Summary: Towards a Necessary and Sufficient Condition
for Waitfree Synchronization ?
James H. Anderson and Mark Moir
Department of Computer Science, The University of Maryland
College Park, Maryland 207423255 U.S.A.
Abstract. We define a class of shared objects called snapshot objects,
and give a necessary and sufficient condition for the existence of a wait
free implementation of such objects from atomic registers. Snapshot ob
jects can be accessed by means of a read operation that returns the entire
object state, or by a set of operations that do not return values. Our con
dition for the existence of a waitfree implementation requires that for
any pair of operation invocations, either the two invocations commute
or one overwrites the other.
The resilient implementation of shared objects is a subject that has received
much recent attention. A shared object is a data structure that is accessed by a
collection of processes by means of a fixed set of operations. An implementation
of a shared object is kresilient iff any process can complete any operation in a
finite number of steps, provided at most k other processes fail undetectably. An