On Sep 6, 2009, at 17:36, John Engelhart wrote:
So, since the Mac OS X documentation uses the term "interior
pointer" in a totally non-standard way, and I can't find anything
wrt/ to what I'm looking for, my question is:
Does the Mac OS X garbage collector support interior pointers (as
defined at http://www.memorymanagement.org/glossary/i.html#interior.pointer
)?
Huh?
You know it doesn't. You've beaten up on GC before, with reference to
*both* senses of "interior pointer".
I certainly hope this isn't the case because this essentially means
that it is fundamentally impossible to write programs that execute
in a deterministic fashion when using GC. It is basically
impossible to write code that guarantees that the base pointer
remains visible to the collector, particularly when __weak and/or
the optimizer is used. Things work the vast majority of the time
because there is (usually) a very small window of time where it
could actually cause a problem and one of two things are true: 1)
When the compiler generates code that, as a side effect, only uses
interior pointers (this happens much, much more frequently than you
would think), there's "something" that covers this fundamental error
with a base pointer. This is invariably due to a happy set of
coincidences and rarely the explicit, intentional result of the
programmer. 2) The collector is not collecting during the window of
vulnerability.
You also know that no one else on this list agrees with you on this
subject, so I don't understand why you're asking about it.
*Of course* every programmer explicitly and intentionally ensures that
the lifetimes of "base" pointers continue for as long as "derived" or
"interior" pointers need to be valid. That's the Mac OS X garbage
collection architecture, for now.
Of course it's possible to forget to maintain the base pointer (or
fail to realize that it's necessary). Of course there are a few cases
where it's much easer to forget than is reasonable. Of course
forgetting to do it opens up a window of vulnerability. Of course that
sucks.
But it's no more broken now than the last time the list discussed
this. There's nothing new here. Time to move on.
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