Re: terminate applications

[christoph.grein@eurocopter.com]

All the methods shown so far work only on a non-tasking program, and then it is 
easy to terminate the application. Ada also has (in package Command_Line) a 
procedure to set the exit status.

But beware when you use tasking:

  with Something;
  procedure Main is
    task Work;
  begin
    ...
    ... raise Some_Exc;
    ...
  exception
    when Some_Exc => null;  -- terminate now
  end Main;

When Some_Exc is raised, Main (the main task) waits for termination of 
subordinate tasks. So if you stop the main task via an exception the program 
will happily go on if there are other tasks (e.g. task Work or library tasks in 
Something) still running.

A common way to write a tasking application is to have a main program without 
any declarations and with a null statement:

  with Something;
  procedure Main is
  begin
    null;
  end Main;

All the work is done in Something.

You face the complicated problem how to terminate all these dependent tasks. 
Raising an exception in one task will silently terminate the task without 
informing any other task (except when in rendez-vous).

To find a solution for this problem is not easy. It depends on your application 
and has to be designed by you. You could use the abort statement, but there are 
abort-deferred regions...

In C there is no built-in tasking so (AFAIK) exiting a program with a call to 
exit(0) is easy (as as easy as in Ada if you have no tasking).

What you have to do if you are running threads in C, I do not know. Perhaps then 
the problem is similar.