1 ;# $Id: Storable.pm,v 1.0.1.13 2001/12/01 13:34:49 ram Exp $
3 ;# Copyright (c) 1995-2000, Raphael Manfredi
5 ;# You may redistribute only under the same terms as Perl 5, as specified
6 ;# in the README file that comes with the distribution.
8 ;# $Log: Storable.pm,v $
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
13 ;# Revision 1.0.1.12 2001/08/28 21:51:51 ram
14 ;# patch13: fixed truncation race with lock_retrieve() in lock_store()
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
20 ;# Revision 1.0.1.10 2001/03/15 00:20:25 ram
21 ;# patch11: updated version number
23 ;# Revision 1.0.1.9 2001/02/17 12:37:32 ram
24 ;# patch10: forgot to increase version number at previous patch
26 ;# Revision 1.0.1.8 2001/02/17 12:24:37 ram
27 ;# patch8: fixed incorrect error message
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
32 ;# Revision 1.0.1.6 2000/11/05 17:20:25 ram
33 ;# patch6: increased version number
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
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
43 ;# Revision 1.0.1.3 2000/09/29 19:49:01 ram
44 ;# patch3: updated version number
46 ;# Revision 1.0.1.2 2000/09/28 21:42:51 ram
47 ;# patch2: added lock_store lock_nstore lock_retrieve
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
53 ;# Revision 1.0 2000/09/01 19:40:41 ram
54 ;# Baseline for first official release.
59 package Storable; @ISA = qw(Exporter DynaLoader);
61 @EXPORT = qw(store retrieve);
63 nstore store_fd nstore_fd fd_retrieve
67 lock_store lock_nstore lock_retrieve
71 use vars qw($forgive_me $VERSION);
74 *AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr...
77 # Use of Log::Agent is optional
80 eval "use Log::Agent";
85 # They might miss :flock in Fcntl
89 if (eval { require Fcntl; 1 } && exists $Fcntl::EXPORT_TAGS{'flock'}) {
90 Fcntl->import(':flock');
99 # Can't Autoload cleanly as this clashes 8.3 with &retrieve
100 sub retrieve_fd { &fd_retrieve } # Backward compatibility
102 # By default restricted hashes are downgraded on earlier perls.
104 $Storable::downgrade_restricted = 1;
109 # Use of Log::Agent is optional. If it hasn't imported these subs then
110 # Autoloader will kindly supply our fallback implementation.
122 # Determine whether locking is possible, but only when needed.
125 sub CAN_FLOCK; my $CAN_FLOCK; sub CAN_FLOCK {
126 return $CAN_FLOCK if defined $CAN_FLOCK;
127 require Config; import Config;
129 $Config{'d_flock'} ||
130 $Config{'d_fcntl_can_lock'} ||
134 sub show_file_magic {
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.
141 0 string perl-store perl Storable(v0.6) data
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)
147 0 string pst0 perl Storable(v0.7) data
149 >>4 byte &01 (network-ordered)
150 >>4 byte =5 (major 2)
151 >>4 byte =4 (major 2)
152 >>5 byte >0 (minor %d)
158 return unless defined $header and length $header > 11;
160 if ($header =~ s/^perl-store//) {
161 die "Can't deal with version 0 headers";
162 } elsif ($header =~ s/^pst0//) {
165 # Assume it's a string.
166 my ($major, $minor, $bytelen) = unpack "C3", $header;
168 my $net_order = $major & 1;
170 @$result{qw(major minor netorder)} = ($major, $minor, $net_order);
172 return $result if $net_order;
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.
177 delete $result->{minor};
178 $header = '.' . $header;
182 @$result{qw(byteorder intsize longsize ptrsize)} =
183 unpack "x3 A$bytelen C3", $header;
185 if ($major >= 2 and $minor >= 2) {
186 $result->{nvsize} = unpack "x6 x$bytelen C", $header;
194 # Store target object hierarchy, identified by a reference to its root.
195 # The stored object tree may later be retrieved to memory via retrieve.
196 # Returns undef if an I/O error occurred, in which case the file is
200 return _store(\&pstore, @_, 0);
206 # Same as store, but in network order.
209 return _store(\&net_pstore, @_, 0);
215 # Same as store, but flock the file first (advisory locking).
218 return _store(\&pstore, @_, 1);
224 # Same as nstore, but flock the file first (advisory locking).
227 return _store(\&net_pstore, @_, 1);
230 # Internal store to file routine
234 my ($file, $use_locking) = @_;
235 logcroak "not a reference" unless ref($self);
236 logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist
239 open(FILE, ">>$file") || logcroak "can't write into $file: $!";
240 unless (&CAN_FLOCK) {
241 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
244 flock(FILE, LOCK_EX) ||
245 logcroak "can't get exclusive lock on $file: $!";
247 # Unlocking will happen when FILE is closed
249 open(FILE, ">$file") || logcroak "can't create $file: $!";
251 binmode FILE; # Archaic systems...
252 my $da = $@; # Don't mess if called from exception handler
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 $@ =~ s/\.?\n$/,/;
260 return $ret ? $ret : undef;
266 # Same as store, but perform on an already opened file descriptor instead.
267 # Returns undef if an I/O error occurred.
270 return _store_fd(\&pstore, @_);
276 # Same as store_fd, but in network order.
279 my ($self, $file) = @_;
280 return _store_fd(\&net_pstore, @_);
283 # Internal store routine on opened file descriptor
288 logcroak "not a reference" unless ref($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
294 # Call C routine nstore or pstore, depending on network order
295 eval { $ret = &$xsptr($file, $self) };
296 logcroak $@ if $@ =~ s/\.?\n$/,/;
297 local $\; print $file ''; # Autoflush the file if wanted
299 return $ret ? $ret : undef;
305 # Store oject and its hierarchy in memory and return a scalar
306 # containing the result.
309 _freeze(\&mstore, @_);
315 # Same as freeze but in network order.
318 _freeze(\&net_mstore, @_);
321 # Internal freeze routine
325 logcroak "not a reference" unless ref($self);
326 logcroak "too many arguments" unless @_ == 0; # No @foo in arglist
327 my $da = $@; # Don't mess if called from exception handler
329 # Call C routine mstore or net_mstore, depending on network order
330 eval { $ret = &$xsptr($self) };
331 logcroak $@ if $@ =~ s/\.?\n$/,/;
333 return $ret ? $ret : undef;
339 # Retrieve object hierarchy from disk, returning a reference to the root
340 # object of that tree.
349 # Same as retrieve, but with advisory locking.
355 # Internal retrieve routine
357 my ($file, $use_locking) = @_;
359 open(FILE, $file) || logcroak "can't open $file: $!";
360 binmode FILE; # Archaic systems...
362 my $da = $@; # Could be from exception handler
364 unless (&CAN_FLOCK) {
365 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
368 flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!";
369 # Unlocking will happen when FILE is closed
371 eval { $self = pretrieve(*FILE) }; # Call C routine
373 logcroak $@ if $@ =~ s/\.?\n$/,/;
381 # Same as retrieve, but perform from an already opened file descriptor instead.
385 my $fd = fileno($file);
386 logcroak "not a valid file descriptor" unless defined $fd;
388 my $da = $@; # Could be from exception handler
389 eval { $self = pretrieve($file) }; # Call C routine
390 logcroak $@ if $@ =~ s/\.?\n$/,/;
398 # Recreate objects in memory from an existing frozen image created
399 # by freeze. If the frozen image passed is undef, return undef.
403 return undef unless defined $frozen;
405 my $da = $@; # Could be from exception handler
406 eval { $self = mretrieve($frozen) }; # Call C routine
407 logcroak $@ if $@ =~ s/\.?\n$/,/;
414 Storable - persistency for perl data structures
419 store \%table, 'file';
420 $hashref = retrieve('file');
422 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);
425 nstore \%table, 'file';
426 $hashref = retrieve('file'); # There is NO nretrieve()
428 # Storing to and retrieving from an already opened file
429 store_fd \@array, \*STDOUT;
430 nstore_fd \%table, \*STDOUT;
431 $aryref = fd_retrieve(\*SOCKET);
432 $hashref = fd_retrieve(\*SOCKET);
434 # Serializing to memory
435 $serialized = freeze \%table;
436 %table_clone = %{ thaw($serialized) };
438 # Deep (recursive) cloning
439 $cloneref = dclone($ref);
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');
449 The Storable package brings persistence to your perl data structures
450 containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be
451 conveniently stored to disk and retrieved at a later time.
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.
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>.
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.
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
472 from a file via C<fd_retrieve>. Those names aren't imported by default,
473 so you will have to do that explicitly 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.
477 store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
478 $hashref = fd_retrieve(*STDIN);
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
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.
489 When using C<fd_retrieve>, objects are retrieved in sequence, one
490 object (i.e. one recursive tree) per associated C<store_fd>.
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).
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.
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.
513 Note that freezing an object structure and immediately thawing it
514 actually achieves a deep cloning of that structure:
516 dclone(.) = thaw(freeze(.))
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 immediately thaws it out.
522 =head1 ADVISORY LOCKING
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.
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.
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.
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.
546 =head1 CANONICAL REPRESENTATION
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.
556 Canonical order does not imply network order, those are two orthogonal
559 =head1 FORWARD COMPATIBILITY
561 This release of Storable can be used on a newer version of Perl to
562 serialize data which is not supported by earlier Perls. By default
563 Storable will attempt to do the right thing, by C<croak()>ing if it
564 encounters data that it cannot deserialize. However, the defaults can be
571 Perl 5.6 added support for Unicode characters with code points > 255,
572 and Perl 5.8 has full support for Unicode characters in hash keys.
573 Perl internally encodes strings with these characters using utf8, and
574 Storable serializes them as utf8. By default, if an older version of
575 Perl encounters a utf8 value it cannot represent, it will C<croak()>.
576 To change this behaviour so that Storable deserializes utf8 encoded
577 values as the string of bytes (effectively dropping the I<is_utf8> flag)
578 set C<$Storable::drop_utf8> to some C<TRUE> value. This is a form of
579 data loss, because with C<$drop_utf8> true, it becomes impossible to tell
580 whether the original data was the Unicode string, or a series of bytes
581 that happen to be valid utf8.
583 =item restricted hashes
585 Perl 5.8 adds support for restricted hashes, which have keys restricted to
586 a given set, and can have values locked to be read only. By default
587 when Storable encounters a restricted hash on a perl that doesn't support
588 them, it will deserialize it as a normal hash, silently discarding any
589 placeholder keys and leaving the keys and all values unlocked. To make
590 Storable C<croak()> instead, set C<$Storable::downgrade_restricted> to
591 a false value. To restore the default set it back to some C<TRUE> value.
595 Both these variables have no effect on a newer Perl which supports the
598 =head1 ERROR REPORTING
600 Storable uses the "exception" paradigm, in that it does not try to workaround
601 failures: if something bad happens, an exception is generated from the
602 caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap
605 When Storable croaks, it tries to report the error via the C<logcroak()>
606 routine from the C<Log::Agent> package, if it is available.
608 Normal errors are reported by having store() or retrieve() return C<undef>.
609 Such errors are usually I/O errors (or truncated stream errors at retrieval).
615 Any class may define hooks that will be called during the serialization
616 and deserialization process on objects that are instances of that class.
617 Those hooks can redefine the way serialization is performed (and therefore,
618 how the symmetrical deserialization should be conducted).
620 Since we said earlier:
622 dclone(.) = thaw(freeze(.))
624 everything we say about hooks should also hold for deep cloning. However,
625 hooks get to know whether the operation is a mere serialization, or a cloning.
627 Therefore, when serializing hooks are involved,
629 dclone(.) <> thaw(freeze(.))
631 Well, you could keep them in sync, but there's no guarantee it will always
632 hold on classes somebody else wrote. Besides, there is little to gain in
633 doing so: a serializing hook could only keep one attribute of an object,
634 which is probably not what should happen during a deep cloning of that
637 Here is the hooking interface:
641 =item C<STORABLE_freeze> I<obj>, I<cloning>
643 The serializing hook, called on the object during serialization. It can be
644 inherited, or defined in the class itself, like any other method.
646 Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating
647 whether we're in a dclone() or a regular serialization via store() or freeze().
649 Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized
650 is the serialized form to be used, and the optional $ref1, $ref2, etc... are
651 extra references that you wish to let the Storable engine serialize.
653 At deserialization time, you will be given back the same LIST, but all the
654 extra references will be pointing into the deserialized structure.
656 The B<first time> the hook is hit in a serialization flow, you may have it
657 return an empty list. That will signal the Storable engine to further
658 discard that hook for this class and to therefore revert to the default
659 serialization of the underlying Perl data. The hook will again be normally
660 processed in the next serialization.
662 Unless you know better, serializing hook should always say:
664 sub STORABLE_freeze {
665 my ($self, $cloning) = @_;
666 return if $cloning; # Regular default serialization
670 in order to keep reasonable dclone() semantics.
672 =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ...
674 The deserializing hook called on the object during deserialization.
675 But wait. If we're deserializing, there's no object yet... right?
677 Wrong: the Storable engine creates an empty one for you. If you know Eiffel,
678 you can view C<STORABLE_thaw> as an alternate creation routine.
680 This means the hook can be inherited like any other method, and that
681 I<obj> is your blessed reference for this particular instance.
683 The other arguments should look familiar if you know C<STORABLE_freeze>:
684 I<cloning> is true when we're part of a deep clone operation, I<serialized>
685 is the serialized string you returned to the engine in C<STORABLE_freeze>,
686 and there may be an optional list of references, in the same order you gave
687 them at serialization time, pointing to the deserialized objects (which
688 have been processed courtesy of the Storable engine).
690 When the Storable engine does not find any C<STORABLE_thaw> hook routine,
691 it tries to load the class by requiring the package dynamically (using
692 the blessed package name), and then re-attempts the lookup. If at that
693 time the hook cannot be located, the engine croaks. Note that this mechanism
694 will fail if you define several classes in the same file, but L<perlmod>
697 It is up to you to use these information to populate I<obj> the way you want.
699 Returned value: none.
705 Predicates are not exportable. They must be called by explicitly prefixing
706 them with the Storable package name.
710 =item C<Storable::last_op_in_netorder>
712 The C<Storable::last_op_in_netorder()> predicate will tell you whether
713 network order was used in the last store or retrieve operation. If you
714 don't know how to use this, just forget about it.
716 =item C<Storable::is_storing>
718 Returns true if within a store operation (via STORABLE_freeze hook).
720 =item C<Storable::is_retrieving>
722 Returns true if within a retrieve operation, (via STORABLE_thaw hook).
728 With hooks comes the ability to recurse back to the Storable engine. Indeed,
729 hooks are regular Perl code, and Storable is convenient when it comes to
730 serialize and deserialize things, so why not use it to handle the
731 serialization string?
733 There are a few things you need to know however:
739 You can create endless loops if the things you serialize via freeze()
740 (for instance) point back to the object we're trying to serialize in the hook.
744 Shared references among objects will not stay shared: if we're serializing
745 the list of object [A, C] where both object A and C refer to the SAME object
746 B, and if there is a serializing hook in A that says freeze(B), then when
747 deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D,
748 a deep clone of B'. The topology was not preserved.
752 That's why C<STORABLE_freeze> lets you provide a list of references
753 to serialize. The engine guarantees that those will be serialized in the
754 same context as the other objects, and therefore that shared objects will
757 In the above [A, C] example, the C<STORABLE_freeze> hook could return:
759 ("something", $self->{B})
761 and the B part would be serialized by the engine. In C<STORABLE_thaw>, you
762 would get back the reference to the B' object, deserialized for you.
764 Therefore, recursion should normally be avoided, but is nonetheless supported.
768 There is a new Clone module available on CPAN which implements deep cloning
769 natively, i.e. without freezing to memory and thawing the result. It is
770 aimed to replace Storable's dclone() some day. However, it does not currently
771 support Storable hooks to redefine the way deep cloning is performed.
773 =head1 Storable magic
775 Yes, there's a lot of that :-) But more precisely, in UNIX systems
776 there's a utility called C<file>, which recognizes data files based on
777 their contents (usually their first few bytes). For this to work,
778 a certain file called F<magic> needs to taught about the I<signature>
779 of the data. Where that configuration file lives depends on the UNIX
780 flavour, often it's something like F</usr/share/misc/magic> or
781 F</etc/magic>. Your system administrator needs to do the updating of
782 the F<magic> file. The necessary signature information is output to
783 STDOUT by invoking Storable::show_file_magic(). Note that the open
784 source implementation of the C<file> utility 3.38 (or later)
785 is expected to contain the support for recognising Storable files,
786 in addition to other kinds of Perl files.
790 Here are some code samples showing a possible usage of Storable:
792 use Storable qw(store retrieve freeze thaw dclone);
794 %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);
796 store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n";
798 $colref = retrieve('/tmp/colors');
799 die "Unable to retrieve from /tmp/colors!\n" unless defined $colref;
800 printf "Blue is still %lf\n", $colref->{'Blue'};
802 $colref2 = dclone(\%color);
804 $str = freeze(\%color);
805 printf "Serialization of %%color is %d bytes long.\n", length($str);
806 $colref3 = thaw($str);
808 which prints (on my machine):
810 Blue is still 0.100000
811 Serialization of %color is 102 bytes long.
815 If you're using references as keys within your hash tables, you're bound
816 to disappointment when retrieving your data. Indeed, Perl stringifies
817 references used as hash table keys. If you later wish to access the
818 items via another reference stringification (i.e. using the same
819 reference that was used for the key originally to record the value into
820 the hash table), it will work because both references stringify to the
823 It won't work across a C<store> and C<retrieve> operations however, because
824 the addresses in the retrieved objects, which are part of the stringified
825 references, will probably differ from the original addresses. The
826 topology of your structure is preserved, but not hidden semantics
829 On platforms where it matters, be sure to call C<binmode()> on the
830 descriptors that you pass to Storable functions.
832 Storing data canonically that contains large hashes can be
833 significantly slower than storing the same data normally, as
834 temporary arrays to hold the keys for each hash have to be allocated,
835 populated, sorted and freed. Some tests have shown a halving of the
836 speed of storing -- the exact penalty will depend on the complexity of
837 your data. There is no slowdown on retrieval.
841 You can't store GLOB, CODE, FORMLINE, etc... If you can define
842 semantics for those operations, feel free to enhance Storable so that
843 it can deal with them.
845 The store functions will C<croak> if they run into such references
846 unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that
847 case, the fatal message is turned in a warning and some
848 meaningless string is stored instead.
850 Setting C<$Storable::canonical> may not yield frozen strings that
851 compare equal due to possible stringification of numbers. When the
852 string version of a scalar exists, it is the form stored, therefore
853 if you happen to use your numbers as strings between two freezing
854 operations on the same data structures, you will get different
857 When storing doubles in network order, their value is stored as text.
858 However, you should also not expect non-numeric floating-point values
859 such as infinity and "not a number" to pass successfully through a
860 nstore()/retrieve() pair.
862 As Storable neither knows nor cares about character sets (although it
863 does know that characters may be more than eight bits wide), any difference
864 in the interpretation of character codes between a host and a target
865 system is your problem. In particular, if host and target use different
866 code points to represent the characters used in the text representation
867 of floating-point numbers, you will not be able be able to exchange
868 floating-point data, even with nstore().
870 C<Storable::drop_utf8> is a blunt tool. There is no facility either to
871 return B<all> strings as utf8 sequences, or to attempt to convert utf8
872 data back to 8 bit and C<croak()> if the conversion fails.
874 Future compatibility does not yet extend to having the option of loading
875 serialized data with higher than current minor version numbers. This
876 ought to be fixed pronto.
880 Thank you to (in chronological order):
882 Jarkko Hietaniemi <jhi@iki.fi>
883 Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de>
884 Benjamin A. Holzman <bah@ecnvantage.com>
885 Andrew Ford <A.Ford@ford-mason.co.uk>
886 Gisle Aas <gisle@aas.no>
887 Jeff Gresham <gresham_jeffrey@jpmorgan.com>
888 Murray Nesbitt <murray@activestate.com>
889 Marc Lehmann <pcg@opengroup.org>
890 Justin Banks <justinb@wamnet.com>
891 Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
892 Salvador Ortiz Garcia <sog@msg.com.mx>
893 Dominic Dunlop <domo@computer.org>
894 Erik Haugan <erik@solbors.no>
896 for their bug reports, suggestions and contributions.
898 Benjamin Holzman contributed the tied variable support, Andrew Ford
899 contributed the canonical order for hashes, and Gisle Aas fixed
900 a few misunderstandings of mine regarding the Perl internals,
901 and optimized the emission of "tags" in the output streams by
902 simply counting the objects instead of tagging them (leading to
903 a binary incompatibility for the Storable image starting at version
904 0.6--older images are of course still properly understood).
905 Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading
906 and reference to tied items support.
910 There is a Japanese translation of this man page available at
911 http://member.nifty.ne.jp/hippo2000/perltips/storable.htm ,
912 courtesy of Kawai, Takanori <kawai@nippon-rad.co.jp>.
916 Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>>