Yes, you can help std.allocator!

[Andrei Alexandrescu via Digitalmars-d]

Following up on Brian's nice offer:

> What's going on with std.allocator? I have a few projects (some on
> Github, some at EMSI) that use it because it seemed like it was on
> its way to being in Phobos. What can I do to help with this?

Things are going well with std.allocator. I broke the code into a 
package with modules, which makes it quite nice to deal with. Also I 
just implemented a simple heterogeneous freelist allocator akin to the 
Kernighan-Ritchie one:

http://erdani.com/d/phobos-prerelease/std_experimental_allocator_kernighan_ritchie.html

I did so more for demo/historical perspective purposes. I plan to add 
the part that adds new chunks on a need basis as a separate artifact.

Now there _is_ something I could help with.

Right now the allocator design works well as a flexible malloc/free 
implementation, but has no support for tracing-based garbage collection.

I am evaluating whether I should add tracing capabilities to 
std.allocator, or stop here. Tracing would most definitely require new 
primitives such as embedding some sort of type information and resolving 
internal pointers.

What would really help this evaluation and any other work on garbage 
collection would be a modularization of the tracing process.

I'm envisioning a simple API that separates the system-dependent part of 
the tracer (stopping all threads, finding the roots in the globals, TLS, 
and stack) from what the collector is supposed to proceed with the tracing.

So I'm thinking e.g. of a range that would iterate through all untyped 
words on all stacks as void* data.

foreach (void* p; GC.traceAllStacks)
{
     ...
}

Then we'd have typed data in TLS and globals. I guess those would come 
as ranges of Tuple!(void[], Typeinfo) or something similar.

I'm sure I'm glossing over a number of details, so I'd need an expert in 
the GC workings to help me connect std.allocator with it. Once the GC 
has a low-level tracing API, I can figure what primitives I need to add 
to std.allocator to accommodate tracing.


Thanks!

Andrei