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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§
Abstract
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