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596596d5 | 1 | ;# $Id: Storable.pm,v 1.0.1.13 2001/12/01 13:34:49 ram Exp $ |
7a6a85bf RG |
2 | ;# |
3 | ;# Copyright (c) 1995-2000, Raphael Manfredi | |
4 | ;# | |
9e21b3d0 JH |
5 | ;# You may redistribute only under the same terms as Perl 5, as specified |
6 | ;# in the README file that comes with the distribution. | |
7a6a85bf RG |
7 | ;# |
8 | ;# $Log: Storable.pm,v $ | |
596596d5 JH |
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 | ;# | |
6e0ac6f5 JH |
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 JH |
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 | ;# | |
8be2b38b JH |
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 JH |
26 | ;# Revision 1.0.1.8 2001/02/17 12:24:37 ram |
27 | ;# patch8: fixed incorrect error message | |
28 | ;# | |
862382c7 JH |
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 JH |
32 | ;# Revision 1.0.1.6 2000/11/05 17:20:25 ram |
33 | ;# patch6: increased version number | |
34 | ;# | |
212e9bde JH |
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 JH |
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 | ;# | |
9e21b3d0 JH |
53 | ;# Revision 1.0 2000/09/01 19:40:41 ram |
54 | ;# Baseline for first official release. | |
7a6a85bf RG |
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( | |
9e21b3d0 | 63 | nstore store_fd nstore_fd fd_retrieve |
7a6a85bf RG |
64 | freeze nfreeze thaw |
65 | dclone | |
9e21b3d0 | 66 | retrieve_fd |
dd19458b | 67 | lock_store lock_nstore lock_retrieve |
7a6a85bf RG |
68 | ); |
69 | ||
70 | use AutoLoader; | |
01d7b99e | 71 | use vars qw($canonical $forgive_me $VERSION); |
7a6a85bf | 72 | |
2aeb6432 | 73 | $VERSION = '2.02'; |
7a6a85bf RG |
74 | *AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr... |
75 | ||
76 | # | |
77 | # Use of Log::Agent is optional | |
78 | # | |
79 | ||
80 | eval "use Log::Agent"; | |
81 | ||
530b72ba | 82 | require Carp; |
7a6a85bf | 83 | |
dd19458b JH |
84 | # |
85 | # They might miss :flock in Fcntl | |
86 | # | |
87 | ||
88 | BEGIN { | |
596596d5 | 89 | if (eval { require Fcntl; 1 } && exists $Fcntl::EXPORT_TAGS{'flock'}) { |
dd19458b JH |
90 | Fcntl->import(':flock'); |
91 | } else { | |
92 | eval q{ | |
93 | sub LOCK_SH () {1} | |
94 | sub LOCK_EX () {2} | |
95 | }; | |
96 | } | |
97 | } | |
98 | ||
b8778c7c | 99 | # Can't Autoload cleanly as this clashes 8.3 with &retrieve |
9e21b3d0 | 100 | sub retrieve_fd { &fd_retrieve } # Backward compatibility |
cb3d9de5 | 101 | |
530b72ba NC |
102 | # By default restricted hashes are downgraded on earlier perls. |
103 | ||
104 | $Storable::downgrade_restricted = 1; | |
e8189732 | 105 | $Storable::accept_future_minor = 1; |
b8778c7c NC |
106 | bootstrap Storable; |
107 | 1; | |
108 | __END__ | |
530b72ba NC |
109 | # |
110 | # Use of Log::Agent is optional. If it hasn't imported these subs then | |
111 | # Autoloader will kindly supply our fallback implementation. | |
112 | # | |
113 | ||
114 | sub logcroak { | |
115 | Carp::croak(@_); | |
116 | } | |
117 | ||
118 | sub logcarp { | |
119 | Carp::carp(@_); | |
120 | } | |
b8778c7c | 121 | |
862382c7 JH |
122 | # |
123 | # Determine whether locking is possible, but only when needed. | |
124 | # | |
125 | ||
530b72ba | 126 | sub CAN_FLOCK; my $CAN_FLOCK; sub CAN_FLOCK { |
862382c7 JH |
127 | return $CAN_FLOCK if defined $CAN_FLOCK; |
128 | require Config; import Config; | |
129 | return $CAN_FLOCK = | |
130 | $Config{'d_flock'} || | |
131 | $Config{'d_fcntl_can_lock'} || | |
132 | $Config{'d_lockf'}; | |
133 | } | |
134 | ||
0a0da639 JH |
135 | sub show_file_magic { |
136 | print <<EOM; | |
137 | # | |
138 | # To recognize the data files of the Perl module Storable, | |
139 | # the following lines need to be added to the local magic(5) file, | |
140 | # usually either /usr/share/misc/magic or /etc/magic. | |
0a0da639 JH |
141 | # |
142 | 0 string perl-store perl Storable(v0.6) data | |
8b793558 JH |
143 | >4 byte >0 (net-order %d) |
144 | >>4 byte &01 (network-ordered) | |
145 | >>4 byte =3 (major 1) | |
146 | >>4 byte =2 (major 1) | |
147 | ||
0a0da639 | 148 | 0 string pst0 perl Storable(v0.7) data |
8b793558 JH |
149 | >4 byte >0 |
150 | >>4 byte &01 (network-ordered) | |
151 | >>4 byte =5 (major 2) | |
152 | >>4 byte =4 (major 2) | |
153 | >>5 byte >0 (minor %d) | |
0a0da639 JH |
154 | EOM |
155 | } | |
156 | ||
b8778c7c NC |
157 | sub read_magic { |
158 | my $header = shift; | |
159 | return unless defined $header and length $header > 11; | |
160 | my $result; | |
161 | if ($header =~ s/^perl-store//) { | |
162 | die "Can't deal with version 0 headers"; | |
163 | } elsif ($header =~ s/^pst0//) { | |
164 | $result->{file} = 1; | |
165 | } | |
166 | # Assume it's a string. | |
167 | my ($major, $minor, $bytelen) = unpack "C3", $header; | |
168 | ||
169 | my $net_order = $major & 1; | |
170 | $major >>= 1; | |
171 | @$result{qw(major minor netorder)} = ($major, $minor, $net_order); | |
172 | ||
173 | return $result if $net_order; | |
174 | ||
175 | # I assume that it is rare to find v1 files, so this is an intentionally | |
176 | # inefficient way of doing it, to make the rest of the code constant. | |
177 | if ($major < 2) { | |
178 | delete $result->{minor}; | |
179 | $header = '.' . $header; | |
180 | $bytelen = $minor; | |
181 | } | |
182 | ||
183 | @$result{qw(byteorder intsize longsize ptrsize)} = | |
184 | unpack "x3 A$bytelen C3", $header; | |
185 | ||
186 | if ($major >= 2 and $minor >= 2) { | |
187 | $result->{nvsize} = unpack "x6 x$bytelen C", $header; | |
188 | } | |
189 | $result; | |
190 | } | |
7a6a85bf RG |
191 | |
192 | # | |
193 | # store | |
194 | # | |
195 | # Store target object hierarchy, identified by a reference to its root. | |
196 | # The stored object tree may later be retrieved to memory via retrieve. | |
197 | # Returns undef if an I/O error occurred, in which case the file is | |
198 | # removed. | |
199 | # | |
200 | sub store { | |
dd19458b | 201 | return _store(\&pstore, @_, 0); |
7a6a85bf RG |
202 | } |
203 | ||
204 | # | |
205 | # nstore | |
206 | # | |
207 | # Same as store, but in network order. | |
208 | # | |
209 | sub nstore { | |
dd19458b JH |
210 | return _store(\&net_pstore, @_, 0); |
211 | } | |
212 | ||
213 | # | |
214 | # lock_store | |
215 | # | |
216 | # Same as store, but flock the file first (advisory locking). | |
217 | # | |
218 | sub lock_store { | |
219 | return _store(\&pstore, @_, 1); | |
220 | } | |
221 | ||
222 | # | |
223 | # lock_nstore | |
224 | # | |
225 | # Same as nstore, but flock the file first (advisory locking). | |
226 | # | |
227 | sub lock_nstore { | |
228 | return _store(\&net_pstore, @_, 1); | |
7a6a85bf RG |
229 | } |
230 | ||
231 | # Internal store to file routine | |
232 | sub _store { | |
233 | my $xsptr = shift; | |
234 | my $self = shift; | |
dd19458b | 235 | my ($file, $use_locking) = @_; |
7a6a85bf | 236 | logcroak "not a reference" unless ref($self); |
b12202d0 | 237 | logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist |
7a6a85bf | 238 | local *FILE; |
dd19458b | 239 | if ($use_locking) { |
6e0ac6f5 | 240 | open(FILE, ">>$file") || logcroak "can't write into $file: $!"; |
862382c7 | 241 | unless (&CAN_FLOCK) { |
b29b780f RM |
242 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
243 | return undef; | |
f567092b | 244 | } |
dd19458b JH |
245 | flock(FILE, LOCK_EX) || |
246 | logcroak "can't get exclusive lock on $file: $!"; | |
247 | truncate FILE, 0; | |
248 | # Unlocking will happen when FILE is closed | |
6e0ac6f5 JH |
249 | } else { |
250 | open(FILE, ">$file") || logcroak "can't create $file: $!"; | |
dd19458b | 251 | } |
6e0ac6f5 | 252 | binmode FILE; # Archaic systems... |
7a6a85bf RG |
253 | my $da = $@; # Don't mess if called from exception handler |
254 | my $ret; | |
255 | # Call C routine nstore or pstore, depending on network order | |
256 | eval { $ret = &$xsptr(*FILE, $self) }; | |
257 | close(FILE) or $ret = undef; | |
258 | unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret; | |
259 | logcroak $@ if $@ =~ s/\.?\n$/,/; | |
260 | $@ = $da; | |
261 | return $ret ? $ret : undef; | |
262 | } | |
263 | ||
264 | # | |
265 | # store_fd | |
266 | # | |
267 | # Same as store, but perform on an already opened file descriptor instead. | |
268 | # Returns undef if an I/O error occurred. | |
269 | # | |
270 | sub store_fd { | |
271 | return _store_fd(\&pstore, @_); | |
272 | } | |
273 | ||
274 | # | |
275 | # nstore_fd | |
276 | # | |
277 | # Same as store_fd, but in network order. | |
278 | # | |
279 | sub nstore_fd { | |
280 | my ($self, $file) = @_; | |
281 | return _store_fd(\&net_pstore, @_); | |
282 | } | |
283 | ||
284 | # Internal store routine on opened file descriptor | |
285 | sub _store_fd { | |
286 | my $xsptr = shift; | |
287 | my $self = shift; | |
288 | my ($file) = @_; | |
289 | logcroak "not a reference" unless ref($self); | |
290 | logcroak "too many arguments" unless @_ == 1; # No @foo in arglist | |
291 | my $fd = fileno($file); | |
292 | logcroak "not a valid file descriptor" unless defined $fd; | |
293 | my $da = $@; # Don't mess if called from exception handler | |
294 | my $ret; | |
295 | # Call C routine nstore or pstore, depending on network order | |
296 | eval { $ret = &$xsptr($file, $self) }; | |
297 | logcroak $@ if $@ =~ s/\.?\n$/,/; | |
596596d5 | 298 | local $\; print $file ''; # Autoflush the file if wanted |
7a6a85bf RG |
299 | $@ = $da; |
300 | return $ret ? $ret : undef; | |
301 | } | |
302 | ||
303 | # | |
304 | # freeze | |
305 | # | |
306 | # Store oject and its hierarchy in memory and return a scalar | |
307 | # containing the result. | |
308 | # | |
309 | sub freeze { | |
310 | _freeze(\&mstore, @_); | |
311 | } | |
312 | ||
313 | # | |
314 | # nfreeze | |
315 | # | |
316 | # Same as freeze but in network order. | |
317 | # | |
318 | sub nfreeze { | |
319 | _freeze(\&net_mstore, @_); | |
320 | } | |
321 | ||
322 | # Internal freeze routine | |
323 | sub _freeze { | |
324 | my $xsptr = shift; | |
325 | my $self = shift; | |
326 | logcroak "not a reference" unless ref($self); | |
327 | logcroak "too many arguments" unless @_ == 0; # No @foo in arglist | |
328 | my $da = $@; # Don't mess if called from exception handler | |
329 | my $ret; | |
330 | # Call C routine mstore or net_mstore, depending on network order | |
331 | eval { $ret = &$xsptr($self) }; | |
332 | logcroak $@ if $@ =~ s/\.?\n$/,/; | |
333 | $@ = $da; | |
334 | return $ret ? $ret : undef; | |
335 | } | |
336 | ||
337 | # | |
338 | # retrieve | |
339 | # | |
340 | # Retrieve object hierarchy from disk, returning a reference to the root | |
341 | # object of that tree. | |
342 | # | |
343 | sub retrieve { | |
dd19458b JH |
344 | _retrieve($_[0], 0); |
345 | } | |
346 | ||
347 | # | |
348 | # lock_retrieve | |
349 | # | |
350 | # Same as retrieve, but with advisory locking. | |
351 | # | |
352 | sub lock_retrieve { | |
353 | _retrieve($_[0], 1); | |
354 | } | |
355 | ||
356 | # Internal retrieve routine | |
357 | sub _retrieve { | |
358 | my ($file, $use_locking) = @_; | |
7a6a85bf | 359 | local *FILE; |
dd19458b | 360 | open(FILE, $file) || logcroak "can't open $file: $!"; |
7a6a85bf RG |
361 | binmode FILE; # Archaic systems... |
362 | my $self; | |
363 | my $da = $@; # Could be from exception handler | |
dd19458b | 364 | if ($use_locking) { |
862382c7 | 365 | unless (&CAN_FLOCK) { |
8be2b38b | 366 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
b29b780f RM |
367 | return undef; |
368 | } | |
8be2b38b | 369 | flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!"; |
dd19458b JH |
370 | # Unlocking will happen when FILE is closed |
371 | } | |
7a6a85bf RG |
372 | eval { $self = pretrieve(*FILE) }; # Call C routine |
373 | close(FILE); | |
374 | logcroak $@ if $@ =~ s/\.?\n$/,/; | |
375 | $@ = $da; | |
376 | return $self; | |
377 | } | |
378 | ||
379 | # | |
9e21b3d0 | 380 | # fd_retrieve |
7a6a85bf RG |
381 | # |
382 | # Same as retrieve, but perform from an already opened file descriptor instead. | |
383 | # | |
9e21b3d0 | 384 | sub fd_retrieve { |
7a6a85bf RG |
385 | my ($file) = @_; |
386 | my $fd = fileno($file); | |
387 | logcroak "not a valid file descriptor" unless defined $fd; | |
388 | my $self; | |
389 | my $da = $@; # Could be from exception handler | |
390 | eval { $self = pretrieve($file) }; # Call C routine | |
391 | logcroak $@ if $@ =~ s/\.?\n$/,/; | |
392 | $@ = $da; | |
393 | return $self; | |
394 | } | |
395 | ||
396 | # | |
397 | # thaw | |
398 | # | |
399 | # Recreate objects in memory from an existing frozen image created | |
400 | # by freeze. If the frozen image passed is undef, return undef. | |
401 | # | |
402 | sub thaw { | |
403 | my ($frozen) = @_; | |
404 | return undef unless defined $frozen; | |
405 | my $self; | |
406 | my $da = $@; # Could be from exception handler | |
407 | eval { $self = mretrieve($frozen) }; # Call C routine | |
408 | logcroak $@ if $@ =~ s/\.?\n$/,/; | |
409 | $@ = $da; | |
410 | return $self; | |
411 | } | |
412 | ||
413 | =head1 NAME | |
414 | ||
f062ea6c | 415 | Storable - persistence for Perl data structures |
7a6a85bf RG |
416 | |
417 | =head1 SYNOPSIS | |
418 | ||
419 | use Storable; | |
420 | store \%table, 'file'; | |
421 | $hashref = retrieve('file'); | |
422 | ||
423 | use Storable qw(nstore store_fd nstore_fd freeze thaw dclone); | |
424 | ||
425 | # Network order | |
426 | nstore \%table, 'file'; | |
427 | $hashref = retrieve('file'); # There is NO nretrieve() | |
428 | ||
429 | # Storing to and retrieving from an already opened file | |
430 | store_fd \@array, \*STDOUT; | |
431 | nstore_fd \%table, \*STDOUT; | |
9e21b3d0 JH |
432 | $aryref = fd_retrieve(\*SOCKET); |
433 | $hashref = fd_retrieve(\*SOCKET); | |
7a6a85bf RG |
434 | |
435 | # Serializing to memory | |
436 | $serialized = freeze \%table; | |
437 | %table_clone = %{ thaw($serialized) }; | |
438 | ||
439 | # Deep (recursive) cloning | |
440 | $cloneref = dclone($ref); | |
441 | ||
dd19458b JH |
442 | # Advisory locking |
443 | use Storable qw(lock_store lock_nstore lock_retrieve) | |
444 | lock_store \%table, 'file'; | |
445 | lock_nstore \%table, 'file'; | |
446 | $hashref = lock_retrieve('file'); | |
447 | ||
7a6a85bf RG |
448 | =head1 DESCRIPTION |
449 | ||
f062ea6c | 450 | The Storable package brings persistence to your Perl data structures |
7a6a85bf | 451 | containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be |
c261f00e | 452 | conveniently stored to disk and retrieved at a later time. |
7a6a85bf RG |
453 | |
454 | It can be used in the regular procedural way by calling C<store> with | |
455 | a reference to the object to be stored, along with the file name where | |
456 | the image should be written. | |
775ecd75 | 457 | |
7a6a85bf RG |
458 | The routine returns C<undef> for I/O problems or other internal error, |
459 | a true value otherwise. Serious errors are propagated as a C<die> exception. | |
460 | ||
f062ea6c PN |
461 | To retrieve data stored to disk, use C<retrieve> with a file name. |
462 | The objects stored into that file are recreated into memory for you, | |
463 | and a I<reference> to the root object is returned. In case an I/O error | |
7a6a85bf RG |
464 | occurs while reading, C<undef> is returned instead. Other serious |
465 | errors are propagated via C<die>. | |
466 | ||
467 | Since storage is performed recursively, you might want to stuff references | |
468 | to objects that share a lot of common data into a single array or hash | |
469 | table, and then store that object. That way, when you retrieve back the | |
470 | whole thing, the objects will continue to share what they originally shared. | |
471 | ||
472 | At the cost of a slight header overhead, you may store to an already | |
473 | opened file descriptor using the C<store_fd> routine, and retrieve | |
9e21b3d0 | 474 | from a file via C<fd_retrieve>. Those names aren't imported by default, |
c261f00e | 475 | so you will have to do that explicitly if you need those routines. |
7a6a85bf RG |
476 | The file descriptor you supply must be already opened, for read |
477 | if you're going to retrieve and for write if you wish to store. | |
478 | ||
479 | store_fd(\%table, *STDOUT) || die "can't store to stdout\n"; | |
9e21b3d0 | 480 | $hashref = fd_retrieve(*STDIN); |
7a6a85bf RG |
481 | |
482 | You can also store data in network order to allow easy sharing across | |
483 | multiple platforms, or when storing on a socket known to be remotely | |
484 | connected. The routines to call have an initial C<n> prefix for I<network>, | |
485 | as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be | |
486 | correctly restored so you don't have to know whether you're restoring | |
dd19458b JH |
487 | from native or network ordered data. Double values are stored stringified |
488 | to ensure portability as well, at the slight risk of loosing some precision | |
489 | in the last decimals. | |
7a6a85bf | 490 | |
9e21b3d0 | 491 | When using C<fd_retrieve>, objects are retrieved in sequence, one |
7a6a85bf RG |
492 | object (i.e. one recursive tree) per associated C<store_fd>. |
493 | ||
494 | If you're more from the object-oriented camp, you can inherit from | |
495 | Storable and directly store your objects by invoking C<store> as | |
496 | a method. The fact that the root of the to-be-stored tree is a | |
497 | blessed reference (i.e. an object) is special-cased so that the | |
498 | retrieve does not provide a reference to that object but rather the | |
499 | blessed object reference itself. (Otherwise, you'd get a reference | |
500 | to that blessed object). | |
501 | ||
502 | =head1 MEMORY STORE | |
503 | ||
504 | The Storable engine can also store data into a Perl scalar instead, to | |
505 | later retrieve them. This is mainly used to freeze a complex structure in | |
506 | some safe compact memory place (where it can possibly be sent to another | |
507 | process via some IPC, since freezing the structure also serializes it in | |
508 | effect). Later on, and maybe somewhere else, you can thaw the Perl scalar | |
509 | out and recreate the original complex structure in memory. | |
510 | ||
511 | Surprisingly, the routines to be called are named C<freeze> and C<thaw>. | |
512 | If you wish to send out the frozen scalar to another machine, use | |
513 | C<nfreeze> instead to get a portable image. | |
514 | ||
515 | Note that freezing an object structure and immediately thawing it | |
516 | actually achieves a deep cloning of that structure: | |
517 | ||
518 | dclone(.) = thaw(freeze(.)) | |
519 | ||
520 | Storable provides you with a C<dclone> interface which does not create | |
521 | that intermediary scalar but instead freezes the structure in some | |
c261f00e | 522 | internal memory space and then immediately thaws it out. |
7a6a85bf | 523 | |
dd19458b JH |
524 | =head1 ADVISORY LOCKING |
525 | ||
f062ea6c PN |
526 | The C<lock_store> and C<lock_nstore> routine are equivalent to |
527 | C<store> and C<nstore>, except that they get an exclusive lock on | |
528 | the file before writing. Likewise, C<lock_retrieve> does the same | |
529 | as C<retrieve>, but also gets a shared lock on the file before reading. | |
dd19458b | 530 | |
f062ea6c PN |
531 | As with any advisory locking scheme, the protection only works if you |
532 | systematically use C<lock_store> and C<lock_retrieve>. If one side of | |
533 | your application uses C<store> whilst the other uses C<lock_retrieve>, | |
dd19458b JH |
534 | you will get no protection at all. |
535 | ||
f062ea6c PN |
536 | The internal advisory locking is implemented using Perl's flock() |
537 | routine. If your system does not support any form of flock(), or if | |
538 | you share your files across NFS, you might wish to use other forms | |
539 | of locking by using modules such as LockFile::Simple which lock a | |
540 | file using a filesystem entry, instead of locking the file descriptor. | |
dd19458b | 541 | |
7a6a85bf RG |
542 | =head1 SPEED |
543 | ||
544 | The heart of Storable is written in C for decent speed. Extra low-level | |
4d3295e3 PN |
545 | optimizations have been made when manipulating perl internals, to |
546 | sacrifice encapsulation for the benefit of greater speed. | |
7a6a85bf RG |
547 | |
548 | =head1 CANONICAL REPRESENTATION | |
549 | ||
f062ea6c | 550 | Normally, Storable stores elements of hashes in the order they are |
7a6a85bf RG |
551 | stored internally by Perl, i.e. pseudo-randomly. If you set |
552 | C<$Storable::canonical> to some C<TRUE> value, Storable will store | |
553 | hashes with the elements sorted by their key. This allows you to | |
554 | compare data structures by comparing their frozen representations (or | |
555 | even the compressed frozen representations), which can be useful for | |
556 | creating lookup tables for complicated queries. | |
557 | ||
f062ea6c | 558 | Canonical order does not imply network order; those are two orthogonal |
7a6a85bf RG |
559 | settings. |
560 | ||
c261f00e NC |
561 | =head1 FORWARD COMPATIBILITY |
562 | ||
563 | This release of Storable can be used on a newer version of Perl to | |
f062ea6c | 564 | serialize data which is not supported by earlier Perls. By default, |
c261f00e | 565 | Storable will attempt to do the right thing, by C<croak()>ing if it |
775ecd75 | 566 | encounters data that it cannot deserialize. However, the defaults |
f062ea6c | 567 | can be changed as follows: |
c261f00e NC |
568 | |
569 | =over 4 | |
570 | ||
571 | =item utf8 data | |
572 | ||
573 | Perl 5.6 added support for Unicode characters with code points > 255, | |
574 | and Perl 5.8 has full support for Unicode characters in hash keys. | |
575 | Perl internally encodes strings with these characters using utf8, and | |
576 | Storable serializes them as utf8. By default, if an older version of | |
577 | Perl encounters a utf8 value it cannot represent, it will C<croak()>. | |
578 | To change this behaviour so that Storable deserializes utf8 encoded | |
579 | values as the string of bytes (effectively dropping the I<is_utf8> flag) | |
580 | set C<$Storable::drop_utf8> to some C<TRUE> value. This is a form of | |
581 | data loss, because with C<$drop_utf8> true, it becomes impossible to tell | |
582 | whether the original data was the Unicode string, or a series of bytes | |
583 | that happen to be valid utf8. | |
584 | ||
585 | =item restricted hashes | |
586 | ||
f062ea6c PN |
587 | Perl 5.8 adds support for restricted hashes, which have keys |
588 | restricted to a given set, and can have values locked to be read only. | |
589 | By default, when Storable encounters a restricted hash on a perl | |
590 | that doesn't support them, it will deserialize it as a normal hash, | |
591 | silently discarding any placeholder keys and leaving the keys and | |
592 | all values unlocked. To make Storable C<croak()> instead, set | |
593 | C<$Storable::downgrade_restricted> to a C<FALSE> value. To restore | |
594 | the default set it back to some C<TRUE> value. | |
c261f00e | 595 | |
e8189732 NC |
596 | =item files from future versions of Storable |
597 | ||
598 | Earlier versions of Storable would immediately croak if they encountered | |
599 | a file with a higher internal version number than the reading Storable | |
600 | knew about. Internal version numbers are increased each time new data | |
601 | types (such as restricted hashes) are added to the vocabulary of the file | |
602 | format. This meant that a newer Storable module had no way of writing a | |
f062ea6c | 603 | file readable by an older Storable, even if the writer didn't store newer |
e8189732 NC |
604 | data types. |
605 | ||
606 | This version of Storable will defer croaking until it encounters a data | |
607 | type in the file that it does not recognize. This means that it will | |
608 | continue to read files generated by newer Storable modules which are careful | |
609 | in what they write out, making it easier to upgrade Storable modules in a | |
610 | mixed environment. | |
611 | ||
612 | The old behaviour of immediate croaking can be re-instated by setting | |
f062ea6c | 613 | C<$Storable::accept_future_minor> to some C<FALSE> value. |
e8189732 | 614 | |
c261f00e NC |
615 | =back |
616 | ||
f062ea6c | 617 | All these variables have no effect on a newer Perl which supports the |
c261f00e NC |
618 | relevant feature. |
619 | ||
7a6a85bf RG |
620 | =head1 ERROR REPORTING |
621 | ||
622 | Storable uses the "exception" paradigm, in that it does not try to workaround | |
623 | failures: if something bad happens, an exception is generated from the | |
624 | caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap | |
625 | those exceptions. | |
626 | ||
627 | When Storable croaks, it tries to report the error via the C<logcroak()> | |
628 | routine from the C<Log::Agent> package, if it is available. | |
629 | ||
212e9bde JH |
630 | Normal errors are reported by having store() or retrieve() return C<undef>. |
631 | Such errors are usually I/O errors (or truncated stream errors at retrieval). | |
632 | ||
7a6a85bf RG |
633 | =head1 WIZARDS ONLY |
634 | ||
635 | =head2 Hooks | |
636 | ||
637 | Any class may define hooks that will be called during the serialization | |
638 | and deserialization process on objects that are instances of that class. | |
639 | Those hooks can redefine the way serialization is performed (and therefore, | |
c261f00e | 640 | how the symmetrical deserialization should be conducted). |
7a6a85bf RG |
641 | |
642 | Since we said earlier: | |
643 | ||
644 | dclone(.) = thaw(freeze(.)) | |
645 | ||
646 | everything we say about hooks should also hold for deep cloning. However, | |
647 | hooks get to know whether the operation is a mere serialization, or a cloning. | |
648 | ||
649 | Therefore, when serializing hooks are involved, | |
650 | ||
651 | dclone(.) <> thaw(freeze(.)) | |
652 | ||
653 | Well, you could keep them in sync, but there's no guarantee it will always | |
654 | hold on classes somebody else wrote. Besides, there is little to gain in | |
f062ea6c | 655 | doing so: a serializing hook could keep only one attribute of an object, |
7a6a85bf RG |
656 | which is probably not what should happen during a deep cloning of that |
657 | same object. | |
658 | ||
659 | Here is the hooking interface: | |
660 | ||
bbc7dcd2 | 661 | =over 4 |
7a6a85bf RG |
662 | |
663 | =item C<STORABLE_freeze> I<obj>, I<cloning> | |
664 | ||
665 | The serializing hook, called on the object during serialization. It can be | |
666 | inherited, or defined in the class itself, like any other method. | |
667 | ||
668 | Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating | |
669 | whether we're in a dclone() or a regular serialization via store() or freeze(). | |
670 | ||
671 | Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized | |
672 | is the serialized form to be used, and the optional $ref1, $ref2, etc... are | |
673 | extra references that you wish to let the Storable engine serialize. | |
674 | ||
675 | At deserialization time, you will be given back the same LIST, but all the | |
676 | extra references will be pointing into the deserialized structure. | |
677 | ||
678 | The B<first time> the hook is hit in a serialization flow, you may have it | |
679 | return an empty list. That will signal the Storable engine to further | |
680 | discard that hook for this class and to therefore revert to the default | |
681 | serialization of the underlying Perl data. The hook will again be normally | |
682 | processed in the next serialization. | |
683 | ||
684 | Unless you know better, serializing hook should always say: | |
685 | ||
686 | sub STORABLE_freeze { | |
687 | my ($self, $cloning) = @_; | |
688 | return if $cloning; # Regular default serialization | |
689 | .... | |
690 | } | |
691 | ||
692 | in order to keep reasonable dclone() semantics. | |
693 | ||
694 | =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ... | |
695 | ||
696 | The deserializing hook called on the object during deserialization. | |
f062ea6c | 697 | But wait: if we're deserializing, there's no object yet... right? |
7a6a85bf RG |
698 | |
699 | Wrong: the Storable engine creates an empty one for you. If you know Eiffel, | |
700 | you can view C<STORABLE_thaw> as an alternate creation routine. | |
701 | ||
702 | This means the hook can be inherited like any other method, and that | |
703 | I<obj> is your blessed reference for this particular instance. | |
704 | ||
705 | The other arguments should look familiar if you know C<STORABLE_freeze>: | |
706 | I<cloning> is true when we're part of a deep clone operation, I<serialized> | |
707 | is the serialized string you returned to the engine in C<STORABLE_freeze>, | |
708 | and there may be an optional list of references, in the same order you gave | |
709 | them at serialization time, pointing to the deserialized objects (which | |
710 | have been processed courtesy of the Storable engine). | |
711 | ||
212e9bde JH |
712 | When the Storable engine does not find any C<STORABLE_thaw> hook routine, |
713 | it tries to load the class by requiring the package dynamically (using | |
714 | the blessed package name), and then re-attempts the lookup. If at that | |
715 | time the hook cannot be located, the engine croaks. Note that this mechanism | |
c261f00e | 716 | will fail if you define several classes in the same file, but L<perlmod> |
212e9bde JH |
717 | warned you. |
718 | ||
f062ea6c | 719 | It is up to you to use this information to populate I<obj> the way you want. |
7a6a85bf RG |
720 | |
721 | Returned value: none. | |
722 | ||
723 | =back | |
724 | ||
725 | =head2 Predicates | |
726 | ||
c261f00e | 727 | Predicates are not exportable. They must be called by explicitly prefixing |
7a6a85bf RG |
728 | them with the Storable package name. |
729 | ||
bbc7dcd2 | 730 | =over 4 |
7a6a85bf RG |
731 | |
732 | =item C<Storable::last_op_in_netorder> | |
733 | ||
734 | The C<Storable::last_op_in_netorder()> predicate will tell you whether | |
735 | network order was used in the last store or retrieve operation. If you | |
736 | don't know how to use this, just forget about it. | |
737 | ||
738 | =item C<Storable::is_storing> | |
739 | ||
740 | Returns true if within a store operation (via STORABLE_freeze hook). | |
741 | ||
742 | =item C<Storable::is_retrieving> | |
743 | ||
f062ea6c | 744 | Returns true if within a retrieve operation (via STORABLE_thaw hook). |
7a6a85bf RG |
745 | |
746 | =back | |
747 | ||
748 | =head2 Recursion | |
749 | ||
f062ea6c PN |
750 | With hooks comes the ability to recurse back to the Storable engine. |
751 | Indeed, hooks are regular Perl code, and Storable is convenient when | |
752 | it comes to serializing and deserializing things, so why not use it | |
753 | to handle the serialization string? | |
7a6a85bf | 754 | |
f062ea6c | 755 | There are a few things you need to know, however: |
7a6a85bf | 756 | |
bbc7dcd2 | 757 | =over 4 |
7a6a85bf RG |
758 | |
759 | =item * | |
760 | ||
761 | You can create endless loops if the things you serialize via freeze() | |
f062ea6c PN |
762 | (for instance) point back to the object we're trying to serialize in |
763 | the hook. | |
7a6a85bf RG |
764 | |
765 | =item * | |
766 | ||
767 | Shared references among objects will not stay shared: if we're serializing | |
768 | the list of object [A, C] where both object A and C refer to the SAME object | |
769 | B, and if there is a serializing hook in A that says freeze(B), then when | |
770 | deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D, | |
771 | a deep clone of B'. The topology was not preserved. | |
772 | ||
773 | =back | |
774 | ||
775 | That's why C<STORABLE_freeze> lets you provide a list of references | |
776 | to serialize. The engine guarantees that those will be serialized in the | |
777 | same context as the other objects, and therefore that shared objects will | |
778 | stay shared. | |
779 | ||
780 | In the above [A, C] example, the C<STORABLE_freeze> hook could return: | |
781 | ||
782 | ("something", $self->{B}) | |
783 | ||
784 | and the B part would be serialized by the engine. In C<STORABLE_thaw>, you | |
785 | would get back the reference to the B' object, deserialized for you. | |
786 | ||
787 | Therefore, recursion should normally be avoided, but is nonetheless supported. | |
788 | ||
789 | =head2 Deep Cloning | |
790 | ||
f062ea6c | 791 | There is a Clone module available on CPAN which implements deep cloning |
7a6a85bf RG |
792 | natively, i.e. without freezing to memory and thawing the result. It is |
793 | aimed to replace Storable's dclone() some day. However, it does not currently | |
794 | support Storable hooks to redefine the way deep cloning is performed. | |
795 | ||
0a0da639 JH |
796 | =head1 Storable magic |
797 | ||
798 | Yes, there's a lot of that :-) But more precisely, in UNIX systems | |
799 | there's a utility called C<file>, which recognizes data files based on | |
800 | their contents (usually their first few bytes). For this to work, | |
8b793558 | 801 | a certain file called F<magic> needs to taught about the I<signature> |
0a0da639 | 802 | of the data. Where that configuration file lives depends on the UNIX |
f062ea6c | 803 | flavour; often it's something like F</usr/share/misc/magic> or |
8b793558 JH |
804 | F</etc/magic>. Your system administrator needs to do the updating of |
805 | the F<magic> file. The necessary signature information is output to | |
f062ea6c PN |
806 | STDOUT by invoking Storable::show_file_magic(). Note that the GNU |
807 | implementation of the C<file> utility, version 3.38 or later, | |
808 | is expected to contain support for recognising Storable files | |
809 | out-of-the-box, in addition to other kinds of Perl files. | |
0a0da639 | 810 | |
7a6a85bf RG |
811 | =head1 EXAMPLES |
812 | ||
813 | Here are some code samples showing a possible usage of Storable: | |
814 | ||
815 | use Storable qw(store retrieve freeze thaw dclone); | |
816 | ||
817 | %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1); | |
818 | ||
819 | store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n"; | |
820 | ||
821 | $colref = retrieve('/tmp/colors'); | |
822 | die "Unable to retrieve from /tmp/colors!\n" unless defined $colref; | |
823 | printf "Blue is still %lf\n", $colref->{'Blue'}; | |
824 | ||
825 | $colref2 = dclone(\%color); | |
826 | ||
827 | $str = freeze(\%color); | |
828 | printf "Serialization of %%color is %d bytes long.\n", length($str); | |
829 | $colref3 = thaw($str); | |
830 | ||
831 | which prints (on my machine): | |
832 | ||
833 | Blue is still 0.100000 | |
834 | Serialization of %color is 102 bytes long. | |
835 | ||
836 | =head1 WARNING | |
837 | ||
838 | If you're using references as keys within your hash tables, you're bound | |
f062ea6c | 839 | to be disappointed when retrieving your data. Indeed, Perl stringifies |
7a6a85bf RG |
840 | references used as hash table keys. If you later wish to access the |
841 | items via another reference stringification (i.e. using the same | |
842 | reference that was used for the key originally to record the value into | |
843 | the hash table), it will work because both references stringify to the | |
844 | same string. | |
845 | ||
6fe6778b PN |
846 | It won't work across a sequence of C<store> and C<retrieve> operations, |
847 | however, because the addresses in the retrieved objects, which are | |
848 | part of the stringified references, will probably differ from the | |
849 | original addresses. The topology of your structure is preserved, | |
850 | but not hidden semantics like those. | |
7a6a85bf RG |
851 | |
852 | On platforms where it matters, be sure to call C<binmode()> on the | |
853 | descriptors that you pass to Storable functions. | |
854 | ||
855 | Storing data canonically that contains large hashes can be | |
856 | significantly slower than storing the same data normally, as | |
c261f00e | 857 | temporary arrays to hold the keys for each hash have to be allocated, |
7a6a85bf RG |
858 | populated, sorted and freed. Some tests have shown a halving of the |
859 | speed of storing -- the exact penalty will depend on the complexity of | |
860 | your data. There is no slowdown on retrieval. | |
861 | ||
862 | =head1 BUGS | |
863 | ||
f062ea6c | 864 | You can't store GLOB, CODE, FORMLINE, etc.... If you can define |
7a6a85bf RG |
865 | semantics for those operations, feel free to enhance Storable so that |
866 | it can deal with them. | |
867 | ||
868 | The store functions will C<croak> if they run into such references | |
869 | unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that | |
870 | case, the fatal message is turned in a warning and some | |
871 | meaningless string is stored instead. | |
872 | ||
873 | Setting C<$Storable::canonical> may not yield frozen strings that | |
874 | compare equal due to possible stringification of numbers. When the | |
f062ea6c | 875 | string version of a scalar exists, it is the form stored; therefore, |
7a6a85bf RG |
876 | if you happen to use your numbers as strings between two freezing |
877 | operations on the same data structures, you will get different | |
878 | results. | |
879 | ||
dd19458b JH |
880 | When storing doubles in network order, their value is stored as text. |
881 | However, you should also not expect non-numeric floating-point values | |
882 | such as infinity and "not a number" to pass successfully through a | |
883 | nstore()/retrieve() pair. | |
884 | ||
885 | As Storable neither knows nor cares about character sets (although it | |
886 | does know that characters may be more than eight bits wide), any difference | |
887 | in the interpretation of character codes between a host and a target | |
888 | system is your problem. In particular, if host and target use different | |
889 | code points to represent the characters used in the text representation | |
890 | of floating-point numbers, you will not be able be able to exchange | |
891 | floating-point data, even with nstore(). | |
892 | ||
c261f00e NC |
893 | C<Storable::drop_utf8> is a blunt tool. There is no facility either to |
894 | return B<all> strings as utf8 sequences, or to attempt to convert utf8 | |
895 | data back to 8 bit and C<croak()> if the conversion fails. | |
896 | ||
7a6a85bf RG |
897 | =head1 CREDITS |
898 | ||
899 | Thank you to (in chronological order): | |
900 | ||
901 | Jarkko Hietaniemi <jhi@iki.fi> | |
902 | Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de> | |
903 | Benjamin A. Holzman <bah@ecnvantage.com> | |
904 | Andrew Ford <A.Ford@ford-mason.co.uk> | |
905 | Gisle Aas <gisle@aas.no> | |
906 | Jeff Gresham <gresham_jeffrey@jpmorgan.com> | |
907 | Murray Nesbitt <murray@activestate.com> | |
908 | Marc Lehmann <pcg@opengroup.org> | |
9e21b3d0 JH |
909 | Justin Banks <justinb@wamnet.com> |
910 | Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!) | |
dd19458b JH |
911 | Salvador Ortiz Garcia <sog@msg.com.mx> |
912 | Dominic Dunlop <domo@computer.org> | |
913 | Erik Haugan <erik@solbors.no> | |
7a6a85bf RG |
914 | |
915 | for their bug reports, suggestions and contributions. | |
916 | ||
917 | Benjamin Holzman contributed the tied variable support, Andrew Ford | |
918 | contributed the canonical order for hashes, and Gisle Aas fixed | |
f062ea6c | 919 | a few misunderstandings of mine regarding the perl internals, |
7a6a85bf RG |
920 | and optimized the emission of "tags" in the output streams by |
921 | simply counting the objects instead of tagging them (leading to | |
922 | a binary incompatibility for the Storable image starting at version | |
f062ea6c | 923 | 0.6--older images are, of course, still properly understood). |
7a6a85bf | 924 | Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading |
f062ea6c | 925 | and references to tied items support. |
7a6a85bf | 926 | |
7a6a85bf RG |
927 | =head1 AUTHOR |
928 | ||
0ba8809e | 929 | Storable was written by Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>> |
775ecd75 | 930 | Maintenance is now done by the perl5-porters F<E<lt>perl5-porters@perl.orgE<gt>> |
0ba8809e NC |
931 | |
932 | Please e-mail us with problems, bug fixes, comments and complaints, | |
933 | although if you have complements you should send them to Raphael. | |
934 | Please don't e-mail Raphael with problems, as he no longer works on | |
935 | Storable, and your message will be delayed while he forwards it to us. | |
7a6a85bf RG |
936 | |
937 | =head1 SEE ALSO | |
938 | ||
c261f00e | 939 | L<Clone>. |
7a6a85bf RG |
940 | |
941 | =cut | |
942 |