Constant alloc::sync::MAX_REFCOUNT

const MAX_REFCOUNT: usize = _; // 9_223_372_036_854_775_807usize

A soft limit on the amount of references that may be made to an Arc.

Going above this limit will abort your program (although not necessarily) at exactly MAX_REFCOUNT + 1 references. Trying to go above it might call a panic (if not actually going above it).

This is a global invariant, and also applies when using a compare-exchange loop.

See comment in Arc::clone.