[Fiber] Improve memory order of reference counter

emper/Fiber.hpp

@@ -91,15 +91,23 @@ class ALIGN_TO_CACHE_LINE Fiber : public Logger<LogSubsystem::F> {
 		return runnable.exchange(false);
 	}
 
-	inline auto doAtomicIncrRefCount() -> unsigned int {
+	inline void doAtomicIncrRefCount() {
 		assert(referenceCounter < UINT_MAX);
 		isMulti = true;
-		return ++referenceCounter;
+		// Note: Although the first impulse is to prevent the re-ordering
+		// of the isMulti store after the reference counter modification,
+		// this *should* not be necessary. The sychronization point where
+		// this ordering is guranteed is, when the fiber is put in a
+		// concurrent queue. There the queue must gurantee that all
+		// previous stores are visible at the time the fiber appears in
+		// the queue to other threads.
+		referenceCounter.fetch_add(1, std::memory_order_relaxed);
 	}
 
 	inline auto doAtomicDecrRefCount() -> unsigned int {
 		assert(referenceCounter > 0);
-		return --referenceCounter;
+		auto previous = referenceCounter.fetch_sub(1, std::memory_order_acq_rel);
+		return previous - 1;
 	}
 
 	template <LogSubsystem>