Steve Fink:
# > > - Easy to forget to remove temporaries from the root set
# > > - Easy to double-anchor objects and forget to remove the
# temporary
# > > anchoring
# > > - longjmp() can bypass the unanchoring
# >
# > The temporary objects could be stored in a stack, which is
# popped when
# > leaving the current function (both with normal exits and longjmp).
# > This should make it a lot less likely to forget the unanchoring.
#
# How do you do this with longjmp? I could see chaining another
# handler onto the longjmp context so that longjmp would
# backtrack through all of these allocations, but that would
# require allocating space for another context. And allocating
# space further slows down the common case...
#
# longjmp is really the major blocker for this option, so if
# you can work around it, then maybe we'll have something. Your
# stack-based approach sounds plausible as a way to make it
# easier to handle the bookkeeping, as long as you don't do it
# with macros. :-) Maybe wrapper functions?
Pseudocode:
void some_func(struct Parrot_Interp *interpreter) {
anchor(interpreter, a);
anchor(interpreter, b);
TRY(interpreter) {
something_that_might_throw_an_exception();
}
CATCH(interpreter) {
}
unanchor(interpreter, b);
unanchor(interpreter, a);
}
#define TRY(interp) if(setup_exception((interp))
#define CATCH(interp) else
BOOLVAL setup_exception(struct Parrot_Interp *interpreter) {
Parrot_jmpbuf jb=NULL;
//setup jmpbuf...
if(setjmp(jmpbuf)) {
jb=stack_pop(interpreter, interpreter->jb_stack);
//Everything above us naturally falls off
interpreter->anchor_stack_top=jb->anchor_stack_top;
}
else {
Parrot_jmpbuf *jb=malloc(sizeof(Parrot_jmpbuf));
jb->real_jmpbuf=jmpbuf;
jb->anchor_stack_top=interpreter->anchor_stack_top;
...
stack_push(interpreter, interpreter->jb_stack, jb);
}
}
Yeah, I know, macros are evil, but they make this code *soooo* much
prettier...
--Brent Dax <[EMAIL PROTECTED]>
@roles=map {"Parrot $_"} qw(embedding regexen Configure)
"If you want to propagate an outrageously evil idea, your conclusion
must be brazenly clear, but your proof unintelligible."
--Ayn Rand, explaining how today's philosophies came to be
