#435 Add ability to learn whether ooRexx is about to shutdown

[Rony G. Flatscher]

When using the native APIs and sending messages to Rexx objects from an external program (that started Rexx), then it is important to know whether such messages can be processed reliably by ooRexx.

This is to say, that in the case that Rexx gets shutdown, then sending messages to Rexx objects in that state of the interpreter will be unreliable and even crash (!) the programs.

One scenario where this can happen on a regular basis is BSF4ooRexx: here it is possible that Rexx objects are boxed as Java objects and Java (e.g. Java event listeners) sends messages to the Rexx proxies which will cause Rexx messages to be sent to these Rexx listener objects. Now, everytime the Rexx interpreter is shutdown such Rexx messages will cause the program to crash!

If there was an ability (some new API) to learn about the status of the Rexx interpreter, the native library could use that, and in the case that it learns that the Rexx interpreter is in shutdown mode or is able to learn that the Rexx intpreter is about to shutdown, then it could react accordingly and raise - a non-destructive - error message in the caller.

In the case of BSF4ooRexx it then would become possible to raise a Java exception with the appropriate information. Currently, the entire process crashes (out of the blue for the users) and cannot be.