vault backup: 2025-03-04 08:39:45

Concurrent Systems/notes/Lezione2.md

@@ -24,3 +24,21 @@ lock(i) :=
 Problems:
 - we don't want the FAIL
 - it is possible to have an execution where nobody accesses its CS, if repeated forever it entails a deadlock
+
+```
+Initialize Y at ⊥, X at any value (e.g., 0)
+
+
+lock(i) :=
+	* FLAG[i] <- up
+	X <- i
+	if Y ≠ ⊥ then FLAG[i] <- down
+		wait Y = ⊥
+		goto *
+	else Y <- i
+	if X = i then return
+	else FLAG[i] <- down
+	∀j.wait FLAG[j] = down
+	if Y = i then return
+	else wait Y = 1
+	goto *