Capítulo 25_ Extension Possibilities

Tabla de contenidos
External Modules
Built_in Modules
The Zend Engine

As shown in Figura 24_1 above, PHP can be extended primarily at three points: external modules, built_in modules, and the Zend engine_ The following sections discuss these options_

External Modules

External modules can be loaded at script runtime using the function dl()_ This function loads a shared object from disk and makes its functionality available to the script to which it's being bound_ After the script is terminated, the external module is discarded from memory_ This method has both advantages and disadvantages, as described in the following table:

Advantages	Disadvantages
External modules don't require recompiling of PHP_	The shared objects need to be loaded every time a script is being executed (every hit), which is very slow_
The size of PHP remains small by "outsourcing" certain functionality_	External additional files clutter up the disk_
	Every script that wants to use an external module's functionality has to specifically include a call to dl(), or the `extension` tag in `php_ini` needs to be modified (which is not always a suitable solution)_

To sum up, external modules are great for third_party products, small additions to PHP that are rarely used, or just for testing purposes_ To develop additional functionality quickly, external modules provide the best results_ For frequent usage, larger implementations, and complex code, the disadvantages outweigh the advantages_

Third parties might consider using the extension tag in php_ini to create additional external modules to PHP_ These external modules are completely detached from the main package, which is a very handy feature in commercial environments_ Commercial distributors can simply ship disks or archives containing only their additional modules, without the need to create fixed and solid PHP binaries that don't allow other modules to be bound to them_