Summary: Waitfree TestandSet
Yehuda Afek 1;4 , Eli Gafni 2? , John Tromp 3 , and Paul M.B. Vitanyi 3;5
1 Computer Science Department, TelAviv University, RamatAviv 69978 Israel.
2 Department of Computer Science, University of California, Los Angeles CA 90024.
3 Centrum voor Wiskunde en Informatica, Kruislaan 413, 1098 SJ Amsterdam, The
4 AT&T Bell Laboratories, 600 Mountain Avenue, Murray Hill, NJ 07974.
5 Faculteit Wiskunde en Informatica, Universiteit van Amsterdam.
Abstract. This paper presents an economical, randomized, waitfree
construction of an nprocess testandset bit from read write registers.
The testandset shared object has two atomic operations, test&set, which
atomically reads the bit and sets its value to 1, and the reset operation
that resets the bit to 0.
We identify two new complexity measures by which to evaluate wait
free algorithms: (a) The amount of randomness used, and (b) `Parallel
Time'---the maximum sequential depth of an execution (i.e. longest chain
of operations that must precede each other).
The previously best known algorithm for nprocess testandset [Her91]