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Synchronizing without Locks is Inherently Expensive Hagit Attiya

Summary: Synchronizing without Locks is Inherently Expensive
Hagit Attiya
Rachid Guerraoui
Danny Hendler
Petr Kouznetsov§
It has been politically correct to blame locks for their fragility, especially since researchers identified
obstruction-freedom: a progress condition that precludes locking while being weak enough to raise
the hope for good performance. This paper attenuates this hope by establishing lower bounds on the
complexity of obstruction-free implementations in contention-free executions: those where obstruction-
freedom was precisely claimed to be effective. Through our lower bounds, we argue for an inherent cost
of concurrent computing without locks.
We first prove that obstruction-free implementations of a large class of objects, using only over-
writing or trivial primitives in contention-free executions, have (n) space complexity and (log2 n)
(obstruction-free) step complexity. These bounds apply to implementations of many popular objects,
including variants of fetch&add, counter, compare&swap, and LL/SC. When arbitrary primitives can be
applied in contention-free executions, we show that, in any implementation of binary consensus, or any
perturbable object, the number of distinct base objects accessed and memory stalls incurred by some
process in a contention free execution is (


Source: Attiya, Hagit - Department of Computer Science, Technion, Israel Institute of Technology


Collections: Computer Technologies and Information Sciences