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1 | ;# $Id: Storable.pm,v 1.0.1.5 2000/10/26 17:10:18 ram Exp ram $ |
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2 | ;# |
3 | ;# Copyright (c) 1995-2000, Raphael Manfredi |
4 | ;# |
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5 | ;# You may redistribute only under the same terms as Perl 5, as specified |
6 | ;# in the README file that comes with the distribution. |
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7 | ;# |
8 | ;# $Log: Storable.pm,v $ |
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9 | ;# Revision 1.0.1.5 2000/10/26 17:10:18 ram |
10 | ;# patch5: documented that store() and retrieve() can return undef |
11 | ;# patch5: added paragraph explaining the auto require for thaw hooks |
12 | ;# |
13 | ;# Revision 1.0.1.4 2000/10/23 18:02:57 ram |
14 | ;# patch4: protected calls to flock() for dos platform |
15 | ;# patch4: added logcarp emulation if they don't have Log::Agent |
16 | ;# |
17 | ;# $Log: Storable.pm,v $ |
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18 | ;# Revision 1.0 2000/09/01 19:40:41 ram |
19 | ;# Baseline for first official release. |
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20 | ;# |
21 | |
22 | require DynaLoader; |
23 | require Exporter; |
24 | package Storable; @ISA = qw(Exporter DynaLoader); |
25 | |
26 | @EXPORT = qw(store retrieve); |
27 | @EXPORT_OK = qw( |
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28 | nstore store_fd nstore_fd fd_retrieve |
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29 | freeze nfreeze thaw |
30 | dclone |
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31 | retrieve_fd |
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32 | lock_store lock_nstore lock_retrieve |
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33 | ); |
34 | |
35 | use AutoLoader; |
36 | use vars qw($forgive_me $VERSION); |
37 | |
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38 | $VERSION = '1.005'; |
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39 | *AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr... |
40 | |
41 | # |
42 | # Use of Log::Agent is optional |
43 | # |
44 | |
45 | eval "use Log::Agent"; |
46 | |
47 | unless (defined @Log::Agent::EXPORT) { |
48 | eval q{ |
49 | sub logcroak { |
50 | require Carp; |
51 | Carp::croak(@_); |
52 | } |
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53 | sub logcarp { |
54 | require Carp; |
55 | Carp::carp(@_); |
56 | } |
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57 | }; |
58 | } |
59 | |
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60 | # |
61 | # They might miss :flock in Fcntl |
62 | # |
63 | |
64 | BEGIN { |
65 | require Fcntl; |
66 | if (exists $Fcntl::EXPORT_TAGS{'flock'}) { |
67 | Fcntl->import(':flock'); |
68 | } else { |
69 | eval q{ |
70 | sub LOCK_SH () {1} |
71 | sub LOCK_EX () {2} |
72 | }; |
73 | } |
74 | } |
75 | |
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76 | sub logcroak; |
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77 | sub logcarp; |
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78 | |
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79 | sub retrieve_fd { &fd_retrieve } # Backward compatibility |
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80 | |
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81 | bootstrap Storable; |
82 | 1; |
83 | __END__ |
84 | |
85 | # |
86 | # store |
87 | # |
88 | # Store target object hierarchy, identified by a reference to its root. |
89 | # The stored object tree may later be retrieved to memory via retrieve. |
90 | # Returns undef if an I/O error occurred, in which case the file is |
91 | # removed. |
92 | # |
93 | sub store { |
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94 | return _store(\&pstore, @_, 0); |
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95 | } |
96 | |
97 | # |
98 | # nstore |
99 | # |
100 | # Same as store, but in network order. |
101 | # |
102 | sub nstore { |
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103 | return _store(\&net_pstore, @_, 0); |
104 | } |
105 | |
106 | # |
107 | # lock_store |
108 | # |
109 | # Same as store, but flock the file first (advisory locking). |
110 | # |
111 | sub lock_store { |
112 | return _store(\&pstore, @_, 1); |
113 | } |
114 | |
115 | # |
116 | # lock_nstore |
117 | # |
118 | # Same as nstore, but flock the file first (advisory locking). |
119 | # |
120 | sub lock_nstore { |
121 | return _store(\&net_pstore, @_, 1); |
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122 | } |
123 | |
124 | # Internal store to file routine |
125 | sub _store { |
126 | my $xsptr = shift; |
127 | my $self = shift; |
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128 | my ($file, $use_locking) = @_; |
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129 | logcroak "not a reference" unless ref($self); |
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130 | logcroak "too many arguments" unless @_ == 2; # No @foo in arglist |
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131 | local *FILE; |
132 | open(FILE, ">$file") || logcroak "can't create $file: $!"; |
133 | binmode FILE; # Archaic systems... |
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134 | if ($use_locking) { |
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135 | if ($^O eq 'dos') { |
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136 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
137 | return undef; |
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138 | } |
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139 | flock(FILE, LOCK_EX) || |
140 | logcroak "can't get exclusive lock on $file: $!"; |
141 | truncate FILE, 0; |
142 | # Unlocking will happen when FILE is closed |
143 | } |
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144 | my $da = $@; # Don't mess if called from exception handler |
145 | my $ret; |
146 | # Call C routine nstore or pstore, depending on network order |
147 | eval { $ret = &$xsptr(*FILE, $self) }; |
148 | close(FILE) or $ret = undef; |
149 | unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret; |
150 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
151 | $@ = $da; |
152 | return $ret ? $ret : undef; |
153 | } |
154 | |
155 | # |
156 | # store_fd |
157 | # |
158 | # Same as store, but perform on an already opened file descriptor instead. |
159 | # Returns undef if an I/O error occurred. |
160 | # |
161 | sub store_fd { |
162 | return _store_fd(\&pstore, @_); |
163 | } |
164 | |
165 | # |
166 | # nstore_fd |
167 | # |
168 | # Same as store_fd, but in network order. |
169 | # |
170 | sub nstore_fd { |
171 | my ($self, $file) = @_; |
172 | return _store_fd(\&net_pstore, @_); |
173 | } |
174 | |
175 | # Internal store routine on opened file descriptor |
176 | sub _store_fd { |
177 | my $xsptr = shift; |
178 | my $self = shift; |
179 | my ($file) = @_; |
180 | logcroak "not a reference" unless ref($self); |
181 | logcroak "too many arguments" unless @_ == 1; # No @foo in arglist |
182 | my $fd = fileno($file); |
183 | logcroak "not a valid file descriptor" unless defined $fd; |
184 | my $da = $@; # Don't mess if called from exception handler |
185 | my $ret; |
186 | # Call C routine nstore or pstore, depending on network order |
187 | eval { $ret = &$xsptr($file, $self) }; |
188 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
189 | $@ = $da; |
190 | return $ret ? $ret : undef; |
191 | } |
192 | |
193 | # |
194 | # freeze |
195 | # |
196 | # Store oject and its hierarchy in memory and return a scalar |
197 | # containing the result. |
198 | # |
199 | sub freeze { |
200 | _freeze(\&mstore, @_); |
201 | } |
202 | |
203 | # |
204 | # nfreeze |
205 | # |
206 | # Same as freeze but in network order. |
207 | # |
208 | sub nfreeze { |
209 | _freeze(\&net_mstore, @_); |
210 | } |
211 | |
212 | # Internal freeze routine |
213 | sub _freeze { |
214 | my $xsptr = shift; |
215 | my $self = shift; |
216 | logcroak "not a reference" unless ref($self); |
217 | logcroak "too many arguments" unless @_ == 0; # No @foo in arglist |
218 | my $da = $@; # Don't mess if called from exception handler |
219 | my $ret; |
220 | # Call C routine mstore or net_mstore, depending on network order |
221 | eval { $ret = &$xsptr($self) }; |
222 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
223 | $@ = $da; |
224 | return $ret ? $ret : undef; |
225 | } |
226 | |
227 | # |
228 | # retrieve |
229 | # |
230 | # Retrieve object hierarchy from disk, returning a reference to the root |
231 | # object of that tree. |
232 | # |
233 | sub retrieve { |
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234 | _retrieve($_[0], 0); |
235 | } |
236 | |
237 | # |
238 | # lock_retrieve |
239 | # |
240 | # Same as retrieve, but with advisory locking. |
241 | # |
242 | sub lock_retrieve { |
243 | _retrieve($_[0], 1); |
244 | } |
245 | |
246 | # Internal retrieve routine |
247 | sub _retrieve { |
248 | my ($file, $use_locking) = @_; |
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249 | local *FILE; |
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250 | open(FILE, $file) || logcroak "can't open $file: $!"; |
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251 | binmode FILE; # Archaic systems... |
252 | my $self; |
253 | my $da = $@; # Could be from exception handler |
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254 | if ($use_locking) { |
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255 | if ($^O eq 'dos') { |
256 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
257 | return undef; |
258 | } |
259 | flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!"; |
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260 | # Unlocking will happen when FILE is closed |
261 | } |
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262 | eval { $self = pretrieve(*FILE) }; # Call C routine |
263 | close(FILE); |
264 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
265 | $@ = $da; |
266 | return $self; |
267 | } |
268 | |
269 | # |
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270 | # fd_retrieve |
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271 | # |
272 | # Same as retrieve, but perform from an already opened file descriptor instead. |
273 | # |
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274 | sub fd_retrieve { |
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275 | my ($file) = @_; |
276 | my $fd = fileno($file); |
277 | logcroak "not a valid file descriptor" unless defined $fd; |
278 | my $self; |
279 | my $da = $@; # Could be from exception handler |
280 | eval { $self = pretrieve($file) }; # Call C routine |
281 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
282 | $@ = $da; |
283 | return $self; |
284 | } |
285 | |
286 | # |
287 | # thaw |
288 | # |
289 | # Recreate objects in memory from an existing frozen image created |
290 | # by freeze. If the frozen image passed is undef, return undef. |
291 | # |
292 | sub thaw { |
293 | my ($frozen) = @_; |
294 | return undef unless defined $frozen; |
295 | my $self; |
296 | my $da = $@; # Could be from exception handler |
297 | eval { $self = mretrieve($frozen) }; # Call C routine |
298 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
299 | $@ = $da; |
300 | return $self; |
301 | } |
302 | |
303 | =head1 NAME |
304 | |
305 | Storable - persistency for perl data structures |
306 | |
307 | =head1 SYNOPSIS |
308 | |
309 | use Storable; |
310 | store \%table, 'file'; |
311 | $hashref = retrieve('file'); |
312 | |
313 | use Storable qw(nstore store_fd nstore_fd freeze thaw dclone); |
314 | |
315 | # Network order |
316 | nstore \%table, 'file'; |
317 | $hashref = retrieve('file'); # There is NO nretrieve() |
318 | |
319 | # Storing to and retrieving from an already opened file |
320 | store_fd \@array, \*STDOUT; |
321 | nstore_fd \%table, \*STDOUT; |
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322 | $aryref = fd_retrieve(\*SOCKET); |
323 | $hashref = fd_retrieve(\*SOCKET); |
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324 | |
325 | # Serializing to memory |
326 | $serialized = freeze \%table; |
327 | %table_clone = %{ thaw($serialized) }; |
328 | |
329 | # Deep (recursive) cloning |
330 | $cloneref = dclone($ref); |
331 | |
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332 | # Advisory locking |
333 | use Storable qw(lock_store lock_nstore lock_retrieve) |
334 | lock_store \%table, 'file'; |
335 | lock_nstore \%table, 'file'; |
336 | $hashref = lock_retrieve('file'); |
337 | |
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338 | =head1 DESCRIPTION |
339 | |
340 | The Storable package brings persistency to your perl data structures |
341 | containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be |
342 | convenientely stored to disk and retrieved at a later time. |
343 | |
344 | It can be used in the regular procedural way by calling C<store> with |
345 | a reference to the object to be stored, along with the file name where |
346 | the image should be written. |
347 | The routine returns C<undef> for I/O problems or other internal error, |
348 | a true value otherwise. Serious errors are propagated as a C<die> exception. |
349 | |
350 | To retrieve data stored to disk, use C<retrieve> with a file name, |
351 | and the objects stored into that file are recreated into memory for you, |
352 | a I<reference> to the root object being returned. In case an I/O error |
353 | occurs while reading, C<undef> is returned instead. Other serious |
354 | errors are propagated via C<die>. |
355 | |
356 | Since storage is performed recursively, you might want to stuff references |
357 | to objects that share a lot of common data into a single array or hash |
358 | table, and then store that object. That way, when you retrieve back the |
359 | whole thing, the objects will continue to share what they originally shared. |
360 | |
361 | At the cost of a slight header overhead, you may store to an already |
362 | opened file descriptor using the C<store_fd> routine, and retrieve |
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363 | from a file via C<fd_retrieve>. Those names aren't imported by default, |
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364 | so you will have to do that explicitely if you need those routines. |
365 | The file descriptor you supply must be already opened, for read |
366 | if you're going to retrieve and for write if you wish to store. |
367 | |
368 | store_fd(\%table, *STDOUT) || die "can't store to stdout\n"; |
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369 | $hashref = fd_retrieve(*STDIN); |
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370 | |
371 | You can also store data in network order to allow easy sharing across |
372 | multiple platforms, or when storing on a socket known to be remotely |
373 | connected. The routines to call have an initial C<n> prefix for I<network>, |
374 | as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be |
375 | correctly restored so you don't have to know whether you're restoring |
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376 | from native or network ordered data. Double values are stored stringified |
377 | to ensure portability as well, at the slight risk of loosing some precision |
378 | in the last decimals. |
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379 | |
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380 | When using C<fd_retrieve>, objects are retrieved in sequence, one |
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381 | object (i.e. one recursive tree) per associated C<store_fd>. |
382 | |
383 | If you're more from the object-oriented camp, you can inherit from |
384 | Storable and directly store your objects by invoking C<store> as |
385 | a method. The fact that the root of the to-be-stored tree is a |
386 | blessed reference (i.e. an object) is special-cased so that the |
387 | retrieve does not provide a reference to that object but rather the |
388 | blessed object reference itself. (Otherwise, you'd get a reference |
389 | to that blessed object). |
390 | |
391 | =head1 MEMORY STORE |
392 | |
393 | The Storable engine can also store data into a Perl scalar instead, to |
394 | later retrieve them. This is mainly used to freeze a complex structure in |
395 | some safe compact memory place (where it can possibly be sent to another |
396 | process via some IPC, since freezing the structure also serializes it in |
397 | effect). Later on, and maybe somewhere else, you can thaw the Perl scalar |
398 | out and recreate the original complex structure in memory. |
399 | |
400 | Surprisingly, the routines to be called are named C<freeze> and C<thaw>. |
401 | If you wish to send out the frozen scalar to another machine, use |
402 | C<nfreeze> instead to get a portable image. |
403 | |
404 | Note that freezing an object structure and immediately thawing it |
405 | actually achieves a deep cloning of that structure: |
406 | |
407 | dclone(.) = thaw(freeze(.)) |
408 | |
409 | Storable provides you with a C<dclone> interface which does not create |
410 | that intermediary scalar but instead freezes the structure in some |
411 | internal memory space and then immediatly thaws it out. |
412 | |
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413 | =head1 ADVISORY LOCKING |
414 | |
415 | The C<lock_store> and C<lock_nstore> routine are equivalent to C<store> |
416 | and C<nstore>, only they get an exclusive lock on the file before |
417 | writing. Likewise, C<lock_retrieve> performs as C<retrieve>, but also |
418 | gets a shared lock on the file before reading. |
419 | |
420 | Like with any advisory locking scheme, the protection only works if |
421 | you systematically use C<lock_store> and C<lock_retrieve>. If one |
422 | side of your application uses C<store> whilst the other uses C<lock_retrieve>, |
423 | you will get no protection at all. |
424 | |
425 | The internal advisory locking is implemented using Perl's flock() routine. |
426 | If your system does not support any form of flock(), or if you share |
427 | your files across NFS, you might wish to use other forms of locking by |
428 | using modules like LockFile::Simple which lock a file using a filesystem |
429 | entry, instead of locking the file descriptor. |
430 | |
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431 | =head1 SPEED |
432 | |
433 | The heart of Storable is written in C for decent speed. Extra low-level |
434 | optimization have been made when manipulating perl internals, to |
435 | sacrifice encapsulation for the benefit of a greater speed. |
436 | |
437 | =head1 CANONICAL REPRESENTATION |
438 | |
439 | Normally Storable stores elements of hashes in the order they are |
440 | stored internally by Perl, i.e. pseudo-randomly. If you set |
441 | C<$Storable::canonical> to some C<TRUE> value, Storable will store |
442 | hashes with the elements sorted by their key. This allows you to |
443 | compare data structures by comparing their frozen representations (or |
444 | even the compressed frozen representations), which can be useful for |
445 | creating lookup tables for complicated queries. |
446 | |
447 | Canonical order does not imply network order, those are two orthogonal |
448 | settings. |
449 | |
450 | =head1 ERROR REPORTING |
451 | |
452 | Storable uses the "exception" paradigm, in that it does not try to workaround |
453 | failures: if something bad happens, an exception is generated from the |
454 | caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap |
455 | those exceptions. |
456 | |
457 | When Storable croaks, it tries to report the error via the C<logcroak()> |
458 | routine from the C<Log::Agent> package, if it is available. |
459 | |
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460 | Normal errors are reported by having store() or retrieve() return C<undef>. |
461 | Such errors are usually I/O errors (or truncated stream errors at retrieval). |
462 | |
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463 | =head1 WIZARDS ONLY |
464 | |
465 | =head2 Hooks |
466 | |
467 | Any class may define hooks that will be called during the serialization |
468 | and deserialization process on objects that are instances of that class. |
469 | Those hooks can redefine the way serialization is performed (and therefore, |
470 | how the symetrical deserialization should be conducted). |
471 | |
472 | Since we said earlier: |
473 | |
474 | dclone(.) = thaw(freeze(.)) |
475 | |
476 | everything we say about hooks should also hold for deep cloning. However, |
477 | hooks get to know whether the operation is a mere serialization, or a cloning. |
478 | |
479 | Therefore, when serializing hooks are involved, |
480 | |
481 | dclone(.) <> thaw(freeze(.)) |
482 | |
483 | Well, you could keep them in sync, but there's no guarantee it will always |
484 | hold on classes somebody else wrote. Besides, there is little to gain in |
485 | doing so: a serializing hook could only keep one attribute of an object, |
486 | which is probably not what should happen during a deep cloning of that |
487 | same object. |
488 | |
489 | Here is the hooking interface: |
490 | |
491 | =over |
492 | |
493 | =item C<STORABLE_freeze> I<obj>, I<cloning> |
494 | |
495 | The serializing hook, called on the object during serialization. It can be |
496 | inherited, or defined in the class itself, like any other method. |
497 | |
498 | Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating |
499 | whether we're in a dclone() or a regular serialization via store() or freeze(). |
500 | |
501 | Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized |
502 | is the serialized form to be used, and the optional $ref1, $ref2, etc... are |
503 | extra references that you wish to let the Storable engine serialize. |
504 | |
505 | At deserialization time, you will be given back the same LIST, but all the |
506 | extra references will be pointing into the deserialized structure. |
507 | |
508 | The B<first time> the hook is hit in a serialization flow, you may have it |
509 | return an empty list. That will signal the Storable engine to further |
510 | discard that hook for this class and to therefore revert to the default |
511 | serialization of the underlying Perl data. The hook will again be normally |
512 | processed in the next serialization. |
513 | |
514 | Unless you know better, serializing hook should always say: |
515 | |
516 | sub STORABLE_freeze { |
517 | my ($self, $cloning) = @_; |
518 | return if $cloning; # Regular default serialization |
519 | .... |
520 | } |
521 | |
522 | in order to keep reasonable dclone() semantics. |
523 | |
524 | =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ... |
525 | |
526 | The deserializing hook called on the object during deserialization. |
527 | But wait. If we're deserializing, there's no object yet... right? |
528 | |
529 | Wrong: the Storable engine creates an empty one for you. If you know Eiffel, |
530 | you can view C<STORABLE_thaw> as an alternate creation routine. |
531 | |
532 | This means the hook can be inherited like any other method, and that |
533 | I<obj> is your blessed reference for this particular instance. |
534 | |
535 | The other arguments should look familiar if you know C<STORABLE_freeze>: |
536 | I<cloning> is true when we're part of a deep clone operation, I<serialized> |
537 | is the serialized string you returned to the engine in C<STORABLE_freeze>, |
538 | and there may be an optional list of references, in the same order you gave |
539 | them at serialization time, pointing to the deserialized objects (which |
540 | have been processed courtesy of the Storable engine). |
541 | |
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542 | When the Storable engine does not find any C<STORABLE_thaw> hook routine, |
543 | it tries to load the class by requiring the package dynamically (using |
544 | the blessed package name), and then re-attempts the lookup. If at that |
545 | time the hook cannot be located, the engine croaks. Note that this mechanism |
546 | will fail if you define several classes in the same file, but perlmod(1) |
547 | warned you. |
548 | |
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549 | It is up to you to use these information to populate I<obj> the way you want. |
550 | |
551 | Returned value: none. |
552 | |
553 | =back |
554 | |
555 | =head2 Predicates |
556 | |
557 | Predicates are not exportable. They must be called by explicitely prefixing |
558 | them with the Storable package name. |
559 | |
560 | =over |
561 | |
562 | =item C<Storable::last_op_in_netorder> |
563 | |
564 | The C<Storable::last_op_in_netorder()> predicate will tell you whether |
565 | network order was used in the last store or retrieve operation. If you |
566 | don't know how to use this, just forget about it. |
567 | |
568 | =item C<Storable::is_storing> |
569 | |
570 | Returns true if within a store operation (via STORABLE_freeze hook). |
571 | |
572 | =item C<Storable::is_retrieving> |
573 | |
574 | Returns true if within a retrieve operation, (via STORABLE_thaw hook). |
575 | |
576 | =back |
577 | |
578 | =head2 Recursion |
579 | |
580 | With hooks comes the ability to recurse back to the Storable engine. Indeed, |
581 | hooks are regular Perl code, and Storable is convenient when it comes to |
582 | serialize and deserialize things, so why not use it to handle the |
583 | serialization string? |
584 | |
585 | There are a few things you need to know however: |
586 | |
587 | =over |
588 | |
589 | =item * |
590 | |
591 | You can create endless loops if the things you serialize via freeze() |
592 | (for instance) point back to the object we're trying to serialize in the hook. |
593 | |
594 | =item * |
595 | |
596 | Shared references among objects will not stay shared: if we're serializing |
597 | the list of object [A, C] where both object A and C refer to the SAME object |
598 | B, and if there is a serializing hook in A that says freeze(B), then when |
599 | deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D, |
600 | a deep clone of B'. The topology was not preserved. |
601 | |
602 | =back |
603 | |
604 | That's why C<STORABLE_freeze> lets you provide a list of references |
605 | to serialize. The engine guarantees that those will be serialized in the |
606 | same context as the other objects, and therefore that shared objects will |
607 | stay shared. |
608 | |
609 | In the above [A, C] example, the C<STORABLE_freeze> hook could return: |
610 | |
611 | ("something", $self->{B}) |
612 | |
613 | and the B part would be serialized by the engine. In C<STORABLE_thaw>, you |
614 | would get back the reference to the B' object, deserialized for you. |
615 | |
616 | Therefore, recursion should normally be avoided, but is nonetheless supported. |
617 | |
618 | =head2 Deep Cloning |
619 | |
620 | There is a new Clone module available on CPAN which implements deep cloning |
621 | natively, i.e. without freezing to memory and thawing the result. It is |
622 | aimed to replace Storable's dclone() some day. However, it does not currently |
623 | support Storable hooks to redefine the way deep cloning is performed. |
624 | |
625 | =head1 EXAMPLES |
626 | |
627 | Here are some code samples showing a possible usage of Storable: |
628 | |
629 | use Storable qw(store retrieve freeze thaw dclone); |
630 | |
631 | %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1); |
632 | |
633 | store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n"; |
634 | |
635 | $colref = retrieve('/tmp/colors'); |
636 | die "Unable to retrieve from /tmp/colors!\n" unless defined $colref; |
637 | printf "Blue is still %lf\n", $colref->{'Blue'}; |
638 | |
639 | $colref2 = dclone(\%color); |
640 | |
641 | $str = freeze(\%color); |
642 | printf "Serialization of %%color is %d bytes long.\n", length($str); |
643 | $colref3 = thaw($str); |
644 | |
645 | which prints (on my machine): |
646 | |
647 | Blue is still 0.100000 |
648 | Serialization of %color is 102 bytes long. |
649 | |
650 | =head1 WARNING |
651 | |
652 | If you're using references as keys within your hash tables, you're bound |
653 | to disapointment when retrieving your data. Indeed, Perl stringifies |
654 | references used as hash table keys. If you later wish to access the |
655 | items via another reference stringification (i.e. using the same |
656 | reference that was used for the key originally to record the value into |
657 | the hash table), it will work because both references stringify to the |
658 | same string. |
659 | |
660 | It won't work across a C<store> and C<retrieve> operations however, because |
661 | the addresses in the retrieved objects, which are part of the stringified |
662 | references, will probably differ from the original addresses. The |
663 | topology of your structure is preserved, but not hidden semantics |
664 | like those. |
665 | |
666 | On platforms where it matters, be sure to call C<binmode()> on the |
667 | descriptors that you pass to Storable functions. |
668 | |
669 | Storing data canonically that contains large hashes can be |
670 | significantly slower than storing the same data normally, as |
671 | temprorary arrays to hold the keys for each hash have to be allocated, |
672 | populated, sorted and freed. Some tests have shown a halving of the |
673 | speed of storing -- the exact penalty will depend on the complexity of |
674 | your data. There is no slowdown on retrieval. |
675 | |
676 | =head1 BUGS |
677 | |
678 | You can't store GLOB, CODE, FORMLINE, etc... If you can define |
679 | semantics for those operations, feel free to enhance Storable so that |
680 | it can deal with them. |
681 | |
682 | The store functions will C<croak> if they run into such references |
683 | unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that |
684 | case, the fatal message is turned in a warning and some |
685 | meaningless string is stored instead. |
686 | |
687 | Setting C<$Storable::canonical> may not yield frozen strings that |
688 | compare equal due to possible stringification of numbers. When the |
689 | string version of a scalar exists, it is the form stored, therefore |
690 | if you happen to use your numbers as strings between two freezing |
691 | operations on the same data structures, you will get different |
692 | results. |
693 | |
dd19458b |
694 | When storing doubles in network order, their value is stored as text. |
695 | However, you should also not expect non-numeric floating-point values |
696 | such as infinity and "not a number" to pass successfully through a |
697 | nstore()/retrieve() pair. |
698 | |
699 | As Storable neither knows nor cares about character sets (although it |
700 | does know that characters may be more than eight bits wide), any difference |
701 | in the interpretation of character codes between a host and a target |
702 | system is your problem. In particular, if host and target use different |
703 | code points to represent the characters used in the text representation |
704 | of floating-point numbers, you will not be able be able to exchange |
705 | floating-point data, even with nstore(). |
706 | |
7a6a85bf |
707 | =head1 CREDITS |
708 | |
709 | Thank you to (in chronological order): |
710 | |
711 | Jarkko Hietaniemi <jhi@iki.fi> |
712 | Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de> |
713 | Benjamin A. Holzman <bah@ecnvantage.com> |
714 | Andrew Ford <A.Ford@ford-mason.co.uk> |
715 | Gisle Aas <gisle@aas.no> |
716 | Jeff Gresham <gresham_jeffrey@jpmorgan.com> |
717 | Murray Nesbitt <murray@activestate.com> |
718 | Marc Lehmann <pcg@opengroup.org> |
9e21b3d0 |
719 | Justin Banks <justinb@wamnet.com> |
720 | Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!) |
dd19458b |
721 | Salvador Ortiz Garcia <sog@msg.com.mx> |
722 | Dominic Dunlop <domo@computer.org> |
723 | Erik Haugan <erik@solbors.no> |
7a6a85bf |
724 | |
725 | for their bug reports, suggestions and contributions. |
726 | |
727 | Benjamin Holzman contributed the tied variable support, Andrew Ford |
728 | contributed the canonical order for hashes, and Gisle Aas fixed |
729 | a few misunderstandings of mine regarding the Perl internals, |
730 | and optimized the emission of "tags" in the output streams by |
731 | simply counting the objects instead of tagging them (leading to |
732 | a binary incompatibility for the Storable image starting at version |
733 | 0.6--older images are of course still properly understood). |
734 | Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading |
735 | and reference to tied items support. |
736 | |
737 | =head1 TRANSLATIONS |
738 | |
739 | There is a Japanese translation of this man page available at |
740 | http://member.nifty.ne.jp/hippo2000/perltips/storable.htm , |
741 | courtesy of Kawai, Takanori <kawai@nippon-rad.co.jp>. |
742 | |
743 | =head1 AUTHOR |
744 | |
745 | Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>> |
746 | |
747 | =head1 SEE ALSO |
748 | |
749 | Clone(3). |
750 | |
751 | =cut |
752 | |