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1 | ;# $Id: Storable.pm,v 1.0.1.10 2001/03/15 00:20:25 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 1.0.1.10 2001/03/15 00:20:25 ram |
10 | ;# patch11: updated version number |
11 | ;# |
12 | ;# Revision 1.0.1.9 2001/02/17 12:37:32 ram |
13 | ;# patch10: forgot to increase version number at previous patch |
14 | ;# |
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15 | ;# Revision 1.0.1.8 2001/02/17 12:24:37 ram |
16 | ;# patch8: fixed incorrect error message |
17 | ;# |
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18 | ;# Revision 1.0.1.7 2001/01/03 09:39:02 ram |
19 | ;# patch7: added CAN_FLOCK to determine whether we can flock() or not |
20 | ;# |
90826881 |
21 | ;# Revision 1.0.1.6 2000/11/05 17:20:25 ram |
22 | ;# patch6: increased version number |
23 | ;# |
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24 | ;# Revision 1.0.1.5 2000/10/26 17:10:18 ram |
25 | ;# patch5: documented that store() and retrieve() can return undef |
26 | ;# patch5: added paragraph explaining the auto require for thaw hooks |
27 | ;# |
28 | ;# Revision 1.0.1.4 2000/10/23 18:02:57 ram |
29 | ;# patch4: protected calls to flock() for dos platform |
30 | ;# patch4: added logcarp emulation if they don't have Log::Agent |
31 | ;# |
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32 | ;# Revision 1.0.1.3 2000/09/29 19:49:01 ram |
33 | ;# patch3: updated version number |
34 | ;# |
35 | ;# Revision 1.0.1.2 2000/09/28 21:42:51 ram |
36 | ;# patch2: added lock_store lock_nstore lock_retrieve |
37 | ;# |
38 | ;# Revision 1.0.1.1 2000/09/17 16:46:21 ram |
39 | ;# patch1: documented that doubles are stringified by nstore() |
40 | ;# patch1: added Salvador Ortiz Garcia in CREDITS section |
41 | ;# |
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42 | ;# Revision 1.0 2000/09/01 19:40:41 ram |
43 | ;# Baseline for first official release. |
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44 | ;# |
45 | |
46 | require DynaLoader; |
47 | require Exporter; |
48 | package Storable; @ISA = qw(Exporter DynaLoader); |
49 | |
50 | @EXPORT = qw(store retrieve); |
51 | @EXPORT_OK = qw( |
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52 | nstore store_fd nstore_fd fd_retrieve |
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53 | freeze nfreeze thaw |
54 | dclone |
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55 | retrieve_fd |
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56 | lock_store lock_nstore lock_retrieve |
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57 | ); |
58 | |
59 | use AutoLoader; |
60 | use vars qw($forgive_me $VERSION); |
61 | |
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62 | $VERSION = '1.011'; |
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63 | *AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr... |
64 | |
65 | # |
66 | # Use of Log::Agent is optional |
67 | # |
68 | |
69 | eval "use Log::Agent"; |
70 | |
71 | unless (defined @Log::Agent::EXPORT) { |
72 | eval q{ |
73 | sub logcroak { |
74 | require Carp; |
75 | Carp::croak(@_); |
76 | } |
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77 | sub logcarp { |
78 | require Carp; |
79 | Carp::carp(@_); |
80 | } |
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81 | }; |
82 | } |
83 | |
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84 | # |
85 | # They might miss :flock in Fcntl |
86 | # |
87 | |
88 | BEGIN { |
89 | require Fcntl; |
90 | if (exists $Fcntl::EXPORT_TAGS{'flock'}) { |
91 | Fcntl->import(':flock'); |
92 | } else { |
93 | eval q{ |
94 | sub LOCK_SH () {1} |
95 | sub LOCK_EX () {2} |
96 | }; |
97 | } |
98 | } |
99 | |
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100 | sub logcroak; |
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101 | sub logcarp; |
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102 | |
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103 | sub retrieve_fd { &fd_retrieve } # Backward compatibility |
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104 | |
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105 | # |
106 | # Determine whether locking is possible, but only when needed. |
107 | # |
108 | |
109 | my $CAN_FLOCK; |
110 | |
111 | sub CAN_FLOCK { |
112 | return $CAN_FLOCK if defined $CAN_FLOCK; |
113 | require Config; import Config; |
114 | return $CAN_FLOCK = |
115 | $Config{'d_flock'} || |
116 | $Config{'d_fcntl_can_lock'} || |
117 | $Config{'d_lockf'}; |
118 | } |
119 | |
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120 | bootstrap Storable; |
121 | 1; |
122 | __END__ |
123 | |
124 | # |
125 | # store |
126 | # |
127 | # Store target object hierarchy, identified by a reference to its root. |
128 | # The stored object tree may later be retrieved to memory via retrieve. |
129 | # Returns undef if an I/O error occurred, in which case the file is |
130 | # removed. |
131 | # |
132 | sub store { |
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133 | return _store(\&pstore, @_, 0); |
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134 | } |
135 | |
136 | # |
137 | # nstore |
138 | # |
139 | # Same as store, but in network order. |
140 | # |
141 | sub nstore { |
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142 | return _store(\&net_pstore, @_, 0); |
143 | } |
144 | |
145 | # |
146 | # lock_store |
147 | # |
148 | # Same as store, but flock the file first (advisory locking). |
149 | # |
150 | sub lock_store { |
151 | return _store(\&pstore, @_, 1); |
152 | } |
153 | |
154 | # |
155 | # lock_nstore |
156 | # |
157 | # Same as nstore, but flock the file first (advisory locking). |
158 | # |
159 | sub lock_nstore { |
160 | return _store(\&net_pstore, @_, 1); |
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161 | } |
162 | |
163 | # Internal store to file routine |
164 | sub _store { |
165 | my $xsptr = shift; |
166 | my $self = shift; |
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167 | my ($file, $use_locking) = @_; |
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168 | logcroak "not a reference" unless ref($self); |
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169 | logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist |
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170 | local *FILE; |
171 | open(FILE, ">$file") || logcroak "can't create $file: $!"; |
172 | binmode FILE; # Archaic systems... |
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173 | if ($use_locking) { |
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174 | unless (&CAN_FLOCK) { |
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175 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
176 | return undef; |
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177 | } |
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178 | flock(FILE, LOCK_EX) || |
179 | logcroak "can't get exclusive lock on $file: $!"; |
180 | truncate FILE, 0; |
181 | # Unlocking will happen when FILE is closed |
182 | } |
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183 | my $da = $@; # Don't mess if called from exception handler |
184 | my $ret; |
185 | # Call C routine nstore or pstore, depending on network order |
186 | eval { $ret = &$xsptr(*FILE, $self) }; |
187 | close(FILE) or $ret = undef; |
188 | unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret; |
189 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
190 | $@ = $da; |
191 | return $ret ? $ret : undef; |
192 | } |
193 | |
194 | # |
195 | # store_fd |
196 | # |
197 | # Same as store, but perform on an already opened file descriptor instead. |
198 | # Returns undef if an I/O error occurred. |
199 | # |
200 | sub store_fd { |
201 | return _store_fd(\&pstore, @_); |
202 | } |
203 | |
204 | # |
205 | # nstore_fd |
206 | # |
207 | # Same as store_fd, but in network order. |
208 | # |
209 | sub nstore_fd { |
210 | my ($self, $file) = @_; |
211 | return _store_fd(\&net_pstore, @_); |
212 | } |
213 | |
214 | # Internal store routine on opened file descriptor |
215 | sub _store_fd { |
216 | my $xsptr = shift; |
217 | my $self = shift; |
218 | my ($file) = @_; |
219 | logcroak "not a reference" unless ref($self); |
220 | logcroak "too many arguments" unless @_ == 1; # No @foo in arglist |
221 | my $fd = fileno($file); |
222 | logcroak "not a valid file descriptor" unless defined $fd; |
223 | my $da = $@; # Don't mess if called from exception handler |
224 | my $ret; |
225 | # Call C routine nstore or pstore, depending on network order |
226 | eval { $ret = &$xsptr($file, $self) }; |
227 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
228 | $@ = $da; |
229 | return $ret ? $ret : undef; |
230 | } |
231 | |
232 | # |
233 | # freeze |
234 | # |
235 | # Store oject and its hierarchy in memory and return a scalar |
236 | # containing the result. |
237 | # |
238 | sub freeze { |
239 | _freeze(\&mstore, @_); |
240 | } |
241 | |
242 | # |
243 | # nfreeze |
244 | # |
245 | # Same as freeze but in network order. |
246 | # |
247 | sub nfreeze { |
248 | _freeze(\&net_mstore, @_); |
249 | } |
250 | |
251 | # Internal freeze routine |
252 | sub _freeze { |
253 | my $xsptr = shift; |
254 | my $self = shift; |
255 | logcroak "not a reference" unless ref($self); |
256 | logcroak "too many arguments" unless @_ == 0; # No @foo in arglist |
257 | my $da = $@; # Don't mess if called from exception handler |
258 | my $ret; |
259 | # Call C routine mstore or net_mstore, depending on network order |
260 | eval { $ret = &$xsptr($self) }; |
261 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
262 | $@ = $da; |
263 | return $ret ? $ret : undef; |
264 | } |
265 | |
266 | # |
267 | # retrieve |
268 | # |
269 | # Retrieve object hierarchy from disk, returning a reference to the root |
270 | # object of that tree. |
271 | # |
272 | sub retrieve { |
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273 | _retrieve($_[0], 0); |
274 | } |
275 | |
276 | # |
277 | # lock_retrieve |
278 | # |
279 | # Same as retrieve, but with advisory locking. |
280 | # |
281 | sub lock_retrieve { |
282 | _retrieve($_[0], 1); |
283 | } |
284 | |
285 | # Internal retrieve routine |
286 | sub _retrieve { |
287 | my ($file, $use_locking) = @_; |
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288 | local *FILE; |
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289 | open(FILE, $file) || logcroak "can't open $file: $!"; |
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290 | binmode FILE; # Archaic systems... |
291 | my $self; |
292 | my $da = $@; # Could be from exception handler |
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293 | if ($use_locking) { |
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294 | unless (&CAN_FLOCK) { |
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295 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
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296 | return undef; |
297 | } |
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298 | flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!"; |
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299 | # Unlocking will happen when FILE is closed |
300 | } |
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301 | eval { $self = pretrieve(*FILE) }; # Call C routine |
302 | close(FILE); |
303 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
304 | $@ = $da; |
305 | return $self; |
306 | } |
307 | |
308 | # |
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309 | # fd_retrieve |
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310 | # |
311 | # Same as retrieve, but perform from an already opened file descriptor instead. |
312 | # |
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313 | sub fd_retrieve { |
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314 | my ($file) = @_; |
315 | my $fd = fileno($file); |
316 | logcroak "not a valid file descriptor" unless defined $fd; |
317 | my $self; |
318 | my $da = $@; # Could be from exception handler |
319 | eval { $self = pretrieve($file) }; # Call C routine |
320 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
321 | $@ = $da; |
322 | return $self; |
323 | } |
324 | |
325 | # |
326 | # thaw |
327 | # |
328 | # Recreate objects in memory from an existing frozen image created |
329 | # by freeze. If the frozen image passed is undef, return undef. |
330 | # |
331 | sub thaw { |
332 | my ($frozen) = @_; |
333 | return undef unless defined $frozen; |
334 | my $self; |
335 | my $da = $@; # Could be from exception handler |
336 | eval { $self = mretrieve($frozen) }; # Call C routine |
337 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
338 | $@ = $da; |
339 | return $self; |
340 | } |
341 | |
342 | =head1 NAME |
343 | |
344 | Storable - persistency for perl data structures |
345 | |
346 | =head1 SYNOPSIS |
347 | |
348 | use Storable; |
349 | store \%table, 'file'; |
350 | $hashref = retrieve('file'); |
351 | |
352 | use Storable qw(nstore store_fd nstore_fd freeze thaw dclone); |
353 | |
354 | # Network order |
355 | nstore \%table, 'file'; |
356 | $hashref = retrieve('file'); # There is NO nretrieve() |
357 | |
358 | # Storing to and retrieving from an already opened file |
359 | store_fd \@array, \*STDOUT; |
360 | nstore_fd \%table, \*STDOUT; |
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361 | $aryref = fd_retrieve(\*SOCKET); |
362 | $hashref = fd_retrieve(\*SOCKET); |
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363 | |
364 | # Serializing to memory |
365 | $serialized = freeze \%table; |
366 | %table_clone = %{ thaw($serialized) }; |
367 | |
368 | # Deep (recursive) cloning |
369 | $cloneref = dclone($ref); |
370 | |
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371 | # Advisory locking |
372 | use Storable qw(lock_store lock_nstore lock_retrieve) |
373 | lock_store \%table, 'file'; |
374 | lock_nstore \%table, 'file'; |
375 | $hashref = lock_retrieve('file'); |
376 | |
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377 | =head1 DESCRIPTION |
378 | |
379 | The Storable package brings persistency to your perl data structures |
380 | containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be |
381 | convenientely stored to disk and retrieved at a later time. |
382 | |
383 | It can be used in the regular procedural way by calling C<store> with |
384 | a reference to the object to be stored, along with the file name where |
385 | the image should be written. |
386 | The routine returns C<undef> for I/O problems or other internal error, |
387 | a true value otherwise. Serious errors are propagated as a C<die> exception. |
388 | |
389 | To retrieve data stored to disk, use C<retrieve> with a file name, |
390 | and the objects stored into that file are recreated into memory for you, |
391 | a I<reference> to the root object being returned. In case an I/O error |
392 | occurs while reading, C<undef> is returned instead. Other serious |
393 | errors are propagated via C<die>. |
394 | |
395 | Since storage is performed recursively, you might want to stuff references |
396 | to objects that share a lot of common data into a single array or hash |
397 | table, and then store that object. That way, when you retrieve back the |
398 | whole thing, the objects will continue to share what they originally shared. |
399 | |
400 | At the cost of a slight header overhead, you may store to an already |
401 | opened file descriptor using the C<store_fd> routine, and retrieve |
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402 | from a file via C<fd_retrieve>. Those names aren't imported by default, |
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403 | so you will have to do that explicitely if you need those routines. |
404 | The file descriptor you supply must be already opened, for read |
405 | if you're going to retrieve and for write if you wish to store. |
406 | |
407 | store_fd(\%table, *STDOUT) || die "can't store to stdout\n"; |
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408 | $hashref = fd_retrieve(*STDIN); |
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409 | |
410 | You can also store data in network order to allow easy sharing across |
411 | multiple platforms, or when storing on a socket known to be remotely |
412 | connected. The routines to call have an initial C<n> prefix for I<network>, |
413 | as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be |
414 | correctly restored so you don't have to know whether you're restoring |
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415 | from native or network ordered data. Double values are stored stringified |
416 | to ensure portability as well, at the slight risk of loosing some precision |
417 | in the last decimals. |
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418 | |
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419 | When using C<fd_retrieve>, objects are retrieved in sequence, one |
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420 | object (i.e. one recursive tree) per associated C<store_fd>. |
421 | |
422 | If you're more from the object-oriented camp, you can inherit from |
423 | Storable and directly store your objects by invoking C<store> as |
424 | a method. The fact that the root of the to-be-stored tree is a |
425 | blessed reference (i.e. an object) is special-cased so that the |
426 | retrieve does not provide a reference to that object but rather the |
427 | blessed object reference itself. (Otherwise, you'd get a reference |
428 | to that blessed object). |
429 | |
430 | =head1 MEMORY STORE |
431 | |
432 | The Storable engine can also store data into a Perl scalar instead, to |
433 | later retrieve them. This is mainly used to freeze a complex structure in |
434 | some safe compact memory place (where it can possibly be sent to another |
435 | process via some IPC, since freezing the structure also serializes it in |
436 | effect). Later on, and maybe somewhere else, you can thaw the Perl scalar |
437 | out and recreate the original complex structure in memory. |
438 | |
439 | Surprisingly, the routines to be called are named C<freeze> and C<thaw>. |
440 | If you wish to send out the frozen scalar to another machine, use |
441 | C<nfreeze> instead to get a portable image. |
442 | |
443 | Note that freezing an object structure and immediately thawing it |
444 | actually achieves a deep cloning of that structure: |
445 | |
446 | dclone(.) = thaw(freeze(.)) |
447 | |
448 | Storable provides you with a C<dclone> interface which does not create |
449 | that intermediary scalar but instead freezes the structure in some |
450 | internal memory space and then immediatly thaws it out. |
451 | |
dd19458b |
452 | =head1 ADVISORY LOCKING |
453 | |
454 | The C<lock_store> and C<lock_nstore> routine are equivalent to C<store> |
455 | and C<nstore>, only they get an exclusive lock on the file before |
456 | writing. Likewise, C<lock_retrieve> performs as C<retrieve>, but also |
457 | gets a shared lock on the file before reading. |
458 | |
459 | Like with any advisory locking scheme, the protection only works if |
460 | you systematically use C<lock_store> and C<lock_retrieve>. If one |
461 | side of your application uses C<store> whilst the other uses C<lock_retrieve>, |
462 | you will get no protection at all. |
463 | |
464 | The internal advisory locking is implemented using Perl's flock() routine. |
465 | If your system does not support any form of flock(), or if you share |
466 | your files across NFS, you might wish to use other forms of locking by |
467 | using modules like LockFile::Simple which lock a file using a filesystem |
468 | entry, instead of locking the file descriptor. |
469 | |
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470 | =head1 SPEED |
471 | |
472 | The heart of Storable is written in C for decent speed. Extra low-level |
473 | optimization have been made when manipulating perl internals, to |
474 | sacrifice encapsulation for the benefit of a greater speed. |
475 | |
476 | =head1 CANONICAL REPRESENTATION |
477 | |
478 | Normally Storable stores elements of hashes in the order they are |
479 | stored internally by Perl, i.e. pseudo-randomly. If you set |
480 | C<$Storable::canonical> to some C<TRUE> value, Storable will store |
481 | hashes with the elements sorted by their key. This allows you to |
482 | compare data structures by comparing their frozen representations (or |
483 | even the compressed frozen representations), which can be useful for |
484 | creating lookup tables for complicated queries. |
485 | |
486 | Canonical order does not imply network order, those are two orthogonal |
487 | settings. |
488 | |
489 | =head1 ERROR REPORTING |
490 | |
491 | Storable uses the "exception" paradigm, in that it does not try to workaround |
492 | failures: if something bad happens, an exception is generated from the |
493 | caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap |
494 | those exceptions. |
495 | |
496 | When Storable croaks, it tries to report the error via the C<logcroak()> |
497 | routine from the C<Log::Agent> package, if it is available. |
498 | |
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499 | Normal errors are reported by having store() or retrieve() return C<undef>. |
500 | Such errors are usually I/O errors (or truncated stream errors at retrieval). |
501 | |
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502 | =head1 WIZARDS ONLY |
503 | |
504 | =head2 Hooks |
505 | |
506 | Any class may define hooks that will be called during the serialization |
507 | and deserialization process on objects that are instances of that class. |
508 | Those hooks can redefine the way serialization is performed (and therefore, |
509 | how the symetrical deserialization should be conducted). |
510 | |
511 | Since we said earlier: |
512 | |
513 | dclone(.) = thaw(freeze(.)) |
514 | |
515 | everything we say about hooks should also hold for deep cloning. However, |
516 | hooks get to know whether the operation is a mere serialization, or a cloning. |
517 | |
518 | Therefore, when serializing hooks are involved, |
519 | |
520 | dclone(.) <> thaw(freeze(.)) |
521 | |
522 | Well, you could keep them in sync, but there's no guarantee it will always |
523 | hold on classes somebody else wrote. Besides, there is little to gain in |
524 | doing so: a serializing hook could only keep one attribute of an object, |
525 | which is probably not what should happen during a deep cloning of that |
526 | same object. |
527 | |
528 | Here is the hooking interface: |
529 | |
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530 | =over 4 |
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531 | |
532 | =item C<STORABLE_freeze> I<obj>, I<cloning> |
533 | |
534 | The serializing hook, called on the object during serialization. It can be |
535 | inherited, or defined in the class itself, like any other method. |
536 | |
537 | Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating |
538 | whether we're in a dclone() or a regular serialization via store() or freeze(). |
539 | |
540 | Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized |
541 | is the serialized form to be used, and the optional $ref1, $ref2, etc... are |
542 | extra references that you wish to let the Storable engine serialize. |
543 | |
544 | At deserialization time, you will be given back the same LIST, but all the |
545 | extra references will be pointing into the deserialized structure. |
546 | |
547 | The B<first time> the hook is hit in a serialization flow, you may have it |
548 | return an empty list. That will signal the Storable engine to further |
549 | discard that hook for this class and to therefore revert to the default |
550 | serialization of the underlying Perl data. The hook will again be normally |
551 | processed in the next serialization. |
552 | |
553 | Unless you know better, serializing hook should always say: |
554 | |
555 | sub STORABLE_freeze { |
556 | my ($self, $cloning) = @_; |
557 | return if $cloning; # Regular default serialization |
558 | .... |
559 | } |
560 | |
561 | in order to keep reasonable dclone() semantics. |
562 | |
563 | =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ... |
564 | |
565 | The deserializing hook called on the object during deserialization. |
566 | But wait. If we're deserializing, there's no object yet... right? |
567 | |
568 | Wrong: the Storable engine creates an empty one for you. If you know Eiffel, |
569 | you can view C<STORABLE_thaw> as an alternate creation routine. |
570 | |
571 | This means the hook can be inherited like any other method, and that |
572 | I<obj> is your blessed reference for this particular instance. |
573 | |
574 | The other arguments should look familiar if you know C<STORABLE_freeze>: |
575 | I<cloning> is true when we're part of a deep clone operation, I<serialized> |
576 | is the serialized string you returned to the engine in C<STORABLE_freeze>, |
577 | and there may be an optional list of references, in the same order you gave |
578 | them at serialization time, pointing to the deserialized objects (which |
579 | have been processed courtesy of the Storable engine). |
580 | |
212e9bde |
581 | When the Storable engine does not find any C<STORABLE_thaw> hook routine, |
582 | it tries to load the class by requiring the package dynamically (using |
583 | the blessed package name), and then re-attempts the lookup. If at that |
584 | time the hook cannot be located, the engine croaks. Note that this mechanism |
585 | will fail if you define several classes in the same file, but perlmod(1) |
586 | warned you. |
587 | |
7a6a85bf |
588 | It is up to you to use these information to populate I<obj> the way you want. |
589 | |
590 | Returned value: none. |
591 | |
592 | =back |
593 | |
594 | =head2 Predicates |
595 | |
596 | Predicates are not exportable. They must be called by explicitely prefixing |
597 | them with the Storable package name. |
598 | |
bbc7dcd2 |
599 | =over 4 |
7a6a85bf |
600 | |
601 | =item C<Storable::last_op_in_netorder> |
602 | |
603 | The C<Storable::last_op_in_netorder()> predicate will tell you whether |
604 | network order was used in the last store or retrieve operation. If you |
605 | don't know how to use this, just forget about it. |
606 | |
607 | =item C<Storable::is_storing> |
608 | |
609 | Returns true if within a store operation (via STORABLE_freeze hook). |
610 | |
611 | =item C<Storable::is_retrieving> |
612 | |
613 | Returns true if within a retrieve operation, (via STORABLE_thaw hook). |
614 | |
615 | =back |
616 | |
617 | =head2 Recursion |
618 | |
619 | With hooks comes the ability to recurse back to the Storable engine. Indeed, |
620 | hooks are regular Perl code, and Storable is convenient when it comes to |
621 | serialize and deserialize things, so why not use it to handle the |
622 | serialization string? |
623 | |
624 | There are a few things you need to know however: |
625 | |
bbc7dcd2 |
626 | =over 4 |
7a6a85bf |
627 | |
628 | =item * |
629 | |
630 | You can create endless loops if the things you serialize via freeze() |
631 | (for instance) point back to the object we're trying to serialize in the hook. |
632 | |
633 | =item * |
634 | |
635 | Shared references among objects will not stay shared: if we're serializing |
636 | the list of object [A, C] where both object A and C refer to the SAME object |
637 | B, and if there is a serializing hook in A that says freeze(B), then when |
638 | deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D, |
639 | a deep clone of B'. The topology was not preserved. |
640 | |
641 | =back |
642 | |
643 | That's why C<STORABLE_freeze> lets you provide a list of references |
644 | to serialize. The engine guarantees that those will be serialized in the |
645 | same context as the other objects, and therefore that shared objects will |
646 | stay shared. |
647 | |
648 | In the above [A, C] example, the C<STORABLE_freeze> hook could return: |
649 | |
650 | ("something", $self->{B}) |
651 | |
652 | and the B part would be serialized by the engine. In C<STORABLE_thaw>, you |
653 | would get back the reference to the B' object, deserialized for you. |
654 | |
655 | Therefore, recursion should normally be avoided, but is nonetheless supported. |
656 | |
657 | =head2 Deep Cloning |
658 | |
659 | There is a new Clone module available on CPAN which implements deep cloning |
660 | natively, i.e. without freezing to memory and thawing the result. It is |
661 | aimed to replace Storable's dclone() some day. However, it does not currently |
662 | support Storable hooks to redefine the way deep cloning is performed. |
663 | |
664 | =head1 EXAMPLES |
665 | |
666 | Here are some code samples showing a possible usage of Storable: |
667 | |
668 | use Storable qw(store retrieve freeze thaw dclone); |
669 | |
670 | %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1); |
671 | |
672 | store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n"; |
673 | |
674 | $colref = retrieve('/tmp/colors'); |
675 | die "Unable to retrieve from /tmp/colors!\n" unless defined $colref; |
676 | printf "Blue is still %lf\n", $colref->{'Blue'}; |
677 | |
678 | $colref2 = dclone(\%color); |
679 | |
680 | $str = freeze(\%color); |
681 | printf "Serialization of %%color is %d bytes long.\n", length($str); |
682 | $colref3 = thaw($str); |
683 | |
684 | which prints (on my machine): |
685 | |
686 | Blue is still 0.100000 |
687 | Serialization of %color is 102 bytes long. |
688 | |
689 | =head1 WARNING |
690 | |
691 | If you're using references as keys within your hash tables, you're bound |
692 | to disapointment when retrieving your data. Indeed, Perl stringifies |
693 | references used as hash table keys. If you later wish to access the |
694 | items via another reference stringification (i.e. using the same |
695 | reference that was used for the key originally to record the value into |
696 | the hash table), it will work because both references stringify to the |
697 | same string. |
698 | |
699 | It won't work across a C<store> and C<retrieve> operations however, because |
700 | the addresses in the retrieved objects, which are part of the stringified |
701 | references, will probably differ from the original addresses. The |
702 | topology of your structure is preserved, but not hidden semantics |
703 | like those. |
704 | |
705 | On platforms where it matters, be sure to call C<binmode()> on the |
706 | descriptors that you pass to Storable functions. |
707 | |
708 | Storing data canonically that contains large hashes can be |
709 | significantly slower than storing the same data normally, as |
710 | temprorary arrays to hold the keys for each hash have to be allocated, |
711 | populated, sorted and freed. Some tests have shown a halving of the |
712 | speed of storing -- the exact penalty will depend on the complexity of |
713 | your data. There is no slowdown on retrieval. |
714 | |
715 | =head1 BUGS |
716 | |
717 | You can't store GLOB, CODE, FORMLINE, etc... If you can define |
718 | semantics for those operations, feel free to enhance Storable so that |
719 | it can deal with them. |
720 | |
721 | The store functions will C<croak> if they run into such references |
722 | unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that |
723 | case, the fatal message is turned in a warning and some |
724 | meaningless string is stored instead. |
725 | |
726 | Setting C<$Storable::canonical> may not yield frozen strings that |
727 | compare equal due to possible stringification of numbers. When the |
728 | string version of a scalar exists, it is the form stored, therefore |
729 | if you happen to use your numbers as strings between two freezing |
730 | operations on the same data structures, you will get different |
731 | results. |
732 | |
dd19458b |
733 | When storing doubles in network order, their value is stored as text. |
734 | However, you should also not expect non-numeric floating-point values |
735 | such as infinity and "not a number" to pass successfully through a |
736 | nstore()/retrieve() pair. |
737 | |
738 | As Storable neither knows nor cares about character sets (although it |
739 | does know that characters may be more than eight bits wide), any difference |
740 | in the interpretation of character codes between a host and a target |
741 | system is your problem. In particular, if host and target use different |
742 | code points to represent the characters used in the text representation |
743 | of floating-point numbers, you will not be able be able to exchange |
744 | floating-point data, even with nstore(). |
745 | |
7a6a85bf |
746 | =head1 CREDITS |
747 | |
748 | Thank you to (in chronological order): |
749 | |
750 | Jarkko Hietaniemi <jhi@iki.fi> |
751 | Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de> |
752 | Benjamin A. Holzman <bah@ecnvantage.com> |
753 | Andrew Ford <A.Ford@ford-mason.co.uk> |
754 | Gisle Aas <gisle@aas.no> |
755 | Jeff Gresham <gresham_jeffrey@jpmorgan.com> |
756 | Murray Nesbitt <murray@activestate.com> |
757 | Marc Lehmann <pcg@opengroup.org> |
9e21b3d0 |
758 | Justin Banks <justinb@wamnet.com> |
759 | Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!) |
dd19458b |
760 | Salvador Ortiz Garcia <sog@msg.com.mx> |
761 | Dominic Dunlop <domo@computer.org> |
762 | Erik Haugan <erik@solbors.no> |
7a6a85bf |
763 | |
764 | for their bug reports, suggestions and contributions. |
765 | |
766 | Benjamin Holzman contributed the tied variable support, Andrew Ford |
767 | contributed the canonical order for hashes, and Gisle Aas fixed |
768 | a few misunderstandings of mine regarding the Perl internals, |
769 | and optimized the emission of "tags" in the output streams by |
770 | simply counting the objects instead of tagging them (leading to |
771 | a binary incompatibility for the Storable image starting at version |
772 | 0.6--older images are of course still properly understood). |
773 | Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading |
774 | and reference to tied items support. |
775 | |
776 | =head1 TRANSLATIONS |
777 | |
778 | There is a Japanese translation of this man page available at |
779 | http://member.nifty.ne.jp/hippo2000/perltips/storable.htm , |
780 | courtesy of Kawai, Takanori <kawai@nippon-rad.co.jp>. |
781 | |
782 | =head1 AUTHOR |
783 | |
784 | Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>> |
785 | |
786 | =head1 SEE ALSO |
787 | |
788 | Clone(3). |
789 | |
790 | =cut |
791 | |