Re: Comparing Pika-syle and JNI-style Tom Lord (15 Jan 2004 03:37 UTC)
Re: Comparing Pika-syle and JNI-style Tom Lord 15 Jan 2004 03:37 UTC
> From: Shiro Kawai <email@example.com>
> > > As Per noted, Boehm GC avoids this if configured with "interior
> > > pointer" flag.
> > Ok, but that doesn't help if the data is separately allocated.
> If you're accessing the data chunk and no reference except
> from the scheme_value local variable points to the string header,
> then the string header can be collected, but that doesn't matter
> (since you don't need it anyway).
In the system where I saw these kinds of bugs, freeing the header
triggered freeing the string data. If the Boehm collector supports
finalizers of some sort then it would admit similar bugs.
> > Or, for that matter, if my pointer is pointed past the end of the
> > string but I'm indexing at a negative offset from it.
> You can point the next address past the end of chunk and still the
> chunk is retained, since in C it is a valid pointer usage.
> (you can change this behavior by configuration option, though).
That's good. Yes, I believe that Boehm's collector can address many
of the bugs -- just not enough to excuse it for critical systems.
> > The whole thing just plays way too fast and loose with C semantics to
> > be acceptable for critical systems.
> Yup. I don't object to this feeling. I just wanted to be precise
> about the facts.
And it's much appreciated. I've learned from you.