diff --git a/src/thread/MtInQueue.hpp b/src/thread/MtInQueue.hpp
index d532c09..fd04180 100644
--- a/src/thread/MtInQueue.hpp
+++ b/src/thread/MtInQueue.hpp
@@ -28,7 +28,9 @@ using namespace std;
 
 namespace RLib
 {
-using ElePair = pair<shared_ptr<void>, size_t>;  // ele & its typeid.hash_code
+// ele & its typeid.hash_code
+// - hash_code is size_t (simplest) vs type_info (complex class, & need more mem)
+using ElePair = pair<shared_ptr<void>, size_t>;
 
 // ***********************************************************************************************
 class MtInQueue
diff --git a/ut/thread/MT_SemphoreTest.cpp b/ut/thread/MT_SemphoreTest.cpp
index 05f9be8..ceeb52e 100644
--- a/ut/thread/MT_SemphoreTest.cpp
+++ b/ut/thread/MT_SemphoreTest.cpp
@@ -126,7 +126,7 @@ TEST_F(MT_SemaphoreTest, GOLD_integrate_MsgSelf_ThreadBack_MtInQueue)  // simula
         for (;;)
         {
             auto elePair = mtQ_.pop();
-            if (elePair.first == nullptr) break;
+            if (elePair.first == nullptr) break;  // handle next eg MsgSelf queue
             msgHdlrs[elePair.second](elePair.first);
         }