Update sdk/metric/internal/aggregate/sum.go

Co-authored-by: Tyler Yahn <[email protected]>

Author: dashpole

sdk/metric/internal/aggregate/sum.go

@@ -57,10 +57,11 @@ func (s *valueMap[N]) measure(ctx context.Context, value N, fltrAttr attribute.S
 	}
 	v, ok := s.values[hotIdx].Load(fltrAttr.Equivalent())
 	if !ok {
-		// It is possible to exceed the attribute limit if it races with other
-		// new attribute sets. This is an accepted tradeoff to avoid locking
-		// for writes.
-		if s.aggLimit > 0 && s.len[hotIdx].Load() >= int64(s.aggLimit-1) {
+		// Pre-increment, reserve a slot first.
+		newLen := s.len[hotIdx].Add(1)
+		if s.aggLimit > 0 && newLen >= int64(s.aggLimit) {
+			// We exceeded the limit, decrement back and use overflow
+			s.len[hotIdx].Add(-1)
 			fltrAttr = overflowSet
 		}
 		var loaded bool