Startup and shutdown functions can be used for one-time initialization and deinitialization of your modules. As discussed earlier in this chapter (see the description of the Zend module descriptor
block), there are module, and request startup and shutdown events.
The module startup and shutdown functions are called whenever a module is loaded and needs initialization; the request startup and shutdown functions are called every time a request is processed
(meaning that a file is being executed).
For dynamic extensions, module and request startup/shutdown events happen at the same time.
Declaration and implementation of these functions can be done with macros; see the earlier section "Declaration of the Zend Module Block" for details.