Safe version of UnsafeArc that accepts only atomic types

[bblum]

To share data such as counters cross-task, you either have to use the performance-impacting RWArc or litter your code with unsafe using an UnsafeArc. If all you want to be doing cross-task is atomically incrementing counters or shuffling AtomicOptions around, it would be safe to avoid the RWArc's overhead.

To do generally, this would require a new Atomic kind, which would be introduced with unsafe attributes in the atomics library and could be derived by other aggregate types that contained only atomics (but NOT enums).

[bblum]

this is a low-priority post-1.0-compatible enhancement

[alexcrichton]

Closing, this is handled with Arc plus Share types. You can safely mutate Arc<AtomicUint> now that we've decided to make mutators use &self instead of &mut self

[bblum]

is that safe with AtomicPtr too?

[alexcrichton]

It is indeed, all of the atomics have changed to taking &self rather than &mut self

[bblum]

I mean... didn't AtomicPtr used to have a get(&'a self) -> &'a T function? If that's still around it seems like you could use two simultaneous &self pointers to mutate the pointer while a pointer to the inside was already in scope.

[alexcrichton]

There's no longer any way to borrow an AtomicXXX (for that reason), I think AtomicPtr has changed over time (now it's Atomic<*mut T>)

[bblum]

huh, so if you want to put a ~T inside, how do you manage when it gets freed?

[alexcrichton]

The AtomicPtr type doesn't manage an allocation (it only deals with *mut T), so there's no need for a destructor. The one you're thinking of may have evolved into AtomicOption<T> which is essentially Atomic<Option<~T>> which has its own destructor to deallocate the ~T if there's one inside on drop.

[bblum]

Oh yeah, that's the one I meant. So there's no AtomicOption::get(&'a self) - > &'a T anymore?

[alexcrichton]

It is indeed gone: http://static.rust-lang.org/doc/master/std/sync/atomics/struct.AtomicOption.html

Only atomic operations are exposed (getting/setting/taking/etc)