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

@@ -101,3 +101,31 @@ this implementation satisfies the three properties of the timestamp generator
 **REMARK:** this implementation doesn’t satisfy the non-blocking property:![[Pasted image 20250324092633.png]]
 
 ### A Wait-free Stack
+REG is an unbounded array of atomic registers (the stack)
+
+For all i, `REG[i]` can be:
+- written
+- read by the `swap(v)` primitives (that atomically writes a new value in it)
+- initialized at `⊥`
+
+NEXT is an atomic register (pointing at the next free location of the stack) that can be
+- read
+- `fetch&add`
+- initialized at 1
+
+```
+push(v) :=
+	i <- NEXT.fetch&add(1)
+	REG[1] <- v
+
+pop() :=
+	k <- NEXT-1
+	for i = k down to 1
+	tmp <- REG[1].swap(⊥)
+	if tmp != ⊥ then
+		return tmp
+	return ⊥
+```
+
+REMARK: crashes do not compromise progress!
+PROBLEM: unboundedness of REG is not realistic