Switch HHWheelTimer::SharedPtr to a standard shared pointer
Summary:
As part of my campaign to get `HHWheelTimer` away from intrusive ref-counting semantics, (cf.
D3237530), I am redefining `HHWheelTimer::SharedPtr`. It is now a true `std::shared_ptr`. This will break clients that attempt the following:
HHWheelTimer::UniquePtr timer1{HHWheelTimer::newTimer()};
HHWheelTimer::SharedPtr timer2{timer1};
In the past, that code would compile, because `timer2` could use the intrusive ref-counting, and `timer1` would still be valid. After this change, the second timer would need to be initialized with `std::move(timer1)` instead. The `UniquePtr` is starting to actually be unique.
There is only one place in the code that actually tries to do such a copy. It's in a test, which I have changed. Any other instances of that behavior would create a compilation error, so it's impossible for one to be overlooked.
Reviewed By: djwatson
Differential Revision:
D3337038
fbshipit-source-id:
085e4da41c9a142d253a1ac0b1dd0fc508dff704