On Monday, 15 September 2014 at 16:22:01 UTC, Andrei Alexandrescu
wrote:
On 9/15/14, 8:58 AM, Rainer Schuetze wrote:
* immutable means implicitely shared between threads, so
you'll have to make RCString thread-safe even if shared isn't
explicitly supported.
Hmmm, good point. That's a bug. Immutable postblit and dtors
should use atomic ops.
Unfortunately, I've yet to see an efficient thread-safe
implementation of reference counting (i.e. without locks).
No locks needed, just interlocked ++/--.
To be fair, you still have to be a bit careful here or things
could be optimized such that data is seen to disappear or change
when it's not expected to. The original boost::shared_ptr used
an atomic integer as an internal refcount, and that's probably a
good template for how to do RC here. The newer implementation is
a lot fancier with spinlocks and such, I believe, and is a lot
more complicated.
Also... this is why I'm not over-fond of having immutable being
implicitly shared. Being unable to create an efficient RCString
that I know is thread-local (the normal case) kind of stinks.
Maybe there can be a
template parameter option along these lines?
