The cleaner is used to remove state files maintained for HTML rendering. Without a cleaning, over time you would run out of disk space as huge numbers of these files accumulated. The cleaner will periodically be run at object destruction time to remove the excess files.
On object destruction, the cleaner is run with probability 1/cleaner.frequency. That is, roughly every cleaner.frequency times that an object is destroyed, the cleaner will be run. It will look at all files beginning with viv_ in the tmp_dir. If the value of cleaner.access_time is not -1, all files that have not been accessed in cleaner.access_time seconds will be removed. The cleaner.create_time setting is calculated the same way as the cleaner.access_time setting. Finally, if there are still more than cleaner.file_limit files remaining, the least recently accessed files will be removed until there are only cleaner.file_limit files left.