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1 | ;# $Id: Storable.pm,v 1.0.1.11 2001/07/01 11:22:14 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 1.0.1.11 2001/07/01 11:22:14 ram |
10 | ;# patch12: systematically use "=over 4" for POD linters |
11 | ;# patch12: updated version number |
12 | ;# |
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13 | ;# Revision 1.0.1.10 2001/03/15 00:20:25 ram |
14 | ;# patch11: updated version number |
15 | ;# |
16 | ;# Revision 1.0.1.9 2001/02/17 12:37:32 ram |
17 | ;# patch10: forgot to increase version number at previous patch |
18 | ;# |
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19 | ;# Revision 1.0.1.8 2001/02/17 12:24:37 ram |
20 | ;# patch8: fixed incorrect error message |
21 | ;# |
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22 | ;# Revision 1.0.1.7 2001/01/03 09:39:02 ram |
23 | ;# patch7: added CAN_FLOCK to determine whether we can flock() or not |
24 | ;# |
90826881 |
25 | ;# Revision 1.0.1.6 2000/11/05 17:20:25 ram |
26 | ;# patch6: increased version number |
27 | ;# |
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28 | ;# Revision 1.0.1.5 2000/10/26 17:10:18 ram |
29 | ;# patch5: documented that store() and retrieve() can return undef |
30 | ;# patch5: added paragraph explaining the auto require for thaw hooks |
31 | ;# |
32 | ;# Revision 1.0.1.4 2000/10/23 18:02:57 ram |
33 | ;# patch4: protected calls to flock() for dos platform |
34 | ;# patch4: added logcarp emulation if they don't have Log::Agent |
35 | ;# |
8be2b38b |
36 | ;# Revision 1.0.1.3 2000/09/29 19:49:01 ram |
37 | ;# patch3: updated version number |
38 | ;# |
39 | ;# Revision 1.0.1.2 2000/09/28 21:42:51 ram |
40 | ;# patch2: added lock_store lock_nstore lock_retrieve |
41 | ;# |
42 | ;# Revision 1.0.1.1 2000/09/17 16:46:21 ram |
43 | ;# patch1: documented that doubles are stringified by nstore() |
44 | ;# patch1: added Salvador Ortiz Garcia in CREDITS section |
45 | ;# |
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46 | ;# Revision 1.0 2000/09/01 19:40:41 ram |
47 | ;# Baseline for first official release. |
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48 | ;# |
49 | |
50 | require DynaLoader; |
51 | require Exporter; |
52 | package Storable; @ISA = qw(Exporter DynaLoader); |
53 | |
54 | @EXPORT = qw(store retrieve); |
55 | @EXPORT_OK = qw( |
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56 | nstore store_fd nstore_fd fd_retrieve |
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57 | freeze nfreeze thaw |
58 | dclone |
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59 | retrieve_fd |
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60 | lock_store lock_nstore lock_retrieve |
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61 | ); |
62 | |
63 | use AutoLoader; |
64 | use vars qw($forgive_me $VERSION); |
65 | |
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66 | $VERSION = '1.012'; |
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67 | *AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr... |
68 | |
69 | # |
70 | # Use of Log::Agent is optional |
71 | # |
72 | |
73 | eval "use Log::Agent"; |
74 | |
75 | unless (defined @Log::Agent::EXPORT) { |
76 | eval q{ |
77 | sub logcroak { |
78 | require Carp; |
79 | Carp::croak(@_); |
80 | } |
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81 | sub logcarp { |
82 | require Carp; |
83 | Carp::carp(@_); |
84 | } |
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85 | }; |
86 | } |
87 | |
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88 | # |
89 | # They might miss :flock in Fcntl |
90 | # |
91 | |
92 | BEGIN { |
93 | require Fcntl; |
94 | if (exists $Fcntl::EXPORT_TAGS{'flock'}) { |
95 | Fcntl->import(':flock'); |
96 | } else { |
97 | eval q{ |
98 | sub LOCK_SH () {1} |
99 | sub LOCK_EX () {2} |
100 | }; |
101 | } |
102 | } |
103 | |
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104 | sub logcroak; |
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105 | sub logcarp; |
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106 | |
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107 | sub retrieve_fd { &fd_retrieve } # Backward compatibility |
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108 | |
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109 | # |
110 | # Determine whether locking is possible, but only when needed. |
111 | # |
112 | |
113 | my $CAN_FLOCK; |
114 | |
115 | sub CAN_FLOCK { |
116 | return $CAN_FLOCK if defined $CAN_FLOCK; |
117 | require Config; import Config; |
118 | return $CAN_FLOCK = |
119 | $Config{'d_flock'} || |
120 | $Config{'d_fcntl_can_lock'} || |
121 | $Config{'d_lockf'}; |
122 | } |
123 | |
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124 | bootstrap Storable; |
125 | 1; |
126 | __END__ |
127 | |
128 | # |
129 | # store |
130 | # |
131 | # Store target object hierarchy, identified by a reference to its root. |
132 | # The stored object tree may later be retrieved to memory via retrieve. |
133 | # Returns undef if an I/O error occurred, in which case the file is |
134 | # removed. |
135 | # |
136 | sub store { |
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137 | return _store(\&pstore, @_, 0); |
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138 | } |
139 | |
140 | # |
141 | # nstore |
142 | # |
143 | # Same as store, but in network order. |
144 | # |
145 | sub nstore { |
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146 | return _store(\&net_pstore, @_, 0); |
147 | } |
148 | |
149 | # |
150 | # lock_store |
151 | # |
152 | # Same as store, but flock the file first (advisory locking). |
153 | # |
154 | sub lock_store { |
155 | return _store(\&pstore, @_, 1); |
156 | } |
157 | |
158 | # |
159 | # lock_nstore |
160 | # |
161 | # Same as nstore, but flock the file first (advisory locking). |
162 | # |
163 | sub lock_nstore { |
164 | return _store(\&net_pstore, @_, 1); |
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165 | } |
166 | |
167 | # Internal store to file routine |
168 | sub _store { |
169 | my $xsptr = shift; |
170 | my $self = shift; |
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171 | my ($file, $use_locking) = @_; |
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172 | logcroak "not a reference" unless ref($self); |
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173 | logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist |
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174 | local *FILE; |
175 | open(FILE, ">$file") || logcroak "can't create $file: $!"; |
176 | binmode FILE; # Archaic systems... |
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177 | if ($use_locking) { |
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178 | unless (&CAN_FLOCK) { |
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179 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
180 | return undef; |
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181 | } |
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182 | flock(FILE, LOCK_EX) || |
183 | logcroak "can't get exclusive lock on $file: $!"; |
184 | truncate FILE, 0; |
185 | # Unlocking will happen when FILE is closed |
186 | } |
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187 | my $da = $@; # Don't mess if called from exception handler |
188 | my $ret; |
189 | # Call C routine nstore or pstore, depending on network order |
190 | eval { $ret = &$xsptr(*FILE, $self) }; |
191 | close(FILE) or $ret = undef; |
192 | unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret; |
193 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
194 | $@ = $da; |
195 | return $ret ? $ret : undef; |
196 | } |
197 | |
198 | # |
199 | # store_fd |
200 | # |
201 | # Same as store, but perform on an already opened file descriptor instead. |
202 | # Returns undef if an I/O error occurred. |
203 | # |
204 | sub store_fd { |
205 | return _store_fd(\&pstore, @_); |
206 | } |
207 | |
208 | # |
209 | # nstore_fd |
210 | # |
211 | # Same as store_fd, but in network order. |
212 | # |
213 | sub nstore_fd { |
214 | my ($self, $file) = @_; |
215 | return _store_fd(\&net_pstore, @_); |
216 | } |
217 | |
218 | # Internal store routine on opened file descriptor |
219 | sub _store_fd { |
220 | my $xsptr = shift; |
221 | my $self = shift; |
222 | my ($file) = @_; |
223 | logcroak "not a reference" unless ref($self); |
224 | logcroak "too many arguments" unless @_ == 1; # No @foo in arglist |
225 | my $fd = fileno($file); |
226 | logcroak "not a valid file descriptor" unless defined $fd; |
227 | my $da = $@; # Don't mess if called from exception handler |
228 | my $ret; |
229 | # Call C routine nstore or pstore, depending on network order |
230 | eval { $ret = &$xsptr($file, $self) }; |
231 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
232 | $@ = $da; |
233 | return $ret ? $ret : undef; |
234 | } |
235 | |
236 | # |
237 | # freeze |
238 | # |
239 | # Store oject and its hierarchy in memory and return a scalar |
240 | # containing the result. |
241 | # |
242 | sub freeze { |
243 | _freeze(\&mstore, @_); |
244 | } |
245 | |
246 | # |
247 | # nfreeze |
248 | # |
249 | # Same as freeze but in network order. |
250 | # |
251 | sub nfreeze { |
252 | _freeze(\&net_mstore, @_); |
253 | } |
254 | |
255 | # Internal freeze routine |
256 | sub _freeze { |
257 | my $xsptr = shift; |
258 | my $self = shift; |
259 | logcroak "not a reference" unless ref($self); |
260 | logcroak "too many arguments" unless @_ == 0; # No @foo in arglist |
261 | my $da = $@; # Don't mess if called from exception handler |
262 | my $ret; |
263 | # Call C routine mstore or net_mstore, depending on network order |
264 | eval { $ret = &$xsptr($self) }; |
265 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
266 | $@ = $da; |
267 | return $ret ? $ret : undef; |
268 | } |
269 | |
270 | # |
271 | # retrieve |
272 | # |
273 | # Retrieve object hierarchy from disk, returning a reference to the root |
274 | # object of that tree. |
275 | # |
276 | sub retrieve { |
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277 | _retrieve($_[0], 0); |
278 | } |
279 | |
280 | # |
281 | # lock_retrieve |
282 | # |
283 | # Same as retrieve, but with advisory locking. |
284 | # |
285 | sub lock_retrieve { |
286 | _retrieve($_[0], 1); |
287 | } |
288 | |
289 | # Internal retrieve routine |
290 | sub _retrieve { |
291 | my ($file, $use_locking) = @_; |
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292 | local *FILE; |
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293 | open(FILE, $file) || logcroak "can't open $file: $!"; |
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294 | binmode FILE; # Archaic systems... |
295 | my $self; |
296 | my $da = $@; # Could be from exception handler |
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297 | if ($use_locking) { |
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298 | unless (&CAN_FLOCK) { |
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299 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
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300 | return undef; |
301 | } |
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302 | flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!"; |
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303 | # Unlocking will happen when FILE is closed |
304 | } |
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305 | eval { $self = pretrieve(*FILE) }; # Call C routine |
306 | close(FILE); |
307 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
308 | $@ = $da; |
309 | return $self; |
310 | } |
311 | |
312 | # |
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313 | # fd_retrieve |
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314 | # |
315 | # Same as retrieve, but perform from an already opened file descriptor instead. |
316 | # |
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317 | sub fd_retrieve { |
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318 | my ($file) = @_; |
319 | my $fd = fileno($file); |
320 | logcroak "not a valid file descriptor" unless defined $fd; |
321 | my $self; |
322 | my $da = $@; # Could be from exception handler |
323 | eval { $self = pretrieve($file) }; # Call C routine |
324 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
325 | $@ = $da; |
326 | return $self; |
327 | } |
328 | |
329 | # |
330 | # thaw |
331 | # |
332 | # Recreate objects in memory from an existing frozen image created |
333 | # by freeze. If the frozen image passed is undef, return undef. |
334 | # |
335 | sub thaw { |
336 | my ($frozen) = @_; |
337 | return undef unless defined $frozen; |
338 | my $self; |
339 | my $da = $@; # Could be from exception handler |
340 | eval { $self = mretrieve($frozen) }; # Call C routine |
341 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
342 | $@ = $da; |
343 | return $self; |
344 | } |
345 | |
346 | =head1 NAME |
347 | |
348 | Storable - persistency for perl data structures |
349 | |
350 | =head1 SYNOPSIS |
351 | |
352 | use Storable; |
353 | store \%table, 'file'; |
354 | $hashref = retrieve('file'); |
355 | |
356 | use Storable qw(nstore store_fd nstore_fd freeze thaw dclone); |
357 | |
358 | # Network order |
359 | nstore \%table, 'file'; |
360 | $hashref = retrieve('file'); # There is NO nretrieve() |
361 | |
362 | # Storing to and retrieving from an already opened file |
363 | store_fd \@array, \*STDOUT; |
364 | nstore_fd \%table, \*STDOUT; |
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365 | $aryref = fd_retrieve(\*SOCKET); |
366 | $hashref = fd_retrieve(\*SOCKET); |
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367 | |
368 | # Serializing to memory |
369 | $serialized = freeze \%table; |
370 | %table_clone = %{ thaw($serialized) }; |
371 | |
372 | # Deep (recursive) cloning |
373 | $cloneref = dclone($ref); |
374 | |
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375 | # Advisory locking |
376 | use Storable qw(lock_store lock_nstore lock_retrieve) |
377 | lock_store \%table, 'file'; |
378 | lock_nstore \%table, 'file'; |
379 | $hashref = lock_retrieve('file'); |
380 | |
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381 | =head1 DESCRIPTION |
382 | |
383 | The Storable package brings persistency to your perl data structures |
384 | containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be |
385 | convenientely stored to disk and retrieved at a later time. |
386 | |
387 | It can be used in the regular procedural way by calling C<store> with |
388 | a reference to the object to be stored, along with the file name where |
389 | the image should be written. |
390 | The routine returns C<undef> for I/O problems or other internal error, |
391 | a true value otherwise. Serious errors are propagated as a C<die> exception. |
392 | |
393 | To retrieve data stored to disk, use C<retrieve> with a file name, |
394 | and the objects stored into that file are recreated into memory for you, |
395 | a I<reference> to the root object being returned. In case an I/O error |
396 | occurs while reading, C<undef> is returned instead. Other serious |
397 | errors are propagated via C<die>. |
398 | |
399 | Since storage is performed recursively, you might want to stuff references |
400 | to objects that share a lot of common data into a single array or hash |
401 | table, and then store that object. That way, when you retrieve back the |
402 | whole thing, the objects will continue to share what they originally shared. |
403 | |
404 | At the cost of a slight header overhead, you may store to an already |
405 | opened file descriptor using the C<store_fd> routine, and retrieve |
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406 | from a file via C<fd_retrieve>. Those names aren't imported by default, |
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407 | so you will have to do that explicitely if you need those routines. |
408 | The file descriptor you supply must be already opened, for read |
409 | if you're going to retrieve and for write if you wish to store. |
410 | |
411 | store_fd(\%table, *STDOUT) || die "can't store to stdout\n"; |
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412 | $hashref = fd_retrieve(*STDIN); |
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413 | |
414 | You can also store data in network order to allow easy sharing across |
415 | multiple platforms, or when storing on a socket known to be remotely |
416 | connected. The routines to call have an initial C<n> prefix for I<network>, |
417 | as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be |
418 | correctly restored so you don't have to know whether you're restoring |
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419 | from native or network ordered data. Double values are stored stringified |
420 | to ensure portability as well, at the slight risk of loosing some precision |
421 | in the last decimals. |
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422 | |
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423 | When using C<fd_retrieve>, objects are retrieved in sequence, one |
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424 | object (i.e. one recursive tree) per associated C<store_fd>. |
425 | |
426 | If you're more from the object-oriented camp, you can inherit from |
427 | Storable and directly store your objects by invoking C<store> as |
428 | a method. The fact that the root of the to-be-stored tree is a |
429 | blessed reference (i.e. an object) is special-cased so that the |
430 | retrieve does not provide a reference to that object but rather the |
431 | blessed object reference itself. (Otherwise, you'd get a reference |
432 | to that blessed object). |
433 | |
434 | =head1 MEMORY STORE |
435 | |
436 | The Storable engine can also store data into a Perl scalar instead, to |
437 | later retrieve them. This is mainly used to freeze a complex structure in |
438 | some safe compact memory place (where it can possibly be sent to another |
439 | process via some IPC, since freezing the structure also serializes it in |
440 | effect). Later on, and maybe somewhere else, you can thaw the Perl scalar |
441 | out and recreate the original complex structure in memory. |
442 | |
443 | Surprisingly, the routines to be called are named C<freeze> and C<thaw>. |
444 | If you wish to send out the frozen scalar to another machine, use |
445 | C<nfreeze> instead to get a portable image. |
446 | |
447 | Note that freezing an object structure and immediately thawing it |
448 | actually achieves a deep cloning of that structure: |
449 | |
450 | dclone(.) = thaw(freeze(.)) |
451 | |
452 | Storable provides you with a C<dclone> interface which does not create |
453 | that intermediary scalar but instead freezes the structure in some |
454 | internal memory space and then immediatly thaws it out. |
455 | |
dd19458b |
456 | =head1 ADVISORY LOCKING |
457 | |
458 | The C<lock_store> and C<lock_nstore> routine are equivalent to C<store> |
459 | and C<nstore>, only they get an exclusive lock on the file before |
460 | writing. Likewise, C<lock_retrieve> performs as C<retrieve>, but also |
461 | gets a shared lock on the file before reading. |
462 | |
463 | Like with any advisory locking scheme, the protection only works if |
464 | you systematically use C<lock_store> and C<lock_retrieve>. If one |
465 | side of your application uses C<store> whilst the other uses C<lock_retrieve>, |
466 | you will get no protection at all. |
467 | |
468 | The internal advisory locking is implemented using Perl's flock() routine. |
469 | If your system does not support any form of flock(), or if you share |
470 | your files across NFS, you might wish to use other forms of locking by |
471 | using modules like LockFile::Simple which lock a file using a filesystem |
472 | entry, instead of locking the file descriptor. |
473 | |
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474 | =head1 SPEED |
475 | |
476 | The heart of Storable is written in C for decent speed. Extra low-level |
477 | optimization have been made when manipulating perl internals, to |
478 | sacrifice encapsulation for the benefit of a greater speed. |
479 | |
480 | =head1 CANONICAL REPRESENTATION |
481 | |
482 | Normally Storable stores elements of hashes in the order they are |
483 | stored internally by Perl, i.e. pseudo-randomly. If you set |
484 | C<$Storable::canonical> to some C<TRUE> value, Storable will store |
485 | hashes with the elements sorted by their key. This allows you to |
486 | compare data structures by comparing their frozen representations (or |
487 | even the compressed frozen representations), which can be useful for |
488 | creating lookup tables for complicated queries. |
489 | |
490 | Canonical order does not imply network order, those are two orthogonal |
491 | settings. |
492 | |
493 | =head1 ERROR REPORTING |
494 | |
495 | Storable uses the "exception" paradigm, in that it does not try to workaround |
496 | failures: if something bad happens, an exception is generated from the |
497 | caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap |
498 | those exceptions. |
499 | |
500 | When Storable croaks, it tries to report the error via the C<logcroak()> |
501 | routine from the C<Log::Agent> package, if it is available. |
502 | |
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503 | Normal errors are reported by having store() or retrieve() return C<undef>. |
504 | Such errors are usually I/O errors (or truncated stream errors at retrieval). |
505 | |
7a6a85bf |
506 | =head1 WIZARDS ONLY |
507 | |
508 | =head2 Hooks |
509 | |
510 | Any class may define hooks that will be called during the serialization |
511 | and deserialization process on objects that are instances of that class. |
512 | Those hooks can redefine the way serialization is performed (and therefore, |
513 | how the symetrical deserialization should be conducted). |
514 | |
515 | Since we said earlier: |
516 | |
517 | dclone(.) = thaw(freeze(.)) |
518 | |
519 | everything we say about hooks should also hold for deep cloning. However, |
520 | hooks get to know whether the operation is a mere serialization, or a cloning. |
521 | |
522 | Therefore, when serializing hooks are involved, |
523 | |
524 | dclone(.) <> thaw(freeze(.)) |
525 | |
526 | Well, you could keep them in sync, but there's no guarantee it will always |
527 | hold on classes somebody else wrote. Besides, there is little to gain in |
528 | doing so: a serializing hook could only keep one attribute of an object, |
529 | which is probably not what should happen during a deep cloning of that |
530 | same object. |
531 | |
532 | Here is the hooking interface: |
533 | |
bbc7dcd2 |
534 | =over 4 |
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535 | |
536 | =item C<STORABLE_freeze> I<obj>, I<cloning> |
537 | |
538 | The serializing hook, called on the object during serialization. It can be |
539 | inherited, or defined in the class itself, like any other method. |
540 | |
541 | Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating |
542 | whether we're in a dclone() or a regular serialization via store() or freeze(). |
543 | |
544 | Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized |
545 | is the serialized form to be used, and the optional $ref1, $ref2, etc... are |
546 | extra references that you wish to let the Storable engine serialize. |
547 | |
548 | At deserialization time, you will be given back the same LIST, but all the |
549 | extra references will be pointing into the deserialized structure. |
550 | |
551 | The B<first time> the hook is hit in a serialization flow, you may have it |
552 | return an empty list. That will signal the Storable engine to further |
553 | discard that hook for this class and to therefore revert to the default |
554 | serialization of the underlying Perl data. The hook will again be normally |
555 | processed in the next serialization. |
556 | |
557 | Unless you know better, serializing hook should always say: |
558 | |
559 | sub STORABLE_freeze { |
560 | my ($self, $cloning) = @_; |
561 | return if $cloning; # Regular default serialization |
562 | .... |
563 | } |
564 | |
565 | in order to keep reasonable dclone() semantics. |
566 | |
567 | =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ... |
568 | |
569 | The deserializing hook called on the object during deserialization. |
570 | But wait. If we're deserializing, there's no object yet... right? |
571 | |
572 | Wrong: the Storable engine creates an empty one for you. If you know Eiffel, |
573 | you can view C<STORABLE_thaw> as an alternate creation routine. |
574 | |
575 | This means the hook can be inherited like any other method, and that |
576 | I<obj> is your blessed reference for this particular instance. |
577 | |
578 | The other arguments should look familiar if you know C<STORABLE_freeze>: |
579 | I<cloning> is true when we're part of a deep clone operation, I<serialized> |
580 | is the serialized string you returned to the engine in C<STORABLE_freeze>, |
581 | and there may be an optional list of references, in the same order you gave |
582 | them at serialization time, pointing to the deserialized objects (which |
583 | have been processed courtesy of the Storable engine). |
584 | |
212e9bde |
585 | When the Storable engine does not find any C<STORABLE_thaw> hook routine, |
586 | it tries to load the class by requiring the package dynamically (using |
587 | the blessed package name), and then re-attempts the lookup. If at that |
588 | time the hook cannot be located, the engine croaks. Note that this mechanism |
589 | will fail if you define several classes in the same file, but perlmod(1) |
590 | warned you. |
591 | |
7a6a85bf |
592 | It is up to you to use these information to populate I<obj> the way you want. |
593 | |
594 | Returned value: none. |
595 | |
596 | =back |
597 | |
598 | =head2 Predicates |
599 | |
600 | Predicates are not exportable. They must be called by explicitely prefixing |
601 | them with the Storable package name. |
602 | |
bbc7dcd2 |
603 | =over 4 |
7a6a85bf |
604 | |
605 | =item C<Storable::last_op_in_netorder> |
606 | |
607 | The C<Storable::last_op_in_netorder()> predicate will tell you whether |
608 | network order was used in the last store or retrieve operation. If you |
609 | don't know how to use this, just forget about it. |
610 | |
611 | =item C<Storable::is_storing> |
612 | |
613 | Returns true if within a store operation (via STORABLE_freeze hook). |
614 | |
615 | =item C<Storable::is_retrieving> |
616 | |
617 | Returns true if within a retrieve operation, (via STORABLE_thaw hook). |
618 | |
619 | =back |
620 | |
621 | =head2 Recursion |
622 | |
623 | With hooks comes the ability to recurse back to the Storable engine. Indeed, |
624 | hooks are regular Perl code, and Storable is convenient when it comes to |
625 | serialize and deserialize things, so why not use it to handle the |
626 | serialization string? |
627 | |
628 | There are a few things you need to know however: |
629 | |
bbc7dcd2 |
630 | =over 4 |
7a6a85bf |
631 | |
632 | =item * |
633 | |
634 | You can create endless loops if the things you serialize via freeze() |
635 | (for instance) point back to the object we're trying to serialize in the hook. |
636 | |
637 | =item * |
638 | |
639 | Shared references among objects will not stay shared: if we're serializing |
640 | the list of object [A, C] where both object A and C refer to the SAME object |
641 | B, and if there is a serializing hook in A that says freeze(B), then when |
642 | deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D, |
643 | a deep clone of B'. The topology was not preserved. |
644 | |
645 | =back |
646 | |
647 | That's why C<STORABLE_freeze> lets you provide a list of references |
648 | to serialize. The engine guarantees that those will be serialized in the |
649 | same context as the other objects, and therefore that shared objects will |
650 | stay shared. |
651 | |
652 | In the above [A, C] example, the C<STORABLE_freeze> hook could return: |
653 | |
654 | ("something", $self->{B}) |
655 | |
656 | and the B part would be serialized by the engine. In C<STORABLE_thaw>, you |
657 | would get back the reference to the B' object, deserialized for you. |
658 | |
659 | Therefore, recursion should normally be avoided, but is nonetheless supported. |
660 | |
661 | =head2 Deep Cloning |
662 | |
663 | There is a new Clone module available on CPAN which implements deep cloning |
664 | natively, i.e. without freezing to memory and thawing the result. It is |
665 | aimed to replace Storable's dclone() some day. However, it does not currently |
666 | support Storable hooks to redefine the way deep cloning is performed. |
667 | |
668 | =head1 EXAMPLES |
669 | |
670 | Here are some code samples showing a possible usage of Storable: |
671 | |
672 | use Storable qw(store retrieve freeze thaw dclone); |
673 | |
674 | %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1); |
675 | |
676 | store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n"; |
677 | |
678 | $colref = retrieve('/tmp/colors'); |
679 | die "Unable to retrieve from /tmp/colors!\n" unless defined $colref; |
680 | printf "Blue is still %lf\n", $colref->{'Blue'}; |
681 | |
682 | $colref2 = dclone(\%color); |
683 | |
684 | $str = freeze(\%color); |
685 | printf "Serialization of %%color is %d bytes long.\n", length($str); |
686 | $colref3 = thaw($str); |
687 | |
688 | which prints (on my machine): |
689 | |
690 | Blue is still 0.100000 |
691 | Serialization of %color is 102 bytes long. |
692 | |
693 | =head1 WARNING |
694 | |
695 | If you're using references as keys within your hash tables, you're bound |
696 | to disapointment when retrieving your data. Indeed, Perl stringifies |
697 | references used as hash table keys. If you later wish to access the |
698 | items via another reference stringification (i.e. using the same |
699 | reference that was used for the key originally to record the value into |
700 | the hash table), it will work because both references stringify to the |
701 | same string. |
702 | |
703 | It won't work across a C<store> and C<retrieve> operations however, because |
704 | the addresses in the retrieved objects, which are part of the stringified |
705 | references, will probably differ from the original addresses. The |
706 | topology of your structure is preserved, but not hidden semantics |
707 | like those. |
708 | |
709 | On platforms where it matters, be sure to call C<binmode()> on the |
710 | descriptors that you pass to Storable functions. |
711 | |
712 | Storing data canonically that contains large hashes can be |
713 | significantly slower than storing the same data normally, as |
714 | temprorary arrays to hold the keys for each hash have to be allocated, |
715 | populated, sorted and freed. Some tests have shown a halving of the |
716 | speed of storing -- the exact penalty will depend on the complexity of |
717 | your data. There is no slowdown on retrieval. |
718 | |
719 | =head1 BUGS |
720 | |
721 | You can't store GLOB, CODE, FORMLINE, etc... If you can define |
722 | semantics for those operations, feel free to enhance Storable so that |
723 | it can deal with them. |
724 | |
725 | The store functions will C<croak> if they run into such references |
726 | unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that |
727 | case, the fatal message is turned in a warning and some |
728 | meaningless string is stored instead. |
729 | |
730 | Setting C<$Storable::canonical> may not yield frozen strings that |
731 | compare equal due to possible stringification of numbers. When the |
732 | string version of a scalar exists, it is the form stored, therefore |
733 | if you happen to use your numbers as strings between two freezing |
734 | operations on the same data structures, you will get different |
735 | results. |
736 | |
dd19458b |
737 | When storing doubles in network order, their value is stored as text. |
738 | However, you should also not expect non-numeric floating-point values |
739 | such as infinity and "not a number" to pass successfully through a |
740 | nstore()/retrieve() pair. |
741 | |
742 | As Storable neither knows nor cares about character sets (although it |
743 | does know that characters may be more than eight bits wide), any difference |
744 | in the interpretation of character codes between a host and a target |
745 | system is your problem. In particular, if host and target use different |
746 | code points to represent the characters used in the text representation |
747 | of floating-point numbers, you will not be able be able to exchange |
748 | floating-point data, even with nstore(). |
749 | |
7a6a85bf |
750 | =head1 CREDITS |
751 | |
752 | Thank you to (in chronological order): |
753 | |
754 | Jarkko Hietaniemi <jhi@iki.fi> |
755 | Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de> |
756 | Benjamin A. Holzman <bah@ecnvantage.com> |
757 | Andrew Ford <A.Ford@ford-mason.co.uk> |
758 | Gisle Aas <gisle@aas.no> |
759 | Jeff Gresham <gresham_jeffrey@jpmorgan.com> |
760 | Murray Nesbitt <murray@activestate.com> |
761 | Marc Lehmann <pcg@opengroup.org> |
9e21b3d0 |
762 | Justin Banks <justinb@wamnet.com> |
763 | Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!) |
dd19458b |
764 | Salvador Ortiz Garcia <sog@msg.com.mx> |
765 | Dominic Dunlop <domo@computer.org> |
766 | Erik Haugan <erik@solbors.no> |
7a6a85bf |
767 | |
768 | for their bug reports, suggestions and contributions. |
769 | |
770 | Benjamin Holzman contributed the tied variable support, Andrew Ford |
771 | contributed the canonical order for hashes, and Gisle Aas fixed |
772 | a few misunderstandings of mine regarding the Perl internals, |
773 | and optimized the emission of "tags" in the output streams by |
774 | simply counting the objects instead of tagging them (leading to |
775 | a binary incompatibility for the Storable image starting at version |
776 | 0.6--older images are of course still properly understood). |
777 | Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading |
778 | and reference to tied items support. |
779 | |
780 | =head1 TRANSLATIONS |
781 | |
782 | There is a Japanese translation of this man page available at |
783 | http://member.nifty.ne.jp/hippo2000/perltips/storable.htm , |
784 | courtesy of Kawai, Takanori <kawai@nippon-rad.co.jp>. |
785 | |
786 | =head1 AUTHOR |
787 | |
788 | Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>> |
789 | |
790 | =head1 SEE ALSO |
791 | |
792 | Clone(3). |
793 | |
794 | =cut |
795 | |