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

[Jason Merrill]

>>>>> George T Talbot <george@moberg.com> writes:

 > Jason Merrill wrote:
 >> 
 >> No; cleanups are registered at compile time in the dwarf2 model.  You'll
 >> need to extend the C frontend to add the notion of cleanups, like a try
 >> ... finally construct, or a cleanup block construct.

 > Ugh.  This is starting to get beyond my skill level.  I can do the C
 > library stuff, but I'm not sure I understand how to extend the compiler
 > this way.

Actually, the simplest approach would be to make them builtin functions,
__builtin_cleanup_push (routine, arg) and __builtin_cleanup_pop (execute).
You would call expand_eh_region_start_tree in stmt.c to register the
cleanup, and if execute is true when popping, extract the cleanup info from
the ehstack and run it directly.  It would be hard to map the existing API
onto try ... finally.

 >>  > If I can do that, then I can rewrite pthread_cleanup_push() and
 >>  > pthread_cleanup_pop() to work with the exception mechanism and I can
 >>  > rewrite pthread_cancel() to throw an exception.
 >> 
 >> push and pop would need to be macros.

 > Yup.  They are now, if you look at pthreads.h.

And I see that they are required to be symmetrical, at the same nesting
level.  Good; this is crucial for the compile-time approach to work.

Jason