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A friend just did a wikipedia search on "user exit" and was brought to this page. They then checked with me as it seemed wrong. I don't agree that a Callback is the same thing as a user exit. At a generic high level a user exit is simply a break in current execution where some 3rd party code or another application is run. I believe the term comes from the need/ability for a user to exit from an application run a command in the shell for example and then return. More commonly now user exits are automatic in that they happen without human intervention where someone wants to execute a script or some code in the middle of something else. A callback is something else entirely (as described correctly in the article)... thoughts? --[[User:Bleveret|Bleveret]] 11:29, 13 March 2007 (UTC)
:I added the term '''user exit''' to this article primarily because there was no suitable article for the term. A [http://en.wikipedia.org/wiki/Special:Search?search=usre+exit&fulltext=Search Wiki search] yielded little more than a reference in ''[[Exit (command)]]''.
:I first heard the term being used by IBM mainframe programmers in the 70s, whereby a user program provided its own versions of predefined subroutines that took the place of the default routines (usually stubs that did nothing but a ''return'') provided by the package/library vendor. Typical usage was in a sort/merge package, which provided user exits for record comparison routines and the like. So by this usage, "user exit" does not quite agree with your definition above.
:I think user exits ''differ'' from callbacks in that they are established by the user program not by being passed to a registration function, but by being linked directly into the executable image. Consequently, they must have the names of the routines they are replacing, instead of having any name the user desires. On the other hand, I think they ''resemble'' callbacks enough to be relevant to this article.
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