Begin optionalizing lb policies: initial code movement

2 files changed, 588 insertions, 0 deletions

diff --git a/src/core/ext/lb_policy/round_robin/round_robin.c b/src/core/ext/lb_policy/round_robin/round_robin.c
new file mode 100644
index 0000000000..31056ea138
--- /dev/null
+++ b/src/core/ext/lb_policy/round_robin/round_robin.c
@@ -0,0 +1,542 @@
+/*
+ *
+ * Copyright 2015-2016, 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/ext/lb_policy/round_robin/round_robin.h"
+
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include "src/core/lib/transport/connectivity_state.h"
+
+typedef struct round_robin_lb_policy round_robin_lb_policy;
+
+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_connected_subchannel **target;
+  grpc_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 {
+  /** index within policy->subchannels */
+  size_t index;
+  /** backpointer to owning policy */
+  round_robin_lb_policy *policy;
+  /** subchannel itself */
+  grpc_subchannel *subchannel;
+  /** notification that connectivity has changed on subchannel */
+  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;
+} subchannel_data;
+
+struct round_robin_lb_policy {
+  /** base policy: must be first */
+  grpc_lb_policy base;
+
+  /** all our subchannels */
+  size_t num_subchannels;
+  subchannel_data **subchannels;
+
+  /** mutex protecting remaining members */
+  gpr_mu mu;
+  /** have we started picking? */
+  int started_picking;
+  /** are we shutting down? */
+  int shutdown;
+  /** 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;
+};
+
+/** 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 *sc) {
+  ready_list *new_elem = gpr_malloc(sizeof(ready_list));
+  new_elem->subchannel = sc;
+  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, sc);
+  }
+  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_exec_ctx *exec_ctx, 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++) {
+    subchannel_data *sd = p->subchannels[i];
+    GRPC_SUBCHANNEL_UNREF(exec_ctx, sd->subchannel, "round_robin");
+    gpr_free(sd);
+  }
+
+  grpc_connectivity_state_destroy(exec_ctx, &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);
+}
+
+void rr_shutdown(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
+  round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
+  pending_pick *pp;
+  size_t i;
+
+  gpr_mu_lock(&p->mu);
+
+  p->shutdown = 1;
+  while ((pp = p->pending_picks)) {
+    p->pending_picks = pp->next;
+    *pp->target = NULL;
+    grpc_exec_ctx_enqueue(exec_ctx, pp->on_complete, false, NULL);
+    gpr_free(pp);
+  }
+  grpc_connectivity_state_set(exec_ctx, &p->state_tracker,
+                              GRPC_CHANNEL_FATAL_FAILURE, "shutdown");
+  for (i = 0; i < p->num_subchannels; i++) {
+    subchannel_data *sd = p->subchannels[i];
+    grpc_subchannel_notify_on_state_change(exec_ctx, sd->subchannel, NULL, NULL,
+                                           &sd->connectivity_changed_closure);
+  }
+  gpr_mu_unlock(&p->mu);
+}
+
+static void rr_cancel_pick(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
+                           grpc_connected_subchannel **target) {
+  round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
+  pending_pick *pp;
+  gpr_mu_lock(&p->mu);
+  pp = p->pending_picks;
+  p->pending_picks = NULL;
+  while (pp != NULL) {
+    pending_pick *next = pp->next;
+    if (pp->target == target) {
+      grpc_pollset_set_del_pollset(exec_ctx, p->base.interested_parties,
+                                   pp->pollset);
+      *target = NULL;
+      grpc_exec_ctx_enqueue(exec_ctx, pp->on_complete, false, NULL);
+      gpr_free(pp);
+    } else {
+      pp->next = p->pending_picks;
+      p->pending_picks = pp;
+    }
+    pp = next;
+  }
+  gpr_mu_unlock(&p->mu);
+}
+
+static void start_picking(grpc_exec_ctx *exec_ctx, round_robin_lb_policy *p) {
+  size_t i;
+  p->started_picking = 1;
+
+  gpr_log(GPR_DEBUG, "LB_POLICY: p=%p num_subchannels=%d", p,
+          p->num_subchannels);
+
+  for (i = 0; i < p->num_subchannels; i++) {
+    subchannel_data *sd = p->subchannels[i];
+    sd->connectivity_state = GRPC_CHANNEL_IDLE;
+    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");
+  }
+}
+
+void rr_exit_idle(grpc_exec_ctx *exec_ctx, 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(exec_ctx, p);
+  }
+  gpr_mu_unlock(&p->mu);
+}
+
+int rr_pick(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol, grpc_pollset *pollset,
+            grpc_metadata_batch *initial_metadata,
+            grpc_connected_subchannel **target, grpc_closure *on_complete) {
+  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 = grpc_subchannel_get_connected_subchannel(selected->subchannel);
+    if (grpc_lb_round_robin_trace) {
+      gpr_log(GPR_DEBUG,
+              "[RR PICK] TARGET <-- CONNECTED SUBCHANNEL %p (NODE %p)",
+              selected->subchannel, selected);
+    }
+    /* only advance the last picked pointer if the selection was used */
+    advance_last_picked_locked(p);
+    return 1;
+  } else {
+    if (!p->started_picking) {
+      start_picking(exec_ctx, p);
+    }
+    grpc_pollset_set_add_pollset(exec_ctx, p->base.interested_parties, 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);
+    return 0;
+  }
+}
+
+static void rr_connectivity_changed(grpc_exec_ctx *exec_ctx, void *arg,
+                                    bool iomgr_success) {
+  subchannel_data *sd = arg;
+  round_robin_lb_policy *p = sd->policy;
+  pending_pick *pp;
+  ready_list *selected;
+
+  int unref = 0;
+
+  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, "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->subchannel);
+        /* 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 =
+              grpc_subchannel_get_connected_subchannel(selected->subchannel);
+          if (grpc_lb_round_robin_trace) {
+            gpr_log(GPR_DEBUG,
+                    "[RR CONN CHANGED] TARGET <-- SUBCHANNEL %p (NODE %p)",
+                    selected->subchannel, selected);
+          }
+          grpc_pollset_set_del_pollset(exec_ctx, p->base.interested_parties,
+                                       pp->pollset);
+          grpc_exec_ctx_enqueue(exec_ctx, pp->on_complete, true, 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,
+                                    "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,
+                                    "connecting_transient_failure");
+        break;
+      case GRPC_CHANNEL_FATAL_FAILURE:
+        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_FATAL_FAILURE,
+                                      "no_more_channels");
+          while ((pp = p->pending_picks)) {
+            p->pending_picks = pp->next;
+            *pp->target = NULL;
+            grpc_exec_ctx_enqueue(exec_ctx, pp->on_complete, true, NULL);
+            gpr_free(pp);
+          }
+        } else {
+          grpc_connectivity_state_set(exec_ctx, &p->state_tracker,
+                                      GRPC_CHANNEL_TRANSIENT_FAILURE,
+                                      "subchannel_failed");
+        }
+    } /* switch */
+  }   /* !unref */
+
+  gpr_mu_unlock(&p->mu);
+
+  if (unref) {
+    GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &p->base, "round_robin_connectivity");
+  }
+}
+
+static grpc_connectivity_state rr_check_connectivity(grpc_exec_ctx *exec_ctx,
+                                                     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_exec_ctx *exec_ctx,
+                                      grpc_lb_policy *pol,
+                                      grpc_connectivity_state *current,
+                                      grpc_closure *notify) {
+  round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
+  gpr_mu_lock(&p->mu);
+  grpc_connectivity_state_notify_on_state_change(exec_ctx, &p->state_tracker,
+                                                 current, notify);
+  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, false, NULL);
+  }
+}
+
+static const grpc_lb_policy_vtable round_robin_lb_policy_vtable = {
+    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) {}
+
+static void round_robin_factory_unref(grpc_lb_policy_factory *factory) {}
+
+static grpc_lb_policy *create_round_robin(grpc_lb_policy_factory *factory,
+                                          grpc_lb_policy_args *args) {
+  size_t i;
+  round_robin_lb_policy *p = gpr_malloc(sizeof(*p));
+  GPR_ASSERT(args->num_subchannels > 0);
+  memset(p, 0, sizeof(*p));
+  grpc_lb_policy_init(&p->base, &round_robin_lb_policy_vtable);
+  p->num_subchannels = args->num_subchannels;
+  p->subchannels = gpr_malloc(sizeof(*p->subchannels) * p->num_subchannels);
+  memset(p->subchannels, 0, sizeof(*p->subchannels) * p->num_subchannels);
+  grpc_connectivity_state_init(&p->state_tracker, GRPC_CHANNEL_IDLE,
+                               "round_robin");
+
+  gpr_mu_init(&p->mu);
+  for (i = 0; i < args->num_subchannels; i++) {
+    subchannel_data *sd = gpr_malloc(sizeof(*sd));
+    memset(sd, 0, sizeof(*sd));
+    p->subchannels[i] = sd;
+    sd->policy = p;
+    sd->index = i;
+    sd->subchannel = args->subchannels[i];
+    grpc_closure_init(&sd->connectivity_changed_closure,
+                      rr_connectivity_changed, sd);
+  }
+
+  /* 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;
+
+  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/ext/lb_policy/round_robin/round_robin.h b/src/core/ext/lb_policy/round_robin/round_robin.h
new file mode 100644
index 0000000000..52db1caa0c
--- /dev/null
+++ b/src/core/ext/lb_policy/round_robin/round_robin.h
@@ -0,0 +1,46 @@
+/*
+ *
+ * Copyright 2015-2016, 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_CORE_LIB_CLIENT_CONFIG_LB_POLICIES_ROUND_ROBIN_H
+#define GRPC_CORE_LIB_CLIENT_CONFIG_LB_POLICIES_ROUND_ROBIN_H
+
+#include "src/core/lib/client_config/lb_policy.h"
+
+extern int grpc_lb_round_robin_trace;
+
+#include "src/core/lib/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 /* GRPC_CORE_LIB_CLIENT_CONFIG_LB_POLICIES_ROUND_ROBIN_H */