Creating references within the constructor can lead to confusing results. This tutorial like section helps you to avoid problems.

This sets the maximum time in seconds a script is allowed to run before it is terminated by the parser. This helps prevent poorly written scripts from tying up the server. The default setting is 30.

This sets the maximum amount of memory in bytes that a script is allowed to allocate. This helps prevent poorly written scripts for eating up all available memory on a server. In order to use this directive you must have enabled it at compile time. So, your configure line would have included enable memory limit. Note that you have to set it to 1 if you don't want any limit for your memory.