Track last ready subchannel index in RoundRobinSubchannelList.

src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc

@@ -162,11 +162,15 @@ class RoundRobin : public LoadBalancingPolicy {
     // subchannels in each state.
     void UpdateRoundRobinStateFromSubchannelStateCountsLocked();
 
+    size_t GetNextReadySubchannelIndexLocked();
+    void UpdateLastReadySubchannelIndexLocked(size_t last_ready_index);
+
    private:
     size_t num_ready_ = 0;
     size_t num_connecting_ = 0;
     size_t num_transient_failure_ = 0;
     grpc_error* last_transient_failure_error_ = GRPC_ERROR_NONE;
+    size_t last_ready_index_ = -1;  // Index into list of last pick.
   };
 
   void ShutdownLocked() override;
@@ -174,8 +178,6 @@ class RoundRobin : public LoadBalancingPolicy {
   void StartPickingLocked();
   bool DoPickLocked(PickState* pick);
   void DrainPendingPicksLocked();
-  size_t GetNextReadySubchannelIndexLocked();
-  void UpdateLastReadySubchannelIndexLocked(size_t last_ready_index);
 
   /** list of subchannels */
   OrphanablePtr<RoundRobinSubchannelList> subchannel_list_;
@@ -193,8 +195,6 @@ class RoundRobin : public LoadBalancingPolicy {
   PickState* pending_picks_ = nullptr;
   /** our connectivity state tracker */
   grpc_connectivity_state_tracker state_tracker_;
-  /** Index into subchannel_list_ for last pick. */
-  size_t last_ready_subchannel_index_ = -1;
 };
 
 RoundRobin::RoundRobin(const Args& args) : LoadBalancingPolicy(args) {
@@ -220,68 +220,6 @@ RoundRobin::~RoundRobin() {
   grpc_subchannel_index_unref();
 }
 
-/** Returns the index into p->subchannel_list->subchannels of the next
- * subchannel in READY state, or p->subchannel_list->num_subchannels if no
- * subchannel is READY.
- *
- * Note that this function does *not* update p->last_ready_subchannel_index.
- * The caller must do that if it returns a pick. */
-size_t RoundRobin::GetNextReadySubchannelIndexLocked() {
-  GPR_ASSERT(subchannel_list_ != nullptr);
-  if (grpc_lb_round_robin_trace.enabled()) {
-    gpr_log(GPR_INFO,
-            "[RR %p] getting next ready subchannel (out of %" PRIuPTR
-            "), "
-            "last_ready_subchannel_index=%" PRIuPTR,
-            this, subchannel_list_->num_subchannels(),
-            last_ready_subchannel_index_);
-  }
-  for (size_t i = 0; i < subchannel_list_->num_subchannels(); ++i) {
-    const size_t index = (i + last_ready_subchannel_index_ + 1) %
-                         subchannel_list_->num_subchannels();
-    if (grpc_lb_round_robin_trace.enabled()) {
-      gpr_log(
-          GPR_INFO,
-          "[RR %p] checking subchannel %p, subchannel_list %p, index %" PRIuPTR
-          ": state=%s",
-          this, subchannel_list_->subchannel(index)->subchannel(),
-          subchannel_list_.get(), index,
-          grpc_connectivity_state_name(
-              subchannel_list_->subchannel(index)->connectivity_state()));
-    }
-    if (subchannel_list_->subchannel(index)->connectivity_state() ==
-        GRPC_CHANNEL_READY) {
-      if (grpc_lb_round_robin_trace.enabled()) {
-        gpr_log(GPR_INFO,
-                "[RR %p] found next ready subchannel (%p) at index %" PRIuPTR
-                " of subchannel_list %p",
-                this, subchannel_list_->subchannel(index)->subchannel(), index,
-                subchannel_list_.get());
-      }
-      return index;
-    }
-  }
-  if (grpc_lb_round_robin_trace.enabled()) {
-    gpr_log(GPR_INFO, "[RR %p] no subchannels in ready state", this);
-  }
-  return subchannel_list_->num_subchannels();
-}
-
-// Sets last_ready_subchannel_index_ to last_ready_index.
-void RoundRobin::UpdateLastReadySubchannelIndexLocked(size_t last_ready_index) {
-  GPR_ASSERT(last_ready_index < subchannel_list_->num_subchannels());
-  last_ready_subchannel_index_ = last_ready_index;
-  if (grpc_lb_round_robin_trace.enabled()) {
-    gpr_log(GPR_INFO,
-            "[RR %p] setting last_ready_subchannel_index=%" PRIuPTR
-            " (SC %p, CSC %p)",
-            this, last_ready_index,
-            subchannel_list_->subchannel(last_ready_index)->subchannel(),
-            subchannel_list_->subchannel(last_ready_index)
-                ->connected_subchannel());
-  }
-}
-
 void RoundRobin::HandOffPendingPicksLocked(LoadBalancingPolicy* new_policy) {
   PickState* pick;
   while ((pick = pending_picks_) != nullptr) {
@@ -366,7 +304,8 @@ void RoundRobin::ExitIdleLocked() {
 }
 
 bool RoundRobin::DoPickLocked(PickState* pick) {
-  const size_t next_ready_index = GetNextReadySubchannelIndexLocked();
+  const size_t next_ready_index =
+      subchannel_list_->GetNextReadySubchannelIndexLocked();
   if (next_ready_index < subchannel_list_->num_subchannels()) {
     /* readily available, report right away */
     RoundRobinSubchannelData* sd =
@@ -384,7 +323,7 @@ bool RoundRobin::DoPickLocked(PickState* pick) {
               sd->subchannel_list(), next_ready_index);
     }
     /* only advance the last picked pointer if the selection was used */
-    UpdateLastReadySubchannelIndexLocked(next_ready_index);
+    subchannel_list_->UpdateLastReadySubchannelIndexLocked(next_ready_index);
     return true;
   }
   return false;
@@ -511,7 +450,7 @@ void RoundRobin::RoundRobinSubchannelList::
       // Promote this list to p->subchannel_list_.
       // This list must be p->latest_pending_subchannel_list_, because
       // any previous update would have been shut down already and
-      // therefore weeded out in ProcessConnectivityChangeLocked().
+      // therefore we would not be receiving a notification for them.
       GPR_ASSERT(p->latest_pending_subchannel_list_.get() == this);
       GPR_ASSERT(!shutting_down());
       if (grpc_lb_round_robin_trace.enabled()) {
@@ -526,7 +465,6 @@ void RoundRobin::RoundRobinSubchannelList::
                 num_subchannels());
       }
       p->subchannel_list_ = std::move(p->latest_pending_subchannel_list_);
-      p->last_ready_subchannel_index_ = -1;
     }
     // Drain pending picks.
     p->DrainPendingPicksLocked();
@@ -580,6 +518,62 @@ void RoundRobin::RoundRobinSubchannelData::ProcessConnectivityChangeLocked(
   RenewConnectivityWatchLocked();
 }
 
+/** Returns the index into p->subchannel_list->subchannels of the next
+ * subchannel in READY state, or p->subchannel_list->num_subchannels if no
+ * subchannel is READY.
+ *
+ * Note that this function does *not* update p->last_ready_subchannel_index.
+ * The caller must do that if it returns a pick. */
+size_t
+RoundRobin::RoundRobinSubchannelList::GetNextReadySubchannelIndexLocked() {
+  if (grpc_lb_round_robin_trace.enabled()) {
+    gpr_log(GPR_INFO,
+            "[RR %p] getting next ready subchannel (out of %" PRIuPTR
+            "), last_ready_index=%" PRIuPTR,
+            policy(), num_subchannels(), last_ready_index_);
+  }
+  for (size_t i = 0; i < num_subchannels(); ++i) {
+    const size_t index = (i + last_ready_index_ + 1) % num_subchannels();
+    if (grpc_lb_round_robin_trace.enabled()) {
+      gpr_log(
+          GPR_INFO,
+          "[RR %p] checking subchannel %p, subchannel_list %p, index %" PRIuPTR
+          ": state=%s",
+          policy(), subchannel(index)->subchannel(), this, index,
+          grpc_connectivity_state_name(
+              subchannel(index)->connectivity_state()));
+    }
+    if (subchannel(index)->connectivity_state() == GRPC_CHANNEL_READY) {
+      if (grpc_lb_round_robin_trace.enabled()) {
+        gpr_log(GPR_INFO,
+                "[RR %p] found next ready subchannel (%p) at index %" PRIuPTR
+                " of subchannel_list %p",
+                policy(), subchannel(index)->subchannel(), index, this);
+      }
+      return index;
+    }
+  }
+  if (grpc_lb_round_robin_trace.enabled()) {
+    gpr_log(GPR_INFO, "[RR %p] no subchannels in ready state", this);
+  }
+  return num_subchannels();
+}
+
+// Sets last_ready_index_ to last_ready_index.
+void RoundRobin::RoundRobinSubchannelList::UpdateLastReadySubchannelIndexLocked(
+    size_t last_ready_index) {
+  GPR_ASSERT(last_ready_index < num_subchannels());
+  last_ready_index_ = last_ready_index;
+  if (grpc_lb_round_robin_trace.enabled()) {
+    gpr_log(GPR_INFO,
+            "[RR %p] setting last_ready_subchannel_index=%" PRIuPTR
+            " (SC %p, CSC %p)",
+            policy(), last_ready_index,
+            subchannel(last_ready_index)->subchannel(),
+            subchannel(last_ready_index)->connected_subchannel());
+  }
+}
+
 grpc_connectivity_state RoundRobin::CheckConnectivityLocked(
     grpc_error** error) {
   return grpc_connectivity_state_get(&state_tracker_, error);
@@ -593,7 +587,8 @@ void RoundRobin::NotifyOnStateChangeLocked(grpc_connectivity_state* current,
 
 void RoundRobin::PingOneLocked(grpc_closure* on_initiate,
                                grpc_closure* on_ack) {
-  const size_t next_ready_index = GetNextReadySubchannelIndexLocked();
+  const size_t next_ready_index =
+      subchannel_list_->GetNextReadySubchannelIndexLocked();
   if (next_ready_index < subchannel_list_->num_subchannels()) {
     RoundRobinSubchannelData* selected =
         subchannel_list_->subchannel(next_ready_index);
@@ -648,7 +643,6 @@ void RoundRobin::UpdateLocked(const grpc_channel_args& args) {
           "rr_update_empty");
     }
     subchannel_list_ = std::move(latest_pending_subchannel_list_);
-    last_ready_subchannel_index_ = -1;
   } else {
     // If we've started picking, start watching the new list.
     latest_pending_subchannel_list_->StartWatchingLocked();