7.1 Run-Time Libraries

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:

• * `Zero-Cost Exceptions' ("ZCX"), which uses binder-generated tables that are interrogated at run time to locate a handler.
• * `setjmp / longjmp' (’SJLJ’), which uses dynamically-set data to establish the set of handlers

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.}

This section summarizes which combinations of threads and exception support are supplied on various GNAT platforms. It then shows how to select a particular library either permanently or temporarily, explains the properties of (and tradeoffs among) the various threads libraries, and provides some additional information about several specific platforms.