> SGCL executes the destructors in a separate thread, so there is no cost to the mutator.

Firstly, that's orthogonal to my original point is that, for example, a semi-space nursery can significantly reduce the cost of short-lived allocations (often being faster than malloc/free on such a workload), but only if there are no destructors.

Secondly, threads typically share resources so running something on a different thread does not magically cause it to not disturb the mutator. Such a claim makes me start to doubt the "real-time" claim in the title...