Lesson plan
User exit
A user exit is a subroutine invoked by a software package for a predefined event in the execution of the package. In some cases the exit is specified by the installation when configuring the package while in other cases the users of the package can substitute their own subroutines in place of the default ones provided by the package vendor to provide customized functionality. In some cases security controls restrict exits to authorized users, e.g., EXCP appendages in MVS. The earliest use of this term involved operating systems to let customized code temporarily take control when a pre-designated event occurred. A more typical use is replacing the user exits provided by a sort/merge package, whereby the user program provides its own subroutines for comparing records. The procedures provided by the user take the place of the default routines (usually stubs that do nothing but return to their caller) provided by the package vendor. Procedures provided as user exits are typically compiled into a static library and linked directly with the package to produce an executable program. Another approach employs dynamic libraries to accomplish the same thing. Finally, user exits may be external programs executed at specific points in the execution of a host package.
Article summary
A user exit is a subroutine invoked by a software package for a predefined event in the execution of the package. In some cases the exit is specified by the installation when configuring the package while in other cases the users of the package can substitute their own subroutines in place of the default ones provided by the package vendor to provide customized functionality. In some cases security controls restrict exits to authorized users, e.g., EXCP appendages in MVS. The earliest use of this term involved operating systems to let customized code temporarily take control when a pre-designated event occurred. A more typical use is replacing the user exits provided by a sort/merge package, whereby the user program provides its own subroutines for comparing records. The procedures provided by the user take the place of the default routines (usually stubs that do nothing but return to their caller) provided by the package vendor. Procedures provided as user exits are typically compiled into a static library and linked directly with the package to produce an executable program. Another approach employs dynamic libraries to accomplish the same thing. Finally, user exits may be external programs executed at specific points in the execution of a host package.
Key claims
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
Bibliography
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Key claims and bibliography are generated from the same tracked claims and sources as the article page.