Esempio n. 1
0
static int cc_pick_subchannel(grpc_exec_ctx *exec_ctx, void *elemp,
                              grpc_metadata_batch *initial_metadata,
                              uint32_t initial_metadata_flags,
                              grpc_connected_subchannel **connected_subchannel,
                              grpc_closure *on_ready) {
  grpc_call_element *elem = elemp;
  channel_data *chand = elem->channel_data;
  call_data *calld = elem->call_data;
  continue_picking_args *cpa;
  grpc_closure *closure;

  GPR_ASSERT(connected_subchannel);

  gpr_mu_lock(&chand->mu_config);
  if (initial_metadata == NULL) {
    if (chand->lb_policy != NULL) {
      grpc_lb_policy_cancel_pick(exec_ctx, chand->lb_policy,
                                 connected_subchannel);
    }
    for (closure = chand->waiting_for_config_closures.head; closure != NULL;
         closure = grpc_closure_next(closure)) {
      cpa = closure->cb_arg;
      if (cpa->connected_subchannel == connected_subchannel) {
        cpa->connected_subchannel = NULL;
        grpc_exec_ctx_enqueue(exec_ctx, cpa->on_ready, false, NULL);
      }
    }
    gpr_mu_unlock(&chand->mu_config);
    return 1;
  }
  if (chand->lb_policy != NULL) {
    grpc_lb_policy *lb_policy = chand->lb_policy;
    int r;
    GRPC_LB_POLICY_REF(lb_policy, "cc_pick_subchannel");
    gpr_mu_unlock(&chand->mu_config);
    r = grpc_lb_policy_pick(exec_ctx, lb_policy, calld->pollset,
                            initial_metadata, initial_metadata_flags,
                            connected_subchannel, on_ready);
    GRPC_LB_POLICY_UNREF(exec_ctx, lb_policy, "cc_pick_subchannel");
    return r;
  }
  if (chand->resolver != NULL && !chand->started_resolving) {
    chand->started_resolving = 1;
    GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
    grpc_resolver_next(exec_ctx, chand->resolver,
                       &chand->incoming_configuration,
                       &chand->on_config_changed);
  }
  cpa = gpr_malloc(sizeof(*cpa));
  cpa->initial_metadata = initial_metadata;
  cpa->initial_metadata_flags = initial_metadata_flags;
  cpa->connected_subchannel = connected_subchannel;
  cpa->on_ready = on_ready;
  cpa->elem = elem;
  grpc_closure_init(&cpa->closure, continue_picking, cpa);
  grpc_closure_list_add(&chand->waiting_for_config_closures, &cpa->closure, 1);
  gpr_mu_unlock(&chand->mu_config);
  return 0;
}
Esempio n. 2
0
static void watch_lb_policy(grpc_exec_ctx *exec_ctx, channel_data *chand,
                            grpc_lb_policy *lb_policy,
                            grpc_connectivity_state current_state) {
  lb_policy_connectivity_watcher *w = gpr_malloc(sizeof(*w));
  GRPC_CHANNEL_STACK_REF(chand->owning_stack, "watch_lb_policy");

  w->chand = chand;
  grpc_closure_init(&w->on_changed, on_lb_policy_state_changed, w);
  w->state = current_state;
  w->lb_policy = lb_policy;
  grpc_lb_policy_notify_on_state_change(exec_ctx, lb_policy, &w->state,
                                        &w->on_changed);
}
Esempio n. 3
0
void grpc_client_channel_watch_connectivity_state(
    grpc_exec_ctx *exec_ctx, grpc_channel_element *elem, grpc_pollset *pollset,
    grpc_connectivity_state *state, grpc_closure *on_complete) {
  channel_data *chand = elem->channel_data;
  external_connectivity_watcher *w = gpr_malloc(sizeof(*w));
  w->chand = chand;
  w->pollset = pollset;
  w->on_complete = on_complete;
  grpc_pollset_set_add_pollset(exec_ctx, chand->interested_parties, pollset);
  grpc_closure_init(&w->my_closure, on_external_watch_complete, w);
  GRPC_CHANNEL_STACK_REF(w->chand->owning_stack,
                         "external_connectivity_watcher");
  gpr_mu_lock(&chand->mu);
  grpc_connectivity_state_notify_on_state_change(
      exec_ctx, &chand->state_tracker, state, &w->my_closure);
  gpr_mu_unlock(&chand->mu);
}
Esempio n. 4
0
void grpc_client_channel_set_resolver(grpc_exec_ctx *exec_ctx,
                                      grpc_channel_stack *channel_stack,
                                      grpc_resolver *resolver) {
  /* post construction initialization: set the transport setup pointer */
  grpc_channel_element *elem = grpc_channel_stack_last_element(channel_stack);
  channel_data *chand = elem->channel_data;
  gpr_mu_lock(&chand->mu);
  GPR_ASSERT(!chand->resolver);
  chand->resolver = resolver;
  GRPC_RESOLVER_REF(resolver, "channel");
  if (!grpc_closure_list_empty(chand->waiting_for_config_closures) ||
      chand->exit_idle_when_lb_policy_arrives) {
    chand->started_resolving = true;
    GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
    grpc_resolver_next(exec_ctx, resolver, &chand->resolver_result,
                       &chand->on_resolver_result_changed);
  }
  gpr_mu_unlock(&chand->mu);
}
Esempio n. 5
0
grpc_connectivity_state grpc_client_channel_check_connectivity_state(
    grpc_exec_ctx *exec_ctx, grpc_channel_element *elem, int try_to_connect) {
  channel_data *chand = elem->channel_data;
  grpc_connectivity_state out;
  gpr_mu_lock(&chand->mu);
  out = grpc_connectivity_state_check(&chand->state_tracker, NULL);
  if (out == GRPC_CHANNEL_IDLE && try_to_connect) {
    if (chand->lb_policy != NULL) {
      grpc_lb_policy_exit_idle(exec_ctx, chand->lb_policy);
    } else {
      chand->exit_idle_when_lb_policy_arrives = true;
      if (!chand->started_resolving && chand->resolver != NULL) {
        GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
        chand->started_resolving = true;
        grpc_resolver_next(exec_ctx, chand->resolver, &chand->resolver_result,
                           &chand->on_resolver_result_changed);
      }
    }
  }
  gpr_mu_unlock(&chand->mu);
  return out;
}
Esempio n. 6
0
static bool pick_subchannel(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
                            grpc_metadata_batch *initial_metadata,
                            uint32_t initial_metadata_flags,
                            grpc_connected_subchannel **connected_subchannel,
                            grpc_closure *on_ready, grpc_error *error) {
  GPR_TIMER_BEGIN("pick_subchannel", 0);

  channel_data *chand = elem->channel_data;
  call_data *calld = elem->call_data;
  continue_picking_args *cpa;
  grpc_closure *closure;

  GPR_ASSERT(connected_subchannel);

  gpr_mu_lock(&chand->mu);
  if (initial_metadata == NULL) {
    if (chand->lb_policy != NULL) {
      grpc_lb_policy_cancel_pick(exec_ctx, chand->lb_policy,
                                 connected_subchannel, GRPC_ERROR_REF(error));
    }
    for (closure = chand->waiting_for_config_closures.head; closure != NULL;
         closure = closure->next_data.next) {
      cpa = closure->cb_arg;
      if (cpa->connected_subchannel == connected_subchannel) {
        cpa->connected_subchannel = NULL;
        grpc_exec_ctx_sched(
            exec_ctx, cpa->on_ready,
            GRPC_ERROR_CREATE_REFERENCING("Pick cancelled", &error, 1), NULL);
      }
    }
    gpr_mu_unlock(&chand->mu);
    GPR_TIMER_END("pick_subchannel", 0);
    GRPC_ERROR_UNREF(error);
    return true;
  }
  GPR_ASSERT(error == GRPC_ERROR_NONE);
  if (chand->lb_policy != NULL) {
    grpc_lb_policy *lb_policy = chand->lb_policy;
    GRPC_LB_POLICY_REF(lb_policy, "pick_subchannel");
    gpr_mu_unlock(&chand->mu);
    // If the application explicitly set wait_for_ready, use that.
    // Otherwise, if the service config specified a value for this
    // method, use that.
    const bool wait_for_ready_set_from_api =
        initial_metadata_flags &
        GRPC_INITIAL_METADATA_WAIT_FOR_READY_EXPLICITLY_SET;
    const bool wait_for_ready_set_from_service_config =
        calld->wait_for_ready_from_service_config != WAIT_FOR_READY_UNSET;
    if (!wait_for_ready_set_from_api &&
        wait_for_ready_set_from_service_config) {
      if (calld->wait_for_ready_from_service_config == WAIT_FOR_READY_TRUE) {
        initial_metadata_flags |= GRPC_INITIAL_METADATA_WAIT_FOR_READY;
      } else {
        initial_metadata_flags &= ~GRPC_INITIAL_METADATA_WAIT_FOR_READY;
      }
    }
    // TODO(dgq): make this deadline configurable somehow.
    const grpc_lb_policy_pick_args inputs = {
        initial_metadata, initial_metadata_flags, &calld->lb_token_mdelem,
        gpr_inf_future(GPR_CLOCK_MONOTONIC)};
    const bool result = grpc_lb_policy_pick(
        exec_ctx, lb_policy, &inputs, connected_subchannel, NULL, on_ready);
    GRPC_LB_POLICY_UNREF(exec_ctx, lb_policy, "pick_subchannel");
    GPR_TIMER_END("pick_subchannel", 0);
    return result;
  }
  if (chand->resolver != NULL && !chand->started_resolving) {
    chand->started_resolving = true;
    GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
    grpc_resolver_next(exec_ctx, chand->resolver, &chand->resolver_result,
                       &chand->on_resolver_result_changed);
  }
  if (chand->resolver != NULL) {
    cpa = gpr_malloc(sizeof(*cpa));
    cpa->initial_metadata = initial_metadata;
    cpa->initial_metadata_flags = initial_metadata_flags;
    cpa->connected_subchannel = connected_subchannel;
    cpa->on_ready = on_ready;
    cpa->elem = elem;
    grpc_closure_init(&cpa->closure, continue_picking, cpa);
    grpc_closure_list_append(&chand->waiting_for_config_closures, &cpa->closure,
                             GRPC_ERROR_NONE);
  } else {
    grpc_exec_ctx_sched(exec_ctx, on_ready, GRPC_ERROR_CREATE("Disconnected"),
                        NULL);
  }
  gpr_mu_unlock(&chand->mu);

  GPR_TIMER_END("pick_subchannel", 0);
  return false;
}
Esempio n. 7
0
static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
                                       grpc_error *error) {
  channel_data *chand = arg;
  grpc_lb_policy *lb_policy = NULL;
  grpc_lb_policy *old_lb_policy;
  grpc_mdstr_hash_table *method_params_table = NULL;
  grpc_connectivity_state state = GRPC_CHANNEL_TRANSIENT_FAILURE;
  bool exit_idle = false;
  grpc_error *state_error = GRPC_ERROR_CREATE("No load balancing policy");

  if (chand->resolver_result != NULL) {
    grpc_lb_policy_args lb_policy_args;
    lb_policy_args.args = chand->resolver_result;
    lb_policy_args.client_channel_factory = chand->client_channel_factory;

    // Find LB policy name.
    const char *lb_policy_name = NULL;
    const grpc_arg *channel_arg =
        grpc_channel_args_find(lb_policy_args.args, GRPC_ARG_LB_POLICY_NAME);
    if (channel_arg != NULL) {
      GPR_ASSERT(channel_arg->type == GRPC_ARG_STRING);
      lb_policy_name = channel_arg->value.string;
    }
    // Special case: If all of the addresses are balancer addresses,
    // assume that we should use the grpclb policy, regardless of what the
    // resolver actually specified.
    channel_arg =
        grpc_channel_args_find(lb_policy_args.args, GRPC_ARG_LB_ADDRESSES);
    if (channel_arg != NULL) {
      GPR_ASSERT(channel_arg->type == GRPC_ARG_POINTER);
      grpc_lb_addresses *addresses = channel_arg->value.pointer.p;
      bool found_backend_address = false;
      for (size_t i = 0; i < addresses->num_addresses; ++i) {
        if (!addresses->addresses[i].is_balancer) {
          found_backend_address = true;
          break;
        }
      }
      if (!found_backend_address) {
        if (lb_policy_name != NULL && strcmp(lb_policy_name, "grpclb") != 0) {
          gpr_log(GPR_INFO,
                  "resolver requested LB policy %s but provided only balancer "
                  "addresses, no backend addresses -- forcing use of grpclb LB "
                  "policy",
                  lb_policy_name);
        }
        lb_policy_name = "grpclb";
      }
    }
    // Use pick_first if nothing was specified and we didn't select grpclb
    // above.
    if (lb_policy_name == NULL) lb_policy_name = "pick_first";

    lb_policy =
        grpc_lb_policy_create(exec_ctx, lb_policy_name, &lb_policy_args);
    if (lb_policy != NULL) {
      GRPC_LB_POLICY_REF(lb_policy, "config_change");
      GRPC_ERROR_UNREF(state_error);
      state =
          grpc_lb_policy_check_connectivity(exec_ctx, lb_policy, &state_error);
    }
    channel_arg =
        grpc_channel_args_find(lb_policy_args.args, GRPC_ARG_SERVICE_CONFIG);
    if (channel_arg != NULL) {
      GPR_ASSERT(channel_arg->type == GRPC_ARG_POINTER);
      method_params_table = grpc_method_config_table_convert(
          (grpc_method_config_table *)channel_arg->value.pointer.p,
          method_config_convert_value, &method_parameters_vtable);
    }
    grpc_channel_args_destroy(chand->resolver_result);
    chand->resolver_result = NULL;
  }

  if (lb_policy != NULL) {
    grpc_pollset_set_add_pollset_set(exec_ctx, lb_policy->interested_parties,
                                     chand->interested_parties);
  }

  gpr_mu_lock(&chand->mu);
  old_lb_policy = chand->lb_policy;
  chand->lb_policy = lb_policy;
  if (chand->method_params_table != NULL) {
    grpc_mdstr_hash_table_unref(chand->method_params_table);
  }
  chand->method_params_table = method_params_table;
  if (lb_policy != NULL) {
    grpc_exec_ctx_enqueue_list(exec_ctx, &chand->waiting_for_config_closures,
                               NULL);
  } else if (chand->resolver == NULL /* disconnected */) {
    grpc_closure_list_fail_all(
        &chand->waiting_for_config_closures,
        GRPC_ERROR_CREATE_REFERENCING("Channel disconnected", &error, 1));
    grpc_exec_ctx_enqueue_list(exec_ctx, &chand->waiting_for_config_closures,
                               NULL);
  }
  if (lb_policy != NULL && chand->exit_idle_when_lb_policy_arrives) {
    GRPC_LB_POLICY_REF(lb_policy, "exit_idle");
    exit_idle = true;
    chand->exit_idle_when_lb_policy_arrives = false;
  }

  if (error == GRPC_ERROR_NONE && chand->resolver) {
    set_channel_connectivity_state_locked(
        exec_ctx, chand, state, GRPC_ERROR_REF(state_error), "new_lb+resolver");
    if (lb_policy != NULL) {
      watch_lb_policy(exec_ctx, chand, lb_policy, state);
    }
    GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
    grpc_resolver_next(exec_ctx, chand->resolver, &chand->resolver_result,
                       &chand->on_resolver_result_changed);
    gpr_mu_unlock(&chand->mu);
  } else {
    if (chand->resolver != NULL) {
      grpc_resolver_shutdown(exec_ctx, chand->resolver);
      GRPC_RESOLVER_UNREF(exec_ctx, chand->resolver, "channel");
      chand->resolver = NULL;
    }
    grpc_error *refs[] = {error, state_error};
    set_channel_connectivity_state_locked(
        exec_ctx, chand, GRPC_CHANNEL_SHUTDOWN,
        GRPC_ERROR_CREATE_REFERENCING("Got config after disconnection", refs,
                                      GPR_ARRAY_SIZE(refs)),
        "resolver_gone");
    gpr_mu_unlock(&chand->mu);
  }

  if (exit_idle) {
    grpc_lb_policy_exit_idle(exec_ctx, lb_policy);
    GRPC_LB_POLICY_UNREF(exec_ctx, lb_policy, "exit_idle");
  }

  if (old_lb_policy != NULL) {
    grpc_pollset_set_del_pollset_set(
        exec_ctx, old_lb_policy->interested_parties, chand->interested_parties);
    GRPC_LB_POLICY_UNREF(exec_ctx, old_lb_policy, "channel");
  }

  if (lb_policy != NULL) {
    GRPC_LB_POLICY_UNREF(exec_ctx, lb_policy, "config_change");
  }

  GRPC_CHANNEL_STACK_UNREF(exec_ctx, chand->owning_stack, "resolver");
  GRPC_ERROR_UNREF(state_error);
}
Esempio n. 8
0
static bool pick_subchannel(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
                            grpc_metadata_batch *initial_metadata,
                            uint32_t initial_metadata_flags,
                            grpc_connected_subchannel **connected_subchannel,
                            grpc_closure *on_ready) {
  GPR_TIMER_BEGIN("pick_subchannel", 0);

  channel_data *chand = elem->channel_data;
  call_data *calld = elem->call_data;
  continue_picking_args *cpa;
  grpc_closure *closure;

  GPR_ASSERT(connected_subchannel);

  gpr_mu_lock(&chand->mu);
  if (initial_metadata == NULL) {
    if (chand->lb_policy != NULL) {
      grpc_lb_policy_cancel_pick(exec_ctx, chand->lb_policy,
                                 connected_subchannel);
    }
    for (closure = chand->waiting_for_config_closures.head; closure != NULL;
         closure = closure->next_data.next) {
      cpa = closure->cb_arg;
      if (cpa->connected_subchannel == connected_subchannel) {
        cpa->connected_subchannel = NULL;
        grpc_exec_ctx_sched(exec_ctx, cpa->on_ready,
                            GRPC_ERROR_CREATE("Pick cancelled"), NULL);
      }
    }
    gpr_mu_unlock(&chand->mu);
    GPR_TIMER_END("pick_subchannel", 0);
    return true;
  }
  if (chand->lb_policy != NULL) {
    grpc_lb_policy *lb_policy = chand->lb_policy;
    int r;
    GRPC_LB_POLICY_REF(lb_policy, "pick_subchannel");
    gpr_mu_unlock(&chand->mu);
    const grpc_lb_policy_pick_args inputs = {calld->pollent, initial_metadata,
                                             initial_metadata_flags,
                                             &calld->lb_token_mdelem};
    r = grpc_lb_policy_pick(exec_ctx, lb_policy, &inputs, connected_subchannel,
                            NULL, on_ready);
    GRPC_LB_POLICY_UNREF(exec_ctx, lb_policy, "pick_subchannel");
    GPR_TIMER_END("pick_subchannel", 0);
    return r;
  }
  if (chand->resolver != NULL && !chand->started_resolving) {
    chand->started_resolving = true;
    GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
    grpc_resolver_next(exec_ctx, chand->resolver, &chand->resolver_result,
                       &chand->on_resolver_result_changed);
  }
  if (chand->resolver != NULL) {
    cpa = gpr_malloc(sizeof(*cpa));
    cpa->initial_metadata = initial_metadata;
    cpa->initial_metadata_flags = initial_metadata_flags;
    cpa->connected_subchannel = connected_subchannel;
    cpa->on_ready = on_ready;
    cpa->elem = elem;
    grpc_closure_init(&cpa->closure, continue_picking, cpa);
    grpc_closure_list_append(&chand->waiting_for_config_closures, &cpa->closure,
                             GRPC_ERROR_NONE);
  } else {
    grpc_exec_ctx_sched(exec_ctx, on_ready, GRPC_ERROR_CREATE("Disconnected"),
                        NULL);
  }
  gpr_mu_unlock(&chand->mu);

  GPR_TIMER_END("pick_subchannel", 0);
  return false;
}
Esempio n. 9
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static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
                                       grpc_error *error) {
  channel_data *chand = arg;
  grpc_lb_policy *lb_policy = NULL;
  grpc_lb_policy *old_lb_policy;
  grpc_connectivity_state state = GRPC_CHANNEL_TRANSIENT_FAILURE;
  bool exit_idle = false;
  grpc_error *state_error = GRPC_ERROR_CREATE("No load balancing policy");

  if (chand->resolver_result != NULL) {
    lb_policy = grpc_resolver_result_get_lb_policy(chand->resolver_result);
    if (lb_policy != NULL) {
      GRPC_LB_POLICY_REF(lb_policy, "channel");
      GRPC_LB_POLICY_REF(lb_policy, "config_change");
      GRPC_ERROR_UNREF(state_error);
      state =
          grpc_lb_policy_check_connectivity(exec_ctx, lb_policy, &state_error);
    }

    grpc_resolver_result_unref(exec_ctx, chand->resolver_result);
  }

  chand->resolver_result = NULL;

  if (lb_policy != NULL) {
    grpc_pollset_set_add_pollset_set(exec_ctx, lb_policy->interested_parties,
                                     chand->interested_parties);
  }

  gpr_mu_lock(&chand->mu);
  old_lb_policy = chand->lb_policy;
  chand->lb_policy = lb_policy;
  if (lb_policy != NULL) {
    grpc_exec_ctx_enqueue_list(exec_ctx, &chand->waiting_for_config_closures,
                               NULL);
  } else if (chand->resolver == NULL /* disconnected */) {
    grpc_closure_list_fail_all(
        &chand->waiting_for_config_closures,
        GRPC_ERROR_CREATE_REFERENCING("Channel disconnected", &error, 1));
    grpc_exec_ctx_enqueue_list(exec_ctx, &chand->waiting_for_config_closures,
                               NULL);
  }
  if (lb_policy != NULL && chand->exit_idle_when_lb_policy_arrives) {
    GRPC_LB_POLICY_REF(lb_policy, "exit_idle");
    exit_idle = true;
    chand->exit_idle_when_lb_policy_arrives = false;
  }

  if (error == GRPC_ERROR_NONE && chand->resolver) {
    set_channel_connectivity_state_locked(
        exec_ctx, chand, state, GRPC_ERROR_REF(state_error), "new_lb+resolver");
    if (lb_policy != NULL) {
      watch_lb_policy(exec_ctx, chand, lb_policy, state);
    }
    GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
    grpc_resolver_next(exec_ctx, chand->resolver, &chand->resolver_result,
                       &chand->on_resolver_result_changed);
    gpr_mu_unlock(&chand->mu);
  } else {
    if (chand->resolver != NULL) {
      grpc_resolver_shutdown(exec_ctx, chand->resolver);
      GRPC_RESOLVER_UNREF(exec_ctx, chand->resolver, "channel");
      chand->resolver = NULL;
    }
    grpc_error *refs[] = {error, state_error};
    set_channel_connectivity_state_locked(
        exec_ctx, chand, GRPC_CHANNEL_SHUTDOWN,
        GRPC_ERROR_CREATE_REFERENCING("Got config after disconnection", refs,
                                      GPR_ARRAY_SIZE(refs)),
        "resolver_gone");
    gpr_mu_unlock(&chand->mu);
  }

  if (exit_idle) {
    grpc_lb_policy_exit_idle(exec_ctx, lb_policy);
    GRPC_LB_POLICY_UNREF(exec_ctx, lb_policy, "exit_idle");
  }

  if (old_lb_policy != NULL) {
    grpc_pollset_set_del_pollset_set(
        exec_ctx, old_lb_policy->interested_parties, chand->interested_parties);
    GRPC_LB_POLICY_UNREF(exec_ctx, old_lb_policy, "channel");
  }

  if (lb_policy != NULL) {
    GRPC_LB_POLICY_UNREF(exec_ctx, lb_policy, "config_change");
  }

  GRPC_CHANNEL_STACK_UNREF(exec_ctx, chand->owning_stack, "resolver");
  GRPC_ERROR_UNREF(state_error);
}
Esempio n. 10
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static void cc_on_config_changed(grpc_exec_ctx *exec_ctx, void *arg,
                                 bool iomgr_success) {
  channel_data *chand = arg;
  grpc_lb_policy *lb_policy = NULL;
  grpc_lb_policy *old_lb_policy;
  grpc_connectivity_state state = GRPC_CHANNEL_TRANSIENT_FAILURE;
  int exit_idle = 0;

  if (chand->incoming_configuration != NULL) {
    lb_policy = grpc_client_config_get_lb_policy(chand->incoming_configuration);
    if (lb_policy != NULL) {
      GRPC_LB_POLICY_REF(lb_policy, "channel");
      GRPC_LB_POLICY_REF(lb_policy, "config_change");
      state = grpc_lb_policy_check_connectivity(exec_ctx, lb_policy);
    }

    grpc_client_config_unref(exec_ctx, chand->incoming_configuration);
  }

  chand->incoming_configuration = NULL;

  if (lb_policy != NULL) {
    grpc_pollset_set_add_pollset_set(exec_ctx, lb_policy->interested_parties,
                                     chand->interested_parties);
  }

  gpr_mu_lock(&chand->mu_config);
  old_lb_policy = chand->lb_policy;
  chand->lb_policy = lb_policy;
  if (lb_policy != NULL || chand->resolver == NULL /* disconnected */) {
    grpc_exec_ctx_enqueue_list(exec_ctx, &chand->waiting_for_config_closures,
                               NULL);
  }
  if (lb_policy != NULL && chand->exit_idle_when_lb_policy_arrives) {
    GRPC_LB_POLICY_REF(lb_policy, "exit_idle");
    exit_idle = 1;
    chand->exit_idle_when_lb_policy_arrives = 0;
  }

  if (iomgr_success && chand->resolver) {
    set_channel_connectivity_state_locked(exec_ctx, chand, state,
                                          "new_lb+resolver");
    if (lb_policy != NULL) {
      watch_lb_policy(exec_ctx, chand, lb_policy, state);
    }
    GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
    grpc_resolver_next(exec_ctx, chand->resolver,
                       &chand->incoming_configuration,
                       &chand->on_config_changed);
    gpr_mu_unlock(&chand->mu_config);
  } else {
    if (chand->resolver != NULL) {
      grpc_resolver_shutdown(exec_ctx, chand->resolver);
      GRPC_RESOLVER_UNREF(exec_ctx, chand->resolver, "channel");
      chand->resolver = NULL;
    }
    set_channel_connectivity_state_locked(
        exec_ctx, chand, GRPC_CHANNEL_FATAL_FAILURE, "resolver_gone");
    gpr_mu_unlock(&chand->mu_config);
  }

  if (exit_idle) {
    grpc_lb_policy_exit_idle(exec_ctx, lb_policy);
    GRPC_LB_POLICY_UNREF(exec_ctx, lb_policy, "exit_idle");
  }

  if (old_lb_policy != NULL) {
    grpc_pollset_set_del_pollset_set(
        exec_ctx, old_lb_policy->interested_parties, chand->interested_parties);
    GRPC_LB_POLICY_UNREF(exec_ctx, old_lb_policy, "channel");
  }

  if (lb_policy != NULL) {
    GRPC_LB_POLICY_UNREF(exec_ctx, lb_policy, "config_change");
  }

  GRPC_CHANNEL_STACK_UNREF(exec_ctx, chand->owning_stack, "resolver");
}