1Storable(3pm) Perl Programmers Reference Guide Storable(3pm)
2
6 Storable - persistence for Perl data structures
7
9 use Storable;
10 store \%table, 'file';
11 $hashref = retrieve('file');
12 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);
14 # Network order
16 nstore \%table, 'file';
17 $hashref = retrieve('file'); # There is NO nretrieve()
18 # Storing to and retrieving from an already opened file
20 store_fd \@array, \*STDOUT;
21 nstore_fd \%table, \*STDOUT;
22 $aryref = fd_retrieve(\*SOCKET);
23 $hashref = fd_retrieve(\*SOCKET);
24 # Serializing to memory
26 $serialized = freeze \%table;
27 %table_clone = %{ thaw($serialized) };
28 # Deep (recursive) cloning
30 $cloneref = dclone($ref);
31 # Advisory locking
33 use Storable qw(lock_store lock_nstore lock_retrieve)
34 lock_store \%table, 'file';
35 lock_nstore \%table, 'file';
36 $hashref = lock_retrieve('file');
37
39 The Storable package brings persistence to your Perl data structures
40 containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can
41 be conveniently stored to disk and retrieved at a later time.
42 It can be used in the regular procedural way by calling "store" with a
44 reference to the object to be stored, along with the file name where
45 the image should be written.
46 The routine returns "undef" for I/O problems or other internal error, a
48 true value otherwise. Serious errors are propagated as a "die"
49 exception.
50 To retrieve data stored to disk, use "retrieve" with a file name. The
52 objects stored into that file are recreated into memory for you, and a
53 reference to the root object is returned. In case an I/O error occurs
54 while reading, "undef" is returned instead. Other serious errors are
55 propagated via "die".
56 Since storage is performed recursively, you might want to stuff
58 references to objects that share a lot of common data into a single
59 array or hash table, and then store that object. That way, when you
60 retrieve back the whole thing, the objects will continue to share what
61 they originally shared.
62 At the cost of a slight header overhead, you may store to an already
64 opened file descriptor using the "store_fd" routine, and retrieve from
65 a file via "fd_retrieve". Those names aren't imported by default, so
66 you will have to do that explicitly if you need those routines. The
67 file descriptor you supply must be already opened, for read if you're
68 going to retrieve and for write if you wish to store.
69 store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
71 $hashref = fd_retrieve(*STDIN);
72 You can also store data in network order to allow easy sharing across
74 multiple platforms, or when storing on a socket known to be remotely
75 connected. The routines to call have an initial "n" prefix for network,
76 as in "nstore" and "nstore_fd". At retrieval time, your data will be
77 correctly restored so you don't have to know whether you're restoring
78 from native or network ordered data. Double values are stored
79 stringified to ensure portability as well, at the slight risk of
80 loosing some precision in the last decimals.
81 When using "fd_retrieve", objects are retrieved in sequence, one object
83 (i.e. one recursive tree) per associated "store_fd".
84 If you're more from the object-oriented camp, you can inherit from
86 Storable and directly store your objects by invoking "store" as a
87 method. The fact that the root of the to-be-stored tree is a blessed
88 reference (i.e. an object) is special-cased so that the retrieve does
89 not provide a reference to that object but rather the blessed object
90 reference itself. (Otherwise, you'd get a reference to that blessed
91 object).
92
94 The Storable engine can also store data into a Perl scalar instead, to
95 later retrieve them. This is mainly used to freeze a complex structure
96 in some safe compact memory place (where it can possibly be sent to
97 another process via some IPC, since freezing the structure also
98 serializes it in effect). Later on, and maybe somewhere else, you can
99 thaw the Perl scalar out and recreate the original complex structure in
100 memory.
101 Surprisingly, the routines to be called are named "freeze" and "thaw".
103 If you wish to send out the frozen scalar to another machine, use
104 "nfreeze" instead to get a portable image.
105 Note that freezing an object structure and immediately thawing it
107 actually achieves a deep cloning of that structure:
108 dclone(.) = thaw(freeze(.))
110 Storable provides you with a "dclone" interface which does not create
112 that intermediary scalar but instead freezes the structure in some
113 internal memory space and then immediately thaws it out.
114
116 The "lock_store" and "lock_nstore" routine are equivalent to "store"
117 and "nstore", except that they get an exclusive lock on the file before
118 writing. Likewise, "lock_retrieve" does the same as "retrieve", but
119 also gets a shared lock on the file before reading.
120 As with any advisory locking scheme, the protection only works if you
122 systematically use "lock_store" and "lock_retrieve". If one side of
123 your application uses "store" whilst the other uses "lock_retrieve",
124 you will get no protection at all.
125 The internal advisory locking is implemented using Perl's flock()
127 routine. If your system does not support any form of flock(), or if
128 you share your files across NFS, you might wish to use other forms of
129 locking by using modules such as LockFile::Simple which lock a file
130 using a filesystem entry, instead of locking the file descriptor.
131
133 The heart of Storable is written in C for decent speed. Extra low-level
134 optimizations have been made when manipulating perl internals, to
135 sacrifice encapsulation for the benefit of greater speed.
136
138 Normally, Storable stores elements of hashes in the order they are
139 stored internally by Perl, i.e. pseudo-randomly. If you set
140 $Storable::canonical to some "TRUE" value, Storable will store hashes
141 with the elements sorted by their key. This allows you to compare data
142 structures by comparing their frozen representations (or even the
143 compressed frozen representations), which can be useful for creating
144 lookup tables for complicated queries.
145 Canonical order does not imply network order; those are two orthogonal
147 settings.
148
150 Since Storable version 2.05, CODE references may be serialized with the
151 help of B::Deparse. To enable this feature, set $Storable::Deparse to a
152 true value. To enable deserialization, $Storable::Eval should be set to
153 a true value. Be aware that deserialization is done through "eval",
154 which is dangerous if the Storable file contains malicious data. You
155 can set $Storable::Eval to a subroutine reference which would be used
156 instead of "eval". See below for an example using a Safe compartment
157 for deserialization of CODE references.
158 If $Storable::Deparse and/or $Storable::Eval are set to false values,
160 then the value of $Storable::forgive_me (see below) is respected while
161 serializing and deserializing.
162
164 This release of Storable can be used on a newer version of Perl to
165 serialize data which is not supported by earlier Perls. By default,
166 Storable will attempt to do the right thing, by "croak()"ing if it
167 encounters data that it cannot deserialize. However, the defaults can
168 be changed as follows:
169 utf8 data
171 Perl 5.6 added support for Unicode characters with code points >
172 255, and Perl 5.8 has full support for Unicode characters in hash
173 keys. Perl internally encodes strings with these characters using
174 utf8, and Storable serializes them as utf8. By default, if an
175 older version of Perl encounters a utf8 value it cannot represent,
176 it will "croak()". To change this behaviour so that Storable
177 deserializes utf8 encoded values as the string of bytes
178 (effectively dropping the is_utf8 flag) set $Storable::drop_utf8 to
179 some "TRUE" value. This is a form of data loss, because with
180 $drop_utf8 true, it becomes impossible to tell whether the original
181 data was the Unicode string, or a series of bytes that happen to be
182 valid utf8.
183 restricted hashes
185 Perl 5.8 adds support for restricted hashes, which have keys
186 restricted to a given set, and can have values locked to be read
187 only. By default, when Storable encounters a restricted hash on a
188 perl that doesn't support them, it will deserialize it as a normal
189 hash, silently discarding any placeholder keys and leaving the keys
190 and all values unlocked. To make Storable "croak()" instead, set
191 $Storable::downgrade_restricted to a "FALSE" value. To restore the
192 default set it back to some "TRUE" value.
193 files from future versions of Storable
195 Earlier versions of Storable would immediately croak if they
196 encountered a file with a higher internal version number than the
197 reading Storable knew about. Internal version numbers are
198 increased each time new data types (such as restricted hashes) are
199 added to the vocabulary of the file format. This meant that a
200 newer Storable module had no way of writing a file readable by an
201 older Storable, even if the writer didn't store newer data types.
202 This version of Storable will defer croaking until it encounters a
204 data type in the file that it does not recognize. This means that
205 it will continue to read files generated by newer Storable modules
206 which are careful in what they write out, making it easier to
207 upgrade Storable modules in a mixed environment.
208 The old behaviour of immediate croaking can be re-instated by
210 setting $Storable::accept_future_minor to some "FALSE" value.
211 All these variables have no effect on a newer Perl which supports the
213 relevant feature.
214
216 Storable uses the "exception" paradigm, in that it does not try to
217 workaround failures: if something bad happens, an exception is
218 generated from the caller's perspective (see Carp and "croak()"). Use
219 eval {} to trap those exceptions.
220 When Storable croaks, it tries to report the error via the "logcroak()"
222 routine from the "Log::Agent" package, if it is available.
223 Normal errors are reported by having store() or retrieve() return
225 "undef". Such errors are usually I/O errors (or truncated stream
226 errors at retrieval).
227
229 Hooks
230 Any class may define hooks that will be called during the serialization
231 and deserialization process on objects that are instances of that
232 class. Those hooks can redefine the way serialization is performed
233 (and therefore, how the symmetrical deserialization should be
234 conducted).
235 Since we said earlier:
237 dclone(.) = thaw(freeze(.))
239 everything we say about hooks should also hold for deep cloning.
241 However, hooks get to know whether the operation is a mere
242 serialization, or a cloning.
243 Therefore, when serializing hooks are involved,
245 dclone(.) <> thaw(freeze(.))
247 Well, you could keep them in sync, but there's no guarantee it will
249 always hold on classes somebody else wrote. Besides, there is little
250 to gain in doing so: a serializing hook could keep only one attribute
251 of an object, which is probably not what should happen during a deep
252 cloning of that same object.
253 Here is the hooking interface:
255 "STORABLE_freeze" obj, cloning
257 The serializing hook, called on the object during serialization.
258 It can be inherited, or defined in the class itself, like any other
259 method.
260 Arguments: obj is the object to serialize, cloning is a flag
262 indicating whether we're in a dclone() or a regular serialization
263 via store() or freeze().
264 Returned value: A LIST "($serialized, $ref1, $ref2, ...)" where
266 $serialized is the serialized form to be used, and the optional
267 $ref1, $ref2, etc... are extra references that you wish to let the
268 Storable engine serialize.
269 At deserialization time, you will be given back the same LIST, but
271 all the extra references will be pointing into the deserialized
272 structure.
273 The first time the hook is hit in a serialization flow, you may
275 have it return an empty list. That will signal the Storable engine
276 to further discard that hook for this class and to therefore revert
277 to the default serialization of the underlying Perl data. The hook
278 will again be normally processed in the next serialization.
279 Unless you know better, serializing hook should always say:
281 sub STORABLE_freeze {
283 my ($self, $cloning) = @_;
284 return if $cloning; # Regular default serialization
285 ....
286 }
287 in order to keep reasonable dclone() semantics.
289 "STORABLE_thaw" obj, cloning, serialized, ...
291 The deserializing hook called on the object during deserialization.
292 But wait: if we're deserializing, there's no object yet... right?
293 Wrong: the Storable engine creates an empty one for you. If you
295 know Eiffel, you can view "STORABLE_thaw" as an alternate creation
296 routine.
297 This means the hook can be inherited like any other method, and
299 that obj is your blessed reference for this particular instance.
300 The other arguments should look familiar if you know
302 "STORABLE_freeze": cloning is true when we're part of a deep clone
303 operation, serialized is the serialized string you returned to the
304 engine in "STORABLE_freeze", and there may be an optional list of
305 references, in the same order you gave them at serialization time,
306 pointing to the deserialized objects (which have been processed
307 courtesy of the Storable engine).
308 When the Storable engine does not find any "STORABLE_thaw" hook
310 routine, it tries to load the class by requiring the package
311 dynamically (using the blessed package name), and then re-attempts
312 the lookup. If at that time the hook cannot be located, the engine
313 croaks. Note that this mechanism will fail if you define several
314 classes in the same file, but perlmod warned you.
315 It is up to you to use this information to populate obj the way you
317 want.
318 Returned value: none.
320 "STORABLE_attach" class, cloning, serialized
322 While "STORABLE_freeze" and "STORABLE_thaw" are useful for classes
323 where each instance is independent, this mechanism has difficulty
324 (or is incompatible) with objects that exist as common process-
325 level or system-level resources, such as singleton objects,
326 database pools, caches or memoized objects.
327 The alternative "STORABLE_attach" method provides a solution for
329 these shared objects. Instead of "STORABLE_freeze" -->
330 "STORABLE_thaw", you implement "STORABLE_freeze" -->
331 "STORABLE_attach" instead.
332 Arguments: class is the class we are attaching to, cloning is a
334 flag indicating whether we're in a dclone() or a regular de-
335 serialization via thaw(), and serialized is the stored string for
336 the resource object.
337 Because these resource objects are considered to be owned by the
339 entire process/system, and not the "property" of whatever is being
340 serialized, no references underneath the object should be included
341 in the serialized string. Thus, in any class that implements
342 "STORABLE_attach", the "STORABLE_freeze" method cannot return any
343 references, and "Storable" will throw an error if "STORABLE_freeze"
344 tries to return references.
345 All information required to "attach" back to the shared resource
347 object must be contained only in the "STORABLE_freeze" return
348 string. Otherwise, "STORABLE_freeze" behaves as normal for
349 "STORABLE_attach" classes.
350 Because "STORABLE_attach" is passed the class (rather than an
352 object), it also returns the object directly, rather than modifying
353 the passed object.
354 Returned value: object of type "class"
356 Predicates
358 Predicates are not exportable. They must be called by explicitly
359 prefixing them with the Storable package name.
360 "Storable::last_op_in_netorder"
362 The "Storable::last_op_in_netorder()" predicate will tell you
363 whether network order was used in the last store or retrieve
364 operation. If you don't know how to use this, just forget about
365 it.
366 "Storable::is_storing"
368 Returns true if within a store operation (via STORABLE_freeze
369 hook).
370 "Storable::is_retrieving"
372 Returns true if within a retrieve operation (via STORABLE_thaw
373 hook).
374 Recursion
376 With hooks comes the ability to recurse back to the Storable engine.
377 Indeed, hooks are regular Perl code, and Storable is convenient when it
378 comes to serializing and deserializing things, so why not use it to
379 handle the serialization string?
380 There are a few things you need to know, however:
382 · You can create endless loops if the things you serialize via
384 freeze() (for instance) point back to the object we're trying to
385 serialize in the hook.
386 · Shared references among objects will not stay shared: if we're
388 serializing the list of object [A, C] where both object A and C
389 refer to the SAME object B, and if there is a serializing hook in A
390 that says freeze(B), then when deserializing, we'll get [A', C']
391 where A' refers to B', but C' refers to D, a deep clone of B'. The
392 topology was not preserved.
393 That's why "STORABLE_freeze" lets you provide a list of references to
395 serialize. The engine guarantees that those will be serialized in the
396 same context as the other objects, and therefore that shared objects
397 will stay shared.
398 In the above [A, C] example, the "STORABLE_freeze" hook could return:
400 ("something", $self->{B})
402 and the B part would be serialized by the engine. In "STORABLE_thaw",
404 you would get back the reference to the B' object, deserialized for
405 you.
406 Therefore, recursion should normally be avoided, but is nonetheless
408 supported.
409 Deep Cloning
411 There is a Clone module available on CPAN which implements deep cloning
412 natively, i.e. without freezing to memory and thawing the result. It
413 is aimed to replace Storable's dclone() some day. However, it does not
414 currently support Storable hooks to redefine the way deep cloning is
415 performed.
416
418 Yes, there's a lot of that :-) But more precisely, in UNIX systems
419 there's a utility called "file", which recognizes data files based on
420 their contents (usually their first few bytes). For this to work, a
421 certain file called magic needs to taught about the signature of the
422 data. Where that configuration file lives depends on the UNIX flavour;
423 often it's something like /usr/share/misc/magic or /etc/magic. Your
424 system administrator needs to do the updating of the magic file. The
425 necessary signature information is output to STDOUT by invoking
426 Storable::show_file_magic(). Note that the GNU implementation of the
427 "file" utility, version 3.38 or later, is expected to contain support
428 for recognising Storable files out-of-the-box, in addition to other
429 kinds of Perl files.
430 You can also use the following functions to extract the file header
432 information from Storable images:
433 $info = Storable::file_magic( $filename )
435 If the given file is a Storable image return a hash describing it.
436 If the file is readable, but not a Storable image return "undef".
437 If the file does not exist or is unreadable then croak.
438 The hash returned has the following elements:
440 "version"
442 This returns the file format version. It is a string like
443 "2.7".
444 Note that this version number is not the same as the version
446 number of the Storable module itself. For instance Storable
447 v0.7 create files in format v2.0 and Storable v2.15 create
448 files in format v2.7. The file format version number only
449 increment when additional features that would confuse older
450 versions of the module are added.
451 Files older than v2.0 will have the one of the version numbers
453 "-1", "0" or "1". No minor number was used at that time.
454 "version_nv"
456 This returns the file format version as number. It is a string
457 like "2.007". This value is suitable for numeric comparisons.
458 The constant function "Storable::BIN_VERSION_NV" returns a
460 comparable number that represent the highest file version
461 number that this version of Storable fully support (but see
462 discussion of $Storable::accept_future_minor above). The
463 constant "Storable::BIN_WRITE_VERSION_NV" function returns what
464 file version is written and might be less than
465 "Storable::BIN_VERSION_NV" in some configuations.
466 "major", "minor"
468 This also returns the file format version. If the version is
469 "2.7" then major would be 2 and minor would be 7. The minor
470 element is missing for when major is less than 2.
471 "hdrsize"
473 The is the number of bytes that the Storable header occupies.
474 "netorder"
476 This is TRUE if the image store data in network order. This
477 means that it was created with nstore() or similar.
478 "byteorder"
480 This is only present when "netorder" is FALSE. It is the
481 $Config{byteorder} string of the perl that created this image.
482 It is a string like "1234" (32 bit little endian) or "87654321"
483 (64 bit big endian). This must match the current perl for the
484 image to be readable by Storable.
485 "intsize", "longsize", "ptrsize", "nvsize"
487 These are only present when "netorder" is FALSE. These are the
488 sizes of various C datatypes of the perl that created this
489 image. These must match the current perl for the image to be
490 readable by Storable.
491 The "nvsize" element is only present for file format v2.2 and
493 higher.
494 "file"
496 The name of the file.
497 $info = Storable::read_magic( $buffer )
499 $info = Storable::read_magic( $buffer, $must_be_file )
500 The $buffer should be a Storable image or the first few bytes of
501 it. If $buffer starts with a Storable header, then a hash
502 describing the image is returned, otherwise "undef" is returned.
503 The hash has the same structure as the one returned by
505 Storable::file_magic(). The "file" element is true if the image is
506 a file image.
507 If the $must_be_file argument is provided and is TRUE, then return
509 "undef" unless the image looks like it belongs to a file dump.
510 The maximum size of a Storable header is currently 21 bytes. If
512 the provided $buffer is only the first part of a Storable image it
513 should at least be this long to ensure that read_magic() will
514 recognize it as such.
515
517 Here are some code samples showing a possible usage of Storable:
518 use Storable qw(store retrieve freeze thaw dclone);
520 %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);
522 store(\%color, 'mycolors') or die "Can't store %a in mycolors!\n";
524 $colref = retrieve('mycolors');
526 die "Unable to retrieve from mycolors!\n" unless defined $colref;
527 printf "Blue is still %lf\n", $colref->{'Blue'};
528 $colref2 = dclone(\%color);
530 $str = freeze(\%color);
532 printf "Serialization of %%color is %d bytes long.\n", length($str);
533 $colref3 = thaw($str);
534 which prints (on my machine):
536 Blue is still 0.100000
538 Serialization of %color is 102 bytes long.
539 Serialization of CODE references and deserialization in a safe
541 compartment:
542 use Storable qw(freeze thaw);
544 use Safe;
545 use strict;
546 my $safe = new Safe;
547 # because of opcodes used in "use strict":
548 $safe->permit(qw(:default require));
549 local $Storable::Deparse = 1;
550 local $Storable::Eval = sub { $safe->reval($_[0]) };
551 my $serialized = freeze(sub { 42 });
552 my $code = thaw($serialized);
553 $code->() == 42;
554
556 If you're using references as keys within your hash tables, you're
557 bound to be disappointed when retrieving your data. Indeed, Perl
558 stringifies references used as hash table keys. If you later wish to
559 access the items via another reference stringification (i.e. using the
560 same reference that was used for the key originally to record the value
561 into the hash table), it will work because both references stringify to
562 the same string.
563 It won't work across a sequence of "store" and "retrieve" operations,
565 however, because the addresses in the retrieved objects, which are part
566 of the stringified references, will probably differ from the original
567 addresses. The topology of your structure is preserved, but not hidden
568 semantics like those.
569 On platforms where it matters, be sure to call "binmode()" on the
571 descriptors that you pass to Storable functions.
572 Storing data canonically that contains large hashes can be
574 significantly slower than storing the same data normally, as temporary
575 arrays to hold the keys for each hash have to be allocated, populated,
576 sorted and freed. Some tests have shown a halving of the speed of
577 storing -- the exact penalty will depend on the complexity of your
578 data. There is no slowdown on retrieval.
579
581 You can't store GLOB, FORMLINE, etc.... If you can define semantics for
582 those operations, feel free to enhance Storable so that it can deal
583 with them.
584 The store functions will "croak" if they run into such references
586 unless you set $Storable::forgive_me to some "TRUE" value. In that
587 case, the fatal message is turned in a warning and some meaningless
588 string is stored instead.
589 Setting $Storable::canonical may not yield frozen strings that compare
591 equal due to possible stringification of numbers. When the string
592 version of a scalar exists, it is the form stored; therefore, if you
593 happen to use your numbers as strings between two freezing operations
594 on the same data structures, you will get different results.
595 When storing doubles in network order, their value is stored as text.
597 However, you should also not expect non-numeric floating-point values
598 such as infinity and "not a number" to pass successfully through a
599 nstore()/retrieve() pair.
600 As Storable neither knows nor cares about character sets (although it
602 does know that characters may be more than eight bits wide), any
603 difference in the interpretation of character codes between a host and
604 a target system is your problem. In particular, if host and target use
605 different code points to represent the characters used in the text
606 representation of floating-point numbers, you will not be able be able
607 to exchange floating-point data, even with nstore().
608 "Storable::drop_utf8" is a blunt tool. There is no facility either to
610 return all strings as utf8 sequences, or to attempt to convert utf8
611 data back to 8 bit and "croak()" if the conversion fails.
612 Prior to Storable 2.01, no distinction was made between signed and
614 unsigned integers on storing. By default Storable prefers to store a
615 scalars string representation (if it has one) so this would only cause
616 problems when storing large unsigned integers that had never been
617 converted to string or floating point. In other words values that had
618 been generated by integer operations such as logic ops and then not
619 used in any string or arithmetic context before storing.
620 64 bit data in perl 5.6.0 and 5.6.1
622 This section only applies to you if you have existing data written out
623 by Storable 2.02 or earlier on perl 5.6.0 or 5.6.1 on Unix or Linux
624 which has been configured with 64 bit integer support (not the default)
625 If you got a precompiled perl, rather than running Configure to build
626 your own perl from source, then it almost certainly does not affect
627 you, and you can stop reading now (unless you're curious). If you're
628 using perl on Windows it does not affect you.
629 Storable writes a file header which contains the sizes of various C
631 language types for the C compiler that built Storable (when not writing
632 in network order), and will refuse to load files written by a Storable
633 not on the same (or compatible) architecture. This check and a check
634 on machine byteorder is needed because the size of various fields in
635 the file are given by the sizes of the C language types, and so files
636 written on different architectures are incompatible. This is done for
637 increased speed. (When writing in network order, all fields are
638 written out as standard lengths, which allows full interworking, but
639 takes longer to read and write)
640 Perl 5.6.x introduced the ability to optional configure the perl
642 interpreter to use C's "long long" type to allow scalars to store 64
643 bit integers on 32 bit systems. However, due to the way the Perl
644 configuration system generated the C configuration files on non-Windows
645 platforms, and the way Storable generates its header, nothing in the
646 Storable file header reflected whether the perl writing was using 32 or
647 64 bit integers, despite the fact that Storable was storing some data
648 differently in the file. Hence Storable running on perl with 64 bit
649 integers will read the header from a file written by a 32 bit perl, not
650 realise that the data is actually in a subtly incompatible format, and
651 then go horribly wrong (possibly crashing) if it encountered a stored
652 integer. This is a design failure.
653 Storable has now been changed to write out and read in a file header
655 with information about the size of integers. It's impossible to detect
656 whether an old file being read in was written with 32 or 64 bit
657 integers (they have the same header) so it's impossible to
658 automatically switch to a correct backwards compatibility mode. Hence
659 this Storable defaults to the new, correct behaviour.
660 What this means is that if you have data written by Storable 1.x
662 running on perl 5.6.0 or 5.6.1 configured with 64 bit integers on Unix
663 or Linux then by default this Storable will refuse to read it, giving
664 the error Byte order is not compatible. If you have such data then you
665 you should set $Storable::interwork_56_64bit to a true value to make
666 this Storable read and write files with the old header. You should
667 also migrate your data, or any older perl you are communicating with,
668 to this current version of Storable.
669 If you don't have data written with specific configuration of perl
671 described above, then you do not and should not do anything. Don't set
672 the flag - not only will Storable on an identically configured perl
673 refuse to load them, but Storable a differently configured perl will
674 load them believing them to be correct for it, and then may well fail
675 or crash part way through reading them.
676
678 Thank you to (in chronological order):
679 Jarkko Hietaniemi <jhi@iki.fi>
681 Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de>
682 Benjamin A. Holzman <bah@ecnvantage.com>
683 Andrew Ford <A.Ford@ford-mason.co.uk>
684 Gisle Aas <gisle@aas.no>
685 Jeff Gresham <gresham_jeffrey@jpmorgan.com>
686 Murray Nesbitt <murray@activestate.com>
687 Marc Lehmann <pcg@opengroup.org>
688 Justin Banks <justinb@wamnet.com>
689 Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
690 Salvador Ortiz Garcia <sog@msg.com.mx>
691 Dominic Dunlop <domo@computer.org>
692 Erik Haugan <erik@solbors.no>
693 for their bug reports, suggestions and contributions.
695 Benjamin Holzman contributed the tied variable support, Andrew Ford
697 contributed the canonical order for hashes, and Gisle Aas fixed a few
698 misunderstandings of mine regarding the perl internals, and optimized
699 the emission of "tags" in the output streams by simply counting the
700 objects instead of tagging them (leading to a binary incompatibility
701 for the Storable image starting at version 0.6--older images are, of
702 course, still properly understood). Murray Nesbitt made Storable
703 thread-safe. Marc Lehmann added overloading and references to tied
704 items support.
705
707 Storable was written by Raphael Manfredi <Raphael_Manfredi@pobox.com>
708 Maintenance is now done by the perl5-porters <perl5-porters@perl.org>
709 Please e-mail us with problems, bug fixes, comments and complaints,
711 although if you have compliments you should send them to Raphael.
712 Please don't e-mail Raphael with problems, as he no longer works on
713 Storable, and your message will be delayed while he forwards it to us.
714
716 Clone.
717perl v5.10.1 2009-05-10 Storable(3pm)