RE: allocation of untagged structures

From: [at]} <frei{>
Date: Mon, 30 Dec 2002 22:35:17 +0100

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Doug,

basically, you have two alternatives:

(1.) use normal tagged pointer types and NEW. But then, as you already
noticed, you have to be very careful about interferences between the
normal BlackBox garbage collector and COM reference counting. Jurg
Gutknecht describes a solution for this problem in his report "Oberon as
an Implementation Language for COM Components: A Case Study in Language
Interoperability". There, the entirety of objects currently in use by
COM is linked to a ring via prev/next pointers in order to prevent the
garbage collector from reclaiming objects used by COM but not by Oberon.
This ring must be anchored in a global variable.

(2.) use untagged pointers and the Windows memory management procedures
(HeapAlloc, HeapFree, etc.). There are also special COM memory
management procedures (CoTaskMemAlloc, CoTaskMemFree, etc.). The latter
procedures are mandatory for allocating [out] and [in, out] pointer
parameters. This is explained in more detail in Dale Rogerson's book
Inside COM or in Don Box's Essential COM.

Best regards,
Marc,
Oberon microsystems, Inc.


-----Original Message-----
From: Douglas G. Danforth [mailto:danforth{([at]})nowhere.xy
Sent: Sonntag, 29. Dezember 2002 18:06
To: blackbox{([at]})nowhere.xy
Subject: allocation of untagged structures


Folks,

I am attempting to do a very simple COM interface following
the suggestion in Platform-Specific Issues Using COM without
special Direct-To-COM compiler.

I had thought this would be easy but NEW cannot be used
to allocate untagged structures which are needed by COM.
So how can I allocate an arbitrary number of instances
of a COM object?

Must I count the number of bytes in the data structure
desired then allocate a BYTE array of that size
using NEW and then assign the address of the first
element of that array to an untagged pointer?

That doesn't seem too safe for when releasing the
data when the reference count goes to zero I somehow
must recapture the actual pointer to the BYTE array
and set it to zero for actual garbage collection.

How do I keep the reference count and garbage collection
processes separate?

-Doug
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Received on Mon Dec 30 2002 - 22:35:17 UTC