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1 | ;# $Id: Storable.pm,v 1.0.1.5 2000/10/26 17:10:18 ram Exp $ |
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2 | ;# |
3 | ;# Copyright (c) 1995-2000, Raphael Manfredi |
4 | ;# |
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5 | ;# You may redistribute only under the same terms as Perl 5, as specified |
6 | ;# in the README file that comes with the distribution. |
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7 | ;# |
8 | ;# $Log: Storable.pm,v $ |
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9 | ;# Revision 1.0.1.6 2000/11/05 17:20:25 ram |
10 | ;# patch6: increased version number |
11 | ;# |
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12 | ;# Revision 1.0.1.5 2000/10/26 17:10:18 ram |
13 | ;# patch5: documented that store() and retrieve() can return undef |
14 | ;# patch5: added paragraph explaining the auto require for thaw hooks |
15 | ;# |
16 | ;# Revision 1.0.1.4 2000/10/23 18:02:57 ram |
17 | ;# patch4: protected calls to flock() for dos platform |
18 | ;# patch4: added logcarp emulation if they don't have Log::Agent |
19 | ;# |
20 | ;# $Log: Storable.pm,v $ |
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21 | ;# Revision 1.0 2000/09/01 19:40:41 ram |
22 | ;# Baseline for first official release. |
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23 | ;# |
24 | |
25 | require DynaLoader; |
26 | require Exporter; |
27 | package Storable; @ISA = qw(Exporter DynaLoader); |
28 | |
29 | @EXPORT = qw(store retrieve); |
30 | @EXPORT_OK = qw( |
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31 | nstore store_fd nstore_fd fd_retrieve |
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32 | freeze nfreeze thaw |
33 | dclone |
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34 | retrieve_fd |
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35 | lock_store lock_nstore lock_retrieve |
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36 | ); |
37 | |
38 | use AutoLoader; |
39 | use vars qw($forgive_me $VERSION); |
40 | |
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41 | $VERSION = '1.006'; |
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42 | *AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr... |
43 | |
44 | # |
45 | # Use of Log::Agent is optional |
46 | # |
47 | |
48 | eval "use Log::Agent"; |
49 | |
50 | unless (defined @Log::Agent::EXPORT) { |
51 | eval q{ |
52 | sub logcroak { |
53 | require Carp; |
54 | Carp::croak(@_); |
55 | } |
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56 | sub logcarp { |
57 | require Carp; |
58 | Carp::carp(@_); |
59 | } |
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60 | }; |
61 | } |
62 | |
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63 | # |
64 | # They might miss :flock in Fcntl |
65 | # |
66 | |
67 | BEGIN { |
68 | require Fcntl; |
69 | if (exists $Fcntl::EXPORT_TAGS{'flock'}) { |
70 | Fcntl->import(':flock'); |
71 | } else { |
72 | eval q{ |
73 | sub LOCK_SH () {1} |
74 | sub LOCK_EX () {2} |
75 | }; |
76 | } |
77 | } |
78 | |
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79 | sub logcroak; |
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80 | sub logcarp; |
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81 | |
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82 | sub retrieve_fd { &fd_retrieve } # Backward compatibility |
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83 | |
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84 | bootstrap Storable; |
85 | 1; |
86 | __END__ |
87 | |
88 | # |
89 | # store |
90 | # |
91 | # Store target object hierarchy, identified by a reference to its root. |
92 | # The stored object tree may later be retrieved to memory via retrieve. |
93 | # Returns undef if an I/O error occurred, in which case the file is |
94 | # removed. |
95 | # |
96 | sub store { |
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97 | return _store(\&pstore, @_, 0); |
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98 | } |
99 | |
100 | # |
101 | # nstore |
102 | # |
103 | # Same as store, but in network order. |
104 | # |
105 | sub nstore { |
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106 | return _store(\&net_pstore, @_, 0); |
107 | } |
108 | |
109 | # |
110 | # lock_store |
111 | # |
112 | # Same as store, but flock the file first (advisory locking). |
113 | # |
114 | sub lock_store { |
115 | return _store(\&pstore, @_, 1); |
116 | } |
117 | |
118 | # |
119 | # lock_nstore |
120 | # |
121 | # Same as nstore, but flock the file first (advisory locking). |
122 | # |
123 | sub lock_nstore { |
124 | return _store(\&net_pstore, @_, 1); |
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125 | } |
126 | |
127 | # Internal store to file routine |
128 | sub _store { |
129 | my $xsptr = shift; |
130 | my $self = shift; |
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131 | my ($file, $use_locking) = @_; |
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132 | logcroak "not a reference" unless ref($self); |
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133 | logcroak "too many arguments" unless @_ == 2; # No @foo in arglist |
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134 | local *FILE; |
135 | open(FILE, ">$file") || logcroak "can't create $file: $!"; |
136 | binmode FILE; # Archaic systems... |
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137 | if ($use_locking) { |
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138 | if ($^O eq 'dos') { |
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139 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
140 | return undef; |
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141 | } |
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142 | flock(FILE, LOCK_EX) || |
143 | logcroak "can't get exclusive lock on $file: $!"; |
144 | truncate FILE, 0; |
145 | # Unlocking will happen when FILE is closed |
146 | } |
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147 | my $da = $@; # Don't mess if called from exception handler |
148 | my $ret; |
149 | # Call C routine nstore or pstore, depending on network order |
150 | eval { $ret = &$xsptr(*FILE, $self) }; |
151 | close(FILE) or $ret = undef; |
152 | unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret; |
153 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
154 | $@ = $da; |
155 | return $ret ? $ret : undef; |
156 | } |
157 | |
158 | # |
159 | # store_fd |
160 | # |
161 | # Same as store, but perform on an already opened file descriptor instead. |
162 | # Returns undef if an I/O error occurred. |
163 | # |
164 | sub store_fd { |
165 | return _store_fd(\&pstore, @_); |
166 | } |
167 | |
168 | # |
169 | # nstore_fd |
170 | # |
171 | # Same as store_fd, but in network order. |
172 | # |
173 | sub nstore_fd { |
174 | my ($self, $file) = @_; |
175 | return _store_fd(\&net_pstore, @_); |
176 | } |
177 | |
178 | # Internal store routine on opened file descriptor |
179 | sub _store_fd { |
180 | my $xsptr = shift; |
181 | my $self = shift; |
182 | my ($file) = @_; |
183 | logcroak "not a reference" unless ref($self); |
184 | logcroak "too many arguments" unless @_ == 1; # No @foo in arglist |
185 | my $fd = fileno($file); |
186 | logcroak "not a valid file descriptor" unless defined $fd; |
187 | my $da = $@; # Don't mess if called from exception handler |
188 | my $ret; |
189 | # Call C routine nstore or pstore, depending on network order |
190 | eval { $ret = &$xsptr($file, $self) }; |
191 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
192 | $@ = $da; |
193 | return $ret ? $ret : undef; |
194 | } |
195 | |
196 | # |
197 | # freeze |
198 | # |
199 | # Store oject and its hierarchy in memory and return a scalar |
200 | # containing the result. |
201 | # |
202 | sub freeze { |
203 | _freeze(\&mstore, @_); |
204 | } |
205 | |
206 | # |
207 | # nfreeze |
208 | # |
209 | # Same as freeze but in network order. |
210 | # |
211 | sub nfreeze { |
212 | _freeze(\&net_mstore, @_); |
213 | } |
214 | |
215 | # Internal freeze routine |
216 | sub _freeze { |
217 | my $xsptr = shift; |
218 | my $self = shift; |
219 | logcroak "not a reference" unless ref($self); |
220 | logcroak "too many arguments" unless @_ == 0; # No @foo in arglist |
221 | my $da = $@; # Don't mess if called from exception handler |
222 | my $ret; |
223 | # Call C routine mstore or net_mstore, depending on network order |
224 | eval { $ret = &$xsptr($self) }; |
225 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
226 | $@ = $da; |
227 | return $ret ? $ret : undef; |
228 | } |
229 | |
230 | # |
231 | # retrieve |
232 | # |
233 | # Retrieve object hierarchy from disk, returning a reference to the root |
234 | # object of that tree. |
235 | # |
236 | sub retrieve { |
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237 | _retrieve($_[0], 0); |
238 | } |
239 | |
240 | # |
241 | # lock_retrieve |
242 | # |
243 | # Same as retrieve, but with advisory locking. |
244 | # |
245 | sub lock_retrieve { |
246 | _retrieve($_[0], 1); |
247 | } |
248 | |
249 | # Internal retrieve routine |
250 | sub _retrieve { |
251 | my ($file, $use_locking) = @_; |
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252 | local *FILE; |
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253 | open(FILE, $file) || logcroak "can't open $file: $!"; |
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254 | binmode FILE; # Archaic systems... |
255 | my $self; |
256 | my $da = $@; # Could be from exception handler |
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257 | if ($use_locking) { |
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258 | if ($^O eq 'dos') { |
259 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
260 | return undef; |
261 | } |
262 | flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!"; |
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263 | # Unlocking will happen when FILE is closed |
264 | } |
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265 | eval { $self = pretrieve(*FILE) }; # Call C routine |
266 | close(FILE); |
267 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
268 | $@ = $da; |
269 | return $self; |
270 | } |
271 | |
272 | # |
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273 | # fd_retrieve |
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274 | # |
275 | # Same as retrieve, but perform from an already opened file descriptor instead. |
276 | # |
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277 | sub fd_retrieve { |
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278 | my ($file) = @_; |
279 | my $fd = fileno($file); |
280 | logcroak "not a valid file descriptor" unless defined $fd; |
281 | my $self; |
282 | my $da = $@; # Could be from exception handler |
283 | eval { $self = pretrieve($file) }; # Call C routine |
284 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
285 | $@ = $da; |
286 | return $self; |
287 | } |
288 | |
289 | # |
290 | # thaw |
291 | # |
292 | # Recreate objects in memory from an existing frozen image created |
293 | # by freeze. If the frozen image passed is undef, return undef. |
294 | # |
295 | sub thaw { |
296 | my ($frozen) = @_; |
297 | return undef unless defined $frozen; |
298 | my $self; |
299 | my $da = $@; # Could be from exception handler |
300 | eval { $self = mretrieve($frozen) }; # Call C routine |
301 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
302 | $@ = $da; |
303 | return $self; |
304 | } |
305 | |
306 | =head1 NAME |
307 | |
308 | Storable - persistency for perl data structures |
309 | |
310 | =head1 SYNOPSIS |
311 | |
312 | use Storable; |
313 | store \%table, 'file'; |
314 | $hashref = retrieve('file'); |
315 | |
316 | use Storable qw(nstore store_fd nstore_fd freeze thaw dclone); |
317 | |
318 | # Network order |
319 | nstore \%table, 'file'; |
320 | $hashref = retrieve('file'); # There is NO nretrieve() |
321 | |
322 | # Storing to and retrieving from an already opened file |
323 | store_fd \@array, \*STDOUT; |
324 | nstore_fd \%table, \*STDOUT; |
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325 | $aryref = fd_retrieve(\*SOCKET); |
326 | $hashref = fd_retrieve(\*SOCKET); |
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327 | |
328 | # Serializing to memory |
329 | $serialized = freeze \%table; |
330 | %table_clone = %{ thaw($serialized) }; |
331 | |
332 | # Deep (recursive) cloning |
333 | $cloneref = dclone($ref); |
334 | |
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335 | # Advisory locking |
336 | use Storable qw(lock_store lock_nstore lock_retrieve) |
337 | lock_store \%table, 'file'; |
338 | lock_nstore \%table, 'file'; |
339 | $hashref = lock_retrieve('file'); |
340 | |
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341 | =head1 DESCRIPTION |
342 | |
343 | The Storable package brings persistency to your perl data structures |
344 | containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be |
345 | convenientely stored to disk and retrieved at a later time. |
346 | |
347 | It can be used in the regular procedural way by calling C<store> with |
348 | a reference to the object to be stored, along with the file name where |
349 | the image should be written. |
350 | The routine returns C<undef> for I/O problems or other internal error, |
351 | a true value otherwise. Serious errors are propagated as a C<die> exception. |
352 | |
353 | To retrieve data stored to disk, use C<retrieve> with a file name, |
354 | and the objects stored into that file are recreated into memory for you, |
355 | a I<reference> to the root object being returned. In case an I/O error |
356 | occurs while reading, C<undef> is returned instead. Other serious |
357 | errors are propagated via C<die>. |
358 | |
359 | Since storage is performed recursively, you might want to stuff references |
360 | to objects that share a lot of common data into a single array or hash |
361 | table, and then store that object. That way, when you retrieve back the |
362 | whole thing, the objects will continue to share what they originally shared. |
363 | |
364 | At the cost of a slight header overhead, you may store to an already |
365 | opened file descriptor using the C<store_fd> routine, and retrieve |
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366 | from a file via C<fd_retrieve>. Those names aren't imported by default, |
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367 | so you will have to do that explicitely if you need those routines. |
368 | The file descriptor you supply must be already opened, for read |
369 | if you're going to retrieve and for write if you wish to store. |
370 | |
371 | store_fd(\%table, *STDOUT) || die "can't store to stdout\n"; |
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372 | $hashref = fd_retrieve(*STDIN); |
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373 | |
374 | You can also store data in network order to allow easy sharing across |
375 | multiple platforms, or when storing on a socket known to be remotely |
376 | connected. The routines to call have an initial C<n> prefix for I<network>, |
377 | as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be |
378 | correctly restored so you don't have to know whether you're restoring |
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379 | from native or network ordered data. Double values are stored stringified |
380 | to ensure portability as well, at the slight risk of loosing some precision |
381 | in the last decimals. |
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382 | |
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383 | When using C<fd_retrieve>, objects are retrieved in sequence, one |
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384 | object (i.e. one recursive tree) per associated C<store_fd>. |
385 | |
386 | If you're more from the object-oriented camp, you can inherit from |
387 | Storable and directly store your objects by invoking C<store> as |
388 | a method. The fact that the root of the to-be-stored tree is a |
389 | blessed reference (i.e. an object) is special-cased so that the |
390 | retrieve does not provide a reference to that object but rather the |
391 | blessed object reference itself. (Otherwise, you'd get a reference |
392 | to that blessed object). |
393 | |
394 | =head1 MEMORY STORE |
395 | |
396 | The Storable engine can also store data into a Perl scalar instead, to |
397 | later retrieve them. This is mainly used to freeze a complex structure in |
398 | some safe compact memory place (where it can possibly be sent to another |
399 | process via some IPC, since freezing the structure also serializes it in |
400 | effect). Later on, and maybe somewhere else, you can thaw the Perl scalar |
401 | out and recreate the original complex structure in memory. |
402 | |
403 | Surprisingly, the routines to be called are named C<freeze> and C<thaw>. |
404 | If you wish to send out the frozen scalar to another machine, use |
405 | C<nfreeze> instead to get a portable image. |
406 | |
407 | Note that freezing an object structure and immediately thawing it |
408 | actually achieves a deep cloning of that structure: |
409 | |
410 | dclone(.) = thaw(freeze(.)) |
411 | |
412 | Storable provides you with a C<dclone> interface which does not create |
413 | that intermediary scalar but instead freezes the structure in some |
414 | internal memory space and then immediatly thaws it out. |
415 | |
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416 | =head1 ADVISORY LOCKING |
417 | |
418 | The C<lock_store> and C<lock_nstore> routine are equivalent to C<store> |
419 | and C<nstore>, only they get an exclusive lock on the file before |
420 | writing. Likewise, C<lock_retrieve> performs as C<retrieve>, but also |
421 | gets a shared lock on the file before reading. |
422 | |
423 | Like with any advisory locking scheme, the protection only works if |
424 | you systematically use C<lock_store> and C<lock_retrieve>. If one |
425 | side of your application uses C<store> whilst the other uses C<lock_retrieve>, |
426 | you will get no protection at all. |
427 | |
428 | The internal advisory locking is implemented using Perl's flock() routine. |
429 | If your system does not support any form of flock(), or if you share |
430 | your files across NFS, you might wish to use other forms of locking by |
431 | using modules like LockFile::Simple which lock a file using a filesystem |
432 | entry, instead of locking the file descriptor. |
433 | |
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434 | =head1 SPEED |
435 | |
436 | The heart of Storable is written in C for decent speed. Extra low-level |
437 | optimization have been made when manipulating perl internals, to |
438 | sacrifice encapsulation for the benefit of a greater speed. |
439 | |
440 | =head1 CANONICAL REPRESENTATION |
441 | |
442 | Normally Storable stores elements of hashes in the order they are |
443 | stored internally by Perl, i.e. pseudo-randomly. If you set |
444 | C<$Storable::canonical> to some C<TRUE> value, Storable will store |
445 | hashes with the elements sorted by their key. This allows you to |
446 | compare data structures by comparing their frozen representations (or |
447 | even the compressed frozen representations), which can be useful for |
448 | creating lookup tables for complicated queries. |
449 | |
450 | Canonical order does not imply network order, those are two orthogonal |
451 | settings. |
452 | |
453 | =head1 ERROR REPORTING |
454 | |
455 | Storable uses the "exception" paradigm, in that it does not try to workaround |
456 | failures: if something bad happens, an exception is generated from the |
457 | caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap |
458 | those exceptions. |
459 | |
460 | When Storable croaks, it tries to report the error via the C<logcroak()> |
461 | routine from the C<Log::Agent> package, if it is available. |
462 | |
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463 | Normal errors are reported by having store() or retrieve() return C<undef>. |
464 | Such errors are usually I/O errors (or truncated stream errors at retrieval). |
465 | |
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466 | =head1 WIZARDS ONLY |
467 | |
468 | =head2 Hooks |
469 | |
470 | Any class may define hooks that will be called during the serialization |
471 | and deserialization process on objects that are instances of that class. |
472 | Those hooks can redefine the way serialization is performed (and therefore, |
473 | how the symetrical deserialization should be conducted). |
474 | |
475 | Since we said earlier: |
476 | |
477 | dclone(.) = thaw(freeze(.)) |
478 | |
479 | everything we say about hooks should also hold for deep cloning. However, |
480 | hooks get to know whether the operation is a mere serialization, or a cloning. |
481 | |
482 | Therefore, when serializing hooks are involved, |
483 | |
484 | dclone(.) <> thaw(freeze(.)) |
485 | |
486 | Well, you could keep them in sync, but there's no guarantee it will always |
487 | hold on classes somebody else wrote. Besides, there is little to gain in |
488 | doing so: a serializing hook could only keep one attribute of an object, |
489 | which is probably not what should happen during a deep cloning of that |
490 | same object. |
491 | |
492 | Here is the hooking interface: |
493 | |
494 | =over |
495 | |
496 | =item C<STORABLE_freeze> I<obj>, I<cloning> |
497 | |
498 | The serializing hook, called on the object during serialization. It can be |
499 | inherited, or defined in the class itself, like any other method. |
500 | |
501 | Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating |
502 | whether we're in a dclone() or a regular serialization via store() or freeze(). |
503 | |
504 | Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized |
505 | is the serialized form to be used, and the optional $ref1, $ref2, etc... are |
506 | extra references that you wish to let the Storable engine serialize. |
507 | |
508 | At deserialization time, you will be given back the same LIST, but all the |
509 | extra references will be pointing into the deserialized structure. |
510 | |
511 | The B<first time> the hook is hit in a serialization flow, you may have it |
512 | return an empty list. That will signal the Storable engine to further |
513 | discard that hook for this class and to therefore revert to the default |
514 | serialization of the underlying Perl data. The hook will again be normally |
515 | processed in the next serialization. |
516 | |
517 | Unless you know better, serializing hook should always say: |
518 | |
519 | sub STORABLE_freeze { |
520 | my ($self, $cloning) = @_; |
521 | return if $cloning; # Regular default serialization |
522 | .... |
523 | } |
524 | |
525 | in order to keep reasonable dclone() semantics. |
526 | |
527 | =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ... |
528 | |
529 | The deserializing hook called on the object during deserialization. |
530 | But wait. If we're deserializing, there's no object yet... right? |
531 | |
532 | Wrong: the Storable engine creates an empty one for you. If you know Eiffel, |
533 | you can view C<STORABLE_thaw> as an alternate creation routine. |
534 | |
535 | This means the hook can be inherited like any other method, and that |
536 | I<obj> is your blessed reference for this particular instance. |
537 | |
538 | The other arguments should look familiar if you know C<STORABLE_freeze>: |
539 | I<cloning> is true when we're part of a deep clone operation, I<serialized> |
540 | is the serialized string you returned to the engine in C<STORABLE_freeze>, |
541 | and there may be an optional list of references, in the same order you gave |
542 | them at serialization time, pointing to the deserialized objects (which |
543 | have been processed courtesy of the Storable engine). |
544 | |
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545 | When the Storable engine does not find any C<STORABLE_thaw> hook routine, |
546 | it tries to load the class by requiring the package dynamically (using |
547 | the blessed package name), and then re-attempts the lookup. If at that |
548 | time the hook cannot be located, the engine croaks. Note that this mechanism |
549 | will fail if you define several classes in the same file, but perlmod(1) |
550 | warned you. |
551 | |
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552 | It is up to you to use these information to populate I<obj> the way you want. |
553 | |
554 | Returned value: none. |
555 | |
556 | =back |
557 | |
558 | =head2 Predicates |
559 | |
560 | Predicates are not exportable. They must be called by explicitely prefixing |
561 | them with the Storable package name. |
562 | |
563 | =over |
564 | |
565 | =item C<Storable::last_op_in_netorder> |
566 | |
567 | The C<Storable::last_op_in_netorder()> predicate will tell you whether |
568 | network order was used in the last store or retrieve operation. If you |
569 | don't know how to use this, just forget about it. |
570 | |
571 | =item C<Storable::is_storing> |
572 | |
573 | Returns true if within a store operation (via STORABLE_freeze hook). |
574 | |
575 | =item C<Storable::is_retrieving> |
576 | |
577 | Returns true if within a retrieve operation, (via STORABLE_thaw hook). |
578 | |
579 | =back |
580 | |
581 | =head2 Recursion |
582 | |
583 | With hooks comes the ability to recurse back to the Storable engine. Indeed, |
584 | hooks are regular Perl code, and Storable is convenient when it comes to |
585 | serialize and deserialize things, so why not use it to handle the |
586 | serialization string? |
587 | |
588 | There are a few things you need to know however: |
589 | |
590 | =over |
591 | |
592 | =item * |
593 | |
594 | You can create endless loops if the things you serialize via freeze() |
595 | (for instance) point back to the object we're trying to serialize in the hook. |
596 | |
597 | =item * |
598 | |
599 | Shared references among objects will not stay shared: if we're serializing |
600 | the list of object [A, C] where both object A and C refer to the SAME object |
601 | B, and if there is a serializing hook in A that says freeze(B), then when |
602 | deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D, |
603 | a deep clone of B'. The topology was not preserved. |
604 | |
605 | =back |
606 | |
607 | That's why C<STORABLE_freeze> lets you provide a list of references |
608 | to serialize. The engine guarantees that those will be serialized in the |
609 | same context as the other objects, and therefore that shared objects will |
610 | stay shared. |
611 | |
612 | In the above [A, C] example, the C<STORABLE_freeze> hook could return: |
613 | |
614 | ("something", $self->{B}) |
615 | |
616 | and the B part would be serialized by the engine. In C<STORABLE_thaw>, you |
617 | would get back the reference to the B' object, deserialized for you. |
618 | |
619 | Therefore, recursion should normally be avoided, but is nonetheless supported. |
620 | |
621 | =head2 Deep Cloning |
622 | |
623 | There is a new Clone module available on CPAN which implements deep cloning |
624 | natively, i.e. without freezing to memory and thawing the result. It is |
625 | aimed to replace Storable's dclone() some day. However, it does not currently |
626 | support Storable hooks to redefine the way deep cloning is performed. |
627 | |
628 | =head1 EXAMPLES |
629 | |
630 | Here are some code samples showing a possible usage of Storable: |
631 | |
632 | use Storable qw(store retrieve freeze thaw dclone); |
633 | |
634 | %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1); |
635 | |
636 | store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n"; |
637 | |
638 | $colref = retrieve('/tmp/colors'); |
639 | die "Unable to retrieve from /tmp/colors!\n" unless defined $colref; |
640 | printf "Blue is still %lf\n", $colref->{'Blue'}; |
641 | |
642 | $colref2 = dclone(\%color); |
643 | |
644 | $str = freeze(\%color); |
645 | printf "Serialization of %%color is %d bytes long.\n", length($str); |
646 | $colref3 = thaw($str); |
647 | |
648 | which prints (on my machine): |
649 | |
650 | Blue is still 0.100000 |
651 | Serialization of %color is 102 bytes long. |
652 | |
653 | =head1 WARNING |
654 | |
655 | If you're using references as keys within your hash tables, you're bound |
656 | to disapointment when retrieving your data. Indeed, Perl stringifies |
657 | references used as hash table keys. If you later wish to access the |
658 | items via another reference stringification (i.e. using the same |
659 | reference that was used for the key originally to record the value into |
660 | the hash table), it will work because both references stringify to the |
661 | same string. |
662 | |
663 | It won't work across a C<store> and C<retrieve> operations however, because |
664 | the addresses in the retrieved objects, which are part of the stringified |
665 | references, will probably differ from the original addresses. The |
666 | topology of your structure is preserved, but not hidden semantics |
667 | like those. |
668 | |
669 | On platforms where it matters, be sure to call C<binmode()> on the |
670 | descriptors that you pass to Storable functions. |
671 | |
672 | Storing data canonically that contains large hashes can be |
673 | significantly slower than storing the same data normally, as |
674 | temprorary arrays to hold the keys for each hash have to be allocated, |
675 | populated, sorted and freed. Some tests have shown a halving of the |
676 | speed of storing -- the exact penalty will depend on the complexity of |
677 | your data. There is no slowdown on retrieval. |
678 | |
679 | =head1 BUGS |
680 | |
681 | You can't store GLOB, CODE, FORMLINE, etc... If you can define |
682 | semantics for those operations, feel free to enhance Storable so that |
683 | it can deal with them. |
684 | |
685 | The store functions will C<croak> if they run into such references |
686 | unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that |
687 | case, the fatal message is turned in a warning and some |
688 | meaningless string is stored instead. |
689 | |
690 | Setting C<$Storable::canonical> may not yield frozen strings that |
691 | compare equal due to possible stringification of numbers. When the |
692 | string version of a scalar exists, it is the form stored, therefore |
693 | if you happen to use your numbers as strings between two freezing |
694 | operations on the same data structures, you will get different |
695 | results. |
696 | |
dd19458b |
697 | When storing doubles in network order, their value is stored as text. |
698 | However, you should also not expect non-numeric floating-point values |
699 | such as infinity and "not a number" to pass successfully through a |
700 | nstore()/retrieve() pair. |
701 | |
702 | As Storable neither knows nor cares about character sets (although it |
703 | does know that characters may be more than eight bits wide), any difference |
704 | in the interpretation of character codes between a host and a target |
705 | system is your problem. In particular, if host and target use different |
706 | code points to represent the characters used in the text representation |
707 | of floating-point numbers, you will not be able be able to exchange |
708 | floating-point data, even with nstore(). |
709 | |
7a6a85bf |
710 | =head1 CREDITS |
711 | |
712 | Thank you to (in chronological order): |
713 | |
714 | Jarkko Hietaniemi <jhi@iki.fi> |
715 | Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de> |
716 | Benjamin A. Holzman <bah@ecnvantage.com> |
717 | Andrew Ford <A.Ford@ford-mason.co.uk> |
718 | Gisle Aas <gisle@aas.no> |
719 | Jeff Gresham <gresham_jeffrey@jpmorgan.com> |
720 | Murray Nesbitt <murray@activestate.com> |
721 | Marc Lehmann <pcg@opengroup.org> |
9e21b3d0 |
722 | Justin Banks <justinb@wamnet.com> |
723 | Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!) |
dd19458b |
724 | Salvador Ortiz Garcia <sog@msg.com.mx> |
725 | Dominic Dunlop <domo@computer.org> |
726 | Erik Haugan <erik@solbors.no> |
7a6a85bf |
727 | |
728 | for their bug reports, suggestions and contributions. |
729 | |
730 | Benjamin Holzman contributed the tied variable support, Andrew Ford |
731 | contributed the canonical order for hashes, and Gisle Aas fixed |
732 | a few misunderstandings of mine regarding the Perl internals, |
733 | and optimized the emission of "tags" in the output streams by |
734 | simply counting the objects instead of tagging them (leading to |
735 | a binary incompatibility for the Storable image starting at version |
736 | 0.6--older images are of course still properly understood). |
737 | Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading |
738 | and reference to tied items support. |
739 | |
740 | =head1 TRANSLATIONS |
741 | |
742 | There is a Japanese translation of this man page available at |
743 | http://member.nifty.ne.jp/hippo2000/perltips/storable.htm , |
744 | courtesy of Kawai, Takanori <kawai@nippon-rad.co.jp>. |
745 | |
746 | =head1 AUTHOR |
747 | |
748 | Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>> |
749 | |
750 | =head1 SEE ALSO |
751 | |
752 | Clone(3). |
753 | |
754 | =cut |
755 | |