[gclist] Some thoughts on finalizer ordering
Tue, 17 Nov 1998 07:56:25 -0600
First I'm presupposing a cooperating system not
something layered on C++ etc.
In this case finalizer ordering is in the semantics
of the mutator and there will be syntax to express
that semantics. That is the user will be able to
express finalizer ordering.
If a buffer object uses a file object in such a way
that the buffer object must finalize first it makes
sense to say all buffer objects in a pass must go
before all file objects. That is ordering can be a
characteristic of class definitions not objects.
In many systems doing this means checks for cycles
can be done at compile time or link time. Where
classes can be defined at run time it is obvious that
no checks can be done at compile time but checks can
be moved back to the point where classes are defined.
If there is partial evaluation that can still mean
Inheritance may make classes less restrictive not
more. Requiring later finalization is more restrictive
than allowing earlier finalization. In terms of
restrictivness the buffer object is less restrictive
than the file object because it could have been
finalized later assuming the finalizer worked.
When objects are composed the parts must all be
finalized at the same time. If there is a confilct
the user must resolve it. The user must use notation
for this so we know he understands the problem. The
ideal notation is to allow the surrounding class to
invoke the sub finalizers in its finalizer.
Suppose you have a file_buffer object with a file
and buffer. There would be notation saying the
sub objects didn't run their own finalizers and
the file_buffer object would run those finalizers.
It would specify its own finalizer sequencing.
Charles Fiterman Geodesic Systems
414 North Orleans Suite 410 Phone 312 832 1221 x223
Chicago IL 60610-4418 FAX 312 832 1230
</color>As the complexity of a system increases our ability to make
precise and yet significant statements about its behavior
diminishes until a threshold is reached beyond which precision
and significance or relevance become almost mutually exclusive
characteristics. -- Lofti Zadeh