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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 = '1.015'; |
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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 | # Can't Autoload cleanly as this clashes 8.3 with &retrieve |
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114 | sub retrieve_fd { &fd_retrieve } # Backward compatibility |
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115 | |
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116 | bootstrap Storable; |
117 | 1; |
118 | __END__ |
119 | |
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120 | # |
121 | # Determine whether locking is possible, but only when needed. |
122 | # |
123 | |
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124 | sub CAN_FLOCK { |
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125 | my $CAN_FLOCK if 0; |
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126 | return $CAN_FLOCK if defined $CAN_FLOCK; |
127 | require Config; import Config; |
128 | return $CAN_FLOCK = |
129 | $Config{'d_flock'} || |
130 | $Config{'d_fcntl_can_lock'} || |
131 | $Config{'d_lockf'}; |
132 | } |
133 | |
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134 | sub show_file_magic { |
135 | print <<EOM; |
136 | # |
137 | # To recognize the data files of the Perl module Storable, |
138 | # the following lines need to be added to the local magic(5) file, |
139 | # usually either /usr/share/misc/magic or /etc/magic. |
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140 | # |
141 | 0 string perl-store perl Storable(v0.6) data |
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142 | >4 byte >0 (net-order %d) |
143 | >>4 byte &01 (network-ordered) |
144 | >>4 byte =3 (major 1) |
145 | >>4 byte =2 (major 1) |
146 | |
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147 | 0 string pst0 perl Storable(v0.7) data |
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148 | >4 byte >0 |
149 | >>4 byte &01 (network-ordered) |
150 | >>4 byte =5 (major 2) |
151 | >>4 byte =4 (major 2) |
152 | >>5 byte >0 (minor %d) |
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153 | EOM |
154 | } |
155 | |
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156 | sub read_magic { |
157 | my $header = shift; |
158 | return unless defined $header and length $header > 11; |
159 | my $result; |
160 | if ($header =~ s/^perl-store//) { |
161 | die "Can't deal with version 0 headers"; |
162 | } elsif ($header =~ s/^pst0//) { |
163 | $result->{file} = 1; |
164 | } |
165 | # Assume it's a string. |
166 | my ($major, $minor, $bytelen) = unpack "C3", $header; |
167 | |
168 | my $net_order = $major & 1; |
169 | $major >>= 1; |
170 | @$result{qw(major minor netorder)} = ($major, $minor, $net_order); |
171 | |
172 | return $result if $net_order; |
173 | |
174 | # I assume that it is rare to find v1 files, so this is an intentionally |
175 | # inefficient way of doing it, to make the rest of the code constant. |
176 | if ($major < 2) { |
177 | delete $result->{minor}; |
178 | $header = '.' . $header; |
179 | $bytelen = $minor; |
180 | } |
181 | |
182 | @$result{qw(byteorder intsize longsize ptrsize)} = |
183 | unpack "x3 A$bytelen C3", $header; |
184 | |
185 | if ($major >= 2 and $minor >= 2) { |
186 | $result->{nvsize} = unpack "x6 x$bytelen C", $header; |
187 | } |
188 | $result; |
189 | } |
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190 | |
191 | # |
192 | # store |
193 | # |
194 | # Store target object hierarchy, identified by a reference to its root. |
195 | # The stored object tree may later be retrieved to memory via retrieve. |
196 | # Returns undef if an I/O error occurred, in which case the file is |
197 | # removed. |
198 | # |
199 | sub store { |
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200 | return _store(\&pstore, @_, 0); |
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201 | } |
202 | |
203 | # |
204 | # nstore |
205 | # |
206 | # Same as store, but in network order. |
207 | # |
208 | sub nstore { |
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209 | return _store(\&net_pstore, @_, 0); |
210 | } |
211 | |
212 | # |
213 | # lock_store |
214 | # |
215 | # Same as store, but flock the file first (advisory locking). |
216 | # |
217 | sub lock_store { |
218 | return _store(\&pstore, @_, 1); |
219 | } |
220 | |
221 | # |
222 | # lock_nstore |
223 | # |
224 | # Same as nstore, but flock the file first (advisory locking). |
225 | # |
226 | sub lock_nstore { |
227 | return _store(\&net_pstore, @_, 1); |
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228 | } |
229 | |
230 | # Internal store to file routine |
231 | sub _store { |
232 | my $xsptr = shift; |
233 | my $self = shift; |
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234 | my ($file, $use_locking) = @_; |
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235 | logcroak "not a reference" unless ref($self); |
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236 | logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist |
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237 | local *FILE; |
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238 | if ($use_locking) { |
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239 | open(FILE, ">>$file") || logcroak "can't write into $file: $!"; |
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240 | unless (&CAN_FLOCK) { |
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241 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
242 | return undef; |
f567092b |
243 | } |
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244 | flock(FILE, LOCK_EX) || |
245 | logcroak "can't get exclusive lock on $file: $!"; |
246 | truncate FILE, 0; |
247 | # Unlocking will happen when FILE is closed |
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248 | } else { |
249 | open(FILE, ">$file") || logcroak "can't create $file: $!"; |
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250 | } |
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251 | binmode FILE; # Archaic systems... |
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252 | my $da = $@; # Don't mess if called from exception handler |
253 | my $ret; |
254 | # Call C routine nstore or pstore, depending on network order |
255 | eval { $ret = &$xsptr(*FILE, $self) }; |
256 | close(FILE) or $ret = undef; |
257 | unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret; |
258 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
259 | $@ = $da; |
260 | return $ret ? $ret : undef; |
261 | } |
262 | |
263 | # |
264 | # store_fd |
265 | # |
266 | # Same as store, but perform on an already opened file descriptor instead. |
267 | # Returns undef if an I/O error occurred. |
268 | # |
269 | sub store_fd { |
270 | return _store_fd(\&pstore, @_); |
271 | } |
272 | |
273 | # |
274 | # nstore_fd |
275 | # |
276 | # Same as store_fd, but in network order. |
277 | # |
278 | sub nstore_fd { |
279 | my ($self, $file) = @_; |
280 | return _store_fd(\&net_pstore, @_); |
281 | } |
282 | |
283 | # Internal store routine on opened file descriptor |
284 | sub _store_fd { |
285 | my $xsptr = shift; |
286 | my $self = shift; |
287 | my ($file) = @_; |
288 | logcroak "not a reference" unless ref($self); |
289 | logcroak "too many arguments" unless @_ == 1; # No @foo in arglist |
290 | my $fd = fileno($file); |
291 | logcroak "not a valid file descriptor" unless defined $fd; |
292 | my $da = $@; # Don't mess if called from exception handler |
293 | my $ret; |
294 | # Call C routine nstore or pstore, depending on network order |
295 | eval { $ret = &$xsptr($file, $self) }; |
296 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
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297 | local $\; print $file ''; # Autoflush the file if wanted |
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298 | $@ = $da; |
299 | return $ret ? $ret : undef; |
300 | } |
301 | |
302 | # |
303 | # freeze |
304 | # |
305 | # Store oject and its hierarchy in memory and return a scalar |
306 | # containing the result. |
307 | # |
308 | sub freeze { |
309 | _freeze(\&mstore, @_); |
310 | } |
311 | |
312 | # |
313 | # nfreeze |
314 | # |
315 | # Same as freeze but in network order. |
316 | # |
317 | sub nfreeze { |
318 | _freeze(\&net_mstore, @_); |
319 | } |
320 | |
321 | # Internal freeze routine |
322 | sub _freeze { |
323 | my $xsptr = shift; |
324 | my $self = shift; |
325 | logcroak "not a reference" unless ref($self); |
326 | logcroak "too many arguments" unless @_ == 0; # No @foo in arglist |
327 | my $da = $@; # Don't mess if called from exception handler |
328 | my $ret; |
329 | # Call C routine mstore or net_mstore, depending on network order |
330 | eval { $ret = &$xsptr($self) }; |
331 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
332 | $@ = $da; |
333 | return $ret ? $ret : undef; |
334 | } |
335 | |
336 | # |
337 | # retrieve |
338 | # |
339 | # Retrieve object hierarchy from disk, returning a reference to the root |
340 | # object of that tree. |
341 | # |
342 | sub retrieve { |
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343 | _retrieve($_[0], 0); |
344 | } |
345 | |
346 | # |
347 | # lock_retrieve |
348 | # |
349 | # Same as retrieve, but with advisory locking. |
350 | # |
351 | sub lock_retrieve { |
352 | _retrieve($_[0], 1); |
353 | } |
354 | |
355 | # Internal retrieve routine |
356 | sub _retrieve { |
357 | my ($file, $use_locking) = @_; |
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358 | local *FILE; |
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359 | open(FILE, $file) || logcroak "can't open $file: $!"; |
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360 | binmode FILE; # Archaic systems... |
361 | my $self; |
362 | my $da = $@; # Could be from exception handler |
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363 | if ($use_locking) { |
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364 | unless (&CAN_FLOCK) { |
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365 | logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; |
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366 | return undef; |
367 | } |
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368 | flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!"; |
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369 | # Unlocking will happen when FILE is closed |
370 | } |
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371 | eval { $self = pretrieve(*FILE) }; # Call C routine |
372 | close(FILE); |
373 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
374 | $@ = $da; |
375 | return $self; |
376 | } |
377 | |
378 | # |
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379 | # fd_retrieve |
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380 | # |
381 | # Same as retrieve, but perform from an already opened file descriptor instead. |
382 | # |
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383 | sub fd_retrieve { |
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384 | my ($file) = @_; |
385 | my $fd = fileno($file); |
386 | logcroak "not a valid file descriptor" unless defined $fd; |
387 | my $self; |
388 | my $da = $@; # Could be from exception handler |
389 | eval { $self = pretrieve($file) }; # Call C routine |
390 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
391 | $@ = $da; |
392 | return $self; |
393 | } |
394 | |
395 | # |
396 | # thaw |
397 | # |
398 | # Recreate objects in memory from an existing frozen image created |
399 | # by freeze. If the frozen image passed is undef, return undef. |
400 | # |
401 | sub thaw { |
402 | my ($frozen) = @_; |
403 | return undef unless defined $frozen; |
404 | my $self; |
405 | my $da = $@; # Could be from exception handler |
406 | eval { $self = mretrieve($frozen) }; # Call C routine |
407 | logcroak $@ if $@ =~ s/\.?\n$/,/; |
408 | $@ = $da; |
409 | return $self; |
410 | } |
411 | |
412 | =head1 NAME |
413 | |
414 | Storable - persistency for perl data structures |
415 | |
416 | =head1 SYNOPSIS |
417 | |
418 | use Storable; |
419 | store \%table, 'file'; |
420 | $hashref = retrieve('file'); |
421 | |
422 | use Storable qw(nstore store_fd nstore_fd freeze thaw dclone); |
423 | |
424 | # Network order |
425 | nstore \%table, 'file'; |
426 | $hashref = retrieve('file'); # There is NO nretrieve() |
427 | |
428 | # Storing to and retrieving from an already opened file |
429 | store_fd \@array, \*STDOUT; |
430 | nstore_fd \%table, \*STDOUT; |
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431 | $aryref = fd_retrieve(\*SOCKET); |
432 | $hashref = fd_retrieve(\*SOCKET); |
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433 | |
434 | # Serializing to memory |
435 | $serialized = freeze \%table; |
436 | %table_clone = %{ thaw($serialized) }; |
437 | |
438 | # Deep (recursive) cloning |
439 | $cloneref = dclone($ref); |
440 | |
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441 | # Advisory locking |
442 | use Storable qw(lock_store lock_nstore lock_retrieve) |
443 | lock_store \%table, 'file'; |
444 | lock_nstore \%table, 'file'; |
445 | $hashref = lock_retrieve('file'); |
446 | |
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447 | =head1 DESCRIPTION |
448 | |
449 | The Storable package brings persistency to your perl data structures |
450 | containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be |
451 | convenientely stored to disk and retrieved at a later time. |
452 | |
453 | It can be used in the regular procedural way by calling C<store> with |
454 | a reference to the object to be stored, along with the file name where |
455 | the image should be written. |
456 | The routine returns C<undef> for I/O problems or other internal error, |
457 | a true value otherwise. Serious errors are propagated as a C<die> exception. |
458 | |
459 | To retrieve data stored to disk, use C<retrieve> with a file name, |
460 | and the objects stored into that file are recreated into memory for you, |
461 | a I<reference> to the root object being returned. In case an I/O error |
462 | occurs while reading, C<undef> is returned instead. Other serious |
463 | errors are propagated via C<die>. |
464 | |
465 | Since storage is performed recursively, you might want to stuff references |
466 | to objects that share a lot of common data into a single array or hash |
467 | table, and then store that object. That way, when you retrieve back the |
468 | whole thing, the objects will continue to share what they originally shared. |
469 | |
470 | At the cost of a slight header overhead, you may store to an already |
471 | opened file descriptor using the C<store_fd> routine, and retrieve |
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472 | from a file via C<fd_retrieve>. Those names aren't imported by default, |
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473 | so you will have to do that explicitely if you need those routines. |
474 | The file descriptor you supply must be already opened, for read |
475 | if you're going to retrieve and for write if you wish to store. |
476 | |
477 | store_fd(\%table, *STDOUT) || die "can't store to stdout\n"; |
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478 | $hashref = fd_retrieve(*STDIN); |
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479 | |
480 | You can also store data in network order to allow easy sharing across |
481 | multiple platforms, or when storing on a socket known to be remotely |
482 | connected. The routines to call have an initial C<n> prefix for I<network>, |
483 | as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be |
484 | correctly restored so you don't have to know whether you're restoring |
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485 | from native or network ordered data. Double values are stored stringified |
486 | to ensure portability as well, at the slight risk of loosing some precision |
487 | in the last decimals. |
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488 | |
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489 | When using C<fd_retrieve>, objects are retrieved in sequence, one |
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490 | object (i.e. one recursive tree) per associated C<store_fd>. |
491 | |
492 | If you're more from the object-oriented camp, you can inherit from |
493 | Storable and directly store your objects by invoking C<store> as |
494 | a method. The fact that the root of the to-be-stored tree is a |
495 | blessed reference (i.e. an object) is special-cased so that the |
496 | retrieve does not provide a reference to that object but rather the |
497 | blessed object reference itself. (Otherwise, you'd get a reference |
498 | to that blessed object). |
499 | |
500 | =head1 MEMORY STORE |
501 | |
502 | The Storable engine can also store data into a Perl scalar instead, to |
503 | later retrieve them. This is mainly used to freeze a complex structure in |
504 | some safe compact memory place (where it can possibly be sent to another |
505 | process via some IPC, since freezing the structure also serializes it in |
506 | effect). Later on, and maybe somewhere else, you can thaw the Perl scalar |
507 | out and recreate the original complex structure in memory. |
508 | |
509 | Surprisingly, the routines to be called are named C<freeze> and C<thaw>. |
510 | If you wish to send out the frozen scalar to another machine, use |
511 | C<nfreeze> instead to get a portable image. |
512 | |
513 | Note that freezing an object structure and immediately thawing it |
514 | actually achieves a deep cloning of that structure: |
515 | |
516 | dclone(.) = thaw(freeze(.)) |
517 | |
518 | Storable provides you with a C<dclone> interface which does not create |
519 | that intermediary scalar but instead freezes the structure in some |
520 | internal memory space and then immediatly thaws it out. |
521 | |
dd19458b |
522 | =head1 ADVISORY LOCKING |
523 | |
524 | The C<lock_store> and C<lock_nstore> routine are equivalent to C<store> |
525 | and C<nstore>, only they get an exclusive lock on the file before |
526 | writing. Likewise, C<lock_retrieve> performs as C<retrieve>, but also |
527 | gets a shared lock on the file before reading. |
528 | |
529 | Like with any advisory locking scheme, the protection only works if |
530 | you systematically use C<lock_store> and C<lock_retrieve>. If one |
531 | side of your application uses C<store> whilst the other uses C<lock_retrieve>, |
532 | you will get no protection at all. |
533 | |
534 | The internal advisory locking is implemented using Perl's flock() routine. |
535 | If your system does not support any form of flock(), or if you share |
536 | your files across NFS, you might wish to use other forms of locking by |
537 | using modules like LockFile::Simple which lock a file using a filesystem |
538 | entry, instead of locking the file descriptor. |
539 | |
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540 | =head1 SPEED |
541 | |
542 | The heart of Storable is written in C for decent speed. Extra low-level |
543 | optimization have been made when manipulating perl internals, to |
544 | sacrifice encapsulation for the benefit of a greater speed. |
545 | |
546 | =head1 CANONICAL REPRESENTATION |
547 | |
548 | Normally Storable stores elements of hashes in the order they are |
549 | stored internally by Perl, i.e. pseudo-randomly. If you set |
550 | C<$Storable::canonical> to some C<TRUE> value, Storable will store |
551 | hashes with the elements sorted by their key. This allows you to |
552 | compare data structures by comparing their frozen representations (or |
553 | even the compressed frozen representations), which can be useful for |
554 | creating lookup tables for complicated queries. |
555 | |
556 | Canonical order does not imply network order, those are two orthogonal |
557 | settings. |
558 | |
559 | =head1 ERROR REPORTING |
560 | |
561 | Storable uses the "exception" paradigm, in that it does not try to workaround |
562 | failures: if something bad happens, an exception is generated from the |
563 | caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap |
564 | those exceptions. |
565 | |
566 | When Storable croaks, it tries to report the error via the C<logcroak()> |
567 | routine from the C<Log::Agent> package, if it is available. |
568 | |
212e9bde |
569 | Normal errors are reported by having store() or retrieve() return C<undef>. |
570 | Such errors are usually I/O errors (or truncated stream errors at retrieval). |
571 | |
7a6a85bf |
572 | =head1 WIZARDS ONLY |
573 | |
574 | =head2 Hooks |
575 | |
576 | Any class may define hooks that will be called during the serialization |
577 | and deserialization process on objects that are instances of that class. |
578 | Those hooks can redefine the way serialization is performed (and therefore, |
579 | how the symetrical deserialization should be conducted). |
580 | |
581 | Since we said earlier: |
582 | |
583 | dclone(.) = thaw(freeze(.)) |
584 | |
585 | everything we say about hooks should also hold for deep cloning. However, |
586 | hooks get to know whether the operation is a mere serialization, or a cloning. |
587 | |
588 | Therefore, when serializing hooks are involved, |
589 | |
590 | dclone(.) <> thaw(freeze(.)) |
591 | |
592 | Well, you could keep them in sync, but there's no guarantee it will always |
593 | hold on classes somebody else wrote. Besides, there is little to gain in |
594 | doing so: a serializing hook could only keep one attribute of an object, |
595 | which is probably not what should happen during a deep cloning of that |
596 | same object. |
597 | |
598 | Here is the hooking interface: |
599 | |
bbc7dcd2 |
600 | =over 4 |
7a6a85bf |
601 | |
602 | =item C<STORABLE_freeze> I<obj>, I<cloning> |
603 | |
604 | The serializing hook, called on the object during serialization. It can be |
605 | inherited, or defined in the class itself, like any other method. |
606 | |
607 | Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating |
608 | whether we're in a dclone() or a regular serialization via store() or freeze(). |
609 | |
610 | Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized |
611 | is the serialized form to be used, and the optional $ref1, $ref2, etc... are |
612 | extra references that you wish to let the Storable engine serialize. |
613 | |
614 | At deserialization time, you will be given back the same LIST, but all the |
615 | extra references will be pointing into the deserialized structure. |
616 | |
617 | The B<first time> the hook is hit in a serialization flow, you may have it |
618 | return an empty list. That will signal the Storable engine to further |
619 | discard that hook for this class and to therefore revert to the default |
620 | serialization of the underlying Perl data. The hook will again be normally |
621 | processed in the next serialization. |
622 | |
623 | Unless you know better, serializing hook should always say: |
624 | |
625 | sub STORABLE_freeze { |
626 | my ($self, $cloning) = @_; |
627 | return if $cloning; # Regular default serialization |
628 | .... |
629 | } |
630 | |
631 | in order to keep reasonable dclone() semantics. |
632 | |
633 | =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ... |
634 | |
635 | The deserializing hook called on the object during deserialization. |
636 | But wait. If we're deserializing, there's no object yet... right? |
637 | |
638 | Wrong: the Storable engine creates an empty one for you. If you know Eiffel, |
639 | you can view C<STORABLE_thaw> as an alternate creation routine. |
640 | |
641 | This means the hook can be inherited like any other method, and that |
642 | I<obj> is your blessed reference for this particular instance. |
643 | |
644 | The other arguments should look familiar if you know C<STORABLE_freeze>: |
645 | I<cloning> is true when we're part of a deep clone operation, I<serialized> |
646 | is the serialized string you returned to the engine in C<STORABLE_freeze>, |
647 | and there may be an optional list of references, in the same order you gave |
648 | them at serialization time, pointing to the deserialized objects (which |
649 | have been processed courtesy of the Storable engine). |
650 | |
212e9bde |
651 | When the Storable engine does not find any C<STORABLE_thaw> hook routine, |
652 | it tries to load the class by requiring the package dynamically (using |
653 | the blessed package name), and then re-attempts the lookup. If at that |
654 | time the hook cannot be located, the engine croaks. Note that this mechanism |
655 | will fail if you define several classes in the same file, but perlmod(1) |
656 | warned you. |
657 | |
7a6a85bf |
658 | It is up to you to use these information to populate I<obj> the way you want. |
659 | |
660 | Returned value: none. |
661 | |
662 | =back |
663 | |
664 | =head2 Predicates |
665 | |
666 | Predicates are not exportable. They must be called by explicitely prefixing |
667 | them with the Storable package name. |
668 | |
bbc7dcd2 |
669 | =over 4 |
7a6a85bf |
670 | |
671 | =item C<Storable::last_op_in_netorder> |
672 | |
673 | The C<Storable::last_op_in_netorder()> predicate will tell you whether |
674 | network order was used in the last store or retrieve operation. If you |
675 | don't know how to use this, just forget about it. |
676 | |
677 | =item C<Storable::is_storing> |
678 | |
679 | Returns true if within a store operation (via STORABLE_freeze hook). |
680 | |
681 | =item C<Storable::is_retrieving> |
682 | |
683 | Returns true if within a retrieve operation, (via STORABLE_thaw hook). |
684 | |
685 | =back |
686 | |
687 | =head2 Recursion |
688 | |
689 | With hooks comes the ability to recurse back to the Storable engine. Indeed, |
690 | hooks are regular Perl code, and Storable is convenient when it comes to |
691 | serialize and deserialize things, so why not use it to handle the |
692 | serialization string? |
693 | |
694 | There are a few things you need to know however: |
695 | |
bbc7dcd2 |
696 | =over 4 |
7a6a85bf |
697 | |
698 | =item * |
699 | |
700 | You can create endless loops if the things you serialize via freeze() |
701 | (for instance) point back to the object we're trying to serialize in the hook. |
702 | |
703 | =item * |
704 | |
705 | Shared references among objects will not stay shared: if we're serializing |
706 | the list of object [A, C] where both object A and C refer to the SAME object |
707 | B, and if there is a serializing hook in A that says freeze(B), then when |
708 | deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D, |
709 | a deep clone of B'. The topology was not preserved. |
710 | |
711 | =back |
712 | |
713 | That's why C<STORABLE_freeze> lets you provide a list of references |
714 | to serialize. The engine guarantees that those will be serialized in the |
715 | same context as the other objects, and therefore that shared objects will |
716 | stay shared. |
717 | |
718 | In the above [A, C] example, the C<STORABLE_freeze> hook could return: |
719 | |
720 | ("something", $self->{B}) |
721 | |
722 | and the B part would be serialized by the engine. In C<STORABLE_thaw>, you |
723 | would get back the reference to the B' object, deserialized for you. |
724 | |
725 | Therefore, recursion should normally be avoided, but is nonetheless supported. |
726 | |
727 | =head2 Deep Cloning |
728 | |
729 | There is a new Clone module available on CPAN which implements deep cloning |
730 | natively, i.e. without freezing to memory and thawing the result. It is |
731 | aimed to replace Storable's dclone() some day. However, it does not currently |
732 | support Storable hooks to redefine the way deep cloning is performed. |
733 | |
0a0da639 |
734 | =head1 Storable magic |
735 | |
736 | Yes, there's a lot of that :-) But more precisely, in UNIX systems |
737 | there's a utility called C<file>, which recognizes data files based on |
738 | their contents (usually their first few bytes). For this to work, |
8b793558 |
739 | a certain file called F<magic> needs to taught about the I<signature> |
0a0da639 |
740 | of the data. Where that configuration file lives depends on the UNIX |
741 | flavour, often it's something like F</usr/share/misc/magic> or |
8b793558 |
742 | F</etc/magic>. Your system administrator needs to do the updating of |
743 | the F<magic> file. The necessary signature information is output to |
744 | stdout by invoking Storable::show_file_magic(). Note that the open |
745 | source implementation of the C<file> utility 3.38 (or later) |
746 | is expected to contain the support for recognising Storable files, |
747 | in addition to other kinds of Perl files. |
0a0da639 |
748 | |
7a6a85bf |
749 | =head1 EXAMPLES |
750 | |
751 | Here are some code samples showing a possible usage of Storable: |
752 | |
753 | use Storable qw(store retrieve freeze thaw dclone); |
754 | |
755 | %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1); |
756 | |
757 | store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n"; |
758 | |
759 | $colref = retrieve('/tmp/colors'); |
760 | die "Unable to retrieve from /tmp/colors!\n" unless defined $colref; |
761 | printf "Blue is still %lf\n", $colref->{'Blue'}; |
762 | |
763 | $colref2 = dclone(\%color); |
764 | |
765 | $str = freeze(\%color); |
766 | printf "Serialization of %%color is %d bytes long.\n", length($str); |
767 | $colref3 = thaw($str); |
768 | |
769 | which prints (on my machine): |
770 | |
771 | Blue is still 0.100000 |
772 | Serialization of %color is 102 bytes long. |
773 | |
774 | =head1 WARNING |
775 | |
776 | If you're using references as keys within your hash tables, you're bound |
777 | to disapointment when retrieving your data. Indeed, Perl stringifies |
778 | references used as hash table keys. If you later wish to access the |
779 | items via another reference stringification (i.e. using the same |
780 | reference that was used for the key originally to record the value into |
781 | the hash table), it will work because both references stringify to the |
782 | same string. |
783 | |
784 | It won't work across a C<store> and C<retrieve> operations however, because |
785 | the addresses in the retrieved objects, which are part of the stringified |
786 | references, will probably differ from the original addresses. The |
787 | topology of your structure is preserved, but not hidden semantics |
788 | like those. |
789 | |
790 | On platforms where it matters, be sure to call C<binmode()> on the |
791 | descriptors that you pass to Storable functions. |
792 | |
793 | Storing data canonically that contains large hashes can be |
794 | significantly slower than storing the same data normally, as |
795 | temprorary arrays to hold the keys for each hash have to be allocated, |
796 | populated, sorted and freed. Some tests have shown a halving of the |
797 | speed of storing -- the exact penalty will depend on the complexity of |
798 | your data. There is no slowdown on retrieval. |
799 | |
800 | =head1 BUGS |
801 | |
802 | You can't store GLOB, CODE, FORMLINE, etc... If you can define |
803 | semantics for those operations, feel free to enhance Storable so that |
804 | it can deal with them. |
805 | |
806 | The store functions will C<croak> if they run into such references |
807 | unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that |
808 | case, the fatal message is turned in a warning and some |
809 | meaningless string is stored instead. |
810 | |
811 | Setting C<$Storable::canonical> may not yield frozen strings that |
812 | compare equal due to possible stringification of numbers. When the |
813 | string version of a scalar exists, it is the form stored, therefore |
814 | if you happen to use your numbers as strings between two freezing |
815 | operations on the same data structures, you will get different |
816 | results. |
817 | |
dd19458b |
818 | When storing doubles in network order, their value is stored as text. |
819 | However, you should also not expect non-numeric floating-point values |
820 | such as infinity and "not a number" to pass successfully through a |
821 | nstore()/retrieve() pair. |
822 | |
823 | As Storable neither knows nor cares about character sets (although it |
824 | does know that characters may be more than eight bits wide), any difference |
825 | in the interpretation of character codes between a host and a target |
826 | system is your problem. In particular, if host and target use different |
827 | code points to represent the characters used in the text representation |
828 | of floating-point numbers, you will not be able be able to exchange |
829 | floating-point data, even with nstore(). |
830 | |
7a6a85bf |
831 | =head1 CREDITS |
832 | |
833 | Thank you to (in chronological order): |
834 | |
835 | Jarkko Hietaniemi <jhi@iki.fi> |
836 | Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de> |
837 | Benjamin A. Holzman <bah@ecnvantage.com> |
838 | Andrew Ford <A.Ford@ford-mason.co.uk> |
839 | Gisle Aas <gisle@aas.no> |
840 | Jeff Gresham <gresham_jeffrey@jpmorgan.com> |
841 | Murray Nesbitt <murray@activestate.com> |
842 | Marc Lehmann <pcg@opengroup.org> |
9e21b3d0 |
843 | Justin Banks <justinb@wamnet.com> |
844 | Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!) |
dd19458b |
845 | Salvador Ortiz Garcia <sog@msg.com.mx> |
846 | Dominic Dunlop <domo@computer.org> |
847 | Erik Haugan <erik@solbors.no> |
7a6a85bf |
848 | |
849 | for their bug reports, suggestions and contributions. |
850 | |
851 | Benjamin Holzman contributed the tied variable support, Andrew Ford |
852 | contributed the canonical order for hashes, and Gisle Aas fixed |
853 | a few misunderstandings of mine regarding the Perl internals, |
854 | and optimized the emission of "tags" in the output streams by |
855 | simply counting the objects instead of tagging them (leading to |
856 | a binary incompatibility for the Storable image starting at version |
857 | 0.6--older images are of course still properly understood). |
858 | Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading |
859 | and reference to tied items support. |
860 | |
861 | =head1 TRANSLATIONS |
862 | |
863 | There is a Japanese translation of this man page available at |
864 | http://member.nifty.ne.jp/hippo2000/perltips/storable.htm , |
865 | courtesy of Kawai, Takanori <kawai@nippon-rad.co.jp>. |
866 | |
867 | =head1 AUTHOR |
868 | |
869 | Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>> |
870 | |
871 | =head1 SEE ALSO |
872 | |
873 | Clone(3). |
874 | |
875 | =cut |
876 | |