vault backup: 2025-04-01 09:29:49

Concurrent Systems/notes/10 - Consensus Implementation.md

@@ -106,3 +106,26 @@ Let S’ be a schedule of operations only from r that leads p(q(C’)) to a deci
 - Since r cannot see any difference between p(q(C’)) and q(p(C’)), if we run S’ from q(p(C’)) we must decide 1 as well
 	- in contradiction with q(p(C')) be 0-val
 
+### CN(Swap) = CN(Fetch&add) = 2
+```
+...
+```
+
+### CN(Compare&swap) = ∞
+
+Let us consider a verison of the compare&swap where, instead of returning a boolean, it always returns the previous value of the object, i.e.:
+
+![[Pasted image 20250401092557.png]]
+
+```
+CS a compare&swap object init at ⊥
+
+propose(v) :=
+	tmp <- CS.compare&swap(⊥, v)
+	if tmp = ⊥ then
+		return v
+	else
+		return tmp
+```
+
+Exercise: devise a consensus object with `CN = ∞` by using the compare&swap