delay 0.0

[Tom Moran <tmoran@bix.com>]

>From a discussion on chat@gnat.com I conclude;
  delay 0.0; may, or may not, cause a task switch.
  If the compiler implements Annex D and the program includes a Pragma
Task_Dispatching_Poicy (FIFO_Within_Priorities); then a delay 0.0;
should definitely cause a task switch (assuming, obviously, there's
another task ready to switch to).
  The compiler should document a value D such that "delay D;" (or
greater than D) will cause blocking and thus task switching.  But if the
time resolution is poor (eg the 55ms common on PCs) the task may block
that long even if D is much less.
  Two questions: Is my understanding correct?  Are there compilers that
don't task switch on "delay 0.0;"?