On Monday, 31 December 2012 at 14:05:01 UTC, Kiith-Sa wrote:
I think you're overthinking this way too much.
I'm writing a game engine, where latency is much more important
than in your case. Even 10ms would translate to visible jitter.
GC's not an issue, and disabling it permanently is very
counterproductive _unless_ you've exhausted all other options
(which you're unlikely to, as you can do everything you can do
in
C++). All you have to do is care about how you allocate and, if
GC seems to be an issue, profile to see _where_ the GC is being
called most and optimize those allocations.
Basic rules:
For classes with one or few instances (singletons, etc.), GC is
not an issue. For classes with hundreds-thousands of instances,
it might be an issue. Profile. For classes with more instances,
it probably is an issue. Profile, reuse instances, use structs,
manually allocate. Arrays: To avoid reallocation on append, use
array.assumeSafeAppend() before the append (Assumes that the
array is not a slice of a bigger array that would get its data
overwritten).
If appending a lot, use std.array.Appender. If you need manually
allocated storage, use std.container.Array, or create a wrapper
around malloc/free. I'm using a templated wrapper that allows me
to record how much memory/instances was allocated with which
types. Destructors: Structs are RAII like in C. And you can
easily create a malloc wrapper that will act exactly like
new/delete in C++.
Classes: call destroy(instance). Calls the dtor, but doesn't
deallocate the class (GC will do that later). Not much different
from deleting a class allocated through new in C++ (which is
what
you do most of the time in C++). If you absolutely need to free
the memory, create malloc/free wrappers for classes. In my
case,
classes are used for polymorphic stuff, which are usually single
or few-instance objects. Structs are used for most of the
many-instance objects (e.g. components of game entities), and
are
usually stored in manually allocated arrays.
GC is _very_ useful for stuff like closures, which can greatly
simplify some code. Also, while I maintain that disabling GC
completely is a bad idea, it might be useful to disable it in a
small area of code _after_ profiling shows that GC is being
called too much there.
In my YAML parser library, I've found after profiling that 18%
of
time was spent in GC. Most of that was in a small piece of code
that repeatedly allocated memory. Disabling GC before this code
and reenabling it after (scope(exit) to avoid leaking disabled
GC) resulted in GC taking ~2% of time, because many unnecessary
collects were consolidated into one after the GC was reenabled.
Memory usage didn't take a hit, because this was actually a
fairly small piece of code, not doing too many allocations per
call, just called very often.
I think it will still take a few generations of programmers until
everyone is confortable with using GC enabled languages for
systems programming scenarios.
Most people nowadays are not aware of what has already been done
in academia, or are burned by bad experiences caused by whatever
reasons.
This situation will only improve when developers start aproaching
the same class of problems with open minds on how to solve them
in new ways.
--
Paulo
