Can I use unwind_* mechanism in my loadable builtin?

[Robert E. Griffith]

In my loadable builtin I have a error handling mechanism based on 
setjmp/longjump. I thought I would use the  unwind_prot.h/c mechanism to 
clean up resources but even though I am calling begin_unwind_frame() and 
discard_unwind_frame() in pairs, sometimes the discard fails because the 
tag set by begin_unwind_frame() does not exist. I think its after my 
builtin invokes the source.def builtin.

Maybe I dont fully understand the unwind mechanism. I thought it is a 
stack and as long as I leave it as it was (ie. each begin is followed by 
a discard or a run) that it should play nice with bashes' use of it.

Am I mistaken on that? Should my builtin provide a similar but separate 
mechanism?

--BobG