To improve performance, the publishing framework caches pipelines. This allows you to reuse filters. Since you can't control a filter's lifetime, you should write the filter to obtain resources using the initFilter method and free them using the destroyFilter method. You should also use the initFilter method to reinitialize parameter values for parameters with default values. If you don't reinitialize parameter values, you could end up with a parameter value from a previous pipeline run, rather than the default value.