Re: Procedure types

From: [at]} <Wojtek>
Date: Sun, 21 Nov 2004 09:12:22 -0500 (EST)

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On Sun, 21 Nov 2004, H. v. L. wrote:

> My question is:
> Are procedure types really a problem for the run time system?
>
> If I am right, BlackBox maintains a list of loaded modules anyway and
> those modules not being top level modules, which therefore cannot be
> unloaded, are dynamically marked. So the run time system checks whether a
> module contains a reference - in this case via inheritance - to another
> module.
> Actually I don't see any difference between checking an inheritance
> relation and checking a pointer to a foreign procedure, the list of
> references does exist, so it only must be enlarged by procedure
> references!?

Inheritance references are static, while procedure variables are assigned
at run time. Furthermore, even the number of procedure variables
in a given module may not be known since procedure variables can be
created dynamically. For example, imagine a type

prVar = POINTER TO RECORD pv: PROCEDURE; next: prVar END;

One can thus create a linked list of records, each one containing
a reference to a procedure. In order to make unloading safe one needs
to maintain those references versus unloading of modules that implement
the "pv" fields.

I am sure one can invent even more vicious scenarios. My question still
stands whether all this is safe in the current version of the run time
system, and if not then whether it can be made safe. I am not yet buing
into Fyodor arguments. Perhaps this problem has been solved already
by the c.s. community. I simply do not know. I am only a user.

W.

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Received on Sun Nov 21 2004 - 15:12:22 UTC