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 global, module, and request startup and shutdown events.
The global startup functions are called once when PHP starts up; similarly, the global shutdown functions are called once when PHP shuts down. Please note that they're really only called once, not when a new Apache process is being created!
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.