Compare and swap has a consensus number of 2. A consensus number is the maximum number of processes for which the object can solve a simple consensus problem. I

Compare and swap has a consensus number of 2. A consensus number is the maximum number of processes for which the object can solve a simple consensus problem. It is impossible to construct a wait-free implementation of an object with consensus number n from an object with a lower consensus number. In other words, test-and-set is weaker than transactions or Paxos for >2 concurrent clients. http://cs.brown.edu/~mph/Herlihy91/p124-herlihy.pdf http://cs.brown.edu/~mph/Herlihy91/p124-herlihy.pdf