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5
Concurrent Systems/notes/1b - Peterson algorithm.md
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@ -90,9 +90,10 @@ unlock(i) :=
FLAG[i] <- 0 FLAG[i] <- 0
return return
``` ```
We say that: We say that: $p_i$ is at level $h$ when it exits from the $h$-th wait $\to$ a process at level $h$ is at any level $<= h$
if $p_i$ is at level $h$ when it exits from the $h$-th wait $\to$ a process at level $h$ is at any level $<= h$
>[!info] What is the `wait` condition actually checking?
>In the wait condition we check that all other processes are at a lower level.
##### MUTEX proof ##### MUTEX proof
Lemma: for every $ℓ \in \{0,\dots,n-1\}$ , at most n-ℓ processes are at level ℓ, this implies MUTEX by taking ℓ = n-1 Lemma: for every $ℓ \in \{0,\dots,n-1\}$ , at most n-ℓ processes are at level ℓ, this implies MUTEX by taking ℓ = n-1