The GNAT run-time implementation may vary with respect to both the underlying threads library and the exception-handling scheme. For threads support, the default run-time will bind to the thread package of the underlying operating system.
For exception handling, either or both of two models are supplied:
Most programs should experience a substantial speed improvement by
being compiled with a ZCX run-time.
This is especially true for
tasking applications or applications with many exception handlers.
Note however that the ZCX run-time does not support asynchronous abort
of tasks (abort and select-then-abort constructs) and will instead
implement abort by polling points in the runtime. You can also add additional
polling points explicitly if needed in your application via pragma
Abort_Defer.
This section summarizes which combinations of threads and exception support are supplied on various GNAT platforms.