chenBright commented on code in PR #3547:
URL: https://github.com/apache/brpc/pull/3547#discussion_r4045623202


##########
src/bvar/reducer.h:
##########
@@ -93,17 +121,18 @@ class BabylonVariable: public Variable {
     }
 
     T get_value() const {
+        CHECK(!(butil::is_same<InvOp, VoidOp>::value) || nullptr == _sampler)
+            << "You should not call Reducer<" << butil::class_name_str<T>()
+            << ", " << butil::class_name_str<Op>() << ">::get_value() when a"
+            << " Window<> is used because the operator does not have inverse.";
         return _counter.value();
     }
 
     T reset() {
-        if (BAIDU_UNLIKELY((!butil::is_same<VoidOp, InvOp>::value))) {
-            CHECK(false) << "You should not call Reducer<" << 
butil::class_name_str<T>()
-                         << ", " << butil::class_name_str<Op>() << 
">::get_value() when a"
-                         << " Window<> is used because the operator does not 
have inverse.";
-            return get_value();
-        }
-
+        // Unlike AgentCombiner::reset_all_agents(), reading and clearing the 
babylon
+        // counter are two separate steps, so values added in between are 
lost. This
+        // only affects explicit reset() by users: sampling of an operator 
without
+        // inverse is the only internal user and it runs in a single thread.

Review Comment:
   > If this is an accepted trade-off for the Babylon backend, could we update 
the comment to acknowledge that it > also applies to normal sampling?
   
   @wasphin You are right. Updated the comment to explicitly state that this 
affects sampler-thread sampling (e.g. Window/series sampling) as well, and that 
it's an accepted trade-off for the babylon backend since minor loss doesn't 
change the overall trend in statistics/monitoring scenarios.



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