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.