Re: AddRef and Release

From:

"Ben Voigt [C++ MVP]" <rbv@nospam.nospam>

Newsgroups:

microsoft.public.vc.language

Date:

Mon, 4 Feb 2008 08:33:06 -0600

Message-ID:

<uoFNLqzZIHA.4196@TK2MSFTNGP04.phx.gbl>

Igor Tandetnik wrote:

"George" <George@discussions.microsoft.com> wrote in message
news:1E9A0E9B-AFA4-4140-9E52-63D867A85E94@microsoft.com

You can omit pairs of matching AddRef/Release in many cases. For
example, in your code you could remove the first such pair if the
first ellipsis doesn't contain pI1->Release() call, and similarly
for the second pair.

I think your method has risk if pI1, pI2 and pI3 are pointing to
different object instances -- it will counter is each different
component in an unmanaged manner, right?

Wrong. Show me exactly how you believe this code is at risk.

The current function must keep a reference count on pI1 while using pI1, or
else another thread could call pI1->Release() and this thread would be
accessing freed memory.

Guaranteeing that pI1->Release() is not called during the interval of access
to pI1 is a lot stronger requirement than "the first ellipsis doesn't
contain pI1->Release() call".

(currently, I think even if the code I wrote is redundant, it should
be safe. And to make it exception safe, I need to use RAII pattern.)

Quite. See CComPtr and CComQIPtr