Thread safety

Most functions and classes are thread safe. Notable exceptions are documented here.

Not thread safe	Comment
enable_verbose_debug_messages()	This function modifies global state.
AbstractFetcher.fetch_all()	When selective_fetch_all=True (default), a temporary Mapper instance may be used. All built-in fetchers (e.g. the SqlFetcher) inherit from this class.
Fetcher.initialize_sources()	Invoked implicitly before all translation tasks. Results are cached when using a MultiFetcher or AbstractFetcher subtype, after which initialize_sources is thread-safe for these types.