Success! (Precisely)

[Jacob Carlborg]

On 10/30/09 06:08, dsimcha wrote:
> After a few evenings of serious hacking, I've integrated precise heap scanning
> into the GC.  Right now, I still need to test it better and debug it, but it
> at least basically works.  I also still need to write the templates to
> generate bit masks at compile time, but this is a simple matter of programming.
>
> A few things:
>
> 1.  Who knows how to write some good stress tests to make sure this works?
>
> 2.  I'm thinking about how to write the bitmask templates.  In the next
> release of DMD, when static arrays are value types and returnable from
> functions, will they be returnable from functions in CTFE?
>
> 3.  new only takes RTTI.  It is not a template.  Unless RTTI gets bitmasks in
> the format I created (which I'll document once I clean things up and release,
> but has only deviated slightly from what I had talked about here), stuff
> allocated using it won't be able to take advantage of precise heap scanning.
> The default bitmask, if none is provided, uses good (bad) old-fashioned
> conservative scanning unless the entire block has no pointers, in which case
> it isn't scanned.  This means that we have all the more incentive to replace
> new with a template of some kind.
>
> 4.  I solved the static array problem, but the solution required using up one
> of the high-order bits.  We have at least one more to play with in my bitmask
> scheme, because I'm storing things by word offsets, not byte offsets, since
> the GC isn't supposed to work with misaligned pointers anyhow.  This leaves
> one more bit before we start limiting T.sizeof to less than full address space
> (on 32-bit, where a word is 4 bytes).  I think it needs to be reserved for
> pinning, in case a copying collector ever gets implemented.  If we're willing
> to not let any precisely scanned object have a T.sizeof of more than half the
> address space (a ridiculously minor limitation; this does not limit the size
> of arrays, only the size of classes and the elements of an array), we could
> throw in a third bit for weak references.

Would this be possible to use with D1 ?