On Sunday, 5 March 2017 at 13:32:04 UTC, Moritz Maxeiner wrote:
I was referring to phobos. I feel intimidated by the idea of
trying to code some of the functions of phobos myself in a
no-gc manner. I'm sure I'd run into things way out of my
knowledge domain.
I get that, though usually Phobos code is fairly readable if
you've got a firm grasp of D templates.
Hmm. This is encouraging news to here, given that templates were
the most recent topic I've learned in D. Maybe I'll just have to
give GC-reliant areas a read. Although I don't know what those
areas would be; AFAIK I'd have to look for @nogc tags, which
sounds tedious.
As for Guillaume Piolat's Advice:
- Use struct RAII wrappers and destructors to release
resources. Typically structs with disabled postblit. However
very often resources are classes objects because they feature
virtual dispatch.
- In destructors, call .destroy on members that are class
objects (reverse order of their creation if possible). Also on
heap allocated struct but those are rare. The idea is that when
the GC kicks in, unreachable objects on the heap should already
have already been destroyed.
- Don't let the GC release resources, with the "GC-proof
resource class idiom". I remember Andrei pushing for the GC not
to call destructors, to no avail. So the GC is calling
destructors and you should use it as a _warning that something
is wrong_ and determinisim wasn't respected, not as a safety
measure and a way to actually release resources (because it's
wrong thread, wrong timing, unreliable).
- Like in C++, if your ownership is in the case where it's
shared, you can introduce artificial owners (eg: arena pool owns
arena pool items).
- The resources that are only memory need no owner and can be
managed by the GC. (eg: strings, a ubyte[] array...)
When you have deterministic destruction, it's simple to offload
work from GC to manual memory management. You don't loose ANY
main feature.
The GC is an efficient way to call free(), and a global owner
not a way to release resources.
This is also encouraging! Thanks for the concrete advice. But, I
think due to my inexperience, to don't really understand some of
your advice. Specifically, the only-memory recourses like strings
and arrays can be managed by the GC, and arena pools. I can just
look these things up, but I figured it'd be easy to ask first.
