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;
105 $Storable::accept_future_minor = 1;
110 # Use of Log::Agent is optional. If it hasn't imported these subs then
111 # Autoloader will kindly supply our fallback implementation.
123 # Determine whether locking is possible, but only when needed.
126 sub CAN_FLOCK; my $CAN_FLOCK; sub CAN_FLOCK {
127 return $CAN_FLOCK if defined $CAN_FLOCK;
128 require Config; import Config;
130 $Config{'d_flock'} ||
131 $Config{'d_fcntl_can_lock'} ||
135 sub show_file_magic {
138 # To recognize the data files of the Perl module Storable,
139 # the following lines need to be added to the local magic(5) file,
140 # usually either /usr/share/misc/magic or /etc/magic.
142 0 string perl-store perl Storable(v0.6) data
143 >4 byte >0 (net-order %d)
144 >>4 byte &01 (network-ordered)
145 >>4 byte =3 (major 1)
146 >>4 byte =2 (major 1)
148 0 string pst0 perl Storable(v0.7) data
150 >>4 byte &01 (network-ordered)
151 >>4 byte =5 (major 2)
152 >>4 byte =4 (major 2)
153 >>5 byte >0 (minor %d)
159 return unless defined $header and length $header > 11;
161 if ($header =~ s/^perl-store//) {
162 die "Can't deal with version 0 headers";
163 } elsif ($header =~ s/^pst0//) {
166 # Assume it's a string.
167 my ($major, $minor, $bytelen) = unpack "C3", $header;
169 my $net_order = $major & 1;
171 @$result{qw(major minor netorder)} = ($major, $minor, $net_order);
173 return $result if $net_order;
175 # I assume that it is rare to find v1 files, so this is an intentionally
176 # inefficient way of doing it, to make the rest of the code constant.
178 delete $result->{minor};
179 $header = '.' . $header;
183 @$result{qw(byteorder intsize longsize ptrsize)} =
184 unpack "x3 A$bytelen C3", $header;
186 if ($major >= 2 and $minor >= 2) {
187 $result->{nvsize} = unpack "x6 x$bytelen C", $header;
195 # Store target object hierarchy, identified by a reference to its root.
196 # The stored object tree may later be retrieved to memory via retrieve.
197 # Returns undef if an I/O error occurred, in which case the file is
201 return _store(\&pstore, @_, 0);
207 # Same as store, but in network order.
210 return _store(\&net_pstore, @_, 0);
216 # Same as store, but flock the file first (advisory locking).
219 return _store(\&pstore, @_, 1);
225 # Same as nstore, but flock the file first (advisory locking).
228 return _store(\&net_pstore, @_, 1);
231 # Internal store to file routine
235 my ($file, $use_locking) = @_;
236 logcroak "not a reference" unless ref($self);
237 logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist
240 open(FILE, ">>$file") || logcroak "can't write into $file: $!";
241 unless (&CAN_FLOCK) {
242 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
245 flock(FILE, LOCK_EX) ||
246 logcroak "can't get exclusive lock on $file: $!";
248 # Unlocking will happen when FILE is closed
250 open(FILE, ">$file") || logcroak "can't create $file: $!";
252 binmode FILE; # Archaic systems...
253 my $da = $@; # Don't mess if called from exception handler
255 # Call C routine nstore or pstore, depending on network order
256 eval { $ret = &$xsptr(*FILE, $self) };
257 close(FILE) or $ret = undef;
258 unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret;
259 logcroak $@ if $@ =~ s/\.?\n$/,/;
261 return $ret ? $ret : undef;
267 # Same as store, but perform on an already opened file descriptor instead.
268 # Returns undef if an I/O error occurred.
271 return _store_fd(\&pstore, @_);
277 # Same as store_fd, but in network order.
280 my ($self, $file) = @_;
281 return _store_fd(\&net_pstore, @_);
284 # Internal store routine on opened file descriptor
289 logcroak "not a reference" unless ref($self);
290 logcroak "too many arguments" unless @_ == 1; # No @foo in arglist
291 my $fd = fileno($file);
292 logcroak "not a valid file descriptor" unless defined $fd;
293 my $da = $@; # Don't mess if called from exception handler
295 # Call C routine nstore or pstore, depending on network order
296 eval { $ret = &$xsptr($file, $self) };
297 logcroak $@ if $@ =~ s/\.?\n$/,/;
298 local $\; print $file ''; # Autoflush the file if wanted
300 return $ret ? $ret : undef;
306 # Store oject and its hierarchy in memory and return a scalar
307 # containing the result.
310 _freeze(\&mstore, @_);
316 # Same as freeze but in network order.
319 _freeze(\&net_mstore, @_);
322 # Internal freeze routine
326 logcroak "not a reference" unless ref($self);
327 logcroak "too many arguments" unless @_ == 0; # No @foo in arglist
328 my $da = $@; # Don't mess if called from exception handler
330 # Call C routine mstore or net_mstore, depending on network order
331 eval { $ret = &$xsptr($self) };
332 logcroak $@ if $@ =~ s/\.?\n$/,/;
334 return $ret ? $ret : undef;
340 # Retrieve object hierarchy from disk, returning a reference to the root
341 # object of that tree.
350 # Same as retrieve, but with advisory locking.
356 # Internal retrieve routine
358 my ($file, $use_locking) = @_;
360 open(FILE, $file) || logcroak "can't open $file: $!";
361 binmode FILE; # Archaic systems...
363 my $da = $@; # Could be from exception handler
365 unless (&CAN_FLOCK) {
366 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
369 flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!";
370 # Unlocking will happen when FILE is closed
372 eval { $self = pretrieve(*FILE) }; # Call C routine
374 logcroak $@ if $@ =~ s/\.?\n$/,/;
382 # Same as retrieve, but perform from an already opened file descriptor instead.
386 my $fd = fileno($file);
387 logcroak "not a valid file descriptor" unless defined $fd;
389 my $da = $@; # Could be from exception handler
390 eval { $self = pretrieve($file) }; # Call C routine
391 logcroak $@ if $@ =~ s/\.?\n$/,/;
399 # Recreate objects in memory from an existing frozen image created
400 # by freeze. If the frozen image passed is undef, return undef.
404 return undef unless defined $frozen;
406 my $da = $@; # Could be from exception handler
407 eval { $self = mretrieve($frozen) }; # Call C routine
408 logcroak $@ if $@ =~ s/\.?\n$/,/;
415 Storable - persistency for perl data structures
420 store \%table, 'file';
421 $hashref = retrieve('file');
423 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);
426 nstore \%table, 'file';
427 $hashref = retrieve('file'); # There is NO nretrieve()
429 # Storing to and retrieving from an already opened file
430 store_fd \@array, \*STDOUT;
431 nstore_fd \%table, \*STDOUT;
432 $aryref = fd_retrieve(\*SOCKET);
433 $hashref = fd_retrieve(\*SOCKET);
435 # Serializing to memory
436 $serialized = freeze \%table;
437 %table_clone = %{ thaw($serialized) };
439 # Deep (recursive) cloning
440 $cloneref = dclone($ref);
443 use Storable qw(lock_store lock_nstore lock_retrieve)
444 lock_store \%table, 'file';
445 lock_nstore \%table, 'file';
446 $hashref = lock_retrieve('file');
450 The Storable package brings persistence to your perl data structures
451 containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be
452 conveniently stored to disk and retrieved at a later time.
454 It can be used in the regular procedural way by calling C<store> with
455 a reference to the object to be stored, along with the file name where
456 the image should be written.
457 The routine returns C<undef> for I/O problems or other internal error,
458 a true value otherwise. Serious errors are propagated as a C<die> exception.
460 To retrieve data stored to disk, use C<retrieve> with a file name,
461 and the objects stored into that file are recreated into memory for you,
462 a I<reference> to the root object being returned. In case an I/O error
463 occurs while reading, C<undef> is returned instead. Other serious
464 errors are propagated via C<die>.
466 Since storage is performed recursively, you might want to stuff references
467 to objects that share a lot of common data into a single array or hash
468 table, and then store that object. That way, when you retrieve back the
469 whole thing, the objects will continue to share what they originally shared.
471 At the cost of a slight header overhead, you may store to an already
472 opened file descriptor using the C<store_fd> routine, and retrieve
473 from a file via C<fd_retrieve>. Those names aren't imported by default,
474 so you will have to do that explicitly if you need those routines.
475 The file descriptor you supply must be already opened, for read
476 if you're going to retrieve and for write if you wish to store.
478 store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
479 $hashref = fd_retrieve(*STDIN);
481 You can also store data in network order to allow easy sharing across
482 multiple platforms, or when storing on a socket known to be remotely
483 connected. The routines to call have an initial C<n> prefix for I<network>,
484 as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be
485 correctly restored so you don't have to know whether you're restoring
486 from native or network ordered data. Double values are stored stringified
487 to ensure portability as well, at the slight risk of loosing some precision
488 in the last decimals.
490 When using C<fd_retrieve>, objects are retrieved in sequence, one
491 object (i.e. one recursive tree) per associated C<store_fd>.
493 If you're more from the object-oriented camp, you can inherit from
494 Storable and directly store your objects by invoking C<store> as
495 a method. The fact that the root of the to-be-stored tree is a
496 blessed reference (i.e. an object) is special-cased so that the
497 retrieve does not provide a reference to that object but rather the
498 blessed object reference itself. (Otherwise, you'd get a reference
499 to that blessed object).
503 The Storable engine can also store data into a Perl scalar instead, to
504 later retrieve them. This is mainly used to freeze a complex structure in
505 some safe compact memory place (where it can possibly be sent to another
506 process via some IPC, since freezing the structure also serializes it in
507 effect). Later on, and maybe somewhere else, you can thaw the Perl scalar
508 out and recreate the original complex structure in memory.
510 Surprisingly, the routines to be called are named C<freeze> and C<thaw>.
511 If you wish to send out the frozen scalar to another machine, use
512 C<nfreeze> instead to get a portable image.
514 Note that freezing an object structure and immediately thawing it
515 actually achieves a deep cloning of that structure:
517 dclone(.) = thaw(freeze(.))
519 Storable provides you with a C<dclone> interface which does not create
520 that intermediary scalar but instead freezes the structure in some
521 internal memory space and then immediately thaws it out.
523 =head1 ADVISORY LOCKING
525 The C<lock_store> and C<lock_nstore> routine are equivalent to C<store>
526 and C<nstore>, only they get an exclusive lock on the file before
527 writing. Likewise, C<lock_retrieve> performs as C<retrieve>, but also
528 gets a shared lock on the file before reading.
530 Like with any advisory locking scheme, the protection only works if
531 you systematically use C<lock_store> and C<lock_retrieve>. If one
532 side of your application uses C<store> whilst the other uses C<lock_retrieve>,
533 you will get no protection at all.
535 The internal advisory locking is implemented using Perl's flock() routine.
536 If your system does not support any form of flock(), or if you share
537 your files across NFS, you might wish to use other forms of locking by
538 using modules like LockFile::Simple which lock a file using a filesystem
539 entry, instead of locking the file descriptor.
543 The heart of Storable is written in C for decent speed. Extra low-level
544 optimizations have been made when manipulating perl internals, to
545 sacrifice encapsulation for the benefit of greater speed.
547 =head1 CANONICAL REPRESENTATION
549 Normally Storable stores elements of hashes in the order they are
550 stored internally by Perl, i.e. pseudo-randomly. If you set
551 C<$Storable::canonical> to some C<TRUE> value, Storable will store
552 hashes with the elements sorted by their key. This allows you to
553 compare data structures by comparing their frozen representations (or
554 even the compressed frozen representations), which can be useful for
555 creating lookup tables for complicated queries.
557 Canonical order does not imply network order, those are two orthogonal
560 =head1 FORWARD COMPATIBILITY
562 This release of Storable can be used on a newer version of Perl to
563 serialize data which is not supported by earlier Perls. By default
564 Storable will attempt to do the right thing, by C<croak()>ing if it
565 encounters data that it cannot deserialize. However, the defaults can be
572 Perl 5.6 added support for Unicode characters with code points > 255,
573 and Perl 5.8 has full support for Unicode characters in hash keys.
574 Perl internally encodes strings with these characters using utf8, and
575 Storable serializes them as utf8. By default, if an older version of
576 Perl encounters a utf8 value it cannot represent, it will C<croak()>.
577 To change this behaviour so that Storable deserializes utf8 encoded
578 values as the string of bytes (effectively dropping the I<is_utf8> flag)
579 set C<$Storable::drop_utf8> to some C<TRUE> value. This is a form of
580 data loss, because with C<$drop_utf8> true, it becomes impossible to tell
581 whether the original data was the Unicode string, or a series of bytes
582 that happen to be valid utf8.
584 =item restricted hashes
586 Perl 5.8 adds support for restricted hashes, which have keys restricted to
587 a given set, and can have values locked to be read only. By default
588 when Storable encounters a restricted hash on a perl that doesn't support
589 them, it will deserialize it as a normal hash, silently discarding any
590 placeholder keys and leaving the keys and all values unlocked. To make
591 Storable C<croak()> instead, set C<$Storable::downgrade_restricted> to
592 a false value. To restore the default set it back to some C<TRUE> value.
594 =item files from future versions of Storable
596 Earlier versions of Storable would immediately croak if they encountered
597 a file with a higher internal version number than the reading Storable
598 knew about. Internal version numbers are increased each time new data
599 types (such as restricted hashes) are added to the vocabulary of the file
600 format. This meant that a newer Storable module had no way of writing a
601 file readable by an older Storable, even if writer didn't store newer
604 This version of Storable will defer croaking until it encounters a data
605 type in the file that it does not recognize. This means that it will
606 continue to read files generated by newer Storable modules which are careful
607 in what they write out, making it easier to upgrade Storable modules in a
610 The old behaviour of immediate croaking can be re-instated by setting
611 C<$Storable::accept_future_minor> to false.
615 Both these variables have no effect on a newer Perl which supports the
618 =head1 ERROR REPORTING
620 Storable uses the "exception" paradigm, in that it does not try to workaround
621 failures: if something bad happens, an exception is generated from the
622 caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap
625 When Storable croaks, it tries to report the error via the C<logcroak()>
626 routine from the C<Log::Agent> package, if it is available.
628 Normal errors are reported by having store() or retrieve() return C<undef>.
629 Such errors are usually I/O errors (or truncated stream errors at retrieval).
635 Any class may define hooks that will be called during the serialization
636 and deserialization process on objects that are instances of that class.
637 Those hooks can redefine the way serialization is performed (and therefore,
638 how the symmetrical deserialization should be conducted).
640 Since we said earlier:
642 dclone(.) = thaw(freeze(.))
644 everything we say about hooks should also hold for deep cloning. However,
645 hooks get to know whether the operation is a mere serialization, or a cloning.
647 Therefore, when serializing hooks are involved,
649 dclone(.) <> thaw(freeze(.))
651 Well, you could keep them in sync, but there's no guarantee it will always
652 hold on classes somebody else wrote. Besides, there is little to gain in
653 doing so: a serializing hook could only keep one attribute of an object,
654 which is probably not what should happen during a deep cloning of that
657 Here is the hooking interface:
661 =item C<STORABLE_freeze> I<obj>, I<cloning>
663 The serializing hook, called on the object during serialization. It can be
664 inherited, or defined in the class itself, like any other method.
666 Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating
667 whether we're in a dclone() or a regular serialization via store() or freeze().
669 Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized
670 is the serialized form to be used, and the optional $ref1, $ref2, etc... are
671 extra references that you wish to let the Storable engine serialize.
673 At deserialization time, you will be given back the same LIST, but all the
674 extra references will be pointing into the deserialized structure.
676 The B<first time> the hook is hit in a serialization flow, you may have it
677 return an empty list. That will signal the Storable engine to further
678 discard that hook for this class and to therefore revert to the default
679 serialization of the underlying Perl data. The hook will again be normally
680 processed in the next serialization.
682 Unless you know better, serializing hook should always say:
684 sub STORABLE_freeze {
685 my ($self, $cloning) = @_;
686 return if $cloning; # Regular default serialization
690 in order to keep reasonable dclone() semantics.
692 =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ...
694 The deserializing hook called on the object during deserialization.
695 But wait. If we're deserializing, there's no object yet... right?
697 Wrong: the Storable engine creates an empty one for you. If you know Eiffel,
698 you can view C<STORABLE_thaw> as an alternate creation routine.
700 This means the hook can be inherited like any other method, and that
701 I<obj> is your blessed reference for this particular instance.
703 The other arguments should look familiar if you know C<STORABLE_freeze>:
704 I<cloning> is true when we're part of a deep clone operation, I<serialized>
705 is the serialized string you returned to the engine in C<STORABLE_freeze>,
706 and there may be an optional list of references, in the same order you gave
707 them at serialization time, pointing to the deserialized objects (which
708 have been processed courtesy of the Storable engine).
710 When the Storable engine does not find any C<STORABLE_thaw> hook routine,
711 it tries to load the class by requiring the package dynamically (using
712 the blessed package name), and then re-attempts the lookup. If at that
713 time the hook cannot be located, the engine croaks. Note that this mechanism
714 will fail if you define several classes in the same file, but L<perlmod>
717 It is up to you to use these information to populate I<obj> the way you want.
719 Returned value: none.
725 Predicates are not exportable. They must be called by explicitly prefixing
726 them with the Storable package name.
730 =item C<Storable::last_op_in_netorder>
732 The C<Storable::last_op_in_netorder()> predicate will tell you whether
733 network order was used in the last store or retrieve operation. If you
734 don't know how to use this, just forget about it.
736 =item C<Storable::is_storing>
738 Returns true if within a store operation (via STORABLE_freeze hook).
740 =item C<Storable::is_retrieving>
742 Returns true if within a retrieve operation, (via STORABLE_thaw hook).
748 With hooks comes the ability to recurse back to the Storable engine. Indeed,
749 hooks are regular Perl code, and Storable is convenient when it comes to
750 serialize and deserialize things, so why not use it to handle the
751 serialization string?
753 There are a few things you need to know however:
759 You can create endless loops if the things you serialize via freeze()
760 (for instance) point back to the object we're trying to serialize in the hook.
764 Shared references among objects will not stay shared: if we're serializing
765 the list of object [A, C] where both object A and C refer to the SAME object
766 B, and if there is a serializing hook in A that says freeze(B), then when
767 deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D,
768 a deep clone of B'. The topology was not preserved.
772 That's why C<STORABLE_freeze> lets you provide a list of references
773 to serialize. The engine guarantees that those will be serialized in the
774 same context as the other objects, and therefore that shared objects will
777 In the above [A, C] example, the C<STORABLE_freeze> hook could return:
779 ("something", $self->{B})
781 and the B part would be serialized by the engine. In C<STORABLE_thaw>, you
782 would get back the reference to the B' object, deserialized for you.
784 Therefore, recursion should normally be avoided, but is nonetheless supported.
788 There is a new Clone module available on CPAN which implements deep cloning
789 natively, i.e. without freezing to memory and thawing the result. It is
790 aimed to replace Storable's dclone() some day. However, it does not currently
791 support Storable hooks to redefine the way deep cloning is performed.
793 =head1 Storable magic
795 Yes, there's a lot of that :-) But more precisely, in UNIX systems
796 there's a utility called C<file>, which recognizes data files based on
797 their contents (usually their first few bytes). For this to work,
798 a certain file called F<magic> needs to taught about the I<signature>
799 of the data. Where that configuration file lives depends on the UNIX
800 flavour, often it's something like F</usr/share/misc/magic> or
801 F</etc/magic>. Your system administrator needs to do the updating of
802 the F<magic> file. The necessary signature information is output to
803 STDOUT by invoking Storable::show_file_magic(). Note that the open
804 source implementation of the C<file> utility 3.38 (or later)
805 is expected to contain the support for recognising Storable files,
806 in addition to other kinds of Perl files.
810 Here are some code samples showing a possible usage of Storable:
812 use Storable qw(store retrieve freeze thaw dclone);
814 %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);
816 store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n";
818 $colref = retrieve('/tmp/colors');
819 die "Unable to retrieve from /tmp/colors!\n" unless defined $colref;
820 printf "Blue is still %lf\n", $colref->{'Blue'};
822 $colref2 = dclone(\%color);
824 $str = freeze(\%color);
825 printf "Serialization of %%color is %d bytes long.\n", length($str);
826 $colref3 = thaw($str);
828 which prints (on my machine):
830 Blue is still 0.100000
831 Serialization of %color is 102 bytes long.
835 If you're using references as keys within your hash tables, you're bound
836 to disappointment when retrieving your data. Indeed, Perl stringifies
837 references used as hash table keys. If you later wish to access the
838 items via another reference stringification (i.e. using the same
839 reference that was used for the key originally to record the value into
840 the hash table), it will work because both references stringify to the
843 It won't work across a C<store> and C<retrieve> operations however, because
844 the addresses in the retrieved objects, which are part of the stringified
845 references, will probably differ from the original addresses. The
846 topology of your structure is preserved, but not hidden semantics
849 On platforms where it matters, be sure to call C<binmode()> on the
850 descriptors that you pass to Storable functions.
852 Storing data canonically that contains large hashes can be
853 significantly slower than storing the same data normally, as
854 temporary arrays to hold the keys for each hash have to be allocated,
855 populated, sorted and freed. Some tests have shown a halving of the
856 speed of storing -- the exact penalty will depend on the complexity of
857 your data. There is no slowdown on retrieval.
861 You can't store GLOB, CODE, FORMLINE, etc... If you can define
862 semantics for those operations, feel free to enhance Storable so that
863 it can deal with them.
865 The store functions will C<croak> if they run into such references
866 unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that
867 case, the fatal message is turned in a warning and some
868 meaningless string is stored instead.
870 Setting C<$Storable::canonical> may not yield frozen strings that
871 compare equal due to possible stringification of numbers. When the
872 string version of a scalar exists, it is the form stored, therefore
873 if you happen to use your numbers as strings between two freezing
874 operations on the same data structures, you will get different
877 When storing doubles in network order, their value is stored as text.
878 However, you should also not expect non-numeric floating-point values
879 such as infinity and "not a number" to pass successfully through a
880 nstore()/retrieve() pair.
882 As Storable neither knows nor cares about character sets (although it
883 does know that characters may be more than eight bits wide), any difference
884 in the interpretation of character codes between a host and a target
885 system is your problem. In particular, if host and target use different
886 code points to represent the characters used in the text representation
887 of floating-point numbers, you will not be able be able to exchange
888 floating-point data, even with nstore().
890 C<Storable::drop_utf8> is a blunt tool. There is no facility either to
891 return B<all> strings as utf8 sequences, or to attempt to convert utf8
892 data back to 8 bit and C<croak()> if the conversion fails.
894 Future compatibility does not yet extend to having the option of loading
895 serialized data with higher than current minor version numbers. This
896 ought to be fixed pronto.
900 Thank you to (in chronological order):
902 Jarkko Hietaniemi <jhi@iki.fi>
903 Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de>
904 Benjamin A. Holzman <bah@ecnvantage.com>
905 Andrew Ford <A.Ford@ford-mason.co.uk>
906 Gisle Aas <gisle@aas.no>
907 Jeff Gresham <gresham_jeffrey@jpmorgan.com>
908 Murray Nesbitt <murray@activestate.com>
909 Marc Lehmann <pcg@opengroup.org>
910 Justin Banks <justinb@wamnet.com>
911 Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
912 Salvador Ortiz Garcia <sog@msg.com.mx>
913 Dominic Dunlop <domo@computer.org>
914 Erik Haugan <erik@solbors.no>
916 for their bug reports, suggestions and contributions.
918 Benjamin Holzman contributed the tied variable support, Andrew Ford
919 contributed the canonical order for hashes, and Gisle Aas fixed
920 a few misunderstandings of mine regarding the Perl internals,
921 and optimized the emission of "tags" in the output streams by
922 simply counting the objects instead of tagging them (leading to
923 a binary incompatibility for the Storable image starting at version
924 0.6--older images are of course still properly understood).
925 Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading
926 and reference to tied items support.
930 There is a Japanese translation of this man page available at
931 http://member.nifty.ne.jp/hippo2000/perltips/storable.htm ,
932 courtesy of Kawai, Takanori <kawai@nippon-rad.co.jp>.
936 Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>>