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Summary: Using Lock-Free Objects in Hard Real-Time Applications
James H. Anderson and Srikanth Ramamurthy
Department of Computer Science, The University of North Carolina at Chapel Hill
Lock-based approaches to object sharing are the ac-
cepted means of interprocess communication in real-
time systems. The main problem that arises under such
approaches is that of priority inversion, i.e., the situ-
ation in which a given task1 waits on another task of
lower priority to exit a critical section. Mechanisms
such as the priority ceiling protocol (PCP) 3]are used to
solve this problem. The PCP requires the operating sys-
tem to identify those tasks that may lock a semaphore,
which results in additional complexity in operating sys-
temservices. This informationisused to ensure that the
priority of a task holding a semaphore is at least that
of the highest-priority task that locks that semaphore.
In 1], we propose using lock-free objects as an alter-
native for object sharing in real-time systems. Lock-free
objects are usuallyimplementedusing\retry loops". For
example, in the universal, lock-free implementationpre-
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