6 files changed, 55 insertions, 2 deletions
diff --git a/src/core/client_config/lb_policies/pick_first.c b/src/core/client_config/lb_policies/pick_first.c
index b91f0609d2..37de3e9f68 100644
--- a/src/core/client_config/lb_policies/pick_first.c
+++ b/src/core/client_config/lb_policies/pick_first.c
@@ -348,8 +348,20 @@ void pf_notify_on_state_change(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
   gpr_mu_unlock(&p->mu);
 }
 
+void pf_ping_one(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
+                 grpc_closure *closure) {
+  pick_first_lb_policy *p = (pick_first_lb_policy *)pol;
+  gpr_mu_lock(&p->mu);
+  if (p->selected) {
+    grpc_connected_subchannel_ping(exec_ctx, p->selected, closure);
+  } else {
+    grpc_exec_ctx_enqueue(exec_ctx, closure, 0);
+  }
+  gpr_mu_unlock(&p->mu);
+}
+
 static const grpc_lb_policy_vtable pick_first_lb_policy_vtable = {
-    pf_destroy, pf_shutdown, pf_pick, pf_cancel_pick, pf_exit_idle,
+    pf_destroy, pf_shutdown, pf_pick, pf_cancel_pick, pf_ping_one, pf_exit_idle,
     pf_check_connectivity, pf_notify_on_state_change};
 
 static void pick_first_factory_ref(grpc_lb_policy_factory *factory) {}
diff --git a/src/core/client_config/lb_policies/round_robin.c b/src/core/client_config/lb_policies/round_robin.c
index b86dba20ee..d487456363 100644
--- a/src/core/client_config/lb_policies/round_robin.c
+++ b/src/core/client_config/lb_policies/round_robin.c
@@ -467,8 +467,24 @@ static void rr_notify_on_state_change(grpc_exec_ctx *exec_ctx,
   gpr_mu_unlock(&p->mu);
 }
 
+static void rr_ping_one(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
+                        grpc_closure *closure) {
+  round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
+  ready_list *selected;
+  grpc_connected_subchannel *target;
+  gpr_mu_lock(&p->mu);
+  if ((selected = peek_next_connected_locked(p))) {
+    gpr_mu_unlock(&p->mu);
+    target = grpc_subchannel_get_connected_subchannel(selected->subchannel);
+    grpc_connected_subchannel_ping(exec_ctx, target, closure);
+  } else {
+    gpr_mu_unlock(&p->mu);
+    grpc_exec_ctx_enqueue(exec_ctx, closure, 0);
+  }
+}
+
 static const grpc_lb_policy_vtable round_robin_lb_policy_vtable = {
-    rr_destroy, rr_shutdown, rr_pick, rr_cancel_pick, rr_exit_idle,
+    rr_destroy, rr_shutdown, rr_pick, rr_cancel_pick, rr_ping_one, rr_exit_idle,
     rr_check_connectivity, rr_notify_on_state_change};
 
 static void round_robin_factory_ref(grpc_lb_policy_factory *factory) {}
diff --git a/src/core/client_config/lb_policy.c b/src/core/client_config/lb_policy.c
index d254161546..d4672f6b25 100644
--- a/src/core/client_config/lb_policy.c
+++ b/src/core/client_config/lb_policy.c
@@ -116,6 +116,11 @@ void grpc_lb_policy_exit_idle(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy) {
   policy->vtable->exit_idle(exec_ctx, policy);
 }
 
+void grpc_lb_policy_ping_one(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
+                             grpc_closure *closure) {
+  policy->vtable->ping_one(exec_ctx, policy, closure);
+}
+
 void grpc_lb_policy_notify_on_state_change(grpc_exec_ctx *exec_ctx,
                                            grpc_lb_policy *policy,
                                            grpc_connectivity_state *state,
diff --git a/src/core/client_config/lb_policy.h b/src/core/client_config/lb_policy.h
index 2f8d655558..db5238c8ca 100644
--- a/src/core/client_config/lb_policy.h
+++ b/src/core/client_config/lb_policy.h
@@ -63,6 +63,9 @@ struct grpc_lb_policy_vtable {
   void (*cancel_pick)(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
                       grpc_connected_subchannel **target);
 
+  void (*ping_one)(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
+                   grpc_closure *closure);
+
   /** try to enter a READY connectivity state */
   void (*exit_idle)(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy);
 
@@ -121,6 +124,9 @@ int grpc_lb_policy_pick(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
                         grpc_connected_subchannel **target,
                         grpc_closure *on_complete);
 
+void grpc_lb_policy_ping_one(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
+                             grpc_closure *closure);
+
 void grpc_lb_policy_cancel_pick(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
                                 grpc_connected_subchannel **target);
 
diff --git a/src/core/client_config/subchannel.c b/src/core/client_config/subchannel.c
index 6631e9bae2..afb1cdbd6d 100644
--- a/src/core/client_config/subchannel.c
+++ b/src/core/client_config/subchannel.c
@@ -461,6 +461,17 @@ void grpc_connected_subchannel_notify_on_state_change(
                                 closure);
 }
 
+void grpc_connected_subchannel_ping(grpc_exec_ctx *exec_ctx,
+                                    grpc_connected_subchannel *con,
+                                    grpc_closure *closure) {
+  grpc_transport_op op;
+  grpc_channel_element *elem;
+  memset(&op, 0, sizeof(op));
+  op.send_ping = closure;
+  elem = grpc_channel_stack_element(CHANNEL_STACK_FROM_CONNECTION(con), 0);
+  elem->filter->start_transport_op(exec_ctx, elem, &op);
+}
+
 static void publish_transport(grpc_exec_ctx *exec_ctx, grpc_subchannel *c) {
   size_t channel_stack_size;
   grpc_connected_subchannel *con;
diff --git a/src/core/client_config/subchannel.h b/src/core/client_config/subchannel.h
index 74ebcecfba..57c7c9dc67 100644
--- a/src/core/client_config/subchannel.h
+++ b/src/core/client_config/subchannel.h
@@ -124,6 +124,9 @@ void grpc_connected_subchannel_notify_on_state_change(
     grpc_exec_ctx *exec_ctx, grpc_connected_subchannel *channel,
     grpc_pollset_set *interested_parties, grpc_connectivity_state *state,
     grpc_closure *notify);
+void grpc_connected_subchannel_ping(grpc_exec_ctx *exec_ctx,
+                                    grpc_connected_subchannel *channel,
+                                    grpc_closure *notify);
 
 /** retrieve the grpc_connected_subchannel - or NULL if called before
     the subchannel becomes connected */