14. Fish nor Fowl

Exit routines are routines that are coded by the users of an application and linked into the application. They offer a tricky path to integration that tends to expose the internals of the application and result in an inflexible relationship between the integrated applications. They are more commonly used in customizing the kernels of operating systems such as Linux. Installing a new application on Linux occasionally involves relinking the kernel with new or additional code. Applications that offer exit routines frequently need to be relinked when the application is upgraded. Although they are tricky, they are also flexible and powerful, amounting to a do-it-yourself programming interface. The right exit routines can make adding a web service to a legacy application possible, even relatively easy, but some routines seem impossible to work with.

A race condition is an error that occurs because messages arrive in an unpredicted order. Usually, this occurs when messages always come in the same order in the development lab, and the developer assumes this is stable activity. If quality assurance testing does not happen to generate an environment that brings out the race condition, the error may not be caught until the application moves to production. Undetected race conditions can appear when a stable on-premises application is moved to a cloud.