Summary: The Power of Multi­objects
Yehuda Afek \Lambda Michael Merritt y Gadi Taubenfeld z
January 1, 1998
Abstract
We consider shared memory systems that support multi­object operations in which pro­
cesses may simultaneously access several objects in one atomic operation. We provide
upper and lower bounds on the synchronization power (consensus number) of multi­
object systems as a function of the type and the number of objects that may be si­
multaneously accessed in one atomic operation. These bounds imply that known clas­
sifications of component objects fail to characterize the synchronization power of their
combination. In particular, we show that in the context of multi­objects, fetch&add ob­
jects are less powerful than swap objects, which in turn are less powerful than queue ob­
jects. This stands in contrast to the fact that swap can be implemented from fetch&add.
Herein we introduce a restricted notion of implementation, called direct implementa­
tion. We show that, if an object Y has a direct implementation from X then also the Y
based multi­object can be implemented from the X based multi­object. Following the
above, we derive results such as: there is no direct implementations of a swap object,
and queue object from any collection of commutative objects (e.g., fetch&add, test&set).
1 Introduction
A shared memory system is a collection of objects accessed by a collection of processes.

Source: Afek, Yehuda - School of Computer Science, Tel Aviv University

Collections: Computer Technologies and Information Sciences