Help: Unwinding the C++ stack...throw, longjmp & threads

["George T. Talbot" <george@moberg.com>]

This is a request for assistance, as I don't know the right person to
ask.

I'm working on a solution for deferred pthread_cancel() under Linux. 
What I want is to unwind the stack when the thread is cancelled so that
C++ destructors for objects on the stack get called.

If I recompile the C library with the -fexceptions flag, I can throw an
exception in a cancellation handler, and this does what I want.  My
platform is Linux x86.

However, after talking to Ulrich Drepper at LWCE, he says that
recompiling the C library with -fexceptions slows it down by around 5%. 
So, obviously, he won't accept a patch to the main-line source to do
this, with very good reason.

I would like to write a function which unwinds the stack similarly to
what happens at a throw in C++, but which wouldn't require recompiling
existing libraries written in C.

Is this possible?  Can anyone point me to the source for how throw
unwinds the stack?  I've been looking at the egcs 1.1.2 source tree, but
there's a lot to look at, and I'm confused with the different models for
throw and catch.  Alternatively, could someone put me in touch with the
folks that work on C++ exceptions in gcc on the x86 processor?

Also, does setjmp()/longjmp() assure that C++ destructors for
stack-based objects are called?

Sorry if some/all of these questions are dumb.  Thanks.

--
George T. Talbot
<george@moberg.com>