On Saturday, 20 September 2014 at 08:39:41 UTC, Walter Bright
wrote:
E.g. TSX is coming even if there is
a bug in lower end CPUs. Suggest making performance oriented
prototypes on
different architectures before concluding.
I'd love to see it.
A 128 bit CAS instruction is at about 19-25 cycles, but a
transaction on the other hand can by using xbegin/xend cover both
refcounting, locking and rollback of multiple objects so you need
cooperation from code gen. Basically all changes between
xbegin/xend are kept in cache and written to memory upon success.
On failure you have a slower fallback.
I don't know what that leads to in amortized cost reduction, but
30-70% might be possible if it is done right.
As soon as you pass a reference to a function, that all goes
out the window. There's a reason why Rust has invested so much
effort in the notion of a "borrowed" pointer.
The pure @nogc crowd care less about safety, but you should be
able to track this using dataflow?
3. True, but you can keep the refcount at a negative offset
for new-based
allocations. Besides it only affects those who do @nogc and
they should know
what they are doing.
If this is so simple, why doesn't everyone do it?
Never said performance and thread safe RC was easy. It is
probably difficult to get below 10 cycles for inc/dec pairs even
with excellent code gen...? And probably closer to 40 cycles for
regular code gen. Just guessing.
