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1 | ;# $Id: Storable.pm,v 1.0.1.8 2001/02/17 12:24:37 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 1.0.1.8 2001/02/17 12:24:37 ram |
10 | ;# patch8: fixed incorrect error message |
11 | ;# |
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12 | ;# Revision 1.0.1.7 2001/01/03 09:39:02 ram |
13 | ;# patch7: added CAN_FLOCK to determine whether we can flock() or not |
14 | ;# |
90826881 |
15 | ;# Revision 1.0.1.6 2000/11/05 17:20:25 ram |
16 | ;# patch6: increased version number |
17 | ;# |
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18 | ;# Revision 1.0.1.5 2000/10/26 17:10:18 ram |
19 | ;# patch5: documented that store() and retrieve() can return undef |
20 | ;# patch5: added paragraph explaining the auto require for thaw hooks |
21 | ;# |
22 | ;# Revision 1.0.1.4 2000/10/23 18:02:57 ram |
23 | ;# patch4: protected calls to flock() for dos platform |
24 | ;# patch4: added logcarp emulation if they don't have Log::Agent |
25 | ;# |
26 | ;# $Log: Storable.pm,v $ |
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27 | ;# Revision 1.0 2000/09/01 19:40:41 ram |
28 | ;# Baseline for first official release. |
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29 | ;# |
30 | |
31 | require DynaLoader; |
32 | require Exporter; |
33 | package Storable; @ISA = qw(Exporter DynaLoader); |
34 | |
35 | @EXPORT = qw(store retrieve); |
36 | @EXPORT_OK = qw( |
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37 | nstore store_fd nstore_fd fd_retrieve |
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38 | freeze nfreeze thaw |
39 | dclone |
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40 | retrieve_fd |
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41 | lock_store lock_nstore lock_retrieve |
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42 | ); |
43 | |
44 | use AutoLoader; |
45 | use vars qw($forgive_me $VERSION); |
46 | |
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47 | $VERSION = '1.007'; |
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48 | *AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr... |
49 | |
50 | # |
51 | # Use of Log::Agent is optional |
52 | # |
53 | |
54 | eval "use Log::Agent"; |
55 | |
56 | unless (defined @Log::Agent::EXPORT) { |
57 | eval q{ |
58 | sub logcroak { |
59 | require Carp; |
60 | Carp::croak(@_); |
61 | } |
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62 | sub logcarp { |
63 | require Carp; |
64 | Carp::carp(@_); |
65 | } |
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66 | }; |
67 | } |
68 | |
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69 | # |
70 | # They might miss :flock in Fcntl |
71 | # |
72 | |
73 | BEGIN { |
74 | require Fcntl; |
75 | if (exists $Fcntl::EXPORT_TAGS{'flock'}) { |
76 | Fcntl->import(':flock'); |
77 | } else { |
78 | eval q{ |
79 | sub LOCK_SH () {1} |
80 | sub LOCK_EX () {2} |
81 | }; |
82 | } |
83 | } |
84 | |
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85 | sub logcroak; |
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86 | sub logcarp; |
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87 | |
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88 | sub retrieve_fd { &fd_retrieve } # Backward compatibility |
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89 | |
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90 | # |
91 | # Determine whether locking is possible, but only when needed. |
92 | # |
93 | |
94 | my $CAN_FLOCK; |
95 | |
96 | sub CAN_FLOCK { |
97 | return $CAN_FLOCK if defined $CAN_FLOCK; |
98 | require Config; import Config; |
99 | return $CAN_FLOCK = |
100 | $Config{'d_flock'} || |
101 | $Config{'d_fcntl_can_lock'} || |
102 | $Config{'d_lockf'}; |
103 | } |
104 | |
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105 | bootstrap Storable; |
106 | 1; |
107 | __END__ |
108 | |
109 | # |
110 | # store |
111 | # |
112 | # Store target object hierarchy, identified by a reference to its root. |
113 | # The stored object tree may later be retrieved to memory via retrieve. |
114 | # Returns undef if an I/O error occurred, in which case the file is |
115 | # removed. |
116 | # |
117 | sub store { |
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118 | return _store(\&pstore, @_, 0); |
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119 | } |
120 | |
121 | # |
122 | # nstore |
123 | # |
124 | # Same as store, but in network order. |
125 | # |
126 | sub nstore { |
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127 | return _store(\&net_pstore, @_, 0); |
128 | } |
129 | |
130 | # |
131 | # lock_store |
132 | # |
133 | # Same as store, but flock the file first (advisory locking). |
134 | # |
135 | sub lock_store { |
136 | return _store(\&pstore, @_, 1); |
137 | } |
138 | |
139 | # |
140 | # lock_nstore |
141 | # |
142 | # Same as nstore, but flock the file first (advisory locking). |
143 | # |
144 | sub lock_nstore { |
145 | return _store(\&net_pstore, @_, 1); |
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146 | } |
147 | |
148 | # Internal store to file routine |
149 | sub _store { |
150 | my $xsptr = shift; |
151 | my $self = shift; |
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152 | my ($file, $use_locking) = @_; |
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153 | logcroak "not a reference" unless ref($self); |
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154 | logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist |
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155 | local *FILE; |
156 | open(FILE, ">$file") || logcroak "can't create $file: $!"; |
157 | binmode FILE; # Archaic systems... |
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158 | if ($use_locking) { |
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159 | unless (&CAN_FLOCK) { |
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160 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
161 | return undef; |
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162 | } |
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163 | flock(FILE, LOCK_EX) || |
164 | logcroak "can't get exclusive lock on $file: $!"; |
165 | truncate FILE, 0; |
166 | # Unlocking will happen when FILE is closed |
167 | } |
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168 | my $da = $@; # Don't mess if called from exception handler |
169 | my $ret; |
170 | # Call C routine nstore or pstore, depending on network order |
171 | eval { $ret = &$xsptr(*FILE, $self) }; |
172 | close(FILE) or $ret = undef; |
173 | unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret; |
174 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
175 | $@ = $da; |
176 | return $ret ? $ret : undef; |
177 | } |
178 | |
179 | # |
180 | # store_fd |
181 | # |
182 | # Same as store, but perform on an already opened file descriptor instead. |
183 | # Returns undef if an I/O error occurred. |
184 | # |
185 | sub store_fd { |
186 | return _store_fd(\&pstore, @_); |
187 | } |
188 | |
189 | # |
190 | # nstore_fd |
191 | # |
192 | # Same as store_fd, but in network order. |
193 | # |
194 | sub nstore_fd { |
195 | my ($self, $file) = @_; |
196 | return _store_fd(\&net_pstore, @_); |
197 | } |
198 | |
199 | # Internal store routine on opened file descriptor |
200 | sub _store_fd { |
201 | my $xsptr = shift; |
202 | my $self = shift; |
203 | my ($file) = @_; |
204 | logcroak "not a reference" unless ref($self); |
205 | logcroak "too many arguments" unless @_ == 1; # No @foo in arglist |
206 | my $fd = fileno($file); |
207 | logcroak "not a valid file descriptor" unless defined $fd; |
208 | my $da = $@; # Don't mess if called from exception handler |
209 | my $ret; |
210 | # Call C routine nstore or pstore, depending on network order |
211 | eval { $ret = &$xsptr($file, $self) }; |
212 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
213 | $@ = $da; |
214 | return $ret ? $ret : undef; |
215 | } |
216 | |
217 | # |
218 | # freeze |
219 | # |
220 | # Store oject and its hierarchy in memory and return a scalar |
221 | # containing the result. |
222 | # |
223 | sub freeze { |
224 | _freeze(\&mstore, @_); |
225 | } |
226 | |
227 | # |
228 | # nfreeze |
229 | # |
230 | # Same as freeze but in network order. |
231 | # |
232 | sub nfreeze { |
233 | _freeze(\&net_mstore, @_); |
234 | } |
235 | |
236 | # Internal freeze routine |
237 | sub _freeze { |
238 | my $xsptr = shift; |
239 | my $self = shift; |
240 | logcroak "not a reference" unless ref($self); |
241 | logcroak "too many arguments" unless @_ == 0; # No @foo in arglist |
242 | my $da = $@; # Don't mess if called from exception handler |
243 | my $ret; |
244 | # Call C routine mstore or net_mstore, depending on network order |
245 | eval { $ret = &$xsptr($self) }; |
246 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
247 | $@ = $da; |
248 | return $ret ? $ret : undef; |
249 | } |
250 | |
251 | # |
252 | # retrieve |
253 | # |
254 | # Retrieve object hierarchy from disk, returning a reference to the root |
255 | # object of that tree. |
256 | # |
257 | sub retrieve { |
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258 | _retrieve($_[0], 0); |
259 | } |
260 | |
261 | # |
262 | # lock_retrieve |
263 | # |
264 | # Same as retrieve, but with advisory locking. |
265 | # |
266 | sub lock_retrieve { |
267 | _retrieve($_[0], 1); |
268 | } |
269 | |
270 | # Internal retrieve routine |
271 | sub _retrieve { |
272 | my ($file, $use_locking) = @_; |
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273 | local *FILE; |
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274 | open(FILE, $file) || logcroak "can't open $file: $!"; |
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275 | binmode FILE; # Archaic systems... |
276 | my $self; |
277 | my $da = $@; # Could be from exception handler |
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278 | if ($use_locking) { |
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279 | unless (&CAN_FLOCK) { |
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280 | logcarp "Storable::lock_retrieve: fcntl/flock emulation broken on $^O"; |
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281 | return undef; |
282 | } |
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283 | flock(FILE, LOCK_SH) || |
284 | logcroak "can't get shared lock on $file: $!"; |
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285 | # Unlocking will happen when FILE is closed |
286 | } |
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287 | eval { $self = pretrieve(*FILE) }; # Call C routine |
288 | close(FILE); |
289 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
290 | $@ = $da; |
291 | return $self; |
292 | } |
293 | |
294 | # |
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295 | # fd_retrieve |
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296 | # |
297 | # Same as retrieve, but perform from an already opened file descriptor instead. |
298 | # |
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299 | sub fd_retrieve { |
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300 | my ($file) = @_; |
301 | my $fd = fileno($file); |
302 | logcroak "not a valid file descriptor" unless defined $fd; |
303 | my $self; |
304 | my $da = $@; # Could be from exception handler |
305 | eval { $self = pretrieve($file) }; # Call C routine |
306 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
307 | $@ = $da; |
308 | return $self; |
309 | } |
310 | |
311 | # |
312 | # thaw |
313 | # |
314 | # Recreate objects in memory from an existing frozen image created |
315 | # by freeze. If the frozen image passed is undef, return undef. |
316 | # |
317 | sub thaw { |
318 | my ($frozen) = @_; |
319 | return undef unless defined $frozen; |
320 | my $self; |
321 | my $da = $@; # Could be from exception handler |
322 | eval { $self = mretrieve($frozen) }; # Call C routine |
323 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
324 | $@ = $da; |
325 | return $self; |
326 | } |
327 | |
328 | =head1 NAME |
329 | |
330 | Storable - persistency for perl data structures |
331 | |
332 | =head1 SYNOPSIS |
333 | |
334 | use Storable; |
335 | store \%table, 'file'; |
336 | $hashref = retrieve('file'); |
337 | |
338 | use Storable qw(nstore store_fd nstore_fd freeze thaw dclone); |
339 | |
340 | # Network order |
341 | nstore \%table, 'file'; |
342 | $hashref = retrieve('file'); # There is NO nretrieve() |
343 | |
344 | # Storing to and retrieving from an already opened file |
345 | store_fd \@array, \*STDOUT; |
346 | nstore_fd \%table, \*STDOUT; |
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347 | $aryref = fd_retrieve(\*SOCKET); |
348 | $hashref = fd_retrieve(\*SOCKET); |
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349 | |
350 | # Serializing to memory |
351 | $serialized = freeze \%table; |
352 | %table_clone = %{ thaw($serialized) }; |
353 | |
354 | # Deep (recursive) cloning |
355 | $cloneref = dclone($ref); |
356 | |
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357 | # Advisory locking |
358 | use Storable qw(lock_store lock_nstore lock_retrieve) |
359 | lock_store \%table, 'file'; |
360 | lock_nstore \%table, 'file'; |
361 | $hashref = lock_retrieve('file'); |
362 | |
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363 | =head1 DESCRIPTION |
364 | |
365 | The Storable package brings persistency to your perl data structures |
366 | containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be |
367 | convenientely stored to disk and retrieved at a later time. |
368 | |
369 | It can be used in the regular procedural way by calling C<store> with |
370 | a reference to the object to be stored, along with the file name where |
371 | the image should be written. |
372 | The routine returns C<undef> for I/O problems or other internal error, |
373 | a true value otherwise. Serious errors are propagated as a C<die> exception. |
374 | |
375 | To retrieve data stored to disk, use C<retrieve> with a file name, |
376 | and the objects stored into that file are recreated into memory for you, |
377 | a I<reference> to the root object being returned. In case an I/O error |
378 | occurs while reading, C<undef> is returned instead. Other serious |
379 | errors are propagated via C<die>. |
380 | |
381 | Since storage is performed recursively, you might want to stuff references |
382 | to objects that share a lot of common data into a single array or hash |
383 | table, and then store that object. That way, when you retrieve back the |
384 | whole thing, the objects will continue to share what they originally shared. |
385 | |
386 | At the cost of a slight header overhead, you may store to an already |
387 | opened file descriptor using the C<store_fd> routine, and retrieve |
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388 | from a file via C<fd_retrieve>. Those names aren't imported by default, |
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389 | so you will have to do that explicitely if you need those routines. |
390 | The file descriptor you supply must be already opened, for read |
391 | if you're going to retrieve and for write if you wish to store. |
392 | |
393 | store_fd(\%table, *STDOUT) || die "can't store to stdout\n"; |
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394 | $hashref = fd_retrieve(*STDIN); |
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395 | |
396 | You can also store data in network order to allow easy sharing across |
397 | multiple platforms, or when storing on a socket known to be remotely |
398 | connected. The routines to call have an initial C<n> prefix for I<network>, |
399 | as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be |
400 | correctly restored so you don't have to know whether you're restoring |
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401 | from native or network ordered data. Double values are stored stringified |
402 | to ensure portability as well, at the slight risk of loosing some precision |
403 | in the last decimals. |
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404 | |
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405 | When using C<fd_retrieve>, objects are retrieved in sequence, one |
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406 | object (i.e. one recursive tree) per associated C<store_fd>. |
407 | |
408 | If you're more from the object-oriented camp, you can inherit from |
409 | Storable and directly store your objects by invoking C<store> as |
410 | a method. The fact that the root of the to-be-stored tree is a |
411 | blessed reference (i.e. an object) is special-cased so that the |
412 | retrieve does not provide a reference to that object but rather the |
413 | blessed object reference itself. (Otherwise, you'd get a reference |
414 | to that blessed object). |
415 | |
416 | =head1 MEMORY STORE |
417 | |
418 | The Storable engine can also store data into a Perl scalar instead, to |
419 | later retrieve them. This is mainly used to freeze a complex structure in |
420 | some safe compact memory place (where it can possibly be sent to another |
421 | process via some IPC, since freezing the structure also serializes it in |
422 | effect). Later on, and maybe somewhere else, you can thaw the Perl scalar |
423 | out and recreate the original complex structure in memory. |
424 | |
425 | Surprisingly, the routines to be called are named C<freeze> and C<thaw>. |
426 | If you wish to send out the frozen scalar to another machine, use |
427 | C<nfreeze> instead to get a portable image. |
428 | |
429 | Note that freezing an object structure and immediately thawing it |
430 | actually achieves a deep cloning of that structure: |
431 | |
432 | dclone(.) = thaw(freeze(.)) |
433 | |
434 | Storable provides you with a C<dclone> interface which does not create |
435 | that intermediary scalar but instead freezes the structure in some |
436 | internal memory space and then immediatly thaws it out. |
437 | |
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438 | =head1 ADVISORY LOCKING |
439 | |
440 | The C<lock_store> and C<lock_nstore> routine are equivalent to C<store> |
441 | and C<nstore>, only they get an exclusive lock on the file before |
442 | writing. Likewise, C<lock_retrieve> performs as C<retrieve>, but also |
443 | gets a shared lock on the file before reading. |
444 | |
445 | Like with any advisory locking scheme, the protection only works if |
446 | you systematically use C<lock_store> and C<lock_retrieve>. If one |
447 | side of your application uses C<store> whilst the other uses C<lock_retrieve>, |
448 | you will get no protection at all. |
449 | |
450 | The internal advisory locking is implemented using Perl's flock() routine. |
451 | If your system does not support any form of flock(), or if you share |
452 | your files across NFS, you might wish to use other forms of locking by |
453 | using modules like LockFile::Simple which lock a file using a filesystem |
454 | entry, instead of locking the file descriptor. |
455 | |
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456 | =head1 SPEED |
457 | |
458 | The heart of Storable is written in C for decent speed. Extra low-level |
459 | optimization have been made when manipulating perl internals, to |
460 | sacrifice encapsulation for the benefit of a greater speed. |
461 | |
462 | =head1 CANONICAL REPRESENTATION |
463 | |
464 | Normally Storable stores elements of hashes in the order they are |
465 | stored internally by Perl, i.e. pseudo-randomly. If you set |
466 | C<$Storable::canonical> to some C<TRUE> value, Storable will store |
467 | hashes with the elements sorted by their key. This allows you to |
468 | compare data structures by comparing their frozen representations (or |
469 | even the compressed frozen representations), which can be useful for |
470 | creating lookup tables for complicated queries. |
471 | |
472 | Canonical order does not imply network order, those are two orthogonal |
473 | settings. |
474 | |
475 | =head1 ERROR REPORTING |
476 | |
477 | Storable uses the "exception" paradigm, in that it does not try to workaround |
478 | failures: if something bad happens, an exception is generated from the |
479 | caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap |
480 | those exceptions. |
481 | |
482 | When Storable croaks, it tries to report the error via the C<logcroak()> |
483 | routine from the C<Log::Agent> package, if it is available. |
484 | |
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485 | Normal errors are reported by having store() or retrieve() return C<undef>. |
486 | Such errors are usually I/O errors (or truncated stream errors at retrieval). |
487 | |
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488 | =head1 WIZARDS ONLY |
489 | |
490 | =head2 Hooks |
491 | |
492 | Any class may define hooks that will be called during the serialization |
493 | and deserialization process on objects that are instances of that class. |
494 | Those hooks can redefine the way serialization is performed (and therefore, |
495 | how the symetrical deserialization should be conducted). |
496 | |
497 | Since we said earlier: |
498 | |
499 | dclone(.) = thaw(freeze(.)) |
500 | |
501 | everything we say about hooks should also hold for deep cloning. However, |
502 | hooks get to know whether the operation is a mere serialization, or a cloning. |
503 | |
504 | Therefore, when serializing hooks are involved, |
505 | |
506 | dclone(.) <> thaw(freeze(.)) |
507 | |
508 | Well, you could keep them in sync, but there's no guarantee it will always |
509 | hold on classes somebody else wrote. Besides, there is little to gain in |
510 | doing so: a serializing hook could only keep one attribute of an object, |
511 | which is probably not what should happen during a deep cloning of that |
512 | same object. |
513 | |
514 | Here is the hooking interface: |
515 | |
516 | =over |
517 | |
518 | =item C<STORABLE_freeze> I<obj>, I<cloning> |
519 | |
520 | The serializing hook, called on the object during serialization. It can be |
521 | inherited, or defined in the class itself, like any other method. |
522 | |
523 | Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating |
524 | whether we're in a dclone() or a regular serialization via store() or freeze(). |
525 | |
526 | Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized |
527 | is the serialized form to be used, and the optional $ref1, $ref2, etc... are |
528 | extra references that you wish to let the Storable engine serialize. |
529 | |
530 | At deserialization time, you will be given back the same LIST, but all the |
531 | extra references will be pointing into the deserialized structure. |
532 | |
533 | The B<first time> the hook is hit in a serialization flow, you may have it |
534 | return an empty list. That will signal the Storable engine to further |
535 | discard that hook for this class and to therefore revert to the default |
536 | serialization of the underlying Perl data. The hook will again be normally |
537 | processed in the next serialization. |
538 | |
539 | Unless you know better, serializing hook should always say: |
540 | |
541 | sub STORABLE_freeze { |
542 | my ($self, $cloning) = @_; |
543 | return if $cloning; # Regular default serialization |
544 | .... |
545 | } |
546 | |
547 | in order to keep reasonable dclone() semantics. |
548 | |
549 | =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ... |
550 | |
551 | The deserializing hook called on the object during deserialization. |
552 | But wait. If we're deserializing, there's no object yet... right? |
553 | |
554 | Wrong: the Storable engine creates an empty one for you. If you know Eiffel, |
555 | you can view C<STORABLE_thaw> as an alternate creation routine. |
556 | |
557 | This means the hook can be inherited like any other method, and that |
558 | I<obj> is your blessed reference for this particular instance. |
559 | |
560 | The other arguments should look familiar if you know C<STORABLE_freeze>: |
561 | I<cloning> is true when we're part of a deep clone operation, I<serialized> |
562 | is the serialized string you returned to the engine in C<STORABLE_freeze>, |
563 | and there may be an optional list of references, in the same order you gave |
564 | them at serialization time, pointing to the deserialized objects (which |
565 | have been processed courtesy of the Storable engine). |
566 | |
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567 | When the Storable engine does not find any C<STORABLE_thaw> hook routine, |
568 | it tries to load the class by requiring the package dynamically (using |
569 | the blessed package name), and then re-attempts the lookup. If at that |
570 | time the hook cannot be located, the engine croaks. Note that this mechanism |
571 | will fail if you define several classes in the same file, but perlmod(1) |
572 | warned you. |
573 | |
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574 | It is up to you to use these information to populate I<obj> the way you want. |
575 | |
576 | Returned value: none. |
577 | |
578 | =back |
579 | |
580 | =head2 Predicates |
581 | |
582 | Predicates are not exportable. They must be called by explicitely prefixing |
583 | them with the Storable package name. |
584 | |
585 | =over |
586 | |
587 | =item C<Storable::last_op_in_netorder> |
588 | |
589 | The C<Storable::last_op_in_netorder()> predicate will tell you whether |
590 | network order was used in the last store or retrieve operation. If you |
591 | don't know how to use this, just forget about it. |
592 | |
593 | =item C<Storable::is_storing> |
594 | |
595 | Returns true if within a store operation (via STORABLE_freeze hook). |
596 | |
597 | =item C<Storable::is_retrieving> |
598 | |
599 | Returns true if within a retrieve operation, (via STORABLE_thaw hook). |
600 | |
601 | =back |
602 | |
603 | =head2 Recursion |
604 | |
605 | With hooks comes the ability to recurse back to the Storable engine. Indeed, |
606 | hooks are regular Perl code, and Storable is convenient when it comes to |
607 | serialize and deserialize things, so why not use it to handle the |
608 | serialization string? |
609 | |
610 | There are a few things you need to know however: |
611 | |
612 | =over |
613 | |
614 | =item * |
615 | |
616 | You can create endless loops if the things you serialize via freeze() |
617 | (for instance) point back to the object we're trying to serialize in the hook. |
618 | |
619 | =item * |
620 | |
621 | Shared references among objects will not stay shared: if we're serializing |
622 | the list of object [A, C] where both object A and C refer to the SAME object |
623 | B, and if there is a serializing hook in A that says freeze(B), then when |
624 | deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D, |
625 | a deep clone of B'. The topology was not preserved. |
626 | |
627 | =back |
628 | |
629 | That's why C<STORABLE_freeze> lets you provide a list of references |
630 | to serialize. The engine guarantees that those will be serialized in the |
631 | same context as the other objects, and therefore that shared objects will |
632 | stay shared. |
633 | |
634 | In the above [A, C] example, the C<STORABLE_freeze> hook could return: |
635 | |
636 | ("something", $self->{B}) |
637 | |
638 | and the B part would be serialized by the engine. In C<STORABLE_thaw>, you |
639 | would get back the reference to the B' object, deserialized for you. |
640 | |
641 | Therefore, recursion should normally be avoided, but is nonetheless supported. |
642 | |
643 | =head2 Deep Cloning |
644 | |
645 | There is a new Clone module available on CPAN which implements deep cloning |
646 | natively, i.e. without freezing to memory and thawing the result. It is |
647 | aimed to replace Storable's dclone() some day. However, it does not currently |
648 | support Storable hooks to redefine the way deep cloning is performed. |
649 | |
650 | =head1 EXAMPLES |
651 | |
652 | Here are some code samples showing a possible usage of Storable: |
653 | |
654 | use Storable qw(store retrieve freeze thaw dclone); |
655 | |
656 | %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1); |
657 | |
658 | store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n"; |
659 | |
660 | $colref = retrieve('/tmp/colors'); |
661 | die "Unable to retrieve from /tmp/colors!\n" unless defined $colref; |
662 | printf "Blue is still %lf\n", $colref->{'Blue'}; |
663 | |
664 | $colref2 = dclone(\%color); |
665 | |
666 | $str = freeze(\%color); |
667 | printf "Serialization of %%color is %d bytes long.\n", length($str); |
668 | $colref3 = thaw($str); |
669 | |
670 | which prints (on my machine): |
671 | |
672 | Blue is still 0.100000 |
673 | Serialization of %color is 102 bytes long. |
674 | |
675 | =head1 WARNING |
676 | |
677 | If you're using references as keys within your hash tables, you're bound |
678 | to disapointment when retrieving your data. Indeed, Perl stringifies |
679 | references used as hash table keys. If you later wish to access the |
680 | items via another reference stringification (i.e. using the same |
681 | reference that was used for the key originally to record the value into |
682 | the hash table), it will work because both references stringify to the |
683 | same string. |
684 | |
685 | It won't work across a C<store> and C<retrieve> operations however, because |
686 | the addresses in the retrieved objects, which are part of the stringified |
687 | references, will probably differ from the original addresses. The |
688 | topology of your structure is preserved, but not hidden semantics |
689 | like those. |
690 | |
691 | On platforms where it matters, be sure to call C<binmode()> on the |
692 | descriptors that you pass to Storable functions. |
693 | |
694 | Storing data canonically that contains large hashes can be |
695 | significantly slower than storing the same data normally, as |
696 | temprorary arrays to hold the keys for each hash have to be allocated, |
697 | populated, sorted and freed. Some tests have shown a halving of the |
698 | speed of storing -- the exact penalty will depend on the complexity of |
699 | your data. There is no slowdown on retrieval. |
700 | |
701 | =head1 BUGS |
702 | |
703 | You can't store GLOB, CODE, FORMLINE, etc... If you can define |
704 | semantics for those operations, feel free to enhance Storable so that |
705 | it can deal with them. |
706 | |
707 | The store functions will C<croak> if they run into such references |
708 | unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that |
709 | case, the fatal message is turned in a warning and some |
710 | meaningless string is stored instead. |
711 | |
712 | Setting C<$Storable::canonical> may not yield frozen strings that |
713 | compare equal due to possible stringification of numbers. When the |
714 | string version of a scalar exists, it is the form stored, therefore |
715 | if you happen to use your numbers as strings between two freezing |
716 | operations on the same data structures, you will get different |
717 | results. |
718 | |
dd19458b |
719 | When storing doubles in network order, their value is stored as text. |
720 | However, you should also not expect non-numeric floating-point values |
721 | such as infinity and "not a number" to pass successfully through a |
722 | nstore()/retrieve() pair. |
723 | |
724 | As Storable neither knows nor cares about character sets (although it |
725 | does know that characters may be more than eight bits wide), any difference |
726 | in the interpretation of character codes between a host and a target |
727 | system is your problem. In particular, if host and target use different |
728 | code points to represent the characters used in the text representation |
729 | of floating-point numbers, you will not be able be able to exchange |
730 | floating-point data, even with nstore(). |
731 | |
7a6a85bf |
732 | =head1 CREDITS |
733 | |
734 | Thank you to (in chronological order): |
735 | |
736 | Jarkko Hietaniemi <jhi@iki.fi> |
737 | Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de> |
738 | Benjamin A. Holzman <bah@ecnvantage.com> |
739 | Andrew Ford <A.Ford@ford-mason.co.uk> |
740 | Gisle Aas <gisle@aas.no> |
741 | Jeff Gresham <gresham_jeffrey@jpmorgan.com> |
742 | Murray Nesbitt <murray@activestate.com> |
743 | Marc Lehmann <pcg@opengroup.org> |
9e21b3d0 |
744 | Justin Banks <justinb@wamnet.com> |
745 | Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!) |
dd19458b |
746 | Salvador Ortiz Garcia <sog@msg.com.mx> |
747 | Dominic Dunlop <domo@computer.org> |
748 | Erik Haugan <erik@solbors.no> |
7a6a85bf |
749 | |
750 | for their bug reports, suggestions and contributions. |
751 | |
752 | Benjamin Holzman contributed the tied variable support, Andrew Ford |
753 | contributed the canonical order for hashes, and Gisle Aas fixed |
754 | a few misunderstandings of mine regarding the Perl internals, |
755 | and optimized the emission of "tags" in the output streams by |
756 | simply counting the objects instead of tagging them (leading to |
757 | a binary incompatibility for the Storable image starting at version |
758 | 0.6--older images are of course still properly understood). |
759 | Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading |
760 | and reference to tied items support. |
761 | |
762 | =head1 TRANSLATIONS |
763 | |
764 | There is a Japanese translation of this man page available at |
765 | http://member.nifty.ne.jp/hippo2000/perltips/storable.htm , |
766 | courtesy of Kawai, Takanori <kawai@nippon-rad.co.jp>. |
767 | |
768 | =head1 AUTHOR |
769 | |
770 | Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>> |
771 | |
772 | =head1 SEE ALSO |
773 | |
774 | Clone(3). |
775 | |
776 | =cut |
777 | |