On 09-04-2012 16:16, Steven Schveighoffer wrote:
On Sun, 08 Apr 2012 16:33:01 -0400, Alex Rønne Petersen
<[email protected]> wrote:
APPENDABLE is, IIRC, mostly an internal attribute used for the array
append cache. You can ignore it entirely (we should document this).
It's used to flag that the block of GC data is actually an appendable
array. If this flag is missing, and you attempt to append data that
points at the block, it will always reallocate. If this flag is present,
it assumes it has a valid the "used" length in the block, and proceed.
Do NOT set this flag unless you know what you are doing. Let the runtime
do it.
FINALIZE is only relevant if the type allocated in the block has a
destructor (it simply specifies that finalization is then desired).
I'll add that it not only identifies the type stored has a dtor, the GC
expects that the layout of the block is of type Object. This is an
important distinction, because it will use that information to traverse
the vtable looking for dtors. For example, just setting this flag for a
struct that has a dtor will not work, because a struct has no vtable.
Something that I've always disliked about the current GC.
In MCI, I can't provide finalization support when programs running in
the VM use the D GC, because that *requires* me to use the Object layout
for runtime objects. That's just not nice, since it adds (IIRC) 3 words
of data that's basically useless to *me*. It would be nice if the GC
supported finalization callbacks similar to how Boehm does it.
-Steve
--
- Alex
