The Actors runtime allows reentrancy by default. This means that if an Actor method of Actor A calls a method on Actor B, which in turn calls another method on Actor A, that method is allowed to run. This is because it is part of the same logical call-chain context. All timer and reminder calls start with the new logical call context. However, reentrancy is a configurable property of Actors and you can disable this feature by decorating your Actor with the Reentrant attribute.

[Reentrant(ReentrancyMode.Disallowed)]