vault backup: 2025-03-03 20:35:00

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Concurrent Systems/notes/Lezione1.md

@@ -239,4 +239,12 @@ Induction (true for ℓ+1, to be proved for ℓ):
 
 ##### Peterson algorithm cost
 - $n$ MRSW registers of $\lceil \log_{2} n\rceil$ bits (FLAG)
-- $n-1$ MRMW
+- $n-1$ MRMW registers of $\lceil \log_{2}n \rceil$ bits (AFTER_YOU)
+- $(n-1)\times(n+2)$ accesses for locking and 1 access for unlocking
+
+It satisfies MUTEX and starvation freedom. It does not satisfy bounded bypass:
+- consider 3 processes, one sleeping in its first wait, the others alternating in the CS
+- when the first process wakes up, it can pass to level 2 and eventually win
+- but the sleep can be arbitrary long and in the meanwhile the other two processes may have entered an unbounded number of CSs
+
+Easy to generalize to k-MUTEX.