Fix TypedValue.CompareAndSwap

wwqgtxx · wwqgtxx · commit 8122af0236b9 · 2025-06-05T13:39:52.000+08:00
tailscale/tailscale@84aa7ff
diff --git a/common/atomic/typed.go b/common/atomic/typed.go
@@ -42,5 +42,9 @@ func (t *TypedValue[T]) Swap(new T) T {
 }
 
 func (t *TypedValue[T]) CompareAndSwap(old, new T) bool {
-	return t.value.CompareAndSwap(typedValue[T]{old}, typedValue[T]{new})
+	return t.value.CompareAndSwap(typedValue[T]{old}, typedValue[T]{new}) ||
+		// In the edge-case where [atomic.Value.Store] is uninitialized
+		// and trying to compare with the zero value of T,
+		// then compare-and-swap with the nil any value.
+		(any(old) == any(common.DefaultValue[T]()) && t.value.CompareAndSwap(any(nil), typedValue[T]{new}))
 }

Original file line number	Diff line number	Diff line change
`@@ -42,5 +42,9 @@ func (t *TypedValue[T]) Swap(new T) T {`
`42`	`42`	`}`
`43`	`43`
`44`	`44`	`func (t *TypedValue[T]) CompareAndSwap(old, new T) bool {`
`45`		`- return t.value.CompareAndSwap(typedValue[T]{old}, typedValue[T]{new})`
	`45`	`+ return t.value.CompareAndSwap(typedValue[T]{old}, typedValue[T]{new}) \|\|`
	`46`	`+ // In the edge-case where [atomic.Value.Store] is uninitialized`
	`47`	`+ // and trying to compare with the zero value of T,`
	`48`	`+ // then compare-and-swap with the nil any value.`
	`49`	`+ (any(old) == any(common.DefaultValue[T]()) && t.value.CompareAndSwap(any(nil), typedValue[T]{new}))`
`46`	`50`	`}`