I'veI’ve had a course that was held by ACM Fellow Tichy about parallel computing. He always wanted to translate everything into good German (he mentioned that most translations / textstexts in Computer Sciencecomputer science are quite bad, as they use English terms as the writers didn'tdidn’t know that German ones existed). He used Einfädig
einfädig und Mehrfädig
mehrfädig for single-threaded
single-threaded and multithreaded
multithreaded. He also spoke of Fäden
Fäden for Threads
Threads. Although I think that Threads
Threads is much more common than Fäden
Fäden, it is consistent with the other terms.
Hence, I would translate it like this:
Das Objekt ist nicht gegen Probleme der Nebenläufigkeit gesichert und darf nur in einfädigen Kontexten verwendet werden.
Alternatively, if you want a translation that uses the common words:
Das Objekt ist nicht threadsicher und darf nur in Single-Thread-Anwendungen verwendet werden.
Quite often, it is a good idea to take a look at the German wikipediaWikipedia to find common translations:
I recommend to use the first version if you write an academic paper and the second version if you write some software documentation that programmers should read.