Added round robin LB policy.

4 files changed, 580 insertions, 1 deletions

diff --git a/src/core/client_config/lb_policies/round_robin.c b/src/core/client_config/lb_policies/round_robin.c
new file mode 100644
index 0000000000..8ab496229c
--- /dev/null
+++ b/src/core/client_config/lb_policies/round_robin.c
@@ -0,0 +1,530 @@
+/*
+ *
+ * Copyright 2015, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/client_config/lb_policies/round_robin.h"
+
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include "src/core/transport/connectivity_state.h"
+
+int grpc_lb_round_robin_trace = 0;
+
+/** List of entities waiting for a pick.
+ *
+ * Once a pick is available, \a target is updated and \a on_complete called. */
+typedef struct pending_pick {
+  struct pending_pick *next;
+  grpc_pollset *pollset;
+  grpc_subchannel **target;
+  grpc_iomgr_closure *on_complete;
+} pending_pick;
+
+/** List of subchannels in a connectivity READY state */
+typedef struct ready_list {
+  grpc_subchannel *subchannel;
+  struct ready_list *next;
+  struct ready_list *prev;
+} ready_list;
+
+typedef struct {
+  size_t subchannel_idx; /**< Index over p->subchannels */
+  void *p; /**< round_robin_lb_policy instance */
+} connectivity_changed_cb_arg;
+
+typedef struct {
+  /** base policy: must be first */
+  grpc_lb_policy base;
+
+  /** all our subchannels */
+  grpc_subchannel **subchannels;
+  size_t num_subchannels;
+
+  /** Callbacks, one per subchannel being watched, to be called when their
+   * respective connectivity changes */
+  grpc_iomgr_closure *connectivity_changed_cbs;
+  connectivity_changed_cb_arg *cb_args;
+
+  /** mutex protecting remaining members */
+  gpr_mu mu;
+  /** have we started picking? */
+  int started_picking;
+  /** are we shutting down? */
+  int shutdown;
+  /** Connectivity state of the subchannels being watched */
+  grpc_connectivity_state *subchannel_connectivity;
+  /** List of picks that are waiting on connectivity */
+  pending_pick *pending_picks;
+
+  /** our connectivity state tracker */
+  grpc_connectivity_state_tracker state_tracker;
+
+  /** (Dummy) root of the doubly linked list containing READY subchannels */
+  ready_list ready_list;
+  /** Last pick from the ready list. */
+  ready_list *ready_list_last_pick;
+
+  /** Subchannel index to ready_list node.
+   *
+   * Kept in order to remove nodes from the ready list associated with a
+   * subchannel */
+  ready_list **subchannel_index_to_readylist_node;
+} round_robin_lb_policy;
+
+/** Returns the next subchannel from the connected list or NULL if the list is
+ * empty.
+ *
+ * Note that this function does *not* advance p->ready_list_last_pick. Use \a
+ * advance_last_picked_locked() for that. */
+static ready_list *peek_next_connected_locked(const round_robin_lb_policy *p) {
+  ready_list *selected;
+  selected = p->ready_list_last_pick->next;
+
+  while (selected != NULL) {
+    if (selected == &p->ready_list) {
+      GPR_ASSERT(selected->subchannel == NULL);
+      /* skip dummy root */
+      selected = selected->next;
+    } else {
+      GPR_ASSERT(selected->subchannel != NULL);
+      return selected;
+    }
+  }
+  return NULL;
+}
+
+/** Advance the \a ready_list picking head. */
+static void advance_last_picked_locked(round_robin_lb_policy *p) {
+  if (p->ready_list_last_pick->next != NULL) { /* non-empty list */
+    p->ready_list_last_pick = p->ready_list_last_pick->next;
+    if (p->ready_list_last_pick == &p->ready_list) {
+      /* skip dummy root */
+      p->ready_list_last_pick = p->ready_list_last_pick->next;
+    }
+  } else { /* should be an empty list */
+    GPR_ASSERT(p->ready_list_last_pick == &p->ready_list);
+  }
+
+  if (grpc_lb_round_robin_trace) {
+    gpr_log(GPR_DEBUG, "[READYLIST] ADVANCED LAST PICK. NOW AT NODE %p (SC %p)",
+            p->ready_list_last_pick, p->ready_list_last_pick->subchannel);
+  }
+}
+
+/** Prepends (relative to the root at p->ready_list) the connected subchannel \a
+ * csc to the list of ready subchannels. */
+static ready_list *add_connected_sc_locked(round_robin_lb_policy *p,
+                                           grpc_subchannel *csc) {
+  ready_list *new_elem = gpr_malloc(sizeof(ready_list));
+  new_elem->subchannel = csc;
+  if (p->ready_list.prev == NULL) {
+    /* first element */
+    new_elem->next = &p->ready_list;
+    new_elem->prev = &p->ready_list;
+    p->ready_list.next = new_elem;
+    p->ready_list.prev = new_elem;
+  } else {
+    new_elem->next = &p->ready_list;
+    new_elem->prev = p->ready_list.prev;
+    p->ready_list.prev->next = new_elem;
+    p->ready_list.prev = new_elem;
+  }
+  if (grpc_lb_round_robin_trace) {
+    gpr_log(GPR_DEBUG,
+            "[READYLIST] ADDING NODE %p (SC %p)", new_elem, csc);
+  }
+  return new_elem;
+}
+
+/** Removes \a node from the list of connected subchannels */
+static void remove_disconnected_sc_locked(round_robin_lb_policy *p,
+                                          ready_list *node) {
+  if (node == NULL) {
+    return;
+  }
+  if (node == p->ready_list_last_pick) {
+    /* If removing the lastly picked node, reset the last pick pointer to the
+     * dummy root of the list */
+    p->ready_list_last_pick = &p->ready_list;
+  }
+
+  /* removing last item */
+  if (node->next == &p->ready_list && node->prev == &p->ready_list) {
+    GPR_ASSERT(p->ready_list.next == node);
+    GPR_ASSERT(p->ready_list.prev == node);
+    p->ready_list.next = NULL;
+    p->ready_list.prev = NULL;
+  } else {
+    node->prev->next = node->next;
+    node->next->prev = node->prev;
+  }
+
+  if (grpc_lb_round_robin_trace) {
+    gpr_log(GPR_DEBUG, "[READYLIST] REMOVED NODE %p (SC %p)", node,
+            node->subchannel);
+  }
+
+  node->next = NULL;
+  node->prev = NULL;
+  node->subchannel = NULL;
+
+  gpr_free(node);
+}
+
+void rr_destroy(grpc_lb_policy *pol) {
+  round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
+  size_t i;
+  ready_list *elem;
+  for (i = 0; i < p->num_subchannels; i++) {
+    GRPC_SUBCHANNEL_UNREF(p->subchannels[i], "round_robin");
+  }
+  gpr_free(p->connectivity_changed_cbs);
+  gpr_free(p->subchannel_connectivity);
+
+  grpc_connectivity_state_destroy(&p->state_tracker);
+  gpr_free(p->subchannels);
+  gpr_mu_destroy(&p->mu);
+
+  elem = p->ready_list.next;
+  while (elem != NULL && elem != &p->ready_list) {
+    ready_list *tmp;
+    tmp = elem->next;
+    elem->next = NULL;
+    elem->prev = NULL;
+    elem->subchannel = NULL;
+    gpr_free(elem);
+    elem = tmp;
+  }
+  gpr_free(p->subchannel_index_to_readylist_node);
+  gpr_free(p->cb_args);
+  gpr_free(p);
+}
+
+void rr_shutdown(grpc_lb_policy *pol) {
+  round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
+  pending_pick *pp;
+  gpr_mu_lock(&p->mu);
+
+  p->shutdown = 1;
+  while ((pp = p->pending_picks)) {
+    p->pending_picks = pp->next;
+    *pp->target = NULL;
+    grpc_iomgr_add_delayed_callback(pp->on_complete, 0);
+    gpr_free(pp);
+  }
+  grpc_connectivity_state_set(&p->state_tracker, GRPC_CHANNEL_FATAL_FAILURE,
+                              "shutdown");
+  gpr_mu_unlock(&p->mu);
+}
+
+static void start_picking(round_robin_lb_policy *p) {
+  size_t i;
+  p->started_picking = 1;
+
+  for (i = 0; i < p->num_subchannels; i++) {
+    p->subchannel_connectivity[i] = GRPC_CHANNEL_IDLE;
+    grpc_subchannel_notify_on_state_change(p->subchannels[i],
+                                           &p->subchannel_connectivity[i],
+                                           &p->connectivity_changed_cbs[i]);
+    GRPC_LB_POLICY_REF(&p->base, "round_robin_connectivity");
+  }
+}
+
+void rr_exit_idle(grpc_lb_policy *pol) {
+  round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
+  gpr_mu_lock(&p->mu);
+  if (!p->started_picking) {
+    start_picking(p);
+  }
+  gpr_mu_unlock(&p->mu);
+}
+
+void rr_pick(grpc_lb_policy *pol, grpc_pollset *pollset,
+             grpc_metadata_batch *initial_metadata, grpc_subchannel **target,
+             grpc_iomgr_closure *on_complete) {
+  size_t i;
+  round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
+  pending_pick *pp;
+  ready_list *selected;
+  gpr_mu_lock(&p->mu);
+  if ((selected = peek_next_connected_locked(p))) {
+    gpr_mu_unlock(&p->mu);
+    *target = selected->subchannel;
+    if (grpc_lb_round_robin_trace) {
+      gpr_log(GPR_DEBUG, "[RR PICK] TARGET <-- SUBCHANNEL %p (NODE %p)",
+              selected->subchannel, selected);
+    }
+    /* only advance the last picked pointer if the selection was used */
+    advance_last_picked_locked(p);
+    on_complete->cb(on_complete->cb_arg, 1);
+  } else {
+    if (!p->started_picking) {
+      start_picking(p);
+    }
+    for (i = 0; i < p->num_subchannels; i++) {
+      grpc_subchannel_add_interested_party(p->subchannels[i], pollset);
+    }
+    pp = gpr_malloc(sizeof(*pp));
+    pp->next = p->pending_picks;
+    pp->pollset = pollset;
+    pp->target = target;
+    pp->on_complete = on_complete;
+    p->pending_picks = pp;
+    gpr_mu_unlock(&p->mu);
+  }
+}
+
+static void rr_connectivity_changed(void *arg, int iomgr_success) {
+  connectivity_changed_cb_arg *cb_arg = arg;
+  round_robin_lb_policy *p = cb_arg->p;
+  /* index over p->subchannels of this cb's subchannel */
+  const size_t this_idx = cb_arg->subchannel_idx;
+  pending_pick *pp;
+  ready_list *selected;
+
+  int unref = 0;
+
+  /* connectivity state of this cb's subchannel */
+  grpc_connectivity_state *this_connectivity;
+
+  gpr_mu_lock(&p->mu);
+
+  this_connectivity =
+      &p->subchannel_connectivity[this_idx];
+
+  if (p->shutdown) {
+    unref = 1;
+  } else {
+    switch (*this_connectivity) {
+      case GRPC_CHANNEL_READY:
+        grpc_connectivity_state_set(&p->state_tracker, GRPC_CHANNEL_READY,
+                                    "connecting_ready");
+        /* add the newly connected subchannel to the list of connected ones.
+         * Note that it goes to the "end of the line". */
+        p->subchannel_index_to_readylist_node[this_idx] =
+            add_connected_sc_locked(p, p->subchannels[this_idx]);
+        /* 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. */
+        selected = peek_next_connected_locked(p);
+        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 = selected->subchannel;
+          if (grpc_lb_round_robin_trace) {
+            gpr_log(GPR_DEBUG,
+                    "[RR CONN CHANGED] TARGET <-- SUBCHANNEL %p (NODE %p)",
+                    selected->subchannel, selected);
+          }
+          grpc_subchannel_del_interested_party(selected->subchannel, pp->pollset);
+          grpc_iomgr_add_delayed_callback(pp->on_complete, 1);
+          gpr_free(pp);
+        }
+        grpc_subchannel_notify_on_state_change(
+            p->subchannels[this_idx], this_connectivity,
+            &p->connectivity_changed_cbs[this_idx]);
+        break;
+      case GRPC_CHANNEL_CONNECTING:
+      case GRPC_CHANNEL_IDLE:
+        grpc_connectivity_state_set(&p->state_tracker, *this_connectivity,
+                                    "connecting_changed");
+        grpc_subchannel_notify_on_state_change(
+            p->subchannels[this_idx], this_connectivity,
+            &p->connectivity_changed_cbs[this_idx]);
+        break;
+      case GRPC_CHANNEL_TRANSIENT_FAILURE:
+        grpc_connectivity_state_set(&p->state_tracker,
+                                    GRPC_CHANNEL_TRANSIENT_FAILURE,
+                                    "connecting_transient_failure");
+
+        /* renew state notification */
+        grpc_subchannel_notify_on_state_change(
+            p->subchannels[this_idx], this_connectivity,
+            &p->connectivity_changed_cbs[this_idx]);
+
+        /* remove for ready list if still present */
+        if (p->subchannel_index_to_readylist_node[this_idx] != NULL) {
+          remove_disconnected_sc_locked(p, p->subchannel_index_to_readylist_node[this_idx]);
+          p->subchannel_index_to_readylist_node[this_idx] = NULL;
+        }
+        break;
+      case GRPC_CHANNEL_FATAL_FAILURE:
+        if (p->subchannel_index_to_readylist_node[this_idx] != NULL) {
+          remove_disconnected_sc_locked(p, p->subchannel_index_to_readylist_node[this_idx]);
+          p->subchannel_index_to_readylist_node[this_idx] = NULL;
+        }
+
+        GPR_SWAP(grpc_subchannel *, p->subchannels[this_idx],
+                 p->subchannels[p->num_subchannels - 1]);
+        p->num_subchannels--;
+        GRPC_SUBCHANNEL_UNREF(p->subchannels[p->num_subchannels],
+                              "round_robin");
+
+        if (p->num_subchannels == 0) {
+          grpc_connectivity_state_set(&p->state_tracker,
+                                      GRPC_CHANNEL_FATAL_FAILURE,
+                                      "no_more_channels");
+          while ((pp = p->pending_picks)) {
+            p->pending_picks = pp->next;
+            *pp->target = NULL;
+            grpc_iomgr_add_delayed_callback(pp->on_complete, 1);
+            gpr_free(pp);
+          }
+          unref = 1;
+        } else {
+          grpc_connectivity_state_set(&p->state_tracker,
+                                      GRPC_CHANNEL_TRANSIENT_FAILURE,
+                                      "subchannel_failed");
+        }
+    }  /* switch */
+  }  /* !unref */
+
+  gpr_mu_unlock(&p->mu);
+
+  if (unref) {
+    GRPC_LB_POLICY_UNREF(&p->base, "round_robin_connectivity");
+  }
+}
+
+static void rr_broadcast(grpc_lb_policy *pol, grpc_transport_op *op) {
+  round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
+  size_t i;
+  size_t n;
+  grpc_subchannel **subchannels;
+
+  gpr_mu_lock(&p->mu);
+  n = p->num_subchannels;
+  subchannels = gpr_malloc(n * sizeof(*subchannels));
+  for (i = 0; i < n; i++) {
+    subchannels[i] = p->subchannels[i];
+    GRPC_SUBCHANNEL_REF(subchannels[i], "rr_broadcast");
+  }
+  gpr_mu_unlock(&p->mu);
+
+  for (i = 0; i < n; i++) {
+    grpc_subchannel_process_transport_op(subchannels[i], op);
+    GRPC_SUBCHANNEL_UNREF(subchannels[i], "rr_broadcast");
+  }
+  gpr_free(subchannels);
+}
+
+static grpc_connectivity_state rr_check_connectivity(grpc_lb_policy *pol) {
+  round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
+  grpc_connectivity_state st;
+  gpr_mu_lock(&p->mu);
+  st = grpc_connectivity_state_check(&p->state_tracker);
+  gpr_mu_unlock(&p->mu);
+  return st;
+}
+
+static void rr_notify_on_state_change(grpc_lb_policy *pol,
+                                      grpc_connectivity_state *current,
+                                      grpc_iomgr_closure *notify) {
+  round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
+  gpr_mu_lock(&p->mu);
+  grpc_connectivity_state_notify_on_state_change(&p->state_tracker, current,
+                                                 notify);
+  gpr_mu_unlock(&p->mu);
+}
+
+static const grpc_lb_policy_vtable round_robin_lb_policy_vtable = {
+    rr_destroy,
+    rr_shutdown,
+    rr_pick,
+    rr_exit_idle,
+    rr_broadcast,
+    rr_check_connectivity,
+    rr_notify_on_state_change};
+
+
+static void round_robin_factory_ref(grpc_lb_policy_factory *factory) {}
+
+static void round_robin_factory_unref(grpc_lb_policy_factory *factory) {}
+
+static grpc_lb_policy *create_round_robin(grpc_lb_policy_factory *factory,
+                                         grpc_subchannel **subchannels,
+                                         size_t num_subchannels) {
+  size_t i;
+  round_robin_lb_policy *p = gpr_malloc(sizeof(*p));
+  GPR_ASSERT(num_subchannels);
+  memset(p, 0, sizeof(*p));
+  grpc_lb_policy_init(&p->base, &round_robin_lb_policy_vtable);
+  p->subchannels = gpr_malloc(sizeof(grpc_subchannel *) * num_subchannels);
+  p->num_subchannels = num_subchannels;
+  grpc_connectivity_state_init(&p->state_tracker, GRPC_CHANNEL_IDLE,
+                               "round_robin");
+  memcpy(p->subchannels, subchannels,
+         sizeof(grpc_subchannel *) * num_subchannels);
+
+  gpr_mu_init(&p->mu);
+  p->connectivity_changed_cbs =
+      gpr_malloc(sizeof(grpc_iomgr_closure) * num_subchannels);
+  p->subchannel_connectivity =
+      gpr_malloc(sizeof(grpc_connectivity_state) * num_subchannels);
+
+  p->cb_args =
+      gpr_malloc(sizeof(connectivity_changed_cb_arg) * num_subchannels);
+  for(i = 0; i < num_subchannels; i++) {
+    p->cb_args[i].subchannel_idx = i;
+    p->cb_args[i].p = p;
+    grpc_iomgr_closure_init(&p->connectivity_changed_cbs[i],
+                            rr_connectivity_changed, &p->cb_args[i]);
+  }
+
+  /* The (dummy node) root of the ready list */
+  p->ready_list.subchannel = NULL;
+  p->ready_list.prev = NULL;
+  p->ready_list.next = NULL;
+  p->ready_list_last_pick = &p->ready_list;
+
+  p->subchannel_index_to_readylist_node =
+      gpr_malloc(sizeof(grpc_subchannel *) * num_subchannels);
+  memset(p->subchannel_index_to_readylist_node, 0,
+         sizeof(grpc_subchannel *) * num_subchannels);
+  return &p->base;
+}
+
+static const grpc_lb_policy_factory_vtable round_robin_factory_vtable = {
+    round_robin_factory_ref, round_robin_factory_unref, create_round_robin,
+    "round_robin"};
+
+static grpc_lb_policy_factory round_robin_lb_policy_factory = {
+    &round_robin_factory_vtable};
+
+grpc_lb_policy_factory *grpc_round_robin_lb_factory_create() {
+  return &round_robin_lb_policy_factory;
+}
diff --git a/src/core/client_config/lb_policies/round_robin.h b/src/core/client_config/lb_policies/round_robin.h
new file mode 100644
index 0000000000..2c81b9ef17
--- /dev/null
+++ b/src/core/client_config/lb_policies/round_robin.h
@@ -0,0 +1,47 @@
+/*
+ *
+ * Copyright 2015, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_INTERNAL_CORE_CLIENT_CONFIG_ROUND_ROBIN_H
+#define GRPC_INTERNAL_CORE_CLIENT_CONFIG_ROUND_ROBIN_H
+
+#include "src/core/client_config/lb_policy.h"
+
+extern int grpc_lb_round_robin_trace;
+
+#include "src/core/client_config/lb_policy_factory.h"
+
+/** Returns a load balancing factory for the round robin policy */
+grpc_lb_policy_factory *grpc_round_robin_lb_factory_create();
+
+
+#endif
diff --git a/src/core/client_config/resolvers/sockaddr_resolver.c b/src/core/client_config/resolvers/sockaddr_resolver.c
index 1bff1d7abf..111c237a0d 100644
--- a/src/core/client_config/resolvers/sockaddr_resolver.c
+++ b/src/core/client_config/resolvers/sockaddr_resolver.c
@@ -337,7 +337,7 @@ static void sockaddr_factory_unref(grpc_resolver_factory *factory) {}
   static grpc_resolver *name##_factory_create_resolver(                     \
       grpc_resolver_factory *factory, grpc_uri *uri,                        \
       grpc_subchannel_factory *subchannel_factory) {                        \
-    return sockaddr_create(uri, "pick_first",                               \
+    return sockaddr_create(uri, "round_robin",                               \
                            subchannel_factory, parse_##name);               \
   }                                                                         \
   static const grpc_resolver_factory_vtable name##_factory_vtable = {       \
diff --git a/src/core/surface/init.c b/src/core/surface/init.c
index 03bd026a42..93c27c77bf 100644
--- a/src/core/surface/init.c
+++ b/src/core/surface/init.c
@@ -42,6 +42,7 @@
 #include "src/core/channel/channel_stack.h"
 #include "src/core/client_config/lb_policy_registry.h"
 #include "src/core/client_config/lb_policies/pick_first.h"
+#include "src/core/client_config/lb_policies/round_robin.h"
 #include "src/core/client_config/resolver_registry.h"
 #include "src/core/client_config/resolvers/dns_resolver.h"
 #include "src/core/client_config/resolvers/sockaddr_resolver.h"
@@ -89,6 +90,7 @@ void grpc_init(void) {
     gpr_time_init();
     grpc_lb_policy_registry_init(grpc_pick_first_lb_factory_create());
     grpc_register_lb_policy(grpc_pick_first_lb_factory_create());
+    grpc_register_lb_policy(grpc_round_robin_lb_factory_create());
     grpc_resolver_registry_init("dns:///");
     grpc_register_resolver_type(grpc_dns_resolver_factory_create());
     grpc_register_resolver_type(grpc_ipv4_resolver_factory_create());