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.