vault backup: 2025-03-03 10:26:24

Concurrent Systems/notes/Lezione1.md

@@ -186,10 +186,24 @@ b) `AFTER_YOU = 1`, this is possible only with the following interleaving:
 ### Peterson algorithm ($n$ processes)
 - FLAG now has $n$ levels (from 0 to n-1)
 	- level 0 means down
-	- level >0 means inv
+	- level >0 means involved in the lock
 - Every level has its own AFTER_YOU
 
 ```
 Initialize FLAG[i] to 0, for all i
 
-lock
+lock(i) :=
+	for lev = 1 to n-1 do
+		FLAG[i] <- lev
+		AFTER_YOU[lev] <- i
+		wait (∀k!=i, FLAG[k] < lev
+			OR AFTER_YOU[lev] != i)
+		return
+
+unlock(i) :=
+	FLAG[i] <- 0
+	return
+```
+We say that pi is at level h when it exits from the h-th wait -> a process at level h is at any level <= h
+
+##### MUTE