 <unk> tokens are used to prevent concurrent accesses from other CPUs and may be held simultaneously by multiple threads , ensuring that only one of those threads is running at any given time . Blocked or sleeping threads therefore do not prevent other threads from accessing the shared resource unlike a thread that is holding a <unk> . Among other things , the use of serializing tokens prevents many of the situations that could result in deadlocks and priority inversions when using mutexes , as well as greatly simplifying the design and implementation of a many @-@ step procedure that would require a resource to be shared among multiple threads . The serializing token code is evolving into something quite similar to the " Read @-@ copy @-@ update " feature now available in Linux . Unlike Linux 's current <unk> implementation , DragonFly 's is being implemented such that only processors competing for the same token are affected rather than all processors in the computer . 
