Summary: Real­Time Computing with Lock­Free
Shared Objects
JAMES H. ANDERSON, SRIKANTH RAMAMURTHY, and KEVIN JEFFAY
University of North Carolina
This paper considers the use of lock­free shared objects within hard real­time systems. As the
name suggests, lock­free shared objects are distinguished by the fact that they are accessed without
locking. As such, they do not give rise to priority inversions, a key advantage over conventional,
lock­based object­sharing approaches. Despite this advantage, it is not immediately apparent
that lock­free shared objects can be employed if tasks must adhere to strict timing constraints. In
particular, lock­free object implementations permit concurrent operations to interfere with each
other, and repeated interferences can cause a given operation to take an arbitrarily long time to
complete.
The main contribution of this paper is to show that such interferences can be bounded by
judicious scheduling. This work pertains to periodic, hard real­time tasks that share lock­free
objects on a uniprocessor. In the first part of the paper, scheduling conditions are derived for
such tasks, for both static and dynamic priority schemes. Based on these conditions, it is formally
shown that lock­free shared objects often incur less overhead than object implementations based
on wait­free algorithms or lock­based schemes. In the last part of the paper, this conclusion is
validated experimentally through work involving a real­time desktop videoconferencing system.
Categories and Subject Descriptors: C.3 [Computer Systems Organization]: Special­Purpose

Source: Anderson, James - Department of Computer Science, University of North Carolina at Chapel Hill

Collections: Computer Technologies and Information Sciences