How to unlock / release files?

I’m trying to use Liquibase programmatically, but I’m running into an issue with file locks.  It seems like Liquibase is keeping the changelog files open after it’s done using them, and I can’t figure out how to close them.  I did some searching around on the internet and couldn’t find anything.  I assume this means the fix is really simple and easy and obvious, and I must be just missing it.  So how do I make Liquibase release filelocks when running changelog sets programmatically?