Fix re-resolution in pick_first

2 files changed, 15 insertions, 15 deletions

diff --git a/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc b/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
index 023281db97..d217dc0e63 100644
--- a/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
@@ -451,6 +451,7 @@ void PickFirst::PickFirstSubchannelData::ProcessConnectivityChangeLocked(
   // latest pending subchannel lists.
   GPR_ASSERT(subchannel_list() == p->subchannel_list_.get() ||
              subchannel_list() == p->latest_pending_subchannel_list_.get());
+  GPR_ASSERT(connectivity_state != GRPC_CHANNEL_SHUTDOWN);
   // Handle updates for the currently selected subchannel.
   if (p->selected_ == this) {
     if (grpc_lb_pick_first_trace.enabled()) {
@@ -480,14 +481,12 @@ void PickFirst::PickFirstSubchannelData::ProcessConnectivityChangeLocked(
                     "update"),
           "selected_not_ready+switch_to_update");
     } else {
-      // TODO(juanlishen): we re-resolve when the selected subchannel goes to
-      // TRANSIENT_FAILURE because we used to shut down in this case before
-      // re-resolution is introduced. But we need to investigate whether we
-      // really want to take any action instead of waiting for the selected
-      // subchannel reconnecting.
-      GPR_ASSERT(connectivity_state != GRPC_CHANNEL_SHUTDOWN);
       if (connectivity_state == GRPC_CHANNEL_TRANSIENT_FAILURE) {
-        // If the selected channel goes bad, request a re-resolution.
+        // If the selected subchannel goes bad, request a re-resolution. We also
+        // set the channel state to IDLE and reset started_picking_. The reason
+        // is that if the new state is TRANSIENT_FAILURE due to a GOAWAY
+        // reception we don't want to connect to the re-resolved backends until
+        // we leave the IDLE state.
         grpc_connectivity_state_set(&p->state_tracker_, GRPC_CHANNEL_IDLE,
                                     GRPC_ERROR_NONE,
                                     "selected_changed+reresolve");
@@ -568,9 +567,10 @@ void PickFirst::PickFirstSubchannelData::ProcessConnectivityChangeLocked(
       // Case 1: Only set state to TRANSIENT_FAILURE if we've tried
       // all subchannels.
       if (sd->Index() == 0 && subchannel_list() == p->subchannel_list_.get()) {
+        p->TryReresolutionLocked(&grpc_lb_pick_first_trace, GRPC_ERROR_NONE);
         grpc_connectivity_state_set(
             &p->state_tracker_, GRPC_CHANNEL_TRANSIENT_FAILURE,
-            GRPC_ERROR_REF(error), "connecting_transient_failure");
+            GRPC_ERROR_REF(error), "exhausted_subchannels");
       }
       sd->StartConnectivityWatchLocked();
       break;
diff --git a/src/core/ext/filters/client_channel/subchannel.cc b/src/core/ext/filters/client_channel/subchannel.cc
index 93df2aff70..71ef8c518b 100644
--- a/src/core/ext/filters/client_channel/subchannel.cc
+++ b/src/core/ext/filters/client_channel/subchannel.cc
@@ -402,8 +402,6 @@ static void continue_connect_locked(grpc_subchannel* c) {
   c->next_attempt_deadline = c->backoff->NextAttemptTime();
   args.deadline = std::max(c->next_attempt_deadline, min_deadline);
   args.channel_args = c->args;
-  grpc_connectivity_state_set(&c->state_tracker, GRPC_CHANNEL_CONNECTING,
-                              GRPC_ERROR_NONE, "state_change");
   grpc_connector_connect(c->connector, &args, &c->connecting_result,
                          &c->on_connected);
 }
@@ -459,27 +457,24 @@ static void maybe_start_connecting_locked(grpc_subchannel* c) {
     /* Don't try to connect if we're already disconnected */
     return;
   }
-
   if (c->connecting) {
     /* Already connecting: don't restart */
     return;
   }
-
   if (c->connected_subchannel != nullptr) {
     /* Already connected: don't restart */
     return;
   }
-
   if (!grpc_connectivity_state_has_watchers(&c->state_tracker)) {
     /* Nobody is interested in connecting: so don't just yet */
     return;
   }
-
   c->connecting = true;
   GRPC_SUBCHANNEL_WEAK_REF(c, "connecting");
-
   if (!c->backoff_begun) {
     c->backoff_begun = true;
+    grpc_connectivity_state_set(&c->state_tracker, GRPC_CHANNEL_CONNECTING,
+                                GRPC_ERROR_NONE, "connecting");
     continue_connect_locked(c);
   } else {
     GPR_ASSERT(!c->have_alarm);
@@ -494,6 +489,11 @@ static void maybe_start_connecting_locked(grpc_subchannel* c) {
     }
     GRPC_CLOSURE_INIT(&c->on_alarm, on_alarm, c, grpc_schedule_on_exec_ctx);
     grpc_timer_init(&c->alarm, c->next_attempt_deadline, &c->on_alarm);
+    // During backoff, we prefer the connectivity state of CONNECTING instead of
+    // TRANSIENT_FAILURE in order to prevent triggering re-resolution
+    // continuously in pick_first.
+    grpc_connectivity_state_set(&c->state_tracker, GRPC_CHANNEL_CONNECTING,
+                                GRPC_ERROR_NONE, "backoff");
   }
 }