UML22 — Reentrancy 1

How is the effect if isReentrant achieved for actions other than call
actions? isReentrant is only on behaviors. Perhaps it should also be
available on actions and operations

The current semantics of isReentrant on behaviors leads to unexpected global mutual exclusion of invocation of a behavior if isReentrant=false, the default (see Issue 9873). However, at the level of the invocation of a behavior in an activity, it is often the case that one execution of such an invocation action should complete before a second can begin (for example, if the activity is modeling a business process with the invoked behavior assigned to a single person, or a manufacturing process with the behavior carried out by a single piece of equipment). Thus, it is reasonable to have "local" non-reentrancy as the default.
In this case, however, it makes as much sense to allow the specification of reentrancy or non-reentrancy on any action, not just on the invocation of a behavior, as requested by the issue submitter. This also allows locally non-reentrant semantics, without the unexpected consequences of global non-reentrancy.