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List:       koffice
Subject:    klibloader
From:       Simon Hausmann <shaus () uermel ! Med ! Uni-Magdeburg ! DE>
Date:       1999-10-27 16:27:22
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Hi!

We store components in shared libraries. Loading them is fine, but we also
have to pay attention to *unloading* them properly when they are not
needed anymore.

I just implemented the necessary mechanism in klibloader. However
KLibLoader can't do all the magic, the application/component progammer
still has to do some things manually :-) , in order to avoid horrible
memory leaks.

So please make sure your koffice application implements/handles the
following things:

- Somewhere in your code you inherit from KLibFactory. In there you
  re-implement one create() method, in which you allocate new KOffice
  document objects. KLibLoader *has* to know about all objects created in
  your factory, so please change your create method to something like
  this:

  ...
  MyDocument *foo = new BarDoc;
  emit objectCreated( foo );
  return foo;

  The important thing is emitting the objectCreated() signal.

- In addition your KOffice component allocates a KInstance object
  somewhere (usually this is in your factory class, too) .

  When a shared library gets unloaded, your factory object gets deleted,
  too, so please make sure that you delete all objects, in the destructor
  of your factory class, which you allocated *beside* the ones allocated
  in your create() method. Usually this is just a KInstance object.



The general approach of how to determine if a shared library is not used
(referenced) anymore is to check if all objects created via the
KLibFactory::create() method have been destroyed (this is done by
connecting to the destroyed() signal of QObject) . This provides you the
comfortable feature that you will never have to call
KLibLoader::self()->unloadLibrary() or so. Just delete the object and
KLibLoader does the rest: It checks if there are any other objects left,
and if none, then it launches a timer. After a timeout of one minute it
will unload (close) the library (and delete the KLibFactory object
before) .


Ciao,
 Simon (...being lazy by trying to choose this way of explaining the
        stuff instead of patching/fixing KOffice :-)

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