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1 | ;# $Id: Storable.pm,v 1.0 2000/09/01 19:40:41 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 2000/09/01 19:40:41 ram |
10 | ;# Baseline for first official release. |
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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( |
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19 | nstore store_fd nstore_fd fd_retrieve |
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20 | freeze nfreeze thaw |
21 | dclone |
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22 | retrieve_fd |
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23 | lock_store lock_nstore lock_retrieve |
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24 | ); |
25 | |
26 | use AutoLoader; |
27 | use vars qw($forgive_me $VERSION); |
28 | |
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29 | $VERSION = '1.003'; |
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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 | } |
44 | }; |
45 | } |
46 | |
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47 | # |
48 | # They might miss :flock in Fcntl |
49 | # |
50 | |
51 | BEGIN { |
52 | require Fcntl; |
53 | if (exists $Fcntl::EXPORT_TAGS{'flock'}) { |
54 | Fcntl->import(':flock'); |
55 | } else { |
56 | eval q{ |
57 | sub LOCK_SH () {1} |
58 | sub LOCK_EX () {2} |
59 | }; |
60 | } |
61 | } |
62 | |
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63 | sub logcroak; |
64 | |
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65 | sub retrieve_fd { &fd_retrieve } # Backward compatibility |
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66 | |
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67 | bootstrap Storable; |
68 | 1; |
69 | __END__ |
70 | |
71 | # |
72 | # store |
73 | # |
74 | # Store target object hierarchy, identified by a reference to its root. |
75 | # The stored object tree may later be retrieved to memory via retrieve. |
76 | # Returns undef if an I/O error occurred, in which case the file is |
77 | # removed. |
78 | # |
79 | sub store { |
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80 | return _store(\&pstore, @_, 0); |
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81 | } |
82 | |
83 | # |
84 | # nstore |
85 | # |
86 | # Same as store, but in network order. |
87 | # |
88 | sub nstore { |
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89 | return _store(\&net_pstore, @_, 0); |
90 | } |
91 | |
92 | # |
93 | # lock_store |
94 | # |
95 | # Same as store, but flock the file first (advisory locking). |
96 | # |
97 | sub lock_store { |
98 | return _store(\&pstore, @_, 1); |
99 | } |
100 | |
101 | # |
102 | # lock_nstore |
103 | # |
104 | # Same as nstore, but flock the file first (advisory locking). |
105 | # |
106 | sub lock_nstore { |
107 | return _store(\&net_pstore, @_, 1); |
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108 | } |
109 | |
110 | # Internal store to file routine |
111 | sub _store { |
112 | my $xsptr = shift; |
113 | my $self = shift; |
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114 | my ($file, $use_locking) = @_; |
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115 | logcroak "not a reference" unless ref($self); |
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116 | logcroak "too many arguments" unless @_ == 2; # No @foo in arglist |
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117 | local *FILE; |
118 | open(FILE, ">$file") || logcroak "can't create $file: $!"; |
119 | binmode FILE; # Archaic systems... |
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120 | if ($use_locking) { |
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121 | if ($^O eq 'dos') { |
122 | require Carp; |
123 | Carp::carp "Storable::lock_store: fcntl/flock emulation broken on $^O\n"; |
124 | return undef; |
125 | } |
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126 | flock(FILE, LOCK_EX) || |
127 | logcroak "can't get exclusive lock on $file: $!"; |
128 | truncate FILE, 0; |
129 | # Unlocking will happen when FILE is closed |
130 | } |
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131 | my $da = $@; # Don't mess if called from exception handler |
132 | my $ret; |
133 | # Call C routine nstore or pstore, depending on network order |
134 | eval { $ret = &$xsptr(*FILE, $self) }; |
135 | close(FILE) or $ret = undef; |
136 | unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret; |
137 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
138 | $@ = $da; |
139 | return $ret ? $ret : undef; |
140 | } |
141 | |
142 | # |
143 | # store_fd |
144 | # |
145 | # Same as store, but perform on an already opened file descriptor instead. |
146 | # Returns undef if an I/O error occurred. |
147 | # |
148 | sub store_fd { |
149 | return _store_fd(\&pstore, @_); |
150 | } |
151 | |
152 | # |
153 | # nstore_fd |
154 | # |
155 | # Same as store_fd, but in network order. |
156 | # |
157 | sub nstore_fd { |
158 | my ($self, $file) = @_; |
159 | return _store_fd(\&net_pstore, @_); |
160 | } |
161 | |
162 | # Internal store routine on opened file descriptor |
163 | sub _store_fd { |
164 | my $xsptr = shift; |
165 | my $self = shift; |
166 | my ($file) = @_; |
167 | logcroak "not a reference" unless ref($self); |
168 | logcroak "too many arguments" unless @_ == 1; # No @foo in arglist |
169 | my $fd = fileno($file); |
170 | logcroak "not a valid file descriptor" unless defined $fd; |
171 | my $da = $@; # Don't mess if called from exception handler |
172 | my $ret; |
173 | # Call C routine nstore or pstore, depending on network order |
174 | eval { $ret = &$xsptr($file, $self) }; |
175 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
176 | $@ = $da; |
177 | return $ret ? $ret : undef; |
178 | } |
179 | |
180 | # |
181 | # freeze |
182 | # |
183 | # Store oject and its hierarchy in memory and return a scalar |
184 | # containing the result. |
185 | # |
186 | sub freeze { |
187 | _freeze(\&mstore, @_); |
188 | } |
189 | |
190 | # |
191 | # nfreeze |
192 | # |
193 | # Same as freeze but in network order. |
194 | # |
195 | sub nfreeze { |
196 | _freeze(\&net_mstore, @_); |
197 | } |
198 | |
199 | # Internal freeze routine |
200 | sub _freeze { |
201 | my $xsptr = shift; |
202 | my $self = shift; |
203 | logcroak "not a reference" unless ref($self); |
204 | logcroak "too many arguments" unless @_ == 0; # No @foo in arglist |
205 | my $da = $@; # Don't mess if called from exception handler |
206 | my $ret; |
207 | # Call C routine mstore or net_mstore, depending on network order |
208 | eval { $ret = &$xsptr($self) }; |
209 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
210 | $@ = $da; |
211 | return $ret ? $ret : undef; |
212 | } |
213 | |
214 | # |
215 | # retrieve |
216 | # |
217 | # Retrieve object hierarchy from disk, returning a reference to the root |
218 | # object of that tree. |
219 | # |
220 | sub retrieve { |
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221 | _retrieve($_[0], 0); |
222 | } |
223 | |
224 | # |
225 | # lock_retrieve |
226 | # |
227 | # Same as retrieve, but with advisory locking. |
228 | # |
229 | sub lock_retrieve { |
230 | _retrieve($_[0], 1); |
231 | } |
232 | |
233 | # Internal retrieve routine |
234 | sub _retrieve { |
235 | my ($file, $use_locking) = @_; |
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236 | local *FILE; |
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237 | open(FILE, $file) || logcroak "can't open $file: $!"; |
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238 | binmode FILE; # Archaic systems... |
239 | my $self; |
240 | my $da = $@; # Could be from exception handler |
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241 | if ($use_locking) { |
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242 | if ($^O eq 'dos') { |
243 | require Carp; |
244 | Carp::carp "Storable::lock_retrieve: fcntl/flock emulation broken on $^O\n"; |
245 | return undef; |
246 | } |
247 | flock(FILE, LOCK_SH) || |
248 | logcroak "can't get shared lock on $file: $!"; |
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249 | # Unlocking will happen when FILE is closed |
250 | } |
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251 | eval { $self = pretrieve(*FILE) }; # Call C routine |
252 | close(FILE); |
253 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
254 | $@ = $da; |
255 | return $self; |
256 | } |
257 | |
258 | # |
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259 | # fd_retrieve |
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260 | # |
261 | # Same as retrieve, but perform from an already opened file descriptor instead. |
262 | # |
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263 | sub fd_retrieve { |
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264 | my ($file) = @_; |
265 | my $fd = fileno($file); |
266 | logcroak "not a valid file descriptor" unless defined $fd; |
267 | my $self; |
268 | my $da = $@; # Could be from exception handler |
269 | eval { $self = pretrieve($file) }; # Call C routine |
270 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
271 | $@ = $da; |
272 | return $self; |
273 | } |
274 | |
275 | # |
276 | # thaw |
277 | # |
278 | # Recreate objects in memory from an existing frozen image created |
279 | # by freeze. If the frozen image passed is undef, return undef. |
280 | # |
281 | sub thaw { |
282 | my ($frozen) = @_; |
283 | return undef unless defined $frozen; |
284 | my $self; |
285 | my $da = $@; # Could be from exception handler |
286 | eval { $self = mretrieve($frozen) }; # Call C routine |
287 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
288 | $@ = $da; |
289 | return $self; |
290 | } |
291 | |
292 | =head1 NAME |
293 | |
294 | Storable - persistency for perl data structures |
295 | |
296 | =head1 SYNOPSIS |
297 | |
298 | use Storable; |
299 | store \%table, 'file'; |
300 | $hashref = retrieve('file'); |
301 | |
302 | use Storable qw(nstore store_fd nstore_fd freeze thaw dclone); |
303 | |
304 | # Network order |
305 | nstore \%table, 'file'; |
306 | $hashref = retrieve('file'); # There is NO nretrieve() |
307 | |
308 | # Storing to and retrieving from an already opened file |
309 | store_fd \@array, \*STDOUT; |
310 | nstore_fd \%table, \*STDOUT; |
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311 | $aryref = fd_retrieve(\*SOCKET); |
312 | $hashref = fd_retrieve(\*SOCKET); |
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313 | |
314 | # Serializing to memory |
315 | $serialized = freeze \%table; |
316 | %table_clone = %{ thaw($serialized) }; |
317 | |
318 | # Deep (recursive) cloning |
319 | $cloneref = dclone($ref); |
320 | |
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321 | # Advisory locking |
322 | use Storable qw(lock_store lock_nstore lock_retrieve) |
323 | lock_store \%table, 'file'; |
324 | lock_nstore \%table, 'file'; |
325 | $hashref = lock_retrieve('file'); |
326 | |
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327 | =head1 DESCRIPTION |
328 | |
329 | The Storable package brings persistency to your perl data structures |
330 | containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be |
331 | convenientely stored to disk and retrieved at a later time. |
332 | |
333 | It can be used in the regular procedural way by calling C<store> with |
334 | a reference to the object to be stored, along with the file name where |
335 | the image should be written. |
336 | The routine returns C<undef> for I/O problems or other internal error, |
337 | a true value otherwise. Serious errors are propagated as a C<die> exception. |
338 | |
339 | To retrieve data stored to disk, use C<retrieve> with a file name, |
340 | and the objects stored into that file are recreated into memory for you, |
341 | a I<reference> to the root object being returned. In case an I/O error |
342 | occurs while reading, C<undef> is returned instead. Other serious |
343 | errors are propagated via C<die>. |
344 | |
345 | Since storage is performed recursively, you might want to stuff references |
346 | to objects that share a lot of common data into a single array or hash |
347 | table, and then store that object. That way, when you retrieve back the |
348 | whole thing, the objects will continue to share what they originally shared. |
349 | |
350 | At the cost of a slight header overhead, you may store to an already |
351 | opened file descriptor using the C<store_fd> routine, and retrieve |
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352 | from a file via C<fd_retrieve>. Those names aren't imported by default, |
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353 | so you will have to do that explicitely if you need those routines. |
354 | The file descriptor you supply must be already opened, for read |
355 | if you're going to retrieve and for write if you wish to store. |
356 | |
357 | store_fd(\%table, *STDOUT) || die "can't store to stdout\n"; |
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358 | $hashref = fd_retrieve(*STDIN); |
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359 | |
360 | You can also store data in network order to allow easy sharing across |
361 | multiple platforms, or when storing on a socket known to be remotely |
362 | connected. The routines to call have an initial C<n> prefix for I<network>, |
363 | as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be |
364 | correctly restored so you don't have to know whether you're restoring |
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365 | from native or network ordered data. Double values are stored stringified |
366 | to ensure portability as well, at the slight risk of loosing some precision |
367 | in the last decimals. |
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368 | |
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369 | When using C<fd_retrieve>, objects are retrieved in sequence, one |
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370 | object (i.e. one recursive tree) per associated C<store_fd>. |
371 | |
372 | If you're more from the object-oriented camp, you can inherit from |
373 | Storable and directly store your objects by invoking C<store> as |
374 | a method. The fact that the root of the to-be-stored tree is a |
375 | blessed reference (i.e. an object) is special-cased so that the |
376 | retrieve does not provide a reference to that object but rather the |
377 | blessed object reference itself. (Otherwise, you'd get a reference |
378 | to that blessed object). |
379 | |
380 | =head1 MEMORY STORE |
381 | |
382 | The Storable engine can also store data into a Perl scalar instead, to |
383 | later retrieve them. This is mainly used to freeze a complex structure in |
384 | some safe compact memory place (where it can possibly be sent to another |
385 | process via some IPC, since freezing the structure also serializes it in |
386 | effect). Later on, and maybe somewhere else, you can thaw the Perl scalar |
387 | out and recreate the original complex structure in memory. |
388 | |
389 | Surprisingly, the routines to be called are named C<freeze> and C<thaw>. |
390 | If you wish to send out the frozen scalar to another machine, use |
391 | C<nfreeze> instead to get a portable image. |
392 | |
393 | Note that freezing an object structure and immediately thawing it |
394 | actually achieves a deep cloning of that structure: |
395 | |
396 | dclone(.) = thaw(freeze(.)) |
397 | |
398 | Storable provides you with a C<dclone> interface which does not create |
399 | that intermediary scalar but instead freezes the structure in some |
400 | internal memory space and then immediatly thaws it out. |
401 | |
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402 | =head1 ADVISORY LOCKING |
403 | |
404 | The C<lock_store> and C<lock_nstore> routine are equivalent to C<store> |
405 | and C<nstore>, only they get an exclusive lock on the file before |
406 | writing. Likewise, C<lock_retrieve> performs as C<retrieve>, but also |
407 | gets a shared lock on the file before reading. |
408 | |
409 | Like with any advisory locking scheme, the protection only works if |
410 | you systematically use C<lock_store> and C<lock_retrieve>. If one |
411 | side of your application uses C<store> whilst the other uses C<lock_retrieve>, |
412 | you will get no protection at all. |
413 | |
414 | The internal advisory locking is implemented using Perl's flock() routine. |
415 | If your system does not support any form of flock(), or if you share |
416 | your files across NFS, you might wish to use other forms of locking by |
417 | using modules like LockFile::Simple which lock a file using a filesystem |
418 | entry, instead of locking the file descriptor. |
419 | |
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420 | =head1 SPEED |
421 | |
422 | The heart of Storable is written in C for decent speed. Extra low-level |
423 | optimization have been made when manipulating perl internals, to |
424 | sacrifice encapsulation for the benefit of a greater speed. |
425 | |
426 | =head1 CANONICAL REPRESENTATION |
427 | |
428 | Normally Storable stores elements of hashes in the order they are |
429 | stored internally by Perl, i.e. pseudo-randomly. If you set |
430 | C<$Storable::canonical> to some C<TRUE> value, Storable will store |
431 | hashes with the elements sorted by their key. This allows you to |
432 | compare data structures by comparing their frozen representations (or |
433 | even the compressed frozen representations), which can be useful for |
434 | creating lookup tables for complicated queries. |
435 | |
436 | Canonical order does not imply network order, those are two orthogonal |
437 | settings. |
438 | |
439 | =head1 ERROR REPORTING |
440 | |
441 | Storable uses the "exception" paradigm, in that it does not try to workaround |
442 | failures: if something bad happens, an exception is generated from the |
443 | caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap |
444 | those exceptions. |
445 | |
446 | When Storable croaks, it tries to report the error via the C<logcroak()> |
447 | routine from the C<Log::Agent> package, if it is available. |
448 | |
449 | =head1 WIZARDS ONLY |
450 | |
451 | =head2 Hooks |
452 | |
453 | Any class may define hooks that will be called during the serialization |
454 | and deserialization process on objects that are instances of that class. |
455 | Those hooks can redefine the way serialization is performed (and therefore, |
456 | how the symetrical deserialization should be conducted). |
457 | |
458 | Since we said earlier: |
459 | |
460 | dclone(.) = thaw(freeze(.)) |
461 | |
462 | everything we say about hooks should also hold for deep cloning. However, |
463 | hooks get to know whether the operation is a mere serialization, or a cloning. |
464 | |
465 | Therefore, when serializing hooks are involved, |
466 | |
467 | dclone(.) <> thaw(freeze(.)) |
468 | |
469 | Well, you could keep them in sync, but there's no guarantee it will always |
470 | hold on classes somebody else wrote. Besides, there is little to gain in |
471 | doing so: a serializing hook could only keep one attribute of an object, |
472 | which is probably not what should happen during a deep cloning of that |
473 | same object. |
474 | |
475 | Here is the hooking interface: |
476 | |
477 | =over |
478 | |
479 | =item C<STORABLE_freeze> I<obj>, I<cloning> |
480 | |
481 | The serializing hook, called on the object during serialization. It can be |
482 | inherited, or defined in the class itself, like any other method. |
483 | |
484 | Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating |
485 | whether we're in a dclone() or a regular serialization via store() or freeze(). |
486 | |
487 | Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized |
488 | is the serialized form to be used, and the optional $ref1, $ref2, etc... are |
489 | extra references that you wish to let the Storable engine serialize. |
490 | |
491 | At deserialization time, you will be given back the same LIST, but all the |
492 | extra references will be pointing into the deserialized structure. |
493 | |
494 | The B<first time> the hook is hit in a serialization flow, you may have it |
495 | return an empty list. That will signal the Storable engine to further |
496 | discard that hook for this class and to therefore revert to the default |
497 | serialization of the underlying Perl data. The hook will again be normally |
498 | processed in the next serialization. |
499 | |
500 | Unless you know better, serializing hook should always say: |
501 | |
502 | sub STORABLE_freeze { |
503 | my ($self, $cloning) = @_; |
504 | return if $cloning; # Regular default serialization |
505 | .... |
506 | } |
507 | |
508 | in order to keep reasonable dclone() semantics. |
509 | |
510 | =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ... |
511 | |
512 | The deserializing hook called on the object during deserialization. |
513 | But wait. If we're deserializing, there's no object yet... right? |
514 | |
515 | Wrong: the Storable engine creates an empty one for you. If you know Eiffel, |
516 | you can view C<STORABLE_thaw> as an alternate creation routine. |
517 | |
518 | This means the hook can be inherited like any other method, and that |
519 | I<obj> is your blessed reference for this particular instance. |
520 | |
521 | The other arguments should look familiar if you know C<STORABLE_freeze>: |
522 | I<cloning> is true when we're part of a deep clone operation, I<serialized> |
523 | is the serialized string you returned to the engine in C<STORABLE_freeze>, |
524 | and there may be an optional list of references, in the same order you gave |
525 | them at serialization time, pointing to the deserialized objects (which |
526 | have been processed courtesy of the Storable engine). |
527 | |
528 | It is up to you to use these information to populate I<obj> the way you want. |
529 | |
530 | Returned value: none. |
531 | |
532 | =back |
533 | |
534 | =head2 Predicates |
535 | |
536 | Predicates are not exportable. They must be called by explicitely prefixing |
537 | them with the Storable package name. |
538 | |
539 | =over |
540 | |
541 | =item C<Storable::last_op_in_netorder> |
542 | |
543 | The C<Storable::last_op_in_netorder()> predicate will tell you whether |
544 | network order was used in the last store or retrieve operation. If you |
545 | don't know how to use this, just forget about it. |
546 | |
547 | =item C<Storable::is_storing> |
548 | |
549 | Returns true if within a store operation (via STORABLE_freeze hook). |
550 | |
551 | =item C<Storable::is_retrieving> |
552 | |
553 | Returns true if within a retrieve operation, (via STORABLE_thaw hook). |
554 | |
555 | =back |
556 | |
557 | =head2 Recursion |
558 | |
559 | With hooks comes the ability to recurse back to the Storable engine. Indeed, |
560 | hooks are regular Perl code, and Storable is convenient when it comes to |
561 | serialize and deserialize things, so why not use it to handle the |
562 | serialization string? |
563 | |
564 | There are a few things you need to know however: |
565 | |
566 | =over |
567 | |
568 | =item * |
569 | |
570 | You can create endless loops if the things you serialize via freeze() |
571 | (for instance) point back to the object we're trying to serialize in the hook. |
572 | |
573 | =item * |
574 | |
575 | Shared references among objects will not stay shared: if we're serializing |
576 | the list of object [A, C] where both object A and C refer to the SAME object |
577 | B, and if there is a serializing hook in A that says freeze(B), then when |
578 | deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D, |
579 | a deep clone of B'. The topology was not preserved. |
580 | |
581 | =back |
582 | |
583 | That's why C<STORABLE_freeze> lets you provide a list of references |
584 | to serialize. The engine guarantees that those will be serialized in the |
585 | same context as the other objects, and therefore that shared objects will |
586 | stay shared. |
587 | |
588 | In the above [A, C] example, the C<STORABLE_freeze> hook could return: |
589 | |
590 | ("something", $self->{B}) |
591 | |
592 | and the B part would be serialized by the engine. In C<STORABLE_thaw>, you |
593 | would get back the reference to the B' object, deserialized for you. |
594 | |
595 | Therefore, recursion should normally be avoided, but is nonetheless supported. |
596 | |
597 | =head2 Deep Cloning |
598 | |
599 | There is a new Clone module available on CPAN which implements deep cloning |
600 | natively, i.e. without freezing to memory and thawing the result. It is |
601 | aimed to replace Storable's dclone() some day. However, it does not currently |
602 | support Storable hooks to redefine the way deep cloning is performed. |
603 | |
604 | =head1 EXAMPLES |
605 | |
606 | Here are some code samples showing a possible usage of Storable: |
607 | |
608 | use Storable qw(store retrieve freeze thaw dclone); |
609 | |
610 | %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1); |
611 | |
612 | store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n"; |
613 | |
614 | $colref = retrieve('/tmp/colors'); |
615 | die "Unable to retrieve from /tmp/colors!\n" unless defined $colref; |
616 | printf "Blue is still %lf\n", $colref->{'Blue'}; |
617 | |
618 | $colref2 = dclone(\%color); |
619 | |
620 | $str = freeze(\%color); |
621 | printf "Serialization of %%color is %d bytes long.\n", length($str); |
622 | $colref3 = thaw($str); |
623 | |
624 | which prints (on my machine): |
625 | |
626 | Blue is still 0.100000 |
627 | Serialization of %color is 102 bytes long. |
628 | |
629 | =head1 WARNING |
630 | |
631 | If you're using references as keys within your hash tables, you're bound |
632 | to disapointment when retrieving your data. Indeed, Perl stringifies |
633 | references used as hash table keys. If you later wish to access the |
634 | items via another reference stringification (i.e. using the same |
635 | reference that was used for the key originally to record the value into |
636 | the hash table), it will work because both references stringify to the |
637 | same string. |
638 | |
639 | It won't work across a C<store> and C<retrieve> operations however, because |
640 | the addresses in the retrieved objects, which are part of the stringified |
641 | references, will probably differ from the original addresses. The |
642 | topology of your structure is preserved, but not hidden semantics |
643 | like those. |
644 | |
645 | On platforms where it matters, be sure to call C<binmode()> on the |
646 | descriptors that you pass to Storable functions. |
647 | |
648 | Storing data canonically that contains large hashes can be |
649 | significantly slower than storing the same data normally, as |
650 | temprorary arrays to hold the keys for each hash have to be allocated, |
651 | populated, sorted and freed. Some tests have shown a halving of the |
652 | speed of storing -- the exact penalty will depend on the complexity of |
653 | your data. There is no slowdown on retrieval. |
654 | |
655 | =head1 BUGS |
656 | |
657 | You can't store GLOB, CODE, FORMLINE, etc... If you can define |
658 | semantics for those operations, feel free to enhance Storable so that |
659 | it can deal with them. |
660 | |
661 | The store functions will C<croak> if they run into such references |
662 | unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that |
663 | case, the fatal message is turned in a warning and some |
664 | meaningless string is stored instead. |
665 | |
666 | Setting C<$Storable::canonical> may not yield frozen strings that |
667 | compare equal due to possible stringification of numbers. When the |
668 | string version of a scalar exists, it is the form stored, therefore |
669 | if you happen to use your numbers as strings between two freezing |
670 | operations on the same data structures, you will get different |
671 | results. |
672 | |
dd19458b |
673 | When storing doubles in network order, their value is stored as text. |
674 | However, you should also not expect non-numeric floating-point values |
675 | such as infinity and "not a number" to pass successfully through a |
676 | nstore()/retrieve() pair. |
677 | |
678 | As Storable neither knows nor cares about character sets (although it |
679 | does know that characters may be more than eight bits wide), any difference |
680 | in the interpretation of character codes between a host and a target |
681 | system is your problem. In particular, if host and target use different |
682 | code points to represent the characters used in the text representation |
683 | of floating-point numbers, you will not be able be able to exchange |
684 | floating-point data, even with nstore(). |
685 | |
7a6a85bf |
686 | =head1 CREDITS |
687 | |
688 | Thank you to (in chronological order): |
689 | |
690 | Jarkko Hietaniemi <jhi@iki.fi> |
691 | Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de> |
692 | Benjamin A. Holzman <bah@ecnvantage.com> |
693 | Andrew Ford <A.Ford@ford-mason.co.uk> |
694 | Gisle Aas <gisle@aas.no> |
695 | Jeff Gresham <gresham_jeffrey@jpmorgan.com> |
696 | Murray Nesbitt <murray@activestate.com> |
697 | Marc Lehmann <pcg@opengroup.org> |
9e21b3d0 |
698 | Justin Banks <justinb@wamnet.com> |
699 | Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!) |
dd19458b |
700 | Salvador Ortiz Garcia <sog@msg.com.mx> |
701 | Dominic Dunlop <domo@computer.org> |
702 | Erik Haugan <erik@solbors.no> |
7a6a85bf |
703 | |
704 | for their bug reports, suggestions and contributions. |
705 | |
706 | Benjamin Holzman contributed the tied variable support, Andrew Ford |
707 | contributed the canonical order for hashes, and Gisle Aas fixed |
708 | a few misunderstandings of mine regarding the Perl internals, |
709 | and optimized the emission of "tags" in the output streams by |
710 | simply counting the objects instead of tagging them (leading to |
711 | a binary incompatibility for the Storable image starting at version |
712 | 0.6--older images are of course still properly understood). |
713 | Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading |
714 | and reference to tied items support. |
715 | |
716 | =head1 TRANSLATIONS |
717 | |
718 | There is a Japanese translation of this man page available at |
719 | http://member.nifty.ne.jp/hippo2000/perltips/storable.htm , |
720 | courtesy of Kawai, Takanori <kawai@nippon-rad.co.jp>. |
721 | |
722 | =head1 AUTHOR |
723 | |
724 | Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>> |
725 | |
726 | =head1 SEE ALSO |
727 | |
728 | Clone(3). |
729 | |
730 | =cut |
731 | |