The i5/OS™ registration facility allows you to define exit points for functions in an application and to register programs that run at those exit points.
Some i5/OS services also support the registration facility for registering exit programs. They have predefined exit points that are registered when those services are installed. The registration facility itself is threadsafe. You can use it to specify attributes of thread safety and multithreaded job actions for exit program entries.
Without careful evaluation, however, you should not consider existing exit programs to be threadsafe, even though you can call exit programs in a multithreaded job. The same restrictions apply to exit programs as to any other code that runs in a multithreaded job. For example, only exit programs written using a threadsafe Integrated Language Environment® (ILE) language that can be made threadsafe.