On Wednesday, 5 February 2014 at 21:03:25 UTC, Brad Anderson
wrote:
On Wednesday, 5 February 2014 at 20:18:33 UTC, Adam D. Ruppe
wrote:
[...]
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).
[...]
My thinking as well. That combination of functionality looks very
advantageous to me. It is more flexible than just providing two
choices to the programmer: GC and RC. To me both GC and RC are
useful, depending on the type of program being written. However,
why limit to just the two? There are other styles of memory
allocation/management I might need to make use of, perhaps even
in the same program.
I really like the new allocator module. I had been thinking that
a goal for its use was to allow replacing the compiler-supported
allocation style with a custom one, either at the module level or
on a function-by-function basis, as shown in the code above. In
my opinion, this would give the necessary flexibility over memory
allocation by giving final control to the programmer (i.e.
control over external and internal allocation style). Doing so
seems good to me as the programmer knows a priori the type of
allocation pattern to support based on the type of program being
produced (e.g. real-time, long-running process, batch system). Of
course minimizing memory allocation in Phobos is an excellent
goal and that work will proceed orthogonal to this effort.
However, in the end, some memory will have to be allocated.
Letting the programmer choose how that memory is to be allocated
by giving full access to std.allocator seems the way to go.
Joseph
