Please note that you have to deal with circular references manually in Objective-C, introducing two types of pointers, strong and weak. I don't think this is optimal. If you want to deal with circular references automatically you again need some other kind of other garbage collection running.
On 29.05.2013 02:46, Steven Schveighoffer wrote:
On Tue, 28 May 2013 20:40:03 -0400, Manu <turkeyman@gmail.com> wrote:
ObjC and WinRT are both used successfully on embedded hardware, I'm
really
wondering if this is the way to go for embedded in D.
V8 uses an incremental collector (somehow?), which I've been saying is
basically mandatory for embedded/realtime use. Apparently Google agree.
Clearly others have already had this quarrel, their resolutions are worth
consideration.
An interesting thing to note, Apple tried garbage collection with Obj-C,
but only on MacOS, and it's now been deprecated since automatic
reference counting was introduced [1]. It never was on iOS.
So that is a telling omission I think.
-Steve
[1] https://en.wikipedia.org/wiki/Objective-C#Garbage_collection
A problem with the naive approach of atomic reference counting a counter inside the object (as usually done in COM interfaces, I don't know how it is done in Objective-C) is that it is not thread-safe to modify a pointer without locking (or a CAS2 operation that you don't have on popular processors). You can avoid that using deferred reference counting (logging pointer changes to some thread local buffer), but that introduces back a garbage collection step with possibly massive destruction. This step might be done concurrently, but that adds another layer of complexity to finding circles.
Another issue might be that incrementing a reference of an object when taking an interior pointer (like you do when using slices) can be pretty expensive because you usually have to find the base of the object to access the counter.
I won't dismiss RC garbage collection as impossible, but doing it efficiently and concurrently is not so easy.