Possible data race using Overlapped
Struct Overlapped implements Sync trait so as to be shared across threads by reference.
It contains a UnsafeCell, and its method
as_mut_ptr will return a mutable ptr to the inner data.
This may cause a crash if one thread writes the data while another is accessing it, all by immutable reference of the struct and will bypass compiler checking. It is rather unsafe but we marked it as safe!!!
I searched for a ref-counting version of this struct, which is much safer.
My suggestion is to replace the current Overlapped with this version.