On 02/14/2011 03:34 PM, Stanislav Blinov wrote:
12.02.2011 18:44, d coder пишет:
Also tango (for D 1.0) implements it.
Link:
http://www.dsource.org/projects/tango/docs/current/tango.core.WeakRef.html
Might be worth a look if you are going to implement it for D 2.0.
I looked at the D1 implementation. It depends on GC methods
weakPointerCreate and weakPointerDestroy. These functions are
implemented in D1 GC as extern C functions.
It seems most of this code should be directly portable to D2, it would
certainly require changes in the DMD2 source code. I have never worked
at that level and have used D2 only for past couple of months. While I
can give that a blind try, it would be useful only if it gets
excepted in DMD2.
What do you guys suggest?
I remember reading a discussion about weak references some time ago. You
*could* implement them using functions rt_attachDisposeEvent and
rt_detachDisposeEvent, which are extern(C) and declared in object.d (actually,
object_.d of dmd's druntime source), and AFAIR Tango uses something similar.
Normally, a (hypothetical) WeakRef would nullify the non-GC-scanned reference
in a dispose handler. But there is an issue with this, as dispose handlers are
run *after* the GC resumes all threads, which means that it is still possible
that a WeakRef implementation would supply the client code a presumably valid
reference just before some thread deletes/clears it - a straight way to
AV/segfault. Of course, this is no problem for single-threaded applications,
but then again, weak references are not that useful in such apps as their
usefulness manifests almost entirely in concurrent code.
People interested in weakref implementation may have a look at Lua. Because
it's in plain standard C99 and lightweight. (but the code is not very beautiful
imo and has very few comments)
Denis
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