198 | # |
199 | sub nfreeze { |
200 | _freeze(\&net_mstore, @_); |
201 | } |
202 | |
203 | # Internal freeze routine |
204 | sub _freeze { |
205 | my $xsptr = shift; |
206 | my $self = shift; |
207 | logcroak "not a reference" unless ref($self); |
208 | logcroak "too many arguments" unless @_ == 0; # No @foo in arglist |
209 | my $da = $@; # Don't mess if called from exception handler |
210 | my $ret; |
211 | # Call C routine mstore or net_mstore, depending on network order |
212 | eval { $ret = &$xsptr($self) }; |
213 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
214 | $@ = $da; |
215 | return $ret ? $ret : undef; |
216 | } |
217 | |
218 | # |
219 | # retrieve |
220 | # |
221 | # Retrieve object hierarchy from disk, returning a reference to the root |
222 | # object of that tree. |
223 | # |
224 | sub retrieve { |
dd19458b |
225 | _retrieve($_[0], 0); |
226 | } |
227 | |
228 | # |
229 | # lock_retrieve |
230 | # |
231 | # Same as retrieve, but with advisory locking. |
232 | # |
233 | sub lock_retrieve { |
234 | _retrieve($_[0], 1); |
235 | } |
236 | |
237 | # Internal retrieve routine |
238 | sub _retrieve { |
239 | my ($file, $use_locking) = @_; |
7a6a85bf |
240 | local *FILE; |
dd19458b |
241 | open(FILE, $file) || logcroak "can't open $file: $!"; |
7a6a85bf |
242 | binmode FILE; # Archaic systems... |
243 | my $self; |
244 | my $da = $@; # Could be from exception handler |
dd19458b |
245 | if ($use_locking) { |
b29b780f |
246 | if ($^O eq 'dos') { |
247 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
248 | return undef; |
249 | } |
250 | flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!"; |
dd19458b |
251 | # Unlocking will happen when FILE is closed |
252 | } |
7a6a85bf |
253 | eval { $self = pretrieve(*FILE) }; # Call C routine |
254 | close(FILE); |
255 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
256 | $@ = $da; |
257 | return $self; |
258 | } |
259 | |
260 | # |
9e21b3d0 |
261 | # fd_retrieve |
7a6a85bf |
262 | # |
263 | # Same as retrieve, but perform from an already opened file descriptor instead. |
264 | # |
9e21b3d0 |
265 | sub fd_retrieve { |
7a6a85bf |
266 | my ($file) = @_; |
267 | my $fd = fileno($file); |
268 | logcroak "not a valid file descriptor" unless defined $fd; |
269 | my $self; |
270 | my $da = $@; # Could be from exception handler |
271 | eval { $self = pretrieve($file) }; # Call C routine |
272 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
273 | $@ = $da; |
274 | return $self; |
275 | } |
276 | |
277 | # |
278 | # thaw |
279 | # |
280 | # Recreate objects in memory from an existing frozen image created |
281 | # by freeze. If the frozen image passed is undef, return undef. |
282 | # |
283 | sub thaw { |
284 | my ($frozen) = @_; |
285 | return undef unless defined $frozen; |
286 | my $self; |
287 | my $da = $@; # Could be from exception handler |
288 | eval { $self = mretrieve($frozen) }; # Call C routine |
289 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
290 | $@ = $da; |
291 | return $self; |
292 | } |
293 | |
294 | =head1 NAME |
295 | |
296 | Storable - persistency for perl data structures |
297 | |
298 | =head1 SYNOPSIS |
299 | |
300 | use Storable; |
301 | store \%table, 'file'; |
302 | $hashref = retrieve('file'); |
303 | |
304 | use Storable qw(nstore store_fd nstore_fd freeze thaw dclone); |
305 | |
306 | # Network order |
307 | nstore \%table, 'file'; |
308 | $hashref = retrieve('file'); # There is NO nretrieve() |
309 | |
310 | # Storing to and retrieving from an already opened file |
311 | store_fd \@array, \*STDOUT; |
312 | nstore_fd \%table, \*STDOUT; |
9e21b3d0 |
313 | $aryref = fd_retrieve(\*SOCKET); |
314 | $hashref = fd_retrieve(\*SOCKET); |
7a6a85bf |
315 | |
316 | # Serializing to memory |
317 | $serialized = freeze \%table; |
318 | %table_clone = %{ thaw($serialized) }; |
319 | |
320 | # Deep (recursive) cloning |
321 | $cloneref = dclone($ref); |
322 | |
dd19458b |
323 | # Advisory locking |
324 | use Storable qw(lock_store lock_nstore lock_retrieve) |
325 | lock_store \%table, 'file'; |
326 | lock_nstore \%table, 'file'; |
327 | $hashref = lock_retrieve('file'); |
328 | |
7a6a85bf |
329 | =head1 DESCRIPTION |
330 | |
331 | The Storable package brings persistency to your perl data structures |
332 | containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be |
333 | convenientely stored to disk and retrieved at a later time. |
334 | |
335 | It can be used in the regular procedural way by calling C<store> with |
336 | a reference to the object to be stored, along with the file name where |
337 | the image should be written. |
338 | The routine returns C<undef> for I/O problems or other internal error, |
339 | a true value otherwise. Serious errors are propagated as a C<die> exception. |
340 | |
341 | To retrieve data stored to disk, use C<retrieve> with a file name, |
342 | and the objects stored into that file are recreated into memory for you, |
343 | a I<reference> to the root object being returned. In case an I/O error |
344 | occurs while reading, C<undef> is returned instead. Other serious |
345 | errors are propagated via C<die>. |
346 | |
347 | Since storage is performed recursively, you might want to stuff references |
348 | to objects that share a lot of common data into a single array or hash |
349 | table, and then store that object. That way, when you retrieve back the |
350 | whole thing, the objects will continue to share what they originally shared. |
351 | |
352 | At the cost of a slight header overhead, you may store to an already |
353 | opened file descriptor using the C<store_fd> routine, and retrieve |
9e21b3d0 |
354 | from a file via C<fd_retrieve>. Those names aren't imported by default, |
7a6a85bf |
355 | so you will have to do that explicitely if you need those routines. |
356 | The file descriptor you supply must be already opened, for read |
357 | if you're going to retrieve and for write if you wish to store. |
358 | |
359 | store_fd(\%table, *STDOUT) || die "can't store to stdout\n"; |
9e21b3d0 |
360 | $hashref = fd_retrieve(*STDIN); |
7a6a85bf |
361 | |
362 | You can also store data in network order to allow easy sharing across |
363 | multiple platforms, or when storing on a socket known to be remotely |
364 | connected. The routines to call have an initial C<n> prefix for I<network>, |
365 | as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be |
366 | correctly restored so you don't have to know whether you're restoring |
dd19458b |
367 | from native or network ordered data. Double values are stored stringified |
368 | to ensure portability as well, at the slight risk of loosing some precision |
369 | in the last decimals. |
7a6a85bf |
370 | |
9e21b3d0 |
371 | When using C<fd_retrieve>, objects are retrieved in sequence, one |
7a6a85bf |
372 | object (i.e. one recursive tree) per associated C<store_fd>. |
373 | |
374 | If you're more from the object-oriented camp, you can inherit from |
375 | Storable and directly store your objects by invoking C<store> as |
376 | a method. The fact that the root of the to-be-stored tree is a |
377 | blessed reference (i.e. an object) is special-cased so that the |
378 | retrieve does not provide a reference to that object but rather the |
379 | blessed object reference itself. (Otherwise, you'd get a reference |
380 | to that blessed object). |
381 | |
382 | =head1 MEMORY STORE |
383 | |
384 | The Storable engine can also store data into a Perl scalar instead, to |
385 | later retrieve them. This is mainly used to freeze a complex structure in |
386 | some safe compact memory place (where it can possibly be sent to another |
387 | process via some IPC, since freezing the structure also serializes it in |
388 | effect). Later on, and maybe somewhere else, you can thaw the Perl scalar |
389 | out and recreate the original complex structure in memory. |
390 | |
391 | Surprisingly, the routines to be called are named C<freeze> and C<thaw>. |
392 | If you wish to send out the frozen scalar to another machine, use |
393 | C<nfreeze> instead to get a portable image. |
394 | |
395 | Note that freezing an object structure and immediately thawing it |
396 | actually achieves a deep cloning of that structure: |
397 | |
398 | dclone(.) = thaw(freeze(.)) |
399 | |
400 | Storable provides you with a C<dclone> interface which does not create |
401 | that intermediary scalar but instead freezes the structure in some |
402 | internal memory space and then immediatly thaws it out. |
403 | |
dd19458b |
404 | =head1 ADVISORY LOCKING |
405 | |
406 | The C<lock_store> and C<lock_nstore> routine are equivalent to C<store> |
407 | and C<nstore>, only they get an exclusive lock on the file before |
408 | writing. Likewise, C<lock_retrieve> performs as C<retrieve>, but also |
409 | gets a shared lock on the file before reading. |
410 | |
411 | Like with any advisory locking scheme, the protection only works if |
412 | you systematically use C<lock_store> and C<lock_retrieve>. If one |
413 | side of your application uses C<store> whilst the other uses C<lock_retrieve>, |
414 | you will get no protection at all. |
415 | |
416 | The internal advisory locking is implemented using Perl's flock() routine. |
417 | If your system does not support any form of flock(), or if you share |
418 | your files across NFS, you might wish to use other forms of locking by |
419 | using modules like LockFile::Simple which lock a file using a filesystem |
420 | entry, instead of locking the file descriptor. |
421 | |
7a6a85bf |
422 | =head1 SPEED |
423 | |
424 | The heart of Storable is written in C for decent speed. Extra low-level |
425 | optimization have been made when manipulating perl internals, to |
426 | sacrifice encapsulation for the benefit of a greater speed. |
427 | |
428 | =head1 CANONICAL REPRESENTATION |
429 | |
430 | Normally Storable stores elements of hashes in the order they are |
431 | stored internally by Perl, i.e. pseudo-randomly. If you set |
432 | C<$Storable::canonical> to some C<TRUE> value, Storable will store |
433 | hashes with the elements sorted by their key. This allows you to |
434 | compare data structures by comparing their frozen representations (or |
435 | even the compressed frozen representations), which can be useful for |
436 | creating lookup tables for complicated queries. |
437 | |
438 | Canonical order does not imply network order, those are two orthogonal |
439 | settings. |
440 | |
441 | =head1 ERROR REPORTING |
442 | |
443 | Storable uses the "exception" paradigm, in that it does not try to workaround |
444 | failures: if something bad happens, an exception is generated from the |
445 | caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap |
446 | those exceptions. |
447 | |
448 | When Storable croaks, it tries to report the error via the C<logcroak()> |
449 | routine from the C<Log::Agent> package, if it is available. |
450 | |
451 | =head1 WIZARDS ONLY |
452 | |
453 | =head2 Hooks |
454 | |
455 | Any class may define hooks that will be called during the serialization |
456 | and deserialization process on objects that are instances of that class. |
457 | Those hooks can redefine the way serialization is performed (and therefore, |
458 | how the symetrical deserialization should be conducted). |
459 | |
460 | Since we said earlier: |
461 | |
462 | dclone(.) = thaw(freeze(.)) |
463 | |
464 | everything we say about hooks should also hold for deep cloning. However, |
465 | hooks get to know whether the operation is a mere serialization, or a cloning. |
466 | |
467 | Therefore, when serializing hooks are involved, |
468 | |
469 | dclone(.) <> thaw(freeze(.)) |
470 | |
471 | Well, you could keep them in sync, but there's no guarantee it will always |
472 | hold on classes somebody else wrote. Besides, there is little to gain in |
473 | doing so: a serializing hook could only keep one attribute of an object, |
474 | which is probably not what should happen during a deep cloning of that |
475 | same object. |
476 | |
477 | Here is the hooking interface: |
478 | |
479 | =over |
480 | |
481 | =item C<STORABLE_freeze> I<obj>, I<cloning> |
482 | |
483 | The serializing hook, called on the object during serialization. It can be |
484 | inherited, or defined in the class itself, like any other method. |
485 | |
486 | Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating |
487 | whether we're in a dclone() or a regular serialization via store() or freeze(). |
488 | |
489 | Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized |
490 | is the serialized form to be used, and the optional $ref1, $ref2, etc... are |
491 | extra references that you wish to let the Storable engine serialize. |
492 | |
493 | At deserialization time, you will be given back the same LIST, but all the |
494 | extra references will be pointing into the deserialized structure. |
495 | |
496 | The B<first time> the hook is hit in a serialization flow, you may have it |
497 | return an empty list. That will signal the Storable engine to further |
498 | discard that hook for this class and to therefore revert to the default |
499 | serialization of the underlying Perl data. The hook will again be normally |
500 | processed in the next serialization. |
501 | |
502 | Unless you know better, serializing hook should always say: |
503 | |
504 | sub STORABLE_freeze { |
505 | my ($self, $cloning) = @_; |
506 | return if $cloning; # Regular default serialization |
507 | .... |
508 | } |
509 | |
510 | in order to keep reasonable dclone() semantics. |
511 | |
512 | =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ... |
513 | |
514 | The deserializing hook called on the object during deserialization. |
515 | But wait. If we're deserializing, there's no object yet... right? |
516 | |
517 | Wrong: the Storable engine creates an empty one for you. If you know Eiffel, |
518 | you can view C<STORABLE_thaw> as an alternate creation routine. |
519 | |
520 | This means the hook can be inherited like any other method, and that |
521 | I<obj> is your blessed reference for this particular instance. |
522 | |
523 | The other arguments should look familiar if you know C<STORABLE_freeze>: |
524 | I<cloning> is true when we're part of a deep clone operation, I<serialized> |
525 | is the serialized string you returned to the engine in C<STORABLE_freeze>, |
526 | and there may be an optional list of references, in the same order you gave |
527 | them at serialization time, pointing to the deserialized objects (which |
528 | have been processed courtesy of the Storable engine). |
529 | |
530 | It is up to you to use these information to populate I<obj> the way you want. |
531 | |
532 | Returned value: none. |
533 | |
534 | =back |
535 | |
536 | =head2 Predicates |
537 | |
538 | Predicates are not exportable. They must be called by explicitely prefixing |
539 | them with the Storable package name. |
540 | |
541 | =over |
542 | |
543 | =item C<Storable::last_op_in_netorder> |
544 | |
545 | The C<Storable::last_op_in_netorder()> predicate will tell you whether |
546 | network order was used in the last store or retrieve operation. If you |
547 | don't know how to use this, just forget about it. |
548 | |
549 | =item C<Storable::is_storing> |
550 | |
551 | Returns true if within a store operation (via STORABLE_freeze hook). |
552 | |
553 | =item C<Storable::is_retrieving> |
554 | |
555 | Returns true if within a retrieve operation, (via STORABLE_thaw hook). |
556 | |
557 | =back |
558 | |
559 | =head2 Recursion |
560 | |
561 | With hooks comes the ability to recurse back to the Storable engine. Indeed, |
562 | hooks are regular Perl code, and Storable is convenient when it comes to |
563 | serialize and deserialize things, so why not use it to handle the |
564 | serialization string? |
565 | |
566 | There are a few things you need to know however: |
567 | |
568 | =over |
569 | |
570 | =item * |
571 | |
572 | You can create endless loops if the things you serialize via freeze() |
573 | (for instance) point back to the object we're trying to serialize in the hook. |
574 | |
575 | =item * |
576 | |
577 | Shared references among objects will not stay shared: if we're serializing |
578 | the list of object [A, C] where both object A and C refer to the SAME object |
579 | B, and if there is a serializing hook in A that says freeze(B), then when |
580 | deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D, |
581 | a deep clone of B'. The topology was not preserved. |
582 | |
583 | =back |
584 | |
585 | That's why C<STORABLE_freeze> lets you provide a list of references |
586 | to serialize. The engine guarantees that those will be serialized in the |
587 | same context as the other objects, and therefore that shared objects will |
588 | stay shared. |
589 | |
590 | In the above [A, C] example, the C<STORABLE_freeze> hook could return: |
591 | |
592 | ("something", $self->{B}) |
593 | |
594 | and the B part would be serialized by the engine. In C<STORABLE_thaw>, you |
595 | would get back the reference to the B' object, deserialized for you. |
596 | |
597 | Therefore, recursion should normally be avoided, but is nonetheless supported. |
598 | |
599 | =head2 Deep Cloning |
600 | |
601 | There is a new Clone module available on CPAN which implements deep cloning |
602 | natively, i.e. without freezing to memory and thawing the result. It is |
603 | aimed to replace Storable's dclone() some day. However, it does not currently |
604 | support Storable hooks to redefine the way deep cloning is performed. |
605 | |
606 | =head1 EXAMPLES |
607 | |
608 | Here are some code samples showing a possible usage of Storable: |
609 | |
610 | use Storable qw(store retrieve freeze thaw dclone); |
611 | |
612 | %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1); |
613 | |
614 | store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n"; |
615 | |
616 | $colref = retrieve('/tmp/colors'); |
617 | die "Unable to retrieve from /tmp/colors!\n" unless defined $colref; |
618 | printf "Blue is still %lf\n", $colref->{'Blue'}; |
619 | |
620 | $colref2 = dclone(\%color); |
621 | |
622 | $str = freeze(\%color); |
623 | printf "Serialization of %%color is %d bytes long.\n", length($str); |
624 | $colref3 = thaw($str); |
625 | |
626 | which prints (on my machine): |
627 | |
628 | Blue is still 0.100000 |
629 | Serialization of %color is 102 bytes long. |
630 | |
631 | =head1 WARNING |
632 | |
633 | If you're using references as keys within your hash tables, you're bound |
634 | to disapointment when retrieving your data. Indeed, Perl stringifies |
635 | references used as hash table keys. If you later wish to access the |
636 | items via another reference stringification (i.e. using the same |
637 | reference that was used for the key originally to record the value into |
638 | the hash table), it will work because both references stringify to the |
639 | same string. |
640 | |
641 | It won't work across a C<store> and C<retrieve> operations however, because |
642 | the addresses in the retrieved objects, which are part of the stringified |
643 | references, will probably differ from the original addresses. The |
644 | topology of your structure is preserved, but not hidden semantics |
645 | like those. |
646 | |
647 | On platforms where it matters, be sure to call C<binmode()> on the |
648 | descriptors that you pass to Storable functions. |
649 | |
650 | Storing data canonically that contains large hashes can be |
651 | significantly slower than storing the same data normally, as |
652 | temprorary arrays to hold the keys for each hash have to be allocated, |
653 | populated, sorted and freed. Some tests have shown a halving of the |
654 | speed of storing -- the exact penalty will depend on the complexity of |
655 | your data. There is no slowdown on retrieval. |
656 | |
657 | =head1 BUGS |
658 | |
659 | You can't store GLOB, CODE, FORMLINE, etc... If you can define |
660 | semantics for those operations, feel free to enhance Storable so that |
661 | it can deal with them. |
662 | |
663 | The store functions will C<croak> if they run into such references |
664 | unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that |
665 | case, the fatal message is turned in a warning and some |
666 | meaningless string is stored instead. |
667 | |
668 | Setting C<$Storable::canonical> may not yield frozen strings that |
669 | compare equal due to possible stringification of numbers. When the |
670 | string version of a scalar exists, it is the form stored, therefore |
671 | if you happen to use your numbers as strings between two freezing |
672 | operations on the same data structures, you will get different |
673 | results. |
674 | |
dd19458b |
675 | When storing doubles in network order, their value is stored as text. |
676 | However, you should also not expect non-numeric floating-point values |
677 | such as infinity and "not a number" to pass successfully through a |
678 | nstore()/retrieve() pair. |
679 | |
680 | As Storable neither knows nor cares about character sets (although it |
681 | does know that characters may be more than eight bits wide), any difference |
682 | in the interpretation of character codes between a host and a target |
683 | system is your problem. In particular, if host and target use different |
684 | code points to represent the characters used in the text representation |
685 | of floating-point numbers, you will not be able be able to exchange |
686 | floating-point data, even with nstore(). |
687 | |
7a6a85bf |
688 | =head1 CREDITS |
689 | |
690 | Thank you to (in chronological order): |
691 | |
692 | Jarkko Hietaniemi <jhi@iki.fi> |
693 | Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de> |
694 | Benjamin A. Holzman <bah@ecnvantage.com> |
695 | Andrew Ford <A.Ford@ford-mason.co.uk> |
696 | Gisle Aas <gisle@aas.no> |
697 | Jeff Gresham <gresham_jeffrey@jpmorgan.com> |
698 | Murray Nesbitt <murray@activestate.com> |
699 | Marc Lehmann <pcg@opengroup.org> |
9e21b3d0 |
700 | Justin Banks <justinb@wamnet.com> |
701 | Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!) |
dd19458b |
702 | Salvador Ortiz Garcia <sog@msg.com.mx> |
703 | Dominic Dunlop <domo@computer.org> |
704 | Erik Haugan <erik@solbors.no> |
7a6a85bf |
705 | |
706 | for their bug reports, suggestions and contributions. |
707 | |
708 | Benjamin Holzman contributed the tied variable support, Andrew Ford |
709 | contributed the canonical order for hashes, and Gisle Aas fixed |
710 | a few misunderstandings of mine regarding the Perl internals, |
711 | and optimized the emission of "tags" in the output streams by |
712 | simply counting the objects instead of tagging them (leading to |
713 | a binary incompatibility for the Storable image starting at version |
714 | 0.6--older images are of course still properly understood). |
715 | Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading |
716 | and reference to tied items support. |
717 | |
718 | =head1 TRANSLATIONS |
719 | |
720 | There is a Japanese translation of this man page available at |
721 | http://member.nifty.ne.jp/hippo2000/perltips/storable.htm , |
722 | courtesy of Kawai, Takanori <kawai@nippon-rad.co.jp>. |
723 | |
724 | =head1 AUTHOR |
725 | |
726 | Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>> |
727 | |
728 | =head1 SEE ALSO |
729 | |
730 | Clone(3). |
731 | |
732 | =cut |
733 | |