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Concurrent Systems/notes/7- MUTEX-free concurrency.md

@@ -70,4 +70,26 @@ this implementation satisfies the three requirements for the splitter
 A **timestamp generator** is a concurrent object that provides a single operation get_ts such that:
 1. (*validity*) not two invocations of get_ts return the same value
 2. (*consistency*) if one process terminates its invocation of get_ts before another one starts, the first receives a timestamp that is smaller than the one received by the second one
-3. (*obstruction freedom*) if run in isolation
+3. (*obstruction freedom*) if run in isolation, it eventually terminates
+
+Idea: use something like a splitter for possible timestamp, so that only the process that receives S (if any) can get that timestamp.
+
+We have:
+- `DOOR[i]`: MRMW boolean atomic register initialized at 1, for all i
+- `LAST[i]`: MRMW atomic register initialized at whatever process index, for all i
+- NEXT: integer initialized at 1
+```
+get_ts(i) :=
+	k <- NEXT
+	while true do
+		LAST[k] <- i
+		if DOOR[k] = 1 then
+			DOOR[k] <- 0
+			if LAST[k] = i then
+				NEXT++
+				return k
+			k++
+```
+
+#### Soundness theorem (yes, again)
+this implementation satisfies the three properties of the timestamp generator