storable.pm

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

	eval { $self = pretrieve($file) };		# Call C routine
	logcroak $@ if $@ =~ s/\.?\n$/,/;
	$@ = $da;
	return $self;
}

#
# thaw
#
# Recreate objects in memory from an existing frozen image created
# by freeze.  If the frozen image passed is undef, return undef.
#
sub thaw {
	my ($frozen) = @_;
	return undef unless defined $frozen;
	my $self;
	my $da = $@;							# Could be from exception handler
	eval { $self = mretrieve($frozen) };	# Call C routine
	logcroak $@ if $@ =~ s/\.?\n$/,/;
	$@ = $da;
	return $self;
}

1;
__END__

=head1 NAME

Storable - persistence for Perl data structures

=head1 SYNOPSIS

 use Storable;
 store \%table, 'file';
 $hashref = retrieve('file');

 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);

 # Network order
 nstore \%table, 'file';
 $hashref = retrieve('file');	# There is NO nretrieve()

 # Storing to and retrieving from an already opened file
 store_fd \@array, \*STDOUT;
 nstore_fd \%table, \*STDOUT;
 $aryref = fd_retrieve(\*SOCKET);
 $hashref = fd_retrieve(\*SOCKET);

 # Serializing to memory
 $serialized = freeze \%table;
 %table_clone = %{ thaw($serialized) };

 # Deep (recursive) cloning
 $cloneref = dclone($ref);

 # Advisory locking
 use Storable qw(lock_store lock_nstore lock_retrieve)
 lock_store \%table, 'file';
 lock_nstore \%table, 'file';
 $hashref = lock_retrieve('file');

=head1 DESCRIPTION

The Storable package brings persistence to your Perl data structures
containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be
conveniently stored to disk and retrieved at a later time.

It can be used in the regular procedural way by calling C<store> with
a reference to the object to be stored, along with the file name where
the image should be written.

The routine returns C<undef> for I/O problems or other internal error,
a true value otherwise. Serious errors are propagated as a C<die> exception.

To retrieve data stored to disk, use C<retrieve> with a file name.
The objects stored into that file are recreated into memory for you,
and a I<reference> to the root object is returned. In case an I/O error
occurs while reading, C<undef> is returned instead. Other serious
errors are propagated via C<die>.

Since storage is performed recursively, you might want to stuff references
to objects that share a lot of common data into a single array or hash
table, and then store that object. That way, when you retrieve back the
whole thing, the objects will continue to share what they originally shared.

At the cost of a slight header overhead, you may store to an already
opened file descriptor using the C<store_fd> routine, and retrieve
from a file via C<fd_retrieve>. Those names aren't imported by default,
so you will have to do that explicitly if you need those routines.
The file descriptor you supply must be already opened, for read
if you're going to retrieve and for write if you wish to store.

	store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
	$hashref = fd_retrieve(*STDIN);

You can also store data in network order to allow easy sharing across
multiple platforms, or when storing on a socket known to be remotely
connected. The routines to call have an initial C<n> prefix for I<network>,
as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be
correctly restored so you don't have to know whether you're restoring
from native or network ordered data.  Double values are stored stringified
to ensure portability as well, at the slight risk of loosing some precision
in the last decimals.

When using C<fd_retrieve>, objects are retrieved in sequence, one
object (i.e. one recursive tree) per associated C<store_fd>.

If you're more from the object-oriented camp, you can inherit from
Storable and directly store your objects by invoking C<store> as
a method. The fact that the root of the to-be-stored tree is a
blessed reference (i.e. an object) is special-cased so that the
retrieve does not provide a reference to that object but rather the
blessed object reference itself. (Otherwise, you'd get a reference
to that blessed object).

=head1 MEMORY STORE

The Storable engine can also store data into a Perl scalar instead, to
later retrieve them. This is mainly used to freeze a complex structure in
some safe compact memory place (where it can possibly be sent to another
process via some IPC, since freezing the structure also serializes it in
effect). Later on, and maybe somewhere else, you can thaw the Perl scalar
out and recreate the original complex structure in memory.

Surprisingly, the routines to be called are named C<freeze> and C<thaw>.
If you wish to send out the frozen scalar to another machine, use
C<nfreeze> instead to get a portable image.

Note that freezing an object structure and immediately thawing it
actually achieves a deep cloning of that structure:

    dclone(.) = thaw(freeze(.))

Storable provides you with a C<dclone> interface which does not create
that intermediary scalar but instead freezes the structure in some
internal memory space and then immediately thaws it out.

=head1 ADVISORY LOCKING

The C<lock_store> and C<lock_nstore> routine are equivalent to
C<store> and C<nstore>, except that they get an exclusive lock on
the file before writing.  Likewise, C<lock_retrieve> does the same
as C<retrieve>, but also gets a shared lock on the file before reading.

As with any advisory locking scheme, the protection only works if you
systematically use C<lock_store> and C<lock_retrieve>.  If one side of
your application uses C<store> whilst the other uses C<lock_retrieve>,
you will get no protection at all.

The internal advisory locking is implemented using Perl's flock()
routine.  If your system does not support any form of flock(), or if
you share your files across NFS, you might wish to use other forms
of locking by using modules such as LockFile::Simple which lock a
file using a filesystem entry, instead of locking the file descriptor.

=head1 SPEED

The heart of Storable is written in C for decent speed. Extra low-level
optimizations have been made when manipulating perl internals, to
sacrifice encapsulation for the benefit of greater speed.

=head1 CANONICAL REPRESENTATION

Normally, Storable stores elements of hashes in the order they are
stored internally by Perl, i.e. pseudo-randomly.  If you set
C<$Storable::canonical> to some C<TRUE> value, Storable will store
hashes with the elements sorted by their key.  This allows you to
compare data structures by comparing their frozen representations (or
even the compressed frozen representations), which can be useful for
creating lookup tables for complicated queries.

Canonical order does not imply network order; those are two orthogonal
settings.

=head1 CODE REFERENCES

Since Storable version 2.05, CODE references may be serialized with
the help of L<B::Deparse>. To enable this feature, set
C<$Storable::Deparse> to a true value. To enable deserialization,
C<$Storable::Eval> should be set to a true value. Be aware that
deserialization is done through C<eval>, which is dangerous if the
Storable file contains malicious data. You can set C<$Storable::Eval>
to a subroutine reference which would be used instead of C<eval>. See
below for an example using a L<Safe> compartment for deserialization
of CODE references.

If C<$Storable::Deparse> and/or C<$Storable::Eval> are set to false
values, then the value of C<$Storable::forgive_me> (see below) is
respected while serializing and deserializing.

=head1 FORWARD COMPATIBILITY

This release of Storable can be used on a newer version of Perl to
serialize data which is not supported by earlier Perls.  By default,
Storable will attempt to do the right thing, by C<croak()>ing if it
encounters data that it cannot deserialize.  However, the defaults
can be changed as follows:

=over 4

=item utf8 data

Perl 5.6 added support for Unicode characters with code points > 255,
and Perl 5.8 has full support for Unicode characters in hash keys.
Perl internally encodes strings with these characters using utf8, and
Storable serializes them as utf8.  By default, if an older version of
Perl encounters a utf8 value it cannot represent, it will C<croak()>.
To change this behaviour so that Storable deserializes utf8 encoded
values as the string of bytes (effectively dropping the I<is_utf8> flag)
set C<$Storable::drop_utf8> to some C<TRUE> value.  This is a form of
data loss, because with C<$drop_utf8> true, it becomes impossible to tell
whether the original data was the Unicode string, or a series of bytes
that happen to be valid utf8.

=item restricted hashes

Perl 5.8 adds support for restricted hashes, which have keys
restricted to a given set, and can have values locked to be read only.
By default, when Storable encounters a restricted hash on a perl
that doesn't support them, it will deserialize it as a normal hash,
silently discarding any placeholder keys and leaving the keys and
all values unlocked.  To make Storable C<croak()> instead, set
C<$Storable::downgrade_restricted> to a C<FALSE> value.  To restore
the default set it back to some C<TRUE> value.

=item files from future versions of Storable

Earlier versions of Storable would immediately croak if they encountered
a file with a higher internal version number than the reading Storable
knew about.  Internal version numbers are increased each time new data
types (such as restricted hashes) are added to the vocabulary of the file
format.  This meant that a newer Storable module had no way of writing a
file readable by an older Storable, even if the writer didn't store newer
data types.

This version of Storable will defer croaking until it encounters a data
type in the file that it does not recognize.  This means that it will
continue to read files generated by newer Storable modules which are careful
in what they write out, making it easier to upgrade Storable modules in a
mixed environment.

The old behaviour of immediate croaking can be re-instated by setting
C<$Storable::accept_future_minor> to some C<FALSE> value.

=back

All these variables have no effect on a newer Perl which supports the
relevant feature.

=head1 ERROR REPORTING

Storable uses the "exception" paradigm, in that it does not try to workaround
failures: if something bad happens, an exception is generated from the
caller's perspective (see L<Carp> and C<croak()>).  Use eval {} to trap
those exceptions.

When Storable croaks, it tries to report the error via the C<logcroak()>
routine from the C<Log::Agent> package, if it is available.

Normal errors are reported by having store() or retrieve() return C<undef>.
Such errors are usually I/O errors (or truncated stream errors at retrieval).

=head1 WIZARDS ONLY

=head2 Hooks

Any class may define hooks that will be called during the serialization
and deserialization process on objects that are instances of that class.
Those hooks can redefine the way serialization is performed (and therefore,
how the symmetrical deserialization should be conducted).

Since we said earlier:

    dclone(.) = thaw(freeze(.))

everything we say about hooks should also hold for deep cloning. However,
hooks get to know whether the operation is a mere serialization, or a cloning.

Therefore, when serializing hooks are involved,

    dclone(.) <> thaw(freeze(.))

Well, you could keep them in sync, but there's no guarantee it will always
hold on classes somebody else wrote.  Besides, there is little to gain in
doing so: a serializing hook could keep only one attribute of an object,
which is probably not what should happen during a deep cloning of that
same object.

Here is the hooking interface:

=over 4

=item C<STORABLE_freeze> I<obj>, I<cloning>

The serializing hook, called on the object during serialization.  It can be
inherited, or defined in the class itself, like any other method.

Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating
whether we're in a dclone() or a regular serialization via store() or freeze().

Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized
is the serialized form to be used, and the optional $ref1, $ref2, etc... are
extra references that you wish to let the Storable engine serialize.

At deserialization time, you will be given back the same LIST, but all the
extra references will be pointing into the deserialized structure.

The B<first time> the hook is hit in a serialization flow, you may have it
return an empty list.  That will signal the Storable engine to further
discard that hook for this class and to therefore revert to the default
serialization of the underlying Perl data.  The hook will again be normally
processed in the next serialization.

Unless you know better, serializing hook should always say:

    sub STORABLE_freeze {
        my ($self, $cloning) = @_;
        return if $cloning;         # Regular default serialization
        ....
    }

in order to keep reasonable dclone() semantics.

=item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ...

The deserializing hook called on the object during deserialization.
But wait: if we're deserializing, there's no object yet... right?

Wrong: the Storable engine creates an empty one for you.  If you know Eiffel,
you can view C<STORABLE_thaw> as an alternate creation routine.

This means the hook can be inherited like any other method, and that
I<obj> is your blessed reference for this particular instance.

The other arguments should look familiar if you know C<STORABLE_freeze>:
I<cloning> is true when we're part of a deep clone operation, I<serialized>
is the serialized string you returned to the engine in C<STORABLE_freeze>,
and there may be an optional list of references, in the same order you gave
them at serialization time, pointing to the deserialized objects (which
have been processed courtesy of the Storable engine).

When the Storable engine does not find any C<STORABLE_thaw> hook routine,
it tries to load the class by requiring the package dynamically (using
the blessed package name), and then re-attempts the lookup.  If at that
time the hook cannot be located, the engine croaks.  Note that this mechanism
will fail if you define several classes in the same file, but L<perlmod>
warned you.

It is up to you to use this information to populate I<obj> the way you want.

Returned value: none.

=item C<STORABLE_attach> I<class>, I<cloning>, I<serialized>

While C<STORABLE_freeze> and C<STORABLE_thaw> are useful for classes where
each instance is independent, this mechanism has difficulty (or is
incompatible) with objects that exist as common process-level or
system-level resources, such as singleton objects, database pools, caches
or memoized objects.

The alternative C<STORABLE_attach> method provides a solution for these
shared objects. Instead of C<STORABLE_freeze> --E<gt> C<STORABLE_thaw>,
you implement C<STORABLE_freeze> --E<gt> C<STORABLE_attach> instead.

Arguments: I<class> is the class we are attaching to, I<cloning> is a flag
indicating whether we're in a dclone() or a regular de-serialization via
thaw(), and I<serialized> is the stored string for the resource object.

Because these resource objects are considered to be owned by the entire
process/system, and not the "property" of whatever is being serialized,
no references underneath the object should be included in the serialized
string. Thus, in any class that implements C<STORABLE_attach>, the
C<STORABLE_freeze> method cannot return any references, and C<Storable>
will throw an error if C<STORABLE_freeze> tries to return references.

All information required to "attach" back to the shared resource object
B<must> be contained B<only> in the C<STORABLE_freeze> return string.
Otherwise, C<STORABLE_freeze> behaves as normal for C<STORABLE_attach>
classes.

Because C<STORABLE_attach> is passed the class (rather than an object),
it also returns the object directly, rather than modifying the passed
object.

Returned value: object of type C<class>

=back

=head2 Predicates

Predicates are not exportable.  They must be called by explicitly prefixing
them with the Storable package name.

=over 4

=item C<Storable::last_op_in_netorder>