Партнёры:
Хостинг:
FreezeThaw - converting Perl structures to strings and back.
use FreezeThaw qw(freeze thaw cmpStr safeFreeze cmpStrHard);
$string = freeze $data1, $data2, $data3;
...
($olddata1, $olddata2, $olddata3) = thaw $string;
if (cmpStr($olddata2,$data2) == 0) {print "OK!"}
Deals with objects, circular lists, repeated appearence of the same refence. Does not deal with overloaded stringify operator yet.
So the package needs to define its own methods only if the fallback methods will fail (for example, for a lot of data the ``content'' of an object is an address of some C data). The methods are called like
$newcooky = $obj->Freeze($cooky); $obj = Package->Thaw($content,$cooky);
To save and restore the data the following method are applicable:
$cooky->FreezeScalar($data,$ignorePackage,$noduplicate);
during Freeze()ing, and
$data = $cooky->ThawScalar;
Two optional arguments $ignorePackage and $noduplicate regulate whether the freezing should not call the methods even if $data is a reference to a blessed object, and whether the data should not be marked as seen already even if it was seen before. The default methods
sub UNIVERSAL::Freeze {
my ($obj, $cooky) = (shift, shift);
$cooky->FreezeScalar($obj,1,1);
}
sub UNIVERSAL::Thaw {
my ($package, $cooky) = (shift, shift);
my $obj = $cooky->ThawScalar;
bless $obj, $package;
}
call the "FreezeScalar" method of the $cooky since the freezing engine will see the data the second time during this call. Indeed, it is the freezing engine who calls UNIVERSAL::Freeze(), and it calls it because it needs to freeze $obj. The above call to $cooky->FreezeScalar() handles the same data back to engine, but because flags are different, the code does not cycle.
Freezing and thawing $cooky also allows the following additional methods:
$cooky->isSafe;
to find out whether the current freeze was initiated by "freeze" or "safeFreeze" command. Analogous method for thaw $cooky returns whether the current thaw operation is considered safe (i.e., either does not contain cached elsewhere data, or comes from the same application). You can use
$cooky->makeSafe;
to prohibit cached data for the duration of the rest of freezing or thawing of current object.
Two methods
$value = $cooky->repeatedOK; $cooky->noRepeated; # Now repeated are prohibited
allow to find out/change the current setting for allowing repeated references.
If you want to flush the cache of saved objects you can use
FreezeThaw->flushCache;
this can invalidate some frozen string, so that thawing them will result in fatal error.
The restriction is that during the allocation step you cannot use any reference to any Perl object that can be referenced from any other place. This restriction is applied since that object may not exist yet.
Correspondingly, during instantiation step the previosly allocated object should be "filled", i.e., it can be changed in any way such that the references to this object remain valid.
The methods are called like this:
$pre_object_ref = Package->Allocate($pre_pre_object_ref);
# Returns reference
Package->Instantiate($pre_object_ref,$cooky);
# Converts into reference to blessed object
The reverse operations are
$object_ref->FreezeEmpty($cooky); $object_ref->FreezeInstance($cooky);
during these calls object can "freezeScalar" some information (in a usual way) that will be used during "Allocate" and "Instantiate" calls (via "thawScalar"). Note that the return value of "FreezeEmpty" is cached during the phase of creation of uninialized objects. This must be used like this: the return value is the reference to the created object, so it is not destructed until other objects are created, thus the frozen values of the different objects will not share the same references. Example of bad result:
$o1->FreezeEmpty($cooky)
freezes "{}", and "$o2->FreezeEmpty($cooky)" makes the same. Now nobody guaranties that that these two copies of "{}" are different, unless a reference to the first one is preserved during the call to "$o2->FreezeEmpty($cooky)". If "$o1->FreezeEmpty($cooky)" returns the value of "{}" it uses, it will be preserved by the engine.
The helper function "FreezeThaw::copyContents" is provided for simplification of instantiation. The syntax is
FreezeThaw::copyContents $to, $from;
The function copies contents the object $from point to into what the object $to points to (including package for blessed references). Both arguments should be references.
The default methods are provided. They do the following:
The objects which can survive freeze()/thaw() cycle must also survive a change of a ``member'' to an equal member. Say, after
$a = [a => 3];
$a->{b} = \ $a->{a};
$a satisfies
$a->{b} == \ $a->{a}
This property will be broken by freeze()/thaw(), but it is also broken by
$a->{a} = delete $a->{a};
|
Закладки на сайте Проследить за страницей |
Created 1996-2024 by Maxim Chirkov Добавить, Поддержать, Вебмастеру |