Programming Tutorials

Execution Lifetime of a PHP script

By: Andi, Stig and Derick Printer Friendly Format    

When embedded in a web server, PHP scripts usually do their job quickly and exit. This paradigm does not fit when using CLI; your scripts may run forever, or at least until the next power failure. For example, if you write a daemon (UNIX lingo for a server process running in the background), the script will typically hang around forever, waiting for some kind of input to process, a timer signal, or something similar.

One of the practical consequences of this is that sloppy coding styles, which are relatively harmless in a short web-server request, have more of an impact in a long-running script. For example, when you open a file or database connection but don’t explicitly close it, PHP closes it for you at the end of therequest. But in a long-running script, “at the end of the request” is not until the script exits, which it does not even have to do.

This does not have to be a problem, because PHP also frees resources when they are no longer referenced. But keep this in mind when programming scripts that are supposed to run for some time. If you are finished with a file, close the file descriptor. If you’re finished with database operations, disconnect. If you don’t need that big array anymore, empty it.