Ikiwiki plugins work by calling a function named hook which lets them tell the ikiwiki compiler that they implement a certain subroutine. Whenever that subroutine needs to be called, the ikiwiki compiler calls run_hooks, and that runs all the registered functions.

For most of these hooked functions (htmlize is the only exception I can think of), all of the registered functions are called, regardless of file type. This is normally not a problem, because the plugin can check the type of content that it is given and only operate on the types of content that it knows anything about.

For external plugins, however, there is a problem. Ikiwiki communicates with external plugins via xml-rpc on stdin and stdout. Every function call that it makes involves writing the function's parameters on stdout. When there is a file type that is unknown to the external plugin, all that effort (I/O is the main time sink I think, but the content must also be encoded correctly for xml-rpc) is wasted.

I have added a parameter named "exclusive" to the optional arguments that are accepted by the hook function. When this argument exists (and is true), the registered function is only run when the type of file is the same as the type of file that the plugin accepts. So far, it only works with the scan and linkify hooks, which were the main areas that slowed my plugin down. However, it is quite simple to get it to work with other hooks as well.