Abstract: “This paper presents the synchronization in LF THREADS , a thread library entirely based on lock-free methods, i.e. no spin-locks or similar synchronization mech- anisms are employed in the implementation of the multithreading. Since lock- freedom is highly desirable in multiprocessors/multicores due to its advantages in parallelism, fault-tolerance, convoy-avoidance and more, there is an increased demand in lock-free methods in parallel applications, hence also in multiproces- sor/multicore system services. This is why a lock-free multithreading library is important. To the best of our knowledge LF THREADS is the first thread library that provides a lock-free implementation of blocking synchronization primitives for application threads. Lock-free implementation of objects with blocking se- mantics may sound like a contradicting goal. However, such objects have benefits: e.g. library operations that block and unblock threads on the same synchronization object can make progress in parallel while maintaining the desired thread-level semantics and without having to wait for any “slow” operations among them. Besides, as no spin-locks or similar synchronization mechanisms are employed, processors are always able to do useful work. As a consequence, applications, too, can enjoy enhanced parallelism and fault-tolerance. The synchronization in LF THREADS is achieved by a new method, which we call responsibility hand-off (RHO), that does not need any special kernel support.”