DynamicBoundedQueue: Round threshold up to avoid threshold 0

Summary: Ensure that threshold is not 0, otherwise when capacity < 10, threshold is 0, which can lead to consumers never transferring credit to producers.

Differential Revision: D26791831

fbshipit-source-id: 741bcf17de18198e43471d4b36d98c79288652fb

folly/concurrency/DynamicBoundedQueue.h

@@ -444,7 +444,7 @@ class DynamicBoundedQueue {
   // Calculation of threshold to move credits in bulk from consumers
   // to producers
   constexpr Weight threshold(Weight capacity) const noexcept {
-    return capacity / 10;
+    return (capacity + 9) / 10;
   }
 
   // Functions called frequently by producers