It is ... eventually. Asset garbage collection is a seperate system process that takes a not-insignificant amount of time to run and is run on a more or less continuous basis.
Knowing when to delete an asset isn't always as easy as just tracking when the item is not in anyone's inventory. Object contents are only known on a per sim basis, except for the hourly sim state saves - and the asset could be referenced in any sim. Scripts may also access items, textures for example, by a hard coded asset id. It wouldn't be right to break the object if the only person with an actual inventory copy deleted it. Doing so could break every SuperFoo that person has sold which has a script that uses the hard coded asset id.
So, yes, if it is truely not referenced anywhere it will eventually get deleted. But not immediately.
Knowing when to delete an asset isn't always as easy as just tracking when the item is not in anyone's inventory. Object contents are only known on a per sim basis, except for the hourly sim state saves - and the asset could be referenced in any sim. Scripts may also access items, textures for example, by a hard coded asset id. It wouldn't be right to break the object if the only person with an actual inventory copy deleted it. Doing so could break every SuperFoo that person has sold which has a script that uses the hard coded asset id.
So, yes, if it is truely not referenced anywhere it will eventually get deleted. But not immediately.
Curious person that i am. How is it determined when something isn't referenced anywhere?
Theory:
As you say it is a continues running thing. So i assume it is running through the sim-state-saves and user/object-inventory. Is it then updateting a timestamp for every asset it encounters? And a second routine is running through the asset server and deletes anything that has a timestamp that is older then current date minus a predefined interval? Is that how it work, or is this to simple?
Second, are scripts checked for keys of other assets? Or do they have to acces the assets once in a while to prevent them from magnetical destruction?