UML22 — Section: Common Behavior - isReentrant should default to true

isReentrant should default to true

Having isReentrant default to false, as it currently does, means that, by default, there can be no concurrent invocations of a behavior, nor can a behavior be recursive. This does not seem to be the normal expectation of modelers when they model the invocation of behavior. Rather, the expected default it that behaviors are reentrant-with the ability to declare them not to be if that makes sense.
On the other hand, it is often the case that, within an activity modeling, for example, a business or manufacturing process, an action invoking a behavior may be locally non-reentrant, in the sense that one invocation must complete before a new one can begin, because there is only a single performer to carry out the action. However, this case is more specifically addressed by Issue 6111. Once this is resolved at the local level, the default for the "global" isReentrant property on Behavior can be allowed to default to true, while "local" reentrancy for actions defaults to false.