Generally, all of Hollywood's API functions are not thread-safe and the plugin functions need also not be thread-safe except where stated. There are a few thread-safe API calls and there are also a few plugin functions that must be thread-safe. In that case, this requirement is explicitly mentioned in this documentation. If nothing is mentioned in an API call's documentation, then the call is not thread-safe or need not be thread-safe in case it is a plugin function to be written by you.