Hi John,

The QNX pthreads implementation is essentially a C library - it doesn't know anything about C++.   Some other clibs 
(such as the GNU clib) include specialized code that interacts with the C++ library in the case of thread cancellation 
to make it behave as if thread cancellation is a magic, uncatchable exception; this leverages the usual C++ stack 
unwinding code to destruct stack local variables.

It is technically possible to port the GNU clib approach to QNX.   I have an x86 implementation of something similar, 
although I wrote it before finding out that the GNU clib behaves this way (it didn't back when I started on that 
project).  Consequently my implementation is somewhat crude by comparison, and not easily portable to other 
architectures.  I did take a look at the GNU implementation, though, and my read of it suggests it should be possible to
 port the key bits to operate with the QNX clib, although it would probably involve a dive into the g++ ABI and 
exception handling layer.  The relevant code is in the nptl sub-library, specifically with regards to stack unwinding.

Hope this helps some,

-Will