[swift-dev] Thread safety of weak properties

[Greg Parker]

> On Dec 14, 2015, at 7:26 PM, Kevin Ballard via swift-dev <swift-dev at swift.org> wrote:
> 
>> On Mon, Dec 14, 2015, at 12:19 PM, Greg Parker via swift-dev wrote:
>> 
>>> On Dec 14, 2015, at 9:47 AM, John McCall via swift-dev <swift-dev at swift.org> wrote:
>>> 
>>>> On Dec 12, 2015, at 7:04 PM, Chris Lattner <clattner at apple.com> wrote:
>>>> #3 sounds like a great approach to me.  I agree with Kevin that if we keep the object husk approach that any use of a weak pointer that returns nil should drop any reference to a husk.
>>> 
>>> Spin locks are, unfortunately, illegal on iOS, which does not guarantee progress in the face of priority inversion.
>> 
>> There is a spinlock algorithm that does work (in practice if not in theory), but it requires a full word of storage instead of a single bit.
> 
> Is that what OSSpinLock uses?

It does not. OSSpinLock is unsafe unless you can guarantee that all users have the same priority.


-- 
Greg Parker     gparker at apple.com     Runtime Wrangler