Merge pull request #8666 from dgquintas/rr_fixall

Fixed wrong connectivity status updates for RR

include/grpc/impl/codegen/connectivity_state.h

@@ -40,6 +40,8 @@ extern "C" {
 
 /** Connectivity state of a channel. */
 typedef enum {
+  /** channel has just been initialized */
+  GRPC_CHANNEL_INIT = -1,
   /** channel is idle */
   GRPC_CHANNEL_IDLE,
   /** channel is connecting */

src/core/ext/lb_policy/pick_first/pick_first.c

@@ -292,6 +292,8 @@ static void pf_connectivity_changed(grpc_exec_ctx *exec_ctx, void *arg,
   } else {
   loop:
     switch (p->checking_connectivity) {
+      case GRPC_CHANNEL_INIT:
+        GPR_UNREACHABLE_CODE();
       case GRPC_CHANNEL_READY:
         grpc_connectivity_state_set(exec_ctx, &p->state_tracker,
                                     GRPC_CHANNEL_READY, GRPC_ERROR_NONE,

src/core/ext/lb_policy/round_robin/round_robin.c

@@ -116,8 +116,13 @@ typedef struct {
   grpc_closure connectivity_changed_closure;
   /** this subchannels current position in subchannel->ready_list */
   ready_list *ready_list_node;
-  /** last observed connectivity */
-  grpc_connectivity_state connectivity_state;
+  /** last observed connectivity. Not updated by
+   * \a grpc_subchannel_notify_on_state_change. Used to determine the previous
+   * state while processing the new state in \a rr_connectivity_changed */
+  grpc_connectivity_state prev_connectivity_state;
+  /** current connectivity state. Updated by \a
+   * grpc_subchannel_notify_on_state_change */
+  grpc_connectivity_state curr_connectivity_state;
   /** the subchannel's target user data */
   void *user_data;
   /** vtable to operate over \a user_data */
@@ -127,6 +132,7 @@ typedef struct {
 struct round_robin_lb_policy {
   /** base policy: must be first */
   grpc_lb_policy base;
+  gpr_mu mu;
 
   /** total number of addresses received at creation time */
   size_t num_addresses;
@@ -135,8 +141,11 @@ struct round_robin_lb_policy {
   size_t num_subchannels;
   subchannel_data **subchannels;
 
-  /** mutex protecting remaining members */
-  gpr_mu mu;
+  /** how many subchannels are in TRANSIENT_FAILURE */
+  size_t num_transient_failures;
+  /** how many subchannels are IDLE */
+  size_t num_idle;
+
   /** have we started picking? */
   int started_picking;
   /** are we shutting down? */
@@ -258,6 +267,10 @@ static void remove_disconnected_sc_locked(round_robin_lb_policy *p,
   gpr_free(node);
 }
 
+static bool is_ready_list_empty(round_robin_lb_policy *p) {
+  return p->ready_list.prev == NULL;
+}
+
 static void rr_destroy(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
   round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
   ready_list *elem;
@@ -268,7 +281,7 @@ static void rr_destroy(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
 
   for (size_t i = 0; i < p->num_subchannels; i++) {
     subchannel_data *sd = p->subchannels[i];
-    GRPC_SUBCHANNEL_UNREF(exec_ctx, sd->subchannel, "round_robin_destroy");
+    GRPC_SUBCHANNEL_UNREF(exec_ctx, sd->subchannel, "rr_destroy");
     if (sd->user_data != NULL) {
       GPR_ASSERT(sd->user_data_vtable != NULL);
       sd->user_data_vtable->destroy(sd->user_data);
@@ -381,18 +394,18 @@ static void start_picking(grpc_exec_ctx *exec_ctx, round_robin_lb_policy *p) {
   size_t i;
   p->started_picking = 1;
 
-  if (grpc_lb_round_robin_trace) {
-    gpr_log(GPR_DEBUG, "LB_POLICY: p=%p num_subchannels=%" PRIuPTR, (void *)p,
-            p->num_subchannels);
-  }
-
   for (i = 0; i < p->num_subchannels; i++) {
     subchannel_data *sd = p->subchannels[i];
-    sd->connectivity_state = GRPC_CHANNEL_IDLE;
+    /* use some sentinel value outside of the range of grpc_connectivity_state
+     * to signal an undefined previous state. We won't be referring to this
+     * value again and it'll be overwritten after the first call to
+     * rr_connectivity_changed */
+    sd->prev_connectivity_state = GRPC_CHANNEL_INIT;
+    sd->curr_connectivity_state = GRPC_CHANNEL_IDLE;
+    GRPC_LB_POLICY_WEAK_REF(&p->base, "rr_connectivity");
     grpc_subchannel_notify_on_state_change(
         exec_ctx, sd->subchannel, p->base.interested_parties,
-        &sd->connectivity_state, &sd->connectivity_changed_closure);
-    GRPC_LB_POLICY_WEAK_REF(&p->base, "round_robin_connectivity");
+        &sd->curr_connectivity_state, &sd->connectivity_changed_closure);
   }
 }
 
@@ -422,7 +435,7 @@ static int rr_pick(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
     /* readily available, report right away */
     *target = GRPC_CONNECTED_SUBCHANNEL_REF(
         grpc_subchannel_get_connected_subchannel(selected->subchannel),
-        "picked");
+        "rr_picked");
 
     if (user_data != NULL) {
       *user_data = selected->user_data;
@@ -453,125 +466,184 @@ static int rr_pick(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
   }
 }
 
+static void update_state_counters(subchannel_data *sd) {
+  round_robin_lb_policy *p = sd->policy;
+
+  /* update p->num_transient_failures (resp. p->num_idle): if the previous
+   * state was TRANSIENT_FAILURE (resp. IDLE), decrement
+   * p->num_transient_failures (resp. p->num_idle). */
+  if (sd->prev_connectivity_state == GRPC_CHANNEL_TRANSIENT_FAILURE) {
+    GPR_ASSERT(p->num_transient_failures > 0);
+    --p->num_transient_failures;
+  } else if (sd->prev_connectivity_state == GRPC_CHANNEL_IDLE) {
+    GPR_ASSERT(p->num_idle > 0);
+    --p->num_idle;
+  }
+}
+
+/* sd is the subchannel_data associted with the updated subchannel.
+ * shutdown_error will only be used upon policy transition to TRANSIENT_FAILURE
+ * or SHUTDOWN */
+static grpc_connectivity_state update_lb_connectivity_status(
+    grpc_exec_ctx *exec_ctx, subchannel_data *sd, grpc_error *error) {
+  /* In priority order. The first rule to match terminates the search (ie, if we
+   * are on rule n, all previous rules were unfulfilled).
+   *
+   * 1) RULE: ANY subchannel is READY => policy is READY.
+   *    CHECK: At least one subchannel is ready iff p->ready_list is NOT empty.
+   *
+   * 2) RULE: ANY subchannel is CONNECTING => policy is CONNECTING.
+   *    CHECK: sd->curr_connectivity_state == CONNECTING.
+   *
+   * 3) RULE: ALL subchannels are SHUTDOWN => policy is SHUTDOWN.
+   *    CHECK: p->num_subchannels = 0.
+   *
+   * 4) RULE: ALL subchannels are TRANSIENT_FAILURE => policy is
+   *    TRANSIENT_FAILURE.
+   *    CHECK: p->num_transient_failures == p->num_subchannels.
+   *
+   * 5) RULE: ALL subchannels are IDLE => policy is IDLE.
+   *    CHECK: p->num_idle == p->num_subchannels.
+   */
+  round_robin_lb_policy *p = sd->policy;
+  if (!is_ready_list_empty(p)) { /* 1) READY */
+    grpc_connectivity_state_set(exec_ctx, &p->state_tracker, GRPC_CHANNEL_READY,
+                                GRPC_ERROR_NONE, "rr_ready");
+    return GRPC_CHANNEL_READY;
+  } else if (sd->curr_connectivity_state ==
+             GRPC_CHANNEL_CONNECTING) { /* 2) CONNECTING */
+    grpc_connectivity_state_set(exec_ctx, &p->state_tracker,
+                                GRPC_CHANNEL_CONNECTING, GRPC_ERROR_NONE,
+                                "rr_connecting");
+    return GRPC_CHANNEL_CONNECTING;
+  } else if (p->num_subchannels == 0) { /* 3) SHUTDOWN */
+    grpc_connectivity_state_set(exec_ctx, &p->state_tracker,
+                                GRPC_CHANNEL_SHUTDOWN, GRPC_ERROR_REF(error),
+                                "rr_shutdown");
+    return GRPC_CHANNEL_SHUTDOWN;
+  } else if (p->num_transient_failures ==
+             p->num_subchannels) { /* 4) TRANSIENT_FAILURE */
+    grpc_connectivity_state_set(exec_ctx, &p->state_tracker,
+                                GRPC_CHANNEL_TRANSIENT_FAILURE,
+                                GRPC_ERROR_REF(error), "rr_transient_failure");
+    return GRPC_CHANNEL_TRANSIENT_FAILURE;
+  } else if (p->num_idle == p->num_subchannels) { /* 5) IDLE */
+    grpc_connectivity_state_set(exec_ctx, &p->state_tracker, GRPC_CHANNEL_IDLE,
+                                GRPC_ERROR_NONE, "rr_idle");
+    return GRPC_CHANNEL_IDLE;
+  }
+  /* no change */
+  return sd->curr_connectivity_state;
+}
+
 static void rr_connectivity_changed(grpc_exec_ctx *exec_ctx, void *arg,
                                     grpc_error *error) {
   subchannel_data *sd = arg;
   round_robin_lb_policy *p = sd->policy;
   pending_pick *pp;
 
-  int unref = 0;
-
   GRPC_ERROR_REF(error);
   gpr_mu_lock(&p->mu);
 
   if (p->shutdown) {
-    unref = 1;
-  } else {
-    switch (sd->connectivity_state) {
-      case GRPC_CHANNEL_READY:
-        grpc_connectivity_state_set(exec_ctx, &p->state_tracker,
-                                    GRPC_CHANNEL_READY, GRPC_ERROR_REF(error),
-                                    "connecting_ready");
-        /* add the newly connected subchannel to the list of connected ones.
-         * Note that it goes to the "end of the line". */
-        sd->ready_list_node = add_connected_sc_locked(p, sd);
-        /* at this point we know there's at least one suitable subchannel. Go
-         * ahead and pick one and notify the pending suitors in
-         * p->pending_picks. This preemtively replicates rr_pick()'s actions. */
-        ready_list *selected = peek_next_connected_locked(p);
-        GPR_ASSERT(selected != NULL);
-        if (p->pending_picks != NULL) {
-          /* if the selected subchannel is going to be used for the pending
-           * picks, update the last picked pointer */
-          advance_last_picked_locked(p);
+    gpr_mu_unlock(&p->mu);
+    GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &p->base, "rr_connectivity");
+    GRPC_ERROR_UNREF(error);
+    return;
+  }
+  switch (sd->curr_connectivity_state) {
+    case GRPC_CHANNEL_INIT:
+      GPR_UNREACHABLE_CODE();
+    case GRPC_CHANNEL_READY:
+      /* add the newly connected subchannel to the list of connected ones.
+       * Note that it goes to the "end of the line". */
+      sd->ready_list_node = add_connected_sc_locked(p, sd);
+      /* at this point we know there's at least one suitable subchannel. Go
+       * ahead and pick one and notify the pending suitors in
+       * p->pending_picks. This preemtively replicates rr_pick()'s actions. */
+      ready_list *selected = peek_next_connected_locked(p);
+      GPR_ASSERT(selected != NULL);
+      if (p->pending_picks != NULL) {
+        /* if the selected subchannel is going to be used for the pending
+         * picks, update the last picked pointer */
+        advance_last_picked_locked(p);
+      }
+      while ((pp = p->pending_picks)) {
+        p->pending_picks = pp->next;
+        *pp->target = GRPC_CONNECTED_SUBCHANNEL_REF(
+            grpc_subchannel_get_connected_subchannel(selected->subchannel),
+            "rr_picked");
+        if (pp->user_data != NULL) {
+          *pp->user_data = selected->user_data;
         }
-
+        if (grpc_lb_round_robin_trace) {
+          gpr_log(GPR_DEBUG,
+                  "[RR CONN CHANGED] TARGET <-- SUBCHANNEL %p (NODE %p)",
+                  (void *)selected->subchannel, (void *)selected);
+        }
+        grpc_exec_ctx_sched(exec_ctx, pp->on_complete, GRPC_ERROR_NONE, NULL);
+        gpr_free(pp);
+      }
+      update_lb_connectivity_status(exec_ctx, sd, error);
+      sd->prev_connectivity_state = sd->curr_connectivity_state;
+      /* renew notification: reuses the "rr_connectivity" weak ref */
+      grpc_subchannel_notify_on_state_change(
+          exec_ctx, sd->subchannel, p->base.interested_parties,
+          &sd->curr_connectivity_state, &sd->connectivity_changed_closure);
+      break;
+    case GRPC_CHANNEL_IDLE:
+      ++p->num_idle;
+    /* fallthrough */
+    case GRPC_CHANNEL_CONNECTING:
+      update_state_counters(sd);
+      update_lb_connectivity_status(exec_ctx, sd, error);
+      sd->prev_connectivity_state = sd->curr_connectivity_state;
+      /* renew notification: reuses the "rr_connectivity" weak ref */
+      grpc_subchannel_notify_on_state_change(
+          exec_ctx, sd->subchannel, p->base.interested_parties,
+          &sd->curr_connectivity_state, &sd->connectivity_changed_closure);
+      break;
+    case GRPC_CHANNEL_TRANSIENT_FAILURE:
+      ++p->num_transient_failures;
+      /* remove from ready list if still present */
+      if (sd->ready_list_node != NULL) {
+        remove_disconnected_sc_locked(p, sd->ready_list_node);
+        sd->ready_list_node = NULL;
+      }
+      update_lb_connectivity_status(exec_ctx, sd, error);
+      sd->prev_connectivity_state = sd->curr_connectivity_state;
+      /* renew notification: reuses the "rr_connectivity" weak ref */
+      grpc_subchannel_notify_on_state_change(
+          exec_ctx, sd->subchannel, p->base.interested_parties,
+          &sd->curr_connectivity_state, &sd->connectivity_changed_closure);
+      break;
+    case GRPC_CHANNEL_SHUTDOWN:
+      update_state_counters(sd);
+      if (sd->ready_list_node != NULL) {
+        remove_disconnected_sc_locked(p, sd->ready_list_node);
+        sd->ready_list_node = NULL;
+      }
+      --p->num_subchannels;
+      GPR_SWAP(subchannel_data *, p->subchannels[sd->index],
+               p->subchannels[p->num_subchannels]);
+      GRPC_SUBCHANNEL_UNREF(exec_ctx, sd->subchannel, "rr_subchannel_shutdown");
+      p->subchannels[sd->index]->index = sd->index;
+      if (update_lb_connectivity_status(exec_ctx, sd, error) ==
+          GRPC_CHANNEL_SHUTDOWN) {
+        /* the policy is shutting down. Flush all the pending picks... */
         while ((pp = p->pending_picks)) {
           p->pending_picks = pp->next;
-
-          *pp->target = GRPC_CONNECTED_SUBCHANNEL_REF(
-              grpc_subchannel_get_connected_subchannel(selected->subchannel),
-              "picked");
-          if (pp->user_data != NULL) {
-            *pp->user_data = selected->user_data;
-          }
-          if (grpc_lb_round_robin_trace) {
-            gpr_log(GPR_DEBUG,
-                    "[RR CONN CHANGED] TARGET <-- SUBCHANNEL %p (NODE %p)",
-                    (void *)selected->subchannel, (void *)selected);
-          }
+          *pp->target = NULL;
           grpc_exec_ctx_sched(exec_ctx, pp->on_complete, GRPC_ERROR_NONE, NULL);
           gpr_free(pp);
         }
-        grpc_subchannel_notify_on_state_change(
-            exec_ctx, sd->subchannel, p->base.interested_parties,
-            &sd->connectivity_state, &sd->connectivity_changed_closure);
-        break;
-      case GRPC_CHANNEL_CONNECTING:
-      case GRPC_CHANNEL_IDLE:
-        grpc_connectivity_state_set(
-            exec_ctx, &p->state_tracker, sd->connectivity_state,
-            GRPC_ERROR_REF(error), "connecting_changed");
-        grpc_subchannel_notify_on_state_change(
-            exec_ctx, sd->subchannel, p->base.interested_parties,
-            &sd->connectivity_state, &sd->connectivity_changed_closure);
-        break;
-      case GRPC_CHANNEL_TRANSIENT_FAILURE:
-        /* renew state notification */
-        grpc_subchannel_notify_on_state_change(
-            exec_ctx, sd->subchannel, p->base.interested_parties,
-            &sd->connectivity_state, &sd->connectivity_changed_closure);
-
-        /* remove from ready list if still present */
-        if (sd->ready_list_node != NULL) {
-          remove_disconnected_sc_locked(p, sd->ready_list_node);
-          sd->ready_list_node = NULL;
-        }
-        grpc_connectivity_state_set(
-            exec_ctx, &p->state_tracker, GRPC_CHANNEL_TRANSIENT_FAILURE,
-            GRPC_ERROR_REF(error), "connecting_transient_failure");
-        break;
-      case GRPC_CHANNEL_SHUTDOWN:
-        if (sd->ready_list_node != NULL) {
-          remove_disconnected_sc_locked(p, sd->ready_list_node);
-          sd->ready_list_node = NULL;
-        }
-
-        p->num_subchannels--;
-        GPR_SWAP(subchannel_data *, p->subchannels[sd->index],
-                 p->subchannels[p->num_subchannels]);
-        GRPC_SUBCHANNEL_UNREF(exec_ctx, sd->subchannel, "round_robin");
-        p->subchannels[sd->index]->index = sd->index;
-        gpr_free(sd);
-
-        unref = 1;
-        if (p->num_subchannels == 0) {
-          grpc_connectivity_state_set(
-              exec_ctx, &p->state_tracker, GRPC_CHANNEL_SHUTDOWN,
-              GRPC_ERROR_CREATE_REFERENCING("Round Robin Channels Exhausted",
-                                            &error, 1),
-              "no_more_channels");
-          while ((pp = p->pending_picks)) {
-            p->pending_picks = pp->next;
-            *pp->target = NULL;
-            grpc_exec_ctx_sched(exec_ctx, pp->on_complete, GRPC_ERROR_NONE,
-                                NULL);
-            gpr_free(pp);
-          }
-        } else {
-          grpc_connectivity_state_set(
-              exec_ctx, &p->state_tracker, GRPC_CHANNEL_TRANSIENT_FAILURE,
-              GRPC_ERROR_REF(error), "subchannel_failed");
-        }
-    } /* switch */
-  }   /* !unref */
-
-  gpr_mu_unlock(&p->mu);
-
-  if (unref) {
-    GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &p->base, "round_robin_connectivity");
+      }
+      gpr_free(sd);
+      /* unref the "rr_connectivity" weak ref from start_picking */
+      GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &p->base, "rr_connectivity");
+      break;
   }
-
+  gpr_mu_unlock(&p->mu);
   GRPC_ERROR_UNREF(error);
 }
 
@@ -607,9 +679,9 @@ static void rr_ping_one(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
     gpr_mu_unlock(&p->mu);
     target = GRPC_CONNECTED_SUBCHANNEL_REF(
         grpc_subchannel_get_connected_subchannel(selected->subchannel),
-        "picked");
+        "rr_picked");
     grpc_connected_subchannel_ping(exec_ctx, target, closure);
-    GRPC_CONNECTED_SUBCHANNEL_UNREF(exec_ctx, target, "picked");
+    GRPC_CONNECTED_SUBCHANNEL_UNREF(exec_ctx, target, "rr_picked");
   } else {
     gpr_mu_unlock(&p->mu);
     grpc_exec_ctx_sched(exec_ctx, closure,
@@ -705,6 +777,11 @@ static grpc_lb_policy *round_robin_create(grpc_exec_ctx *exec_ctx,
   grpc_lb_policy_init(&p->base, &round_robin_lb_policy_vtable);
   grpc_connectivity_state_init(&p->state_tracker, GRPC_CHANNEL_IDLE,
                                "round_robin");
+
+  if (grpc_lb_round_robin_trace) {
+    gpr_log(GPR_DEBUG, "Created RR policy at %p with %lu subchannels",
+            (void *)p, (unsigned long)p->num_subchannels);
+  }
   gpr_mu_init(&p->mu);
   return &p->base;
 }

src/core/lib/transport/connectivity_state.c

@@ -43,6 +43,8 @@ int grpc_connectivity_state_trace = 0;
 
 const char *grpc_connectivity_state_name(grpc_connectivity_state state) {
   switch (state) {
+    case GRPC_CHANNEL_INIT:
+      return "INIT";
     case GRPC_CHANNEL_IDLE:
       return "IDLE";
     case GRPC_CHANNEL_CONNECTING:
@@ -159,6 +161,7 @@ void grpc_connectivity_state_set(grpc_exec_ctx *exec_ctx,
     grpc_error_free_string(error_string);
   }
   switch (state) {
+    case GRPC_CHANNEL_INIT:
     case GRPC_CHANNEL_CONNECTING:
     case GRPC_CHANNEL_IDLE:
     case GRPC_CHANNEL_READY:

test/core/client_channel/lb_policies_test.c

@@ -62,8 +62,14 @@ typedef struct servers_fixture {
   grpc_metadata_array *request_metadata_recv;
 } servers_fixture;
 
+typedef struct request_sequences {
+  size_t n;
+  int *connections;
+  int *connectivity_states;
+} request_sequences;
+
 typedef void (*verifier_fn)(const servers_fixture *, grpc_channel *,
-                            const int *, const size_t);
+                            const request_sequences *, const size_t);
 
 typedef struct test_spec {
   size_t num_iters;
@@ -227,9 +233,24 @@ static void teardown_servers(servers_fixture *f) {
   gpr_free(f);
 }
 
+static request_sequences request_sequences_create(size_t n) {
+  request_sequences res;
+  res.n = n;
+  res.connections = gpr_malloc(sizeof(*res.connections) * n);
+  res.connectivity_states = gpr_malloc(sizeof(*res.connectivity_states) * n);
+  return res;
+}
+
+static void request_sequences_destroy(const request_sequences *rseqs) {
+  gpr_free(rseqs->connections);
+  gpr_free(rseqs->connectivity_states);
+}
+
 /** Returns connection sequence (server indices), which must be freed */
-static int *perform_request(servers_fixture *f, grpc_channel *client,
-                            request_data *rdata, const test_spec *spec) {
+static request_sequences perform_request(servers_fixture *f,
+                                         grpc_channel *client,
+                                         request_data *rdata,
+                                         const test_spec *spec) {
   grpc_call *c;
   int s_idx;
   int *s_valid;
@@ -239,11 +260,10 @@ static int *perform_request(servers_fixture *f, grpc_channel *client,
   size_t i, iter_num;
   grpc_event ev;
   int read_tag;
-  int *connection_sequence;
   int completed_client;
+  const request_sequences sequences = request_sequences_create(spec->num_iters);
 
   s_valid = gpr_malloc(sizeof(int) * f->num_servers);
-  connection_sequence = gpr_malloc(sizeof(int) * spec->num_iters);
 
   for (iter_num = 0; iter_num < spec->num_iters; iter_num++) {
     cq_verifier *cqv = cq_verifier_create(f->cq);
@@ -260,7 +280,7 @@ static int *perform_request(servers_fixture *f, grpc_channel *client,
       }
     }
 
-    connection_sequence[iter_num] = -1;
+    sequences.connections[iter_num] = -1;
     grpc_metadata_array_init(&rdata->initial_metadata_recv);
     grpc_metadata_array_init(&rdata->trailing_metadata_recv);
 
@@ -305,12 +325,14 @@ static int *perform_request(servers_fixture *f, grpc_channel *client,
                grpc_call_start_batch(c, ops, (size_t)(op - ops), tag(1), NULL));
 
     s_idx = -1;
-    while (
-        (ev = grpc_completion_queue_next(
-             f->cq, GRPC_TIMEOUT_MILLIS_TO_DEADLINE(10 * RETRY_TIMEOUT), NULL))
-            .type != GRPC_QUEUE_TIMEOUT) {
+    while ((ev = grpc_completion_queue_next(
+                f->cq, GRPC_TIMEOUT_MILLIS_TO_DEADLINE(RETRY_TIMEOUT), NULL))
+               .type != GRPC_QUEUE_TIMEOUT) {
       GPR_ASSERT(ev.type == GRPC_OP_COMPLETE);
       read_tag = ((int)(intptr_t)ev.tag);
+      const grpc_connectivity_state conn_state =
+          grpc_channel_check_connectivity_state(client, 0);
+      sequences.connectivity_states[iter_num] = conn_state;
       gpr_log(GPR_DEBUG, "EVENT: success:%d, type:%d, tag:%d iter:%" PRIuPTR,
               ev.success, ev.type, read_tag, iter_num);
       if (ev.success && read_tag >= 1000) {
@@ -318,7 +340,7 @@ static int *perform_request(servers_fixture *f, grpc_channel *client,
         /* only server notifications for non-shutdown events */
         s_idx = read_tag - 1000;
         s_valid[s_idx] = 1;
-        connection_sequence[iter_num] = s_idx;
+        sequences.connections[iter_num] = s_idx;
         break;
       } else if (read_tag == 1) {
         gpr_log(GPR_DEBUG, "client timed out");
@@ -381,10 +403,9 @@ static int *perform_request(servers_fixture *f, grpc_channel *client,
       }
     }
 
-    GPR_ASSERT(
-        grpc_completion_queue_next(
-            f->cq, GRPC_TIMEOUT_MILLIS_TO_DEADLINE(2 * RETRY_TIMEOUT), NULL)
-            .type == GRPC_QUEUE_TIMEOUT);
+    GPR_ASSERT(grpc_completion_queue_next(
+                   f->cq, GRPC_TIMEOUT_MILLIS_TO_DEADLINE(RETRY_TIMEOUT), NULL)
+                   .type == GRPC_QUEUE_TIMEOUT);
 
     grpc_metadata_array_destroy(&rdata->initial_metadata_recv);
     grpc_metadata_array_destroy(&rdata->trailing_metadata_recv);
@@ -401,7 +422,7 @@ static int *perform_request(servers_fixture *f, grpc_channel *client,
 
   gpr_free(s_valid);
 
-  return connection_sequence;
+  return sequences;
 }
 
 static grpc_call **perform_multirequest(servers_fixture *f,
@@ -441,62 +462,10 @@ static grpc_call **perform_multirequest(servers_fixture *f,
   return calls;
 }
 
-static void assert_channel_connectivity(grpc_channel *ch,
-                                        size_t num_accepted_conn_states,
-                                        int accepted_conn_state, ...) {
-  size_t i;
-  grpc_channel_stack *client_stack;
-  grpc_channel_element *client_channel_filter;
-  grpc_connectivity_state actual_conn_state;
-  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
-  va_list ap;
-
-  client_stack = grpc_channel_get_channel_stack(ch);
-  client_channel_filter = grpc_channel_stack_last_element(client_stack);
-
-  actual_conn_state = grpc_client_channel_check_connectivity_state(
-      &exec_ctx, client_channel_filter, 0 /* don't try to connect */);
-  grpc_exec_ctx_finish(&exec_ctx);
-  va_start(ap, accepted_conn_state);
-  for (i = 0; i < num_accepted_conn_states; i++) {
-    if ((int)actual_conn_state == accepted_conn_state) {
-      break;
-    }
-    accepted_conn_state = va_arg(ap, grpc_connectivity_state);
-  }
-  va_end(ap);
-  if (i == num_accepted_conn_states) {
-    char **accepted_strs =
-        gpr_malloc(sizeof(char *) * num_accepted_conn_states);
-    char *accepted_str_joined;
-    va_start(ap, accepted_conn_state);
-    for (i = 0; i < num_accepted_conn_states; i++) {
-      GPR_ASSERT(gpr_asprintf(&accepted_strs[i], "%d", accepted_conn_state) >
-                 0);
-      accepted_conn_state = va_arg(ap, grpc_connectivity_state);
-    }
-    va_end(ap);
-    accepted_str_joined = gpr_strjoin_sep((const char **)accepted_strs,
-                                          num_accepted_conn_states, ", ", NULL);
-    gpr_log(
-        GPR_ERROR,
-        "Channel connectivity assertion failed: expected <one of [%s]>, got %d",
-        accepted_str_joined, actual_conn_state);
-
-    for (i = 0; i < num_accepted_conn_states; i++) {
-      gpr_free(accepted_strs[i]);
-    }
-    gpr_free(accepted_strs);
-    gpr_free(accepted_str_joined);
-    abort();
-  }
-}
-
 void run_spec(const test_spec *spec) {
   grpc_channel *client;
   char *client_hostport;
   char *servers_hostports_str;
-  int *actual_connection_sequence;
   request_data rdata;
   servers_fixture *f;
   grpc_channel_args args;
@@ -524,14 +493,14 @@ void run_spec(const test_spec *spec) {
   gpr_log(GPR_INFO, "Testing '%s' with servers=%s client=%s", spec->description,
           servers_hostports_str, client_hostport);
 
-  actual_connection_sequence = perform_request(f, client, &rdata, spec);
+  const request_sequences sequences = perform_request(f, client, &rdata, spec);
 
-  spec->verifier(f, client, actual_connection_sequence, spec->num_iters);
+  spec->verifier(f, client, &sequences, spec->num_iters);
 
   gpr_free(client_hostport);
   gpr_free(servers_hostports_str);
-  gpr_free(actual_connection_sequence);
   gpr_free(rdata.call_details);
+  request_sequences_destroy(&sequences);
 
   grpc_channel_destroy(client); /* calls the LB's shutdown func */
   teardown_servers(f);
@@ -684,29 +653,43 @@ static void print_failed_expectations(const int *expected_connection_sequence,
 
 static void verify_vanilla_round_robin(const servers_fixture *f,
                                        grpc_channel *client,
-                                       const int *actual_connection_sequence,
+                                       const request_sequences *sequences,
                                        const size_t num_iters) {
-  int *expected_connection_sequence;
-  size_t i;
   const size_t expected_seq_length = f->num_servers;
 
   /* verify conn. seq. expectation */
   /* get the first sequence of "num_servers" elements */
-  expected_connection_sequence = gpr_malloc(sizeof(int) * expected_seq_length);
-  memcpy(expected_connection_sequence, actual_connection_sequence,
+  int *expected_connection_sequence =
+      gpr_malloc(sizeof(int) * expected_seq_length);
+  memcpy(expected_connection_sequence, sequences->connections,
          sizeof(int) * expected_seq_length);
 
-  for (i = 0; i < num_iters; i++) {
-    const int actual = actual_connection_sequence[i];
+  for (size_t i = 0; i < num_iters; i++) {
+    const int actual = sequences->connections[i];
     const int expected = expected_connection_sequence[i % expected_seq_length];
     if (actual != expected) {
-      print_failed_expectations(expected_connection_sequence,
-                                actual_connection_sequence, expected_seq_length,
-                                num_iters);
+      gpr_log(
+          GPR_ERROR,
+          "CONNECTION SEQUENCE FAILURE: expected %d, got %d at iteration #%d",
+          expected, actual, (int)i);
+      abort();
+    }
+  }
+
+  /* All servers are available, therefore all client subchannels are READY, even
+   * when we only need one for the client channel state to be READY */
+  for (size_t i = 0; i < sequences->n; i++) {
+    const grpc_connectivity_state actual = sequences->connectivity_states[i];
+    const grpc_connectivity_state expected = GRPC_CHANNEL_READY;
+    if (actual != expected) {
+      gpr_log(GPR_ERROR,
+              "CONNECTIVITY STATUS SEQUENCE FAILURE: expected '%s', got '%s' "
+              "at iteration #%d",
+              grpc_connectivity_state_name(expected),
+              grpc_connectivity_state_name(actual), (int)i);
       abort();
     }
   }
-  assert_channel_connectivity(client, 1, GRPC_CHANNEL_READY);
 
   gpr_free(expected_connection_sequence);
 }
@@ -715,7 +698,7 @@ static void verify_vanilla_round_robin(const servers_fixture *f,
  * given in "f") are killed */
 static void verify_vanishing_floor_round_robin(
     const servers_fixture *f, grpc_channel *client,
-    const int *actual_connection_sequence, const size_t num_iters) {
+    const request_sequences *sequences, const size_t num_iters) {
   int *expected_connection_sequence;
   const size_t expected_seq_length = 2;
   size_t i;
@@ -723,57 +706,83 @@ static void verify_vanishing_floor_round_robin(
   /* verify conn. seq. expectation */
   /* copy the first full sequence (without -1s) */
   expected_connection_sequence = gpr_malloc(sizeof(int) * expected_seq_length);
-  memcpy(expected_connection_sequence, actual_connection_sequence + 2,
+  memcpy(expected_connection_sequence, sequences->connections + 2,
          expected_seq_length * sizeof(int));
 
   /* first two elements of the sequence should be [0 (1st server), -1 (failure)]
    */
-  GPR_ASSERT(actual_connection_sequence[0] == 0);
-  GPR_ASSERT(actual_connection_sequence[1] == -1);
+  GPR_ASSERT(sequences->connections[0] == 0);
+  GPR_ASSERT(sequences->connections[1] == -1);
 
   /* the next two element must be [3, 0], repeating from that point: the 3 is
    * brought forth by servers 1 and 2 disappearing after the intial pick of 0 */
-  GPR_ASSERT(actual_connection_sequence[2] == 3);
-  GPR_ASSERT(actual_connection_sequence[3] == 0);
+  GPR_ASSERT(sequences->connections[2] == 3);
+  GPR_ASSERT(sequences->connections[3] == 0);
 
   /* make sure that the expectation obliges */
   for (i = 2; i < num_iters; i++) {
-    const int actual = actual_connection_sequence[i];
+    const int actual = sequences->connections[i];
     const int expected = expected_connection_sequence[i % expected_seq_length];
     if (actual != expected) {
       print_failed_expectations(expected_connection_sequence,
-                                actual_connection_sequence, expected_seq_length,
+                                sequences->connections, expected_seq_length,
                                 num_iters);
       abort();
     }
   }
+
+  /* There's always at least one subchannel READY (connected), therefore the
+   * overall state of the client channel is READY at all times. */
+  for (i = 0; i < sequences->n; i++) {
+    const grpc_connectivity_state actual = sequences->connectivity_states[i];
+    const grpc_connectivity_state expected = GRPC_CHANNEL_READY;
+    if (actual != expected) {
+      gpr_log(GPR_ERROR,
+              "CONNECTIVITY STATUS SEQUENCE FAILURE: expected '%s', got '%s' "
+              "at iteration #%d",
+              grpc_connectivity_state_name(expected),
+              grpc_connectivity_state_name(actual), (int)i);
+      abort();
+    }
+  }
+
   gpr_free(expected_connection_sequence);
 }
 
-static void verify_total_carnage_round_robin(
-    const servers_fixture *f, grpc_channel *client,
-    const int *actual_connection_sequence, const size_t num_iters) {
-  size_t i;
-
-  for (i = 0; i < num_iters; i++) {
-    const int actual = actual_connection_sequence[i];
+static void verify_total_carnage_round_robin(const servers_fixture *f,
+                                             grpc_channel *client,
+                                             const request_sequences *sequences,
+                                             const size_t num_iters) {
+  for (size_t i = 0; i < num_iters; i++) {
+    const int actual = sequences->connections[i];
     const int expected = -1;
     if (actual != expected) {
-      gpr_log(GPR_ERROR, "FAILURE: expected %d, actual %d at iter %" PRIuPTR,
-              expected, actual, i);
+      gpr_log(
+          GPR_ERROR,
+          "CONNECTION SEQUENCE FAILURE: expected %d, got %d at iteration #%d",
+          expected, actual, (int)i);
       abort();
     }
   }
 
-  /* even though we know all the servers are dead, the client is still trying
-   * retrying, believing it's in a transient failure situation */
-  assert_channel_connectivity(client, 2, GRPC_CHANNEL_TRANSIENT_FAILURE,
-                              GRPC_CHANNEL_CONNECTING);
+  /* no server is ever available. The persistent state is TRANSIENT_FAILURE */
+  for (size_t i = 0; i < sequences->n; i++) {
+    const grpc_connectivity_state actual = sequences->connectivity_states[i];
+    const grpc_connectivity_state expected = GRPC_CHANNEL_TRANSIENT_FAILURE;
+    if (actual != expected) {
+      gpr_log(GPR_ERROR,
+              "CONNECTIVITY STATUS SEQUENCE FAILURE: expected '%s', got '%s' "
+              "at iteration #%d",
+              grpc_connectivity_state_name(expected),
+              grpc_connectivity_state_name(actual), (int)i);
+      abort();
+    }
+  }
 }
 
 static void verify_partial_carnage_round_robin(
     const servers_fixture *f, grpc_channel *client,
-    const int *actual_connection_sequence, const size_t num_iters) {
+    const request_sequences *sequences, const size_t num_iters) {
   int *expected_connection_sequence;
   size_t i;
   const size_t expected_seq_length = f->num_servers;
@@ -781,15 +790,15 @@ static void verify_partial_carnage_round_robin(
   /* verify conn. seq. expectation */
   /* get the first sequence of "num_servers" elements */
   expected_connection_sequence = gpr_malloc(sizeof(int) * expected_seq_length);
-  memcpy(expected_connection_sequence, actual_connection_sequence,
+  memcpy(expected_connection_sequence, sequences->connections,
          sizeof(int) * expected_seq_length);
 
   for (i = 0; i < num_iters / 2; i++) {
-    const int actual = actual_connection_sequence[i];
+    const int actual = sequences->connections[i];
     const int expected = expected_connection_sequence[i % expected_seq_length];
     if (actual != expected) {
       print_failed_expectations(expected_connection_sequence,
-                                actual_connection_sequence, expected_seq_length,
+                                sequences->connections, expected_seq_length,
                                 num_iters);
       abort();
     }
@@ -797,13 +806,34 @@ static void verify_partial_carnage_round_robin(
 
   /* second half of the iterations go without response */
   for (; i < num_iters; i++) {
-    GPR_ASSERT(actual_connection_sequence[i] == -1);
+    GPR_ASSERT(sequences->connections[i] == -1);
+  }
+
+  /* We can assert that the first client channel state should be READY, when all
+   * servers were available; and that the last one should be TRANSIENT_FAILURE,
+   * after all servers are gone. */
+  grpc_connectivity_state actual = sequences->connectivity_states[0];
+  grpc_connectivity_state expected = GRPC_CHANNEL_READY;
+  if (actual != expected) {
+    gpr_log(GPR_ERROR,
+            "CONNECTIVITY STATUS SEQUENCE FAILURE: expected '%s', got '%s' "
+            "at iteration #%d",
+            grpc_connectivity_state_name(expected),
+            grpc_connectivity_state_name(actual), 0);
+    abort();
+  }
+
+  actual = sequences->connectivity_states[num_iters - 1];
+  expected = GRPC_CHANNEL_TRANSIENT_FAILURE;
+  if (actual != expected) {
+    gpr_log(GPR_ERROR,
+            "CONNECTIVITY STATUS SEQUENCE FAILURE: expected '%s', got '%s' "
+            "at iteration #%d",
+            grpc_connectivity_state_name(expected),
+            grpc_connectivity_state_name(actual), (int)num_iters - 1);
+    abort();
   }
 
-  /* even though we know all the servers are dead, the client is still trying
-   * retrying, believing it's in a transient failure situation */
-  assert_channel_connectivity(client, 2, GRPC_CHANNEL_TRANSIENT_FAILURE,
-                              GRPC_CHANNEL_CONNECTING);
   gpr_free(expected_connection_sequence);
 }
 
@@ -826,15 +856,14 @@ static void dump_array(const char *desc, const int *data, const size_t count) {
 
 static void verify_rebirth_round_robin(const servers_fixture *f,
                                        grpc_channel *client,
-                                       const int *actual_connection_sequence,
+                                       const request_sequences *sequences,
                                        const size_t num_iters) {
   int *expected_connection_sequence;
   size_t i, j, unique_seq_last_idx, unique_seq_first_idx;
   const size_t expected_seq_length = f->num_servers;
   int *seen_elements;
 
-  dump_array("actual_connection_sequence", actual_connection_sequence,
-             num_iters);
+  dump_array("actual_connection_sequence", sequences->connections, num_iters);
 
   /* verify conn. seq. expectation */
   /* get the first unique run of length "num_servers". */
@@ -845,13 +874,13 @@ static void verify_rebirth_round_robin(const servers_fixture *f,
 
   memset(seen_elements, 0, sizeof(int) * expected_seq_length);
   for (i = 0; i < num_iters; i++) {
-    if (actual_connection_sequence[i] < 0 ||
-        seen_elements[actual_connection_sequence[i]] != 0) {
+    if (sequences->connections[i] < 0 ||
+        seen_elements[sequences->connections[i]] != 0) {
       /* if anything breaks the uniqueness of the run, back to square zero */
       memset(seen_elements, 0, sizeof(int) * expected_seq_length);
       continue;
     }
-    seen_elements[actual_connection_sequence[i]] = 1;
+    seen_elements[sequences->connections[i]] = 1;
     for (j = 0; j < expected_seq_length; j++) {
       if (seen_elements[j] == 0) break;
     }
@@ -870,30 +899,72 @@ static void verify_rebirth_round_robin(const servers_fixture *f,
 
   unique_seq_first_idx = (unique_seq_last_idx - expected_seq_length + 1);
   memcpy(expected_connection_sequence,
-         actual_connection_sequence + unique_seq_first_idx,
+         sequences->connections + unique_seq_first_idx,
          sizeof(int) * expected_seq_length);
 
   /* first iteration succeeds */
-  GPR_ASSERT(actual_connection_sequence[0] != -1);
+  GPR_ASSERT(sequences->connections[0] != -1);
   /* then we fail for a while... */
-  GPR_ASSERT(actual_connection_sequence[1] == -1);
+  GPR_ASSERT(sequences->connections[1] == -1);
   /* ... but should be up at "unique_seq_first_idx" */
-  GPR_ASSERT(actual_connection_sequence[unique_seq_first_idx] != -1);
+  GPR_ASSERT(sequences->connections[unique_seq_first_idx] != -1);
 
   for (j = 0, i = unique_seq_first_idx; i < num_iters; i++) {
-    const int actual = actual_connection_sequence[i];
+    const int actual = sequences->connections[i];
     const int expected =
         expected_connection_sequence[j++ % expected_seq_length];
     if (actual != expected) {
       print_failed_expectations(expected_connection_sequence,
-                                actual_connection_sequence, expected_seq_length,
+                                sequences->connections, expected_seq_length,
                                 num_iters);
       abort();
     }
   }
 
-  /* things are fine once the servers are brought back up */
-  assert_channel_connectivity(client, 1, GRPC_CHANNEL_READY);
+  /* We can assert that the first client channel state should be READY, when all
+   * servers were available; same thing for the last one. In the middle
+   * somewhere there must exist at least one TRANSIENT_FAILURE */
+  grpc_connectivity_state actual = sequences->connectivity_states[0];
+  grpc_connectivity_state expected = GRPC_CHANNEL_READY;
+  if (actual != expected) {
+    gpr_log(GPR_ERROR,
+            "CONNECTIVITY STATUS SEQUENCE FAILURE: expected '%s', got '%s' "
+            "at iteration #%d",
+            grpc_connectivity_state_name(expected),
+            grpc_connectivity_state_name(actual), 0);
+    abort();
+  }
+
+  actual = sequences->connectivity_states[num_iters - 1];
+  expected = GRPC_CHANNEL_READY;
+  if (actual != expected) {
+    gpr_log(GPR_ERROR,
+            "CONNECTIVITY STATUS SEQUENCE FAILURE: expected '%s', got '%s' "
+            "at iteration #%d",
+            grpc_connectivity_state_name(expected),
+            grpc_connectivity_state_name(actual), (int)num_iters - 1);
+    abort();
+  }
+
+  bool found_failure_status = false;
+  for (i = 1; i < sequences->n - 1; i++) {
+    if (sequences->connectivity_states[i] == GRPC_CHANNEL_TRANSIENT_FAILURE) {
+      found_failure_status = true;
+      break;
+    }
+  }
+  if (!found_failure_status) {
+    gpr_log(
+        GPR_ERROR,
+        "CONNECTIVITY STATUS SEQUENCE FAILURE: "
+        "GRPC_CHANNEL_TRANSIENT_FAILURE status not found. Got the following "
+        "instead:");
+    for (i = 0; i < num_iters; i++) {
+      gpr_log(GPR_ERROR, "[%d]: %s", (int)i,
+              grpc_connectivity_state_name(sequences->connectivity_states[i]));
+    }
+  }
+
   gpr_free(expected_connection_sequence);
   gpr_free(seen_elements);
 }
@@ -934,7 +1005,7 @@ int main(int argc, char **argv) {
    * This should knock down the server bound to be selected next */
   test_spec_reset(spec);
   spec->verifier = verify_vanishing_floor_round_robin;
-  spec->description = "test_kill_all_server_at_2nd_iteration";
+  spec->description = "test_kill_middle_servers_at_2nd_iteration";
   for (i = 1; i < NUM_SERVERS - 1; i++) {
     spec->kill_at[1][i] = 1;
   }