On Wednesday, 5 February 2014 at 20:18:33 UTC, Adam D. Ruppe
wrote:
On Wednesday, 5 February 2014 at 19:39:43 UTC, Andrei
Alexandrescu wrote:
You do figure that complicates usage considerably, right?
I don't see much evidence for that. Many, many newer modules in
Phobos are currently allocation free yet still pretty easy to
use.
A major source of little allocations in my code is std.conv and
std.string. But these aren't difficult to change to external
allocation, in theory at least:
string s = to!string(50); // GC allocates (I'd keep this for
convenience and compatibility)
char[16] buffer;
char[] s = toBuffer(buffer[], 50); // same thing, using a buffer
char[] s = toLowerBuffer(buffer[], "FOO");
assert(buffer.ptr is s);
assert(s == "foo");
That's not hard to use (though remembering that s is a borrowed
reference to a stack buffer might be - escape analysis is
something we should really have).
And it gives full control over both allocation and
deallocation. It'd take some changes in phobos, but so does the
RCSlice sooo yeah, and this actually decouples it from the GC.
Yeah, because RCSlice would require changes to Phobos too I'd
much rather have this approach because it is just so much more
flexible and hardly adds any inconvenience.
Combined with the upcoming allocators it would be incredibly
powerful. You could have an output range that uses an allocator
which stores on the stack unless it grows too big (and the stack
size could be completely customizable by the user who knows
best). Or you could pass in an output range that reference counts
its memory. Or an output range that must remain unique and frees
its contents when it goes out of scope.
I think three things would work together really well for
addressing users that want to avoid the GC while making use of
Phobos. 1) Increasing the support for output ranges, 2) Andrei's
slick allocator design, and 3) @nogc. With those three I really
think managing memory and avoiding the GC will be rather
pleasant. @nogc would enable people trying to avoid all the tough
to spot implicit GC allocations to identify them easily. Once
uncovered, they just switch to the output range version of a
function in Phobos and they then use std.allocator with the
output range they feed in to create an ideal allocation strategy
for their use case (whether it stack, GC, scope freed heap,
reference counted, a memory pool, or some hybrid of those).
The tricky part might be making it work with buffers, growable
buffers, sink functions, etc., but we've solved similar
problems with input ranges.
I was thinking RCSlice would be a better alternative.
I very rarely care about when little slices are freed. Large
blocks of memory might be another story (I've used malloc+free
for a big internal buffer in my png.d after getting memory
leaks from false poitners with teh gc) but those can be handled
on a case by case basis. std.base64 for example might make
sense to return one of these animals.
I don't have a problem with refcounting on principle but most
the time, it just doesn't matter.
