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1 | ;# $Id: Storable.pm,v 1.0.1.13 2001/12/01 13:34:49 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 1.0.1.13 2001/12/01 13:34:49 ram |
10 | ;# patch14: avoid requiring Fcntl upfront, useful to embedded runtimes |
11 | ;# patch14: store_fd() will now correctly autoflush file if needed |
12 | ;# |
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13 | ;# Revision 1.0.1.12 2001/08/28 21:51:51 ram |
14 | ;# patch13: fixed truncation race with lock_retrieve() in lock_store() |
15 | ;# |
e993d95c |
16 | ;# Revision 1.0.1.11 2001/07/01 11:22:14 ram |
17 | ;# patch12: systematically use "=over 4" for POD linters |
18 | ;# patch12: updated version number |
19 | ;# |
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20 | ;# Revision 1.0.1.10 2001/03/15 00:20:25 ram |
21 | ;# patch11: updated version number |
22 | ;# |
23 | ;# Revision 1.0.1.9 2001/02/17 12:37:32 ram |
24 | ;# patch10: forgot to increase version number at previous patch |
25 | ;# |
b12202d0 |
26 | ;# Revision 1.0.1.8 2001/02/17 12:24:37 ram |
27 | ;# patch8: fixed incorrect error message |
28 | ;# |
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29 | ;# Revision 1.0.1.7 2001/01/03 09:39:02 ram |
30 | ;# patch7: added CAN_FLOCK to determine whether we can flock() or not |
31 | ;# |
90826881 |
32 | ;# Revision 1.0.1.6 2000/11/05 17:20:25 ram |
33 | ;# patch6: increased version number |
34 | ;# |
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35 | ;# Revision 1.0.1.5 2000/10/26 17:10:18 ram |
36 | ;# patch5: documented that store() and retrieve() can return undef |
37 | ;# patch5: added paragraph explaining the auto require for thaw hooks |
38 | ;# |
39 | ;# Revision 1.0.1.4 2000/10/23 18:02:57 ram |
40 | ;# patch4: protected calls to flock() for dos platform |
41 | ;# patch4: added logcarp emulation if they don't have Log::Agent |
42 | ;# |
8be2b38b |
43 | ;# Revision 1.0.1.3 2000/09/29 19:49:01 ram |
44 | ;# patch3: updated version number |
45 | ;# |
46 | ;# Revision 1.0.1.2 2000/09/28 21:42:51 ram |
47 | ;# patch2: added lock_store lock_nstore lock_retrieve |
48 | ;# |
49 | ;# Revision 1.0.1.1 2000/09/17 16:46:21 ram |
50 | ;# patch1: documented that doubles are stringified by nstore() |
51 | ;# patch1: added Salvador Ortiz Garcia in CREDITS section |
52 | ;# |
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53 | ;# Revision 1.0 2000/09/01 19:40:41 ram |
54 | ;# Baseline for first official release. |
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55 | ;# |
56 | |
57 | require DynaLoader; |
58 | require Exporter; |
59 | package Storable; @ISA = qw(Exporter DynaLoader); |
60 | |
61 | @EXPORT = qw(store retrieve); |
62 | @EXPORT_OK = qw( |
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63 | nstore store_fd nstore_fd fd_retrieve |
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64 | freeze nfreeze thaw |
65 | dclone |
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66 | retrieve_fd |
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67 | lock_store lock_nstore lock_retrieve |
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68 | ); |
69 | |
70 | use AutoLoader; |
71 | use vars qw($forgive_me $VERSION); |
72 | |
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73 | $VERSION = '1.014'; |
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74 | *AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr... |
75 | |
76 | # |
77 | # Use of Log::Agent is optional |
78 | # |
79 | |
80 | eval "use Log::Agent"; |
81 | |
82 | unless (defined @Log::Agent::EXPORT) { |
83 | eval q{ |
84 | sub logcroak { |
85 | require Carp; |
86 | Carp::croak(@_); |
87 | } |
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88 | sub logcarp { |
89 | require Carp; |
90 | Carp::carp(@_); |
91 | } |
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92 | }; |
93 | } |
94 | |
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95 | # |
96 | # They might miss :flock in Fcntl |
97 | # |
98 | |
99 | BEGIN { |
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100 | if (eval { require Fcntl; 1 } && exists $Fcntl::EXPORT_TAGS{'flock'}) { |
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101 | Fcntl->import(':flock'); |
102 | } else { |
103 | eval q{ |
104 | sub LOCK_SH () {1} |
105 | sub LOCK_EX () {2} |
106 | }; |
107 | } |
108 | } |
109 | |
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110 | sub logcroak; |
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111 | sub logcarp; |
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112 | |
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113 | sub retrieve_fd { &fd_retrieve } # Backward compatibility |
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114 | |
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115 | # |
116 | # Determine whether locking is possible, but only when needed. |
117 | # |
118 | |
119 | my $CAN_FLOCK; |
120 | |
121 | sub CAN_FLOCK { |
122 | return $CAN_FLOCK if defined $CAN_FLOCK; |
123 | require Config; import Config; |
124 | return $CAN_FLOCK = |
125 | $Config{'d_flock'} || |
126 | $Config{'d_fcntl_can_lock'} || |
127 | $Config{'d_lockf'}; |
128 | } |
129 | |
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130 | bootstrap Storable; |
131 | 1; |
132 | __END__ |
133 | |
134 | # |
135 | # store |
136 | # |
137 | # Store target object hierarchy, identified by a reference to its root. |
138 | # The stored object tree may later be retrieved to memory via retrieve. |
139 | # Returns undef if an I/O error occurred, in which case the file is |
140 | # removed. |
141 | # |
142 | sub store { |
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143 | return _store(\&pstore, @_, 0); |
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144 | } |
145 | |
146 | # |
147 | # nstore |
148 | # |
149 | # Same as store, but in network order. |
150 | # |
151 | sub nstore { |
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152 | return _store(\&net_pstore, @_, 0); |
153 | } |
154 | |
155 | # |
156 | # lock_store |
157 | # |
158 | # Same as store, but flock the file first (advisory locking). |
159 | # |
160 | sub lock_store { |
161 | return _store(\&pstore, @_, 1); |
162 | } |
163 | |
164 | # |
165 | # lock_nstore |
166 | # |
167 | # Same as nstore, but flock the file first (advisory locking). |
168 | # |
169 | sub lock_nstore { |
170 | return _store(\&net_pstore, @_, 1); |
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171 | } |
172 | |
173 | # Internal store to file routine |
174 | sub _store { |
175 | my $xsptr = shift; |
176 | my $self = shift; |
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177 | my ($file, $use_locking) = @_; |
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178 | logcroak "not a reference" unless ref($self); |
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179 | logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist |
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180 | local *FILE; |
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181 | if ($use_locking) { |
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182 | open(FILE, ">>$file") || logcroak "can't write into $file: $!"; |
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183 | unless (&CAN_FLOCK) { |
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184 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
185 | return undef; |
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186 | } |
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187 | flock(FILE, LOCK_EX) || |
188 | logcroak "can't get exclusive lock on $file: $!"; |
189 | truncate FILE, 0; |
190 | # Unlocking will happen when FILE is closed |
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191 | } else { |
192 | open(FILE, ">$file") || logcroak "can't create $file: $!"; |
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193 | } |
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194 | binmode FILE; # Archaic systems... |
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195 | my $da = $@; # Don't mess if called from exception handler |
196 | my $ret; |
197 | # Call C routine nstore or pstore, depending on network order |
198 | eval { $ret = &$xsptr(*FILE, $self) }; |
199 | close(FILE) or $ret = undef; |
200 | unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret; |
201 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
202 | $@ = $da; |
203 | return $ret ? $ret : undef; |
204 | } |
205 | |
206 | # |
207 | # store_fd |
208 | # |
209 | # Same as store, but perform on an already opened file descriptor instead. |
210 | # Returns undef if an I/O error occurred. |
211 | # |
212 | sub store_fd { |
213 | return _store_fd(\&pstore, @_); |
214 | } |
215 | |
216 | # |
217 | # nstore_fd |
218 | # |
219 | # Same as store_fd, but in network order. |
220 | # |
221 | sub nstore_fd { |
222 | my ($self, $file) = @_; |
223 | return _store_fd(\&net_pstore, @_); |
224 | } |
225 | |
226 | # Internal store routine on opened file descriptor |
227 | sub _store_fd { |
228 | my $xsptr = shift; |
229 | my $self = shift; |
230 | my ($file) = @_; |
231 | logcroak "not a reference" unless ref($self); |
232 | logcroak "too many arguments" unless @_ == 1; # No @foo in arglist |
233 | my $fd = fileno($file); |
234 | logcroak "not a valid file descriptor" unless defined $fd; |
235 | my $da = $@; # Don't mess if called from exception handler |
236 | my $ret; |
237 | # Call C routine nstore or pstore, depending on network order |
238 | eval { $ret = &$xsptr($file, $self) }; |
239 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
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240 | local $\; print $file ''; # Autoflush the file if wanted |
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241 | $@ = $da; |
242 | return $ret ? $ret : undef; |
243 | } |
244 | |
245 | # |
246 | # freeze |
247 | # |
248 | # Store oject and its hierarchy in memory and return a scalar |
249 | # containing the result. |
250 | # |
251 | sub freeze { |
252 | _freeze(\&mstore, @_); |
253 | } |
254 | |
255 | # |
256 | # nfreeze |
257 | # |
258 | # Same as freeze but in network order. |
259 | # |
260 | sub nfreeze { |
261 | _freeze(\&net_mstore, @_); |
262 | } |
263 | |
264 | # Internal freeze routine |
265 | sub _freeze { |
266 | my $xsptr = shift; |
267 | my $self = shift; |
268 | logcroak "not a reference" unless ref($self); |
269 | logcroak "too many arguments" unless @_ == 0; # No @foo in arglist |
270 | my $da = $@; # Don't mess if called from exception handler |
271 | my $ret; |
272 | # Call C routine mstore or net_mstore, depending on network order |
273 | eval { $ret = &$xsptr($self) }; |
274 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
275 | $@ = $da; |
276 | return $ret ? $ret : undef; |
277 | } |
278 | |
279 | # |
280 | # retrieve |
281 | # |
282 | # Retrieve object hierarchy from disk, returning a reference to the root |
283 | # object of that tree. |
284 | # |
285 | sub retrieve { |
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286 | _retrieve($_[0], 0); |
287 | } |
288 | |
289 | # |
290 | # lock_retrieve |
291 | # |
292 | # Same as retrieve, but with advisory locking. |
293 | # |
294 | sub lock_retrieve { |
295 | _retrieve($_[0], 1); |
296 | } |
297 | |
298 | # Internal retrieve routine |
299 | sub _retrieve { |
300 | my ($file, $use_locking) = @_; |
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301 | local *FILE; |
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302 | open(FILE, $file) || logcroak "can't open $file: $!"; |
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303 | binmode FILE; # Archaic systems... |
304 | my $self; |
305 | my $da = $@; # Could be from exception handler |
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306 | if ($use_locking) { |
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307 | unless (&CAN_FLOCK) { |
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308 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
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309 | return undef; |
310 | } |
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311 | flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!"; |
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312 | # Unlocking will happen when FILE is closed |
313 | } |
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314 | eval { $self = pretrieve(*FILE) }; # Call C routine |
315 | close(FILE); |
316 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
317 | $@ = $da; |
318 | return $self; |
319 | } |
320 | |
321 | # |
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322 | # fd_retrieve |
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323 | # |
324 | # Same as retrieve, but perform from an already opened file descriptor instead. |
325 | # |
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326 | sub fd_retrieve { |
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327 | my ($file) = @_; |
328 | my $fd = fileno($file); |
329 | logcroak "not a valid file descriptor" unless defined $fd; |
330 | my $self; |
331 | my $da = $@; # Could be from exception handler |
332 | eval { $self = pretrieve($file) }; # Call C routine |
333 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
334 | $@ = $da; |
335 | return $self; |
336 | } |
337 | |
338 | # |
339 | # thaw |
340 | # |
341 | # Recreate objects in memory from an existing frozen image created |
342 | # by freeze. If the frozen image passed is undef, return undef. |
343 | # |
344 | sub thaw { |
345 | my ($frozen) = @_; |
346 | return undef unless defined $frozen; |
347 | my $self; |
348 | my $da = $@; # Could be from exception handler |
349 | eval { $self = mretrieve($frozen) }; # Call C routine |
350 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
351 | $@ = $da; |
352 | return $self; |
353 | } |
354 | |
355 | =head1 NAME |
356 | |
357 | Storable - persistency for perl data structures |
358 | |
359 | =head1 SYNOPSIS |
360 | |
361 | use Storable; |
362 | store \%table, 'file'; |
363 | $hashref = retrieve('file'); |
364 | |
365 | use Storable qw(nstore store_fd nstore_fd freeze thaw dclone); |
366 | |
367 | # Network order |
368 | nstore \%table, 'file'; |
369 | $hashref = retrieve('file'); # There is NO nretrieve() |
370 | |
371 | # Storing to and retrieving from an already opened file |
372 | store_fd \@array, \*STDOUT; |
373 | nstore_fd \%table, \*STDOUT; |
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374 | $aryref = fd_retrieve(\*SOCKET); |
375 | $hashref = fd_retrieve(\*SOCKET); |
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376 | |
377 | # Serializing to memory |
378 | $serialized = freeze \%table; |
379 | %table_clone = %{ thaw($serialized) }; |
380 | |
381 | # Deep (recursive) cloning |
382 | $cloneref = dclone($ref); |
383 | |
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384 | # Advisory locking |
385 | use Storable qw(lock_store lock_nstore lock_retrieve) |
386 | lock_store \%table, 'file'; |
387 | lock_nstore \%table, 'file'; |
388 | $hashref = lock_retrieve('file'); |
389 | |
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390 | =head1 DESCRIPTION |
391 | |
392 | The Storable package brings persistency to your perl data structures |
393 | containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be |
394 | convenientely stored to disk and retrieved at a later time. |
395 | |
396 | It can be used in the regular procedural way by calling C<store> with |
397 | a reference to the object to be stored, along with the file name where |
398 | the image should be written. |
399 | The routine returns C<undef> for I/O problems or other internal error, |
400 | a true value otherwise. Serious errors are propagated as a C<die> exception. |
401 | |
402 | To retrieve data stored to disk, use C<retrieve> with a file name, |
403 | and the objects stored into that file are recreated into memory for you, |
404 | a I<reference> to the root object being returned. In case an I/O error |
405 | occurs while reading, C<undef> is returned instead. Other serious |
406 | errors are propagated via C<die>. |
407 | |
408 | Since storage is performed recursively, you might want to stuff references |
409 | to objects that share a lot of common data into a single array or hash |
410 | table, and then store that object. That way, when you retrieve back the |
411 | whole thing, the objects will continue to share what they originally shared. |
412 | |
413 | At the cost of a slight header overhead, you may store to an already |
414 | opened file descriptor using the C<store_fd> routine, and retrieve |
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415 | from a file via C<fd_retrieve>. Those names aren't imported by default, |
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416 | so you will have to do that explicitely if you need those routines. |
417 | The file descriptor you supply must be already opened, for read |
418 | if you're going to retrieve and for write if you wish to store. |
419 | |
420 | store_fd(\%table, *STDOUT) || die "can't store to stdout\n"; |
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421 | $hashref = fd_retrieve(*STDIN); |
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422 | |
423 | You can also store data in network order to allow easy sharing across |
424 | multiple platforms, or when storing on a socket known to be remotely |
425 | connected. The routines to call have an initial C<n> prefix for I<network>, |
426 | as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be |
427 | correctly restored so you don't have to know whether you're restoring |
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428 | from native or network ordered data. Double values are stored stringified |
429 | to ensure portability as well, at the slight risk of loosing some precision |
430 | in the last decimals. |
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431 | |
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432 | When using C<fd_retrieve>, objects are retrieved in sequence, one |
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433 | object (i.e. one recursive tree) per associated C<store_fd>. |
434 | |
435 | If you're more from the object-oriented camp, you can inherit from |
436 | Storable and directly store your objects by invoking C<store> as |
437 | a method. The fact that the root of the to-be-stored tree is a |
438 | blessed reference (i.e. an object) is special-cased so that the |
439 | retrieve does not provide a reference to that object but rather the |
440 | blessed object reference itself. (Otherwise, you'd get a reference |
441 | to that blessed object). |
442 | |
443 | =head1 MEMORY STORE |
444 | |
445 | The Storable engine can also store data into a Perl scalar instead, to |
446 | later retrieve them. This is mainly used to freeze a complex structure in |
447 | some safe compact memory place (where it can possibly be sent to another |
448 | process via some IPC, since freezing the structure also serializes it in |
449 | effect). Later on, and maybe somewhere else, you can thaw the Perl scalar |
450 | out and recreate the original complex structure in memory. |
451 | |
452 | Surprisingly, the routines to be called are named C<freeze> and C<thaw>. |
453 | If you wish to send out the frozen scalar to another machine, use |
454 | C<nfreeze> instead to get a portable image. |
455 | |
456 | Note that freezing an object structure and immediately thawing it |
457 | actually achieves a deep cloning of that structure: |
458 | |
459 | dclone(.) = thaw(freeze(.)) |
460 | |
461 | Storable provides you with a C<dclone> interface which does not create |
462 | that intermediary scalar but instead freezes the structure in some |
463 | internal memory space and then immediatly thaws it out. |
464 | |
dd19458b |
465 | =head1 ADVISORY LOCKING |
466 | |
467 | The C<lock_store> and C<lock_nstore> routine are equivalent to C<store> |
468 | and C<nstore>, only they get an exclusive lock on the file before |
469 | writing. Likewise, C<lock_retrieve> performs as C<retrieve>, but also |
470 | gets a shared lock on the file before reading. |
471 | |
472 | Like with any advisory locking scheme, the protection only works if |
473 | you systematically use C<lock_store> and C<lock_retrieve>. If one |
474 | side of your application uses C<store> whilst the other uses C<lock_retrieve>, |
475 | you will get no protection at all. |
476 | |
477 | The internal advisory locking is implemented using Perl's flock() routine. |
478 | If your system does not support any form of flock(), or if you share |
479 | your files across NFS, you might wish to use other forms of locking by |
480 | using modules like LockFile::Simple which lock a file using a filesystem |
481 | entry, instead of locking the file descriptor. |
482 | |
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483 | =head1 SPEED |
484 | |
485 | The heart of Storable is written in C for decent speed. Extra low-level |
486 | optimization have been made when manipulating perl internals, to |
487 | sacrifice encapsulation for the benefit of a greater speed. |
488 | |
489 | =head1 CANONICAL REPRESENTATION |
490 | |
491 | Normally Storable stores elements of hashes in the order they are |
492 | stored internally by Perl, i.e. pseudo-randomly. If you set |
493 | C<$Storable::canonical> to some C<TRUE> value, Storable will store |
494 | hashes with the elements sorted by their key. This allows you to |
495 | compare data structures by comparing their frozen representations (or |
496 | even the compressed frozen representations), which can be useful for |
497 | creating lookup tables for complicated queries. |
498 | |
499 | Canonical order does not imply network order, those are two orthogonal |
500 | settings. |
501 | |
502 | =head1 ERROR REPORTING |
503 | |
504 | Storable uses the "exception" paradigm, in that it does not try to workaround |
505 | failures: if something bad happens, an exception is generated from the |
506 | caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap |
507 | those exceptions. |
508 | |
509 | When Storable croaks, it tries to report the error via the C<logcroak()> |
510 | routine from the C<Log::Agent> package, if it is available. |
511 | |
212e9bde |
512 | Normal errors are reported by having store() or retrieve() return C<undef>. |
513 | Such errors are usually I/O errors (or truncated stream errors at retrieval). |
514 | |
7a6a85bf |
515 | =head1 WIZARDS ONLY |
516 | |
517 | =head2 Hooks |
518 | |
519 | Any class may define hooks that will be called during the serialization |
520 | and deserialization process on objects that are instances of that class. |
521 | Those hooks can redefine the way serialization is performed (and therefore, |
522 | how the symetrical deserialization should be conducted). |
523 | |
524 | Since we said earlier: |
525 | |
526 | dclone(.) = thaw(freeze(.)) |
527 | |
528 | everything we say about hooks should also hold for deep cloning. However, |
529 | hooks get to know whether the operation is a mere serialization, or a cloning. |
530 | |
531 | Therefore, when serializing hooks are involved, |
532 | |
533 | dclone(.) <> thaw(freeze(.)) |
534 | |
535 | Well, you could keep them in sync, but there's no guarantee it will always |
536 | hold on classes somebody else wrote. Besides, there is little to gain in |
537 | doing so: a serializing hook could only keep one attribute of an object, |
538 | which is probably not what should happen during a deep cloning of that |
539 | same object. |
540 | |
541 | Here is the hooking interface: |
542 | |
bbc7dcd2 |
543 | =over 4 |
7a6a85bf |
544 | |
545 | =item C<STORABLE_freeze> I<obj>, I<cloning> |
546 | |
547 | The serializing hook, called on the object during serialization. It can be |
548 | inherited, or defined in the class itself, like any other method. |
549 | |
550 | Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating |
551 | whether we're in a dclone() or a regular serialization via store() or freeze(). |
552 | |
553 | Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized |
554 | is the serialized form to be used, and the optional $ref1, $ref2, etc... are |
555 | extra references that you wish to let the Storable engine serialize. |
556 | |
557 | At deserialization time, you will be given back the same LIST, but all the |
558 | extra references will be pointing into the deserialized structure. |
559 | |
560 | The B<first time> the hook is hit in a serialization flow, you may have it |
561 | return an empty list. That will signal the Storable engine to further |
562 | discard that hook for this class and to therefore revert to the default |
563 | serialization of the underlying Perl data. The hook will again be normally |
564 | processed in the next serialization. |
565 | |
566 | Unless you know better, serializing hook should always say: |
567 | |
568 | sub STORABLE_freeze { |
569 | my ($self, $cloning) = @_; |
570 | return if $cloning; # Regular default serialization |
571 | .... |
572 | } |
573 | |
574 | in order to keep reasonable dclone() semantics. |
575 | |
576 | =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ... |
577 | |
578 | The deserializing hook called on the object during deserialization. |
579 | But wait. If we're deserializing, there's no object yet... right? |
580 | |
581 | Wrong: the Storable engine creates an empty one for you. If you know Eiffel, |
582 | you can view C<STORABLE_thaw> as an alternate creation routine. |
583 | |
584 | This means the hook can be inherited like any other method, and that |
585 | I<obj> is your blessed reference for this particular instance. |
586 | |
587 | The other arguments should look familiar if you know C<STORABLE_freeze>: |
588 | I<cloning> is true when we're part of a deep clone operation, I<serialized> |
589 | is the serialized string you returned to the engine in C<STORABLE_freeze>, |
590 | and there may be an optional list of references, in the same order you gave |
591 | them at serialization time, pointing to the deserialized objects (which |
592 | have been processed courtesy of the Storable engine). |
593 | |
212e9bde |
594 | When the Storable engine does not find any C<STORABLE_thaw> hook routine, |
595 | it tries to load the class by requiring the package dynamically (using |
596 | the blessed package name), and then re-attempts the lookup. If at that |
597 | time the hook cannot be located, the engine croaks. Note that this mechanism |
598 | will fail if you define several classes in the same file, but perlmod(1) |
599 | warned you. |
600 | |
7a6a85bf |
601 | It is up to you to use these information to populate I<obj> the way you want. |
602 | |
603 | Returned value: none. |
604 | |
605 | =back |
606 | |
607 | =head2 Predicates |
608 | |
609 | Predicates are not exportable. They must be called by explicitely prefixing |
610 | them with the Storable package name. |
611 | |
bbc7dcd2 |
612 | =over 4 |
7a6a85bf |
613 | |
614 | =item C<Storable::last_op_in_netorder> |
615 | |
616 | The C<Storable::last_op_in_netorder()> predicate will tell you whether |
617 | network order was used in the last store or retrieve operation. If you |
618 | don't know how to use this, just forget about it. |
619 | |
620 | =item C<Storable::is_storing> |
621 | |
622 | Returns true if within a store operation (via STORABLE_freeze hook). |
623 | |
624 | =item C<Storable::is_retrieving> |
625 | |
626 | Returns true if within a retrieve operation, (via STORABLE_thaw hook). |
627 | |
628 | =back |
629 | |
630 | =head2 Recursion |
631 | |
632 | With hooks comes the ability to recurse back to the Storable engine. Indeed, |
633 | hooks are regular Perl code, and Storable is convenient when it comes to |
634 | serialize and deserialize things, so why not use it to handle the |
635 | serialization string? |
636 | |
637 | There are a few things you need to know however: |
638 | |
bbc7dcd2 |
639 | =over 4 |
7a6a85bf |
640 | |
641 | =item * |
642 | |
643 | You can create endless loops if the things you serialize via freeze() |
644 | (for instance) point back to the object we're trying to serialize in the hook. |
645 | |
646 | =item * |
647 | |
648 | Shared references among objects will not stay shared: if we're serializing |
649 | the list of object [A, C] where both object A and C refer to the SAME object |
650 | B, and if there is a serializing hook in A that says freeze(B), then when |
651 | deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D, |
652 | a deep clone of B'. The topology was not preserved. |
653 | |
654 | =back |
655 | |
656 | That's why C<STORABLE_freeze> lets you provide a list of references |
657 | to serialize. The engine guarantees that those will be serialized in the |
658 | same context as the other objects, and therefore that shared objects will |
659 | stay shared. |
660 | |
661 | In the above [A, C] example, the C<STORABLE_freeze> hook could return: |
662 | |
663 | ("something", $self->{B}) |
664 | |
665 | and the B part would be serialized by the engine. In C<STORABLE_thaw>, you |
666 | would get back the reference to the B' object, deserialized for you. |
667 | |
668 | Therefore, recursion should normally be avoided, but is nonetheless supported. |
669 | |
670 | =head2 Deep Cloning |
671 | |
672 | There is a new Clone module available on CPAN which implements deep cloning |
673 | natively, i.e. without freezing to memory and thawing the result. It is |
674 | aimed to replace Storable's dclone() some day. However, it does not currently |
675 | support Storable hooks to redefine the way deep cloning is performed. |
676 | |
677 | =head1 EXAMPLES |
678 | |
679 | Here are some code samples showing a possible usage of Storable: |
680 | |
681 | use Storable qw(store retrieve freeze thaw dclone); |
682 | |
683 | %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1); |
684 | |
685 | store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n"; |
686 | |
687 | $colref = retrieve('/tmp/colors'); |
688 | die "Unable to retrieve from /tmp/colors!\n" unless defined $colref; |
689 | printf "Blue is still %lf\n", $colref->{'Blue'}; |
690 | |
691 | $colref2 = dclone(\%color); |
692 | |
693 | $str = freeze(\%color); |
694 | printf "Serialization of %%color is %d bytes long.\n", length($str); |
695 | $colref3 = thaw($str); |
696 | |
697 | which prints (on my machine): |
698 | |
699 | Blue is still 0.100000 |
700 | Serialization of %color is 102 bytes long. |
701 | |
702 | =head1 WARNING |
703 | |
704 | If you're using references as keys within your hash tables, you're bound |
705 | to disapointment when retrieving your data. Indeed, Perl stringifies |
706 | references used as hash table keys. If you later wish to access the |
707 | items via another reference stringification (i.e. using the same |
708 | reference that was used for the key originally to record the value into |
709 | the hash table), it will work because both references stringify to the |
710 | same string. |
711 | |
712 | It won't work across a C<store> and C<retrieve> operations however, because |
713 | the addresses in the retrieved objects, which are part of the stringified |
714 | references, will probably differ from the original addresses. The |
715 | topology of your structure is preserved, but not hidden semantics |
716 | like those. |
717 | |
718 | On platforms where it matters, be sure to call C<binmode()> on the |
719 | descriptors that you pass to Storable functions. |
720 | |
721 | Storing data canonically that contains large hashes can be |
722 | significantly slower than storing the same data normally, as |
723 | temprorary arrays to hold the keys for each hash have to be allocated, |
724 | populated, sorted and freed. Some tests have shown a halving of the |
725 | speed of storing -- the exact penalty will depend on the complexity of |
726 | your data. There is no slowdown on retrieval. |
727 | |
728 | =head1 BUGS |
729 | |
730 | You can't store GLOB, CODE, FORMLINE, etc... If you can define |
731 | semantics for those operations, feel free to enhance Storable so that |
732 | it can deal with them. |
733 | |
734 | The store functions will C<croak> if they run into such references |
735 | unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that |
736 | case, the fatal message is turned in a warning and some |
737 | meaningless string is stored instead. |
738 | |
739 | Setting C<$Storable::canonical> may not yield frozen strings that |
740 | compare equal due to possible stringification of numbers. When the |
741 | string version of a scalar exists, it is the form stored, therefore |
742 | if you happen to use your numbers as strings between two freezing |
743 | operations on the same data structures, you will get different |
744 | results. |
745 | |
dd19458b |
746 | When storing doubles in network order, their value is stored as text. |
747 | However, you should also not expect non-numeric floating-point values |
748 | such as infinity and "not a number" to pass successfully through a |
749 | nstore()/retrieve() pair. |
750 | |
751 | As Storable neither knows nor cares about character sets (although it |
752 | does know that characters may be more than eight bits wide), any difference |
753 | in the interpretation of character codes between a host and a target |
754 | system is your problem. In particular, if host and target use different |
755 | code points to represent the characters used in the text representation |
756 | of floating-point numbers, you will not be able be able to exchange |
757 | floating-point data, even with nstore(). |
758 | |
7a6a85bf |
759 | =head1 CREDITS |
760 | |
761 | Thank you to (in chronological order): |
762 | |
763 | Jarkko Hietaniemi <jhi@iki.fi> |
764 | Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de> |
765 | Benjamin A. Holzman <bah@ecnvantage.com> |
766 | Andrew Ford <A.Ford@ford-mason.co.uk> |
767 | Gisle Aas <gisle@aas.no> |
768 | Jeff Gresham <gresham_jeffrey@jpmorgan.com> |
769 | Murray Nesbitt <murray@activestate.com> |
770 | Marc Lehmann <pcg@opengroup.org> |
9e21b3d0 |
771 | Justin Banks <justinb@wamnet.com> |
772 | Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!) |
dd19458b |
773 | Salvador Ortiz Garcia <sog@msg.com.mx> |
774 | Dominic Dunlop <domo@computer.org> |
775 | Erik Haugan <erik@solbors.no> |
7a6a85bf |
776 | |
777 | for their bug reports, suggestions and contributions. |
778 | |
779 | Benjamin Holzman contributed the tied variable support, Andrew Ford |
780 | contributed the canonical order for hashes, and Gisle Aas fixed |
781 | a few misunderstandings of mine regarding the Perl internals, |
782 | and optimized the emission of "tags" in the output streams by |
783 | simply counting the objects instead of tagging them (leading to |
784 | a binary incompatibility for the Storable image starting at version |
785 | 0.6--older images are of course still properly understood). |
786 | Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading |
787 | and reference to tied items support. |
788 | |
789 | =head1 TRANSLATIONS |
790 | |
791 | There is a Japanese translation of this man page available at |
792 | http://member.nifty.ne.jp/hippo2000/perltips/storable.htm , |
793 | courtesy of Kawai, Takanori <kawai@nippon-rad.co.jp>. |
794 | |
795 | =head1 AUTHOR |
796 | |
797 | Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>> |
798 | |
799 | =head1 SEE ALSO |
800 | |
801 | Clone(3). |
802 | |
803 | =cut |
804 | |