Initial checkin of gRPC to third_party/

third_party/grpc/src/core/client_config/subchannel.c

+/*
+ *
+ * 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/client_config/subchannel.h"
+
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/avl.h>
+
+#include "src/core/channel/channel_args.h"
+#include "src/core/channel/client_channel.h"
+#include "src/core/channel/connected_channel.h"
+#include "src/core/client_config/initial_connect_string.h"
+#include "src/core/client_config/subchannel_index.h"
+#include "src/core/iomgr/timer.h"
+#include "src/core/profiling/timers.h"
+#include "src/core/surface/channel.h"
+#include "src/core/transport/connectivity_state.h"
+
+#define INTERNAL_REF_BITS 16
+#define STRONG_REF_MASK (~(gpr_atm)((1 << INTERNAL_REF_BITS) - 1))
+
+#define GRPC_SUBCHANNEL_MIN_CONNECT_TIMEOUT_SECONDS 20
+#define GRPC_SUBCHANNEL_INITIAL_CONNECT_BACKOFF_SECONDS 1
+#define GRPC_SUBCHANNEL_RECONNECT_BACKOFF_MULTIPLIER 1.6
+#define GRPC_SUBCHANNEL_RECONNECT_MAX_BACKOFF_SECONDS 120
+#define GRPC_SUBCHANNEL_RECONNECT_JITTER 0.2
+
+#define GET_CONNECTED_SUBCHANNEL(subchannel, barrier)      \
+  ((grpc_connected_subchannel *)(gpr_atm_##barrier##_load( \
+      &(subchannel)->connected_subchannel)))
+
+typedef struct {
+  grpc_closure closure;
+  grpc_subchannel *subchannel;
+  grpc_connectivity_state connectivity_state;
+} state_watcher;
+
+typedef struct external_state_watcher {
+  grpc_subchannel *subchannel;
+  grpc_pollset_set *pollset_set;
+  grpc_closure *notify;
+  grpc_closure closure;
+  struct external_state_watcher *next;
+  struct external_state_watcher *prev;
+} external_state_watcher;
+
+struct grpc_subchannel {
+  grpc_connector *connector;
+
+  /** refcount
+      - lower INTERNAL_REF_BITS bits are for internal references:
+        these do not keep the subchannel open.
+      - upper remaining bits are for public references: these do
+        keep the subchannel open */
+  gpr_atm ref_pair;
+
+  /** non-transport related channel filters */
+  const grpc_channel_filter **filters;
+  size_t num_filters;
+  /** channel arguments */
+  grpc_channel_args *args;
+  /** address to connect to */
+  struct sockaddr *addr;
+  size_t addr_len;
+
+  grpc_subchannel_key *key;
+
+  /** initial string to send to peer */
+  gpr_slice initial_connect_string;
+
+  /** set during connection */
+  grpc_connect_out_args connecting_result;
+
+  /** callback for connection finishing */
+  grpc_closure connected;
+
+  /** pollset_set tracking who's interested in a connection
+      being setup */
+  grpc_pollset_set *pollset_set;
+
+  /** active connection, or null; of type grpc_connected_subchannel */
+  gpr_atm connected_subchannel;
+
+  /** mutex protecting remaining elements */
+  gpr_mu mu;
+
+  /** have we seen a disconnection? */
+  int disconnected;
+  /** are we connecting */
+  int connecting;
+  /** connectivity state tracking */
+  grpc_connectivity_state_tracker state_tracker;
+
+  external_state_watcher root_external_state_watcher;
+
+  /** next connect attempt time */
+  gpr_timespec next_attempt;
+  /** amount to backoff each failure */
+  gpr_timespec backoff_delta;
+  /** do we have an active alarm? */
+  int have_alarm;
+  /** our alarm */
+  grpc_timer alarm;
+  /** current random value */
+  uint32_t random;
+};
+
+struct grpc_subchannel_call {
+  grpc_connected_subchannel *connection;
+};
+
+#define SUBCHANNEL_CALL_TO_CALL_STACK(call) ((grpc_call_stack *)((call) + 1))
+#define CHANNEL_STACK_FROM_CONNECTION(con) ((grpc_channel_stack *)(con))
+#define CALLSTACK_TO_SUBCHANNEL_CALL(callstack) \
+  (((grpc_subchannel_call *)(callstack)) - 1)
+
+static gpr_timespec compute_connect_deadline(grpc_subchannel *c);
+static void subchannel_connected(grpc_exec_ctx *exec_ctx, void *subchannel,
+                                 bool iomgr_success);
+
+#ifdef GRPC_STREAM_REFCOUNT_DEBUG
+#define REF_REASON reason
+#define REF_LOG(name, p)                                                  \
+  gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG, "%s: %p   ref %d -> %d %s", \
+          (name), (p), (p)->refs.count, (p)->refs.count + 1, reason)
+#define UNREF_LOG(name, p)                                                \
+  gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG, "%s: %p unref %d -> %d %s", \
+          (name), (p), (p)->refs.count, (p)->refs.count - 1, reason)
+#define REF_MUTATE_EXTRA_ARGS \
+  GRPC_SUBCHANNEL_REF_EXTRA_ARGS, const char *purpose
+#define REF_MUTATE_PURPOSE(x) , file, line, reason, x
+#else
+#define REF_REASON ""
+#define REF_LOG(name, p) \
+  do {                   \
+  } while (0)
+#define UNREF_LOG(name, p) \
+  do {                     \
+  } while (0)
+#define REF_MUTATE_EXTRA_ARGS
+#define REF_MUTATE_PURPOSE(x)
+#endif
+
+/*
+ * connection implementation
+ */
+
+static void connection_destroy(grpc_exec_ctx *exec_ctx, void *arg,
+                               bool success) {
+  grpc_connected_subchannel *c = arg;
+  grpc_channel_stack_destroy(exec_ctx, CHANNEL_STACK_FROM_CONNECTION(c));
+  gpr_free(c);
+}
+
+void grpc_connected_subchannel_ref(grpc_connected_subchannel *c
+                                       GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+  GRPC_CHANNEL_STACK_REF(CHANNEL_STACK_FROM_CONNECTION(c), REF_REASON);
+}
+
+void grpc_connected_subchannel_unref(grpc_exec_ctx *exec_ctx,
+                                     grpc_connected_subchannel *c
+                                         GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+  GRPC_CHANNEL_STACK_UNREF(exec_ctx, CHANNEL_STACK_FROM_CONNECTION(c),
+                           REF_REASON);
+}
+
+/*
+ * grpc_subchannel implementation
+ */
+
+static void subchannel_destroy(grpc_exec_ctx *exec_ctx, void *arg,
+                               bool success) {
+  grpc_subchannel *c = arg;
+  gpr_free((void *)c->filters);
+  grpc_channel_args_destroy(c->args);
+  gpr_free(c->addr);
+  gpr_slice_unref(c->initial_connect_string);
+  grpc_connectivity_state_destroy(exec_ctx, &c->state_tracker);
+  grpc_connector_unref(exec_ctx, c->connector);
+  grpc_pollset_set_destroy(c->pollset_set);
+  grpc_subchannel_key_destroy(exec_ctx, c->key);
+  gpr_free(c);
+}
+
+static gpr_atm ref_mutate(grpc_subchannel *c, gpr_atm delta,
+                          int barrier REF_MUTATE_EXTRA_ARGS) {
+  gpr_atm old_val = barrier ? gpr_atm_full_fetch_add(&c->ref_pair, delta)
+                            : gpr_atm_no_barrier_fetch_add(&c->ref_pair, delta);
+#ifdef GRPC_STREAM_REFCOUNT_DEBUG
+  gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG,
+          "SUBCHANNEL: %p % 12s 0x%08x -> 0x%08x [%s]", c, purpose, old_val,
+          old_val + delta, reason);
+#endif
+  return old_val;
+}
+
+grpc_subchannel *grpc_subchannel_ref(grpc_subchannel *c
+                                         GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+  gpr_atm old_refs;
+  old_refs = ref_mutate(c, (1 << INTERNAL_REF_BITS),
+                        0 REF_MUTATE_PURPOSE("STRONG_REF"));
+  GPR_ASSERT((old_refs & STRONG_REF_MASK) != 0);
+  return c;
+}
+
+grpc_subchannel *grpc_subchannel_weak_ref(grpc_subchannel *c
+                                              GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+  gpr_atm old_refs;
+  old_refs = ref_mutate(c, 1, 0 REF_MUTATE_PURPOSE("WEAK_REF"));
+  GPR_ASSERT(old_refs != 0);
+  return c;
+}
+
+grpc_subchannel *grpc_subchannel_ref_from_weak_ref(
+    grpc_subchannel *c GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+  if (!c) return NULL;
+  for (;;) {
+    gpr_atm old_refs = gpr_atm_acq_load(&c->ref_pair);
+    if (old_refs >= (1 << INTERNAL_REF_BITS)) {
+      gpr_atm new_refs = old_refs + (1 << INTERNAL_REF_BITS);
+      if (gpr_atm_rel_cas(&c->ref_pair, old_refs, new_refs)) {
+        return c;
+      }
+    } else {
+      return NULL;
+    }
+  }
+}
+
+static void disconnect(grpc_exec_ctx *exec_ctx, grpc_subchannel *c) {
+  grpc_connected_subchannel *con;
+  grpc_subchannel_index_unregister(exec_ctx, c->key, c);
+  gpr_mu_lock(&c->mu);
+  GPR_ASSERT(!c->disconnected);
+  c->disconnected = 1;
+  grpc_connector_shutdown(exec_ctx, c->connector);
+  con = GET_CONNECTED_SUBCHANNEL(c, no_barrier);
+  if (con != NULL) {
+    GRPC_CONNECTED_SUBCHANNEL_UNREF(exec_ctx, con, "connection");
+    gpr_atm_no_barrier_store(&c->connected_subchannel, 0xdeadbeef);
+  }
+  gpr_mu_unlock(&c->mu);
+}
+
+void grpc_subchannel_unref(grpc_exec_ctx *exec_ctx,
+                           grpc_subchannel *c GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+  gpr_atm old_refs;
+  old_refs = ref_mutate(c, (gpr_atm)1 - (gpr_atm)(1 << INTERNAL_REF_BITS),
+                        1 REF_MUTATE_PURPOSE("STRONG_UNREF"));
+  if ((old_refs & STRONG_REF_MASK) == (1 << INTERNAL_REF_BITS)) {
+    disconnect(exec_ctx, c);
+  }
+  GRPC_SUBCHANNEL_WEAK_UNREF(exec_ctx, c, "strong-unref");
+}
+
+void grpc_subchannel_weak_unref(grpc_exec_ctx *exec_ctx,
+                                grpc_subchannel *c
+                                    GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+  gpr_atm old_refs;
+  old_refs = ref_mutate(c, -(gpr_atm)1, 1 REF_MUTATE_PURPOSE("WEAK_UNREF"));
+  if (old_refs == 1) {
+    grpc_exec_ctx_enqueue(exec_ctx, grpc_closure_create(subchannel_destroy, c),
+                          true, NULL);
+  }
+}
+
+static uint32_t random_seed() {
+  return (uint32_t)(gpr_time_to_millis(gpr_now(GPR_CLOCK_MONOTONIC)));
+}
+
+grpc_subchannel *grpc_subchannel_create(grpc_exec_ctx *exec_ctx,
+                                        grpc_connector *connector,
+                                        grpc_subchannel_args *args) {
+  grpc_subchannel_key *key = grpc_subchannel_key_create(connector, args);
+  grpc_subchannel *c = grpc_subchannel_index_find(exec_ctx, key);
+  if (c) {
+    grpc_subchannel_key_destroy(exec_ctx, key);
+    return c;
+  }
+
+  c = gpr_malloc(sizeof(*c));
+  memset(c, 0, sizeof(*c));
+  c->key = key;
+  gpr_atm_no_barrier_store(&c->ref_pair, 1 << INTERNAL_REF_BITS);
+  c->connector = connector;
+  grpc_connector_ref(c->connector);
+  c->num_filters = args->filter_count;
+  if (c->num_filters > 0) {
+    c->filters = gpr_malloc(sizeof(grpc_channel_filter *) * c->num_filters);
+    memcpy((void *)c->filters, args->filters,
+           sizeof(grpc_channel_filter *) * c->num_filters);
+  } else {
+    c->filters = NULL;
+  }
+  c->addr = gpr_malloc(args->addr_len);
+  memcpy(c->addr, args->addr, args->addr_len);
+  c->pollset_set = grpc_pollset_set_create();
+  c->addr_len = args->addr_len;
+  grpc_set_initial_connect_string(&c->addr, &c->addr_len,
+                                  &c->initial_connect_string);
+  c->args = grpc_channel_args_copy(args->args);
+  c->random = random_seed();
+  c->root_external_state_watcher.next = c->root_external_state_watcher.prev =
+      &c->root_external_state_watcher;
+  grpc_closure_init(&c->connected, subchannel_connected, c);
+  grpc_connectivity_state_init(&c->state_tracker, GRPC_CHANNEL_IDLE,
+                               "subchannel");
+  gpr_mu_init(&c->mu);
+
+  return grpc_subchannel_index_register(exec_ctx, key, c);
+}
+
+static void continue_connect(grpc_exec_ctx *exec_ctx, grpc_subchannel *c) {
+  grpc_connect_in_args args;
+
+  args.interested_parties = c->pollset_set;
+  args.addr = c->addr;
+  args.addr_len = c->addr_len;
+  args.deadline = compute_connect_deadline(c);
+  args.channel_args = c->args;
+  args.initial_connect_string = c->initial_connect_string;
+
+  grpc_connectivity_state_set(exec_ctx, &c->state_tracker,
+                              GRPC_CHANNEL_CONNECTING, "state_change");
+  grpc_connector_connect(exec_ctx, c->connector, &args, &c->connecting_result,
+                         &c->connected);
+}
+
+static void start_connect(grpc_exec_ctx *exec_ctx, grpc_subchannel *c) {
+  c->backoff_delta = gpr_time_from_seconds(
+      GRPC_SUBCHANNEL_INITIAL_CONNECT_BACKOFF_SECONDS, GPR_TIMESPAN);
+  c->next_attempt =
+      gpr_time_add(gpr_now(GPR_CLOCK_MONOTONIC), c->backoff_delta);
+  continue_connect(exec_ctx, c);
+}
+
+grpc_connectivity_state grpc_subchannel_check_connectivity(grpc_subchannel *c) {
+  grpc_connectivity_state state;
+  gpr_mu_lock(&c->mu);
+  state = grpc_connectivity_state_check(&c->state_tracker);
+  gpr_mu_unlock(&c->mu);
+  return state;
+}
+
+static void on_external_state_watcher_done(grpc_exec_ctx *exec_ctx, void *arg,
+                                           bool success) {
+  external_state_watcher *w = arg;
+  grpc_closure *follow_up = w->notify;
+  if (w->pollset_set != NULL) {
+    grpc_pollset_set_del_pollset_set(exec_ctx, w->subchannel->pollset_set,
+                                     w->pollset_set);
+  }
+  gpr_mu_lock(&w->subchannel->mu);
+  w->next->prev = w->prev;
+  w->prev->next = w->next;
+  gpr_mu_unlock(&w->subchannel->mu);
+  GRPC_SUBCHANNEL_WEAK_UNREF(exec_ctx, w->subchannel, "external_state_watcher");
+  gpr_free(w);
+  follow_up->cb(exec_ctx, follow_up->cb_arg, success);
+}
+
+void grpc_subchannel_notify_on_state_change(
+    grpc_exec_ctx *exec_ctx, grpc_subchannel *c,
+    grpc_pollset_set *interested_parties, grpc_connectivity_state *state,
+    grpc_closure *notify) {
+  external_state_watcher *w;
+
+  if (state == NULL) {
+    gpr_mu_lock(&c->mu);
+    for (w = c->root_external_state_watcher.next;
+         w != &c->root_external_state_watcher; w = w->next) {
+      if (w->notify == notify) {
+        grpc_connectivity_state_notify_on_state_change(
+            exec_ctx, &c->state_tracker, NULL, &w->closure);
+      }
+    }
+    gpr_mu_unlock(&c->mu);
+  } else {
+    w = gpr_malloc(sizeof(*w));
+    w->subchannel = c;
+    w->pollset_set = interested_parties;
+    w->notify = notify;
+    grpc_closure_init(&w->closure, on_external_state_watcher_done, w);
+    if (interested_parties != NULL) {
+      grpc_pollset_set_add_pollset_set(exec_ctx, c->pollset_set,
+                                       interested_parties);
+    }
+    GRPC_SUBCHANNEL_WEAK_REF(c, "external_state_watcher");
+    gpr_mu_lock(&c->mu);
+    w->next = &c->root_external_state_watcher;
+    w->prev = w->next->prev;
+    w->next->prev = w->prev->next = w;
+    if (grpc_connectivity_state_notify_on_state_change(
+            exec_ctx, &c->state_tracker, state, &w->closure)) {
+      c->connecting = 1;
+      /* released by connection */
+      GRPC_SUBCHANNEL_WEAK_REF(c, "connecting");
+      start_connect(exec_ctx, c);
+    }
+    gpr_mu_unlock(&c->mu);
+  }
+}
+
+void grpc_connected_subchannel_process_transport_op(
+    grpc_exec_ctx *exec_ctx, grpc_connected_subchannel *con,
+    grpc_transport_op *op) {
+  grpc_channel_stack *channel_stack = CHANNEL_STACK_FROM_CONNECTION(con);
+  grpc_channel_element *top_elem = grpc_channel_stack_element(channel_stack, 0);
+  top_elem->filter->start_transport_op(exec_ctx, top_elem, op);
+}
+
+static void subchannel_on_child_state_changed(grpc_exec_ctx *exec_ctx, void *p,
+                                              bool iomgr_success) {
+  state_watcher *sw = p;
+  grpc_subchannel *c = sw->subchannel;
+  gpr_mu *mu = &c->mu;
+
+  gpr_mu_lock(mu);
+
+  /* if we failed just leave this closure */
+  if (iomgr_success) {
+    if (sw->connectivity_state == GRPC_CHANNEL_TRANSIENT_FAILURE) {
+      /* any errors on a subchannel ==> we're done, create a new one */
+      sw->connectivity_state = GRPC_CHANNEL_FATAL_FAILURE;
+    }
+    grpc_connectivity_state_set(exec_ctx, &c->state_tracker,
+                                sw->connectivity_state, "reflect_child");
+    if (sw->connectivity_state != GRPC_CHANNEL_FATAL_FAILURE) {
+      grpc_connected_subchannel_notify_on_state_change(
+          exec_ctx, GET_CONNECTED_SUBCHANNEL(c, no_barrier), NULL,
+          &sw->connectivity_state, &sw->closure);
+      GRPC_SUBCHANNEL_WEAK_REF(c, "state_watcher");
+      sw = NULL;
+    }
+  }
+
+  gpr_mu_unlock(mu);
+  GRPC_SUBCHANNEL_WEAK_UNREF(exec_ctx, c, "state_watcher");
+  gpr_free(sw);
+}
+
+static void connected_subchannel_state_op(grpc_exec_ctx *exec_ctx,
+                                          grpc_connected_subchannel *con,
+                                          grpc_pollset_set *interested_parties,
+                                          grpc_connectivity_state *state,
+                                          grpc_closure *closure) {
+  grpc_transport_op op;
+  grpc_channel_element *elem;
+  memset(&op, 0, sizeof(op));
+  op.connectivity_state = state;
+  op.on_connectivity_state_change = closure;
+  op.bind_pollset_set = interested_parties;
+  elem = grpc_channel_stack_element(CHANNEL_STACK_FROM_CONNECTION(con), 0);
+  elem->filter->start_transport_op(exec_ctx, elem, &op);
+}
+
+void grpc_connected_subchannel_notify_on_state_change(
+    grpc_exec_ctx *exec_ctx, grpc_connected_subchannel *con,
+    grpc_pollset_set *interested_parties, grpc_connectivity_state *state,
+    grpc_closure *closure) {
+  connected_subchannel_state_op(exec_ctx, con, interested_parties, state,
+                                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;
+  grpc_channel_stack *stk;
+  size_t num_filters;
+  const grpc_channel_filter **filters;
+  state_watcher *sw_subchannel;
+
+  /* build final filter list */
+  num_filters = c->num_filters + c->connecting_result.num_filters + 1;
+  filters = gpr_malloc(sizeof(*filters) * num_filters);
+  if (c->num_filters > 0) {
+    memcpy((void *)filters, c->filters, sizeof(*filters) * c->num_filters);
+  }
+  memcpy((void *)(filters + c->num_filters), c->connecting_result.filters,
+         sizeof(*filters) * c->connecting_result.num_filters);
+  filters[num_filters - 1] = &grpc_connected_channel_filter;
+
+  /* construct channel stack */
+  channel_stack_size = grpc_channel_stack_size(filters, num_filters);
+  con = gpr_malloc(channel_stack_size);
+  stk = CHANNEL_STACK_FROM_CONNECTION(con);
+  grpc_channel_stack_init(exec_ctx, 1, connection_destroy, con, filters,
+                          num_filters, c->connecting_result.channel_args,
+                          "CONNECTED_SUBCHANNEL", stk);
+  grpc_connected_channel_bind_transport(stk, c->connecting_result.transport);
+  gpr_free((void *)c->connecting_result.filters);
+  memset(&c->connecting_result, 0, sizeof(c->connecting_result));
+
+  /* initialize state watcher */
+  sw_subchannel = gpr_malloc(sizeof(*sw_subchannel));
+  sw_subchannel->subchannel = c;
+  sw_subchannel->connectivity_state = GRPC_CHANNEL_READY;
+  grpc_closure_init(&sw_subchannel->closure, subchannel_on_child_state_changed,
+                    sw_subchannel);
+
+  gpr_mu_lock(&c->mu);
+
+  if (c->disconnected) {
+    gpr_mu_unlock(&c->mu);
+    gpr_free(sw_subchannel);
+    gpr_free((void *)filters);
+    grpc_channel_stack_destroy(exec_ctx, stk);
+    gpr_free(con);
+    GRPC_SUBCHANNEL_WEAK_UNREF(exec_ctx, c, "connecting");
+    return;
+  }
+
+  /* publish */
+  /* TODO(ctiller): this full barrier seems to clear up a TSAN failure.
+                    I'd have expected the rel_cas below to be enough, but
+                    seemingly it's not.
+                    Re-evaluate if we really need this. */
+  gpr_atm_full_barrier();
+  GPR_ASSERT(gpr_atm_rel_cas(&c->connected_subchannel, 0, (gpr_atm)con));
+  c->connecting = 0;
+
+  /* setup subchannel watching connected subchannel for changes; subchannel ref
+     for connecting is donated
+     to the state watcher */
+  GRPC_SUBCHANNEL_WEAK_REF(c, "state_watcher");
+  GRPC_SUBCHANNEL_WEAK_UNREF(exec_ctx, c, "connecting");
+  grpc_connected_subchannel_notify_on_state_change(
+      exec_ctx, con, c->pollset_set, &sw_subchannel->connectivity_state,
+      &sw_subchannel->closure);
+
+  /* signal completion */
+  grpc_connectivity_state_set(exec_ctx, &c->state_tracker, GRPC_CHANNEL_READY,
+                              "connected");
+
+  gpr_mu_unlock(&c->mu);
+  gpr_free((void *)filters);
+}
+
+/* Generate a random number between 0 and 1. */
+static double generate_uniform_random_number(grpc_subchannel *c) {
+  c->random = (1103515245 * c->random + 12345) % ((uint32_t)1 << 31);
+  return c->random / (double)((uint32_t)1 << 31);
+}
+
+/* Update backoff_delta and next_attempt in subchannel */
+static void update_reconnect_parameters(grpc_subchannel *c) {
+  size_t i;
+  int32_t backoff_delta_millis, jitter;
+  int32_t max_backoff_millis =
+      GRPC_SUBCHANNEL_RECONNECT_MAX_BACKOFF_SECONDS * 1000;
+  double jitter_range;
+
+  if (c->args) {
+    for (i = 0; i < c->args->num_args; i++) {
+      if (0 == strcmp(c->args->args[i].key,
+                      "grpc.testing.fixed_reconnect_backoff")) {
+        GPR_ASSERT(c->args->args[i].type == GRPC_ARG_INTEGER);
+        c->next_attempt = gpr_time_add(
+            gpr_now(GPR_CLOCK_MONOTONIC),
+            gpr_time_from_millis(c->args->args[i].value.integer, GPR_TIMESPAN));
+        return;
+      }
+    }
+  }
+
+  backoff_delta_millis =
+      (int32_t)(gpr_time_to_millis(c->backoff_delta) *
+                GRPC_SUBCHANNEL_RECONNECT_BACKOFF_MULTIPLIER);
+  if (backoff_delta_millis > max_backoff_millis) {
+    backoff_delta_millis = max_backoff_millis;
+  }
+  c->backoff_delta = gpr_time_from_millis(backoff_delta_millis, GPR_TIMESPAN);
+  c->next_attempt =
+      gpr_time_add(gpr_now(GPR_CLOCK_MONOTONIC), c->backoff_delta);
+
+  jitter_range = GRPC_SUBCHANNEL_RECONNECT_JITTER * backoff_delta_millis;
+  jitter =
+      (int32_t)((2 * generate_uniform_random_number(c) - 1) * jitter_range);
+  c->next_attempt =
+      gpr_time_add(c->next_attempt, gpr_time_from_millis(jitter, GPR_TIMESPAN));
+}
+
+static void on_alarm(grpc_exec_ctx *exec_ctx, void *arg, bool iomgr_success) {
+  grpc_subchannel *c = arg;
+  gpr_mu_lock(&c->mu);
+  c->have_alarm = 0;
+  if (c->disconnected) {
+    iomgr_success = 0;
+  }
+  if (iomgr_success) {
+    update_reconnect_parameters(c);
+    continue_connect(exec_ctx, c);
+    gpr_mu_unlock(&c->mu);
+  } else {
+    gpr_mu_unlock(&c->mu);
+    GRPC_SUBCHANNEL_WEAK_UNREF(exec_ctx, c, "connecting");
+  }
+}
+
+static void subchannel_connected(grpc_exec_ctx *exec_ctx, void *arg,
+                                 bool iomgr_success) {
+  grpc_subchannel *c = arg;
+
+  if (c->connecting_result.transport != NULL) {
+    publish_transport(exec_ctx, c);
+  } else if (c->disconnected) {
+    GRPC_SUBCHANNEL_WEAK_UNREF(exec_ctx, c, "connecting");
+  } else {
+    gpr_timespec now = gpr_now(GPR_CLOCK_MONOTONIC);
+    gpr_mu_lock(&c->mu);
+    GPR_ASSERT(!c->have_alarm);
+    c->have_alarm = 1;
+    grpc_connectivity_state_set(exec_ctx, &c->state_tracker,
+                                GRPC_CHANNEL_TRANSIENT_FAILURE,
+                                "connect_failed");
+    grpc_timer_init(exec_ctx, &c->alarm, c->next_attempt, on_alarm, c, now);
+    gpr_mu_unlock(&c->mu);
+  }
+}
+
+static gpr_timespec compute_connect_deadline(grpc_subchannel *c) {
+  gpr_timespec current_deadline =
+      gpr_time_add(c->next_attempt, c->backoff_delta);
+  gpr_timespec min_deadline = gpr_time_add(
+      gpr_now(GPR_CLOCK_MONOTONIC),
+      gpr_time_from_seconds(GRPC_SUBCHANNEL_MIN_CONNECT_TIMEOUT_SECONDS,
+                            GPR_TIMESPAN));
+  return gpr_time_cmp(current_deadline, min_deadline) > 0 ? current_deadline
+                                                          : min_deadline;
+}
+
+/*
+ * grpc_subchannel_call implementation
+ */
+
+static void subchannel_call_destroy(grpc_exec_ctx *exec_ctx, void *call,
+                                    bool success) {
+  grpc_subchannel_call *c = call;
+  GPR_TIMER_BEGIN("grpc_subchannel_call_unref.destroy", 0);
+  grpc_call_stack_destroy(exec_ctx, SUBCHANNEL_CALL_TO_CALL_STACK(c));
+  GRPC_CONNECTED_SUBCHANNEL_UNREF(exec_ctx, c->connection, "subchannel_call");
+  gpr_free(c);
+  GPR_TIMER_END("grpc_subchannel_call_unref.destroy", 0);
+}
+
+void grpc_subchannel_call_ref(grpc_subchannel_call *c
+                                  GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+  GRPC_CALL_STACK_REF(SUBCHANNEL_CALL_TO_CALL_STACK(c), REF_REASON);
+}
+
+void grpc_subchannel_call_unref(grpc_exec_ctx *exec_ctx,
+                                grpc_subchannel_call *c
+                                    GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+  GRPC_CALL_STACK_UNREF(exec_ctx, SUBCHANNEL_CALL_TO_CALL_STACK(c), REF_REASON);
+}
+
+char *grpc_subchannel_call_get_peer(grpc_exec_ctx *exec_ctx,
+                                    grpc_subchannel_call *call) {
+  grpc_call_stack *call_stack = SUBCHANNEL_CALL_TO_CALL_STACK(call);
+  grpc_call_element *top_elem = grpc_call_stack_element(call_stack, 0);
+  return top_elem->filter->get_peer(exec_ctx, top_elem);
+}
+
+void grpc_subchannel_call_process_op(grpc_exec_ctx *exec_ctx,
+                                     grpc_subchannel_call *call,
+                                     grpc_transport_stream_op *op) {
+  grpc_call_stack *call_stack = SUBCHANNEL_CALL_TO_CALL_STACK(call);
+  grpc_call_element *top_elem = grpc_call_stack_element(call_stack, 0);
+  top_elem->filter->start_transport_stream_op(exec_ctx, top_elem, op);
+}
+
+grpc_connected_subchannel *grpc_subchannel_get_connected_subchannel(
+    grpc_subchannel *c) {
+  return GET_CONNECTED_SUBCHANNEL(c, acq);
+}
+
+grpc_subchannel_call *grpc_connected_subchannel_create_call(
+    grpc_exec_ctx *exec_ctx, grpc_connected_subchannel *con,
+    grpc_pollset *pollset) {
+  grpc_channel_stack *chanstk = CHANNEL_STACK_FROM_CONNECTION(con);
+  grpc_subchannel_call *call =
+      gpr_malloc(sizeof(grpc_subchannel_call) + chanstk->call_stack_size);
+  grpc_call_stack *callstk = SUBCHANNEL_CALL_TO_CALL_STACK(call);
+  call->connection = con;
+  GRPC_CONNECTED_SUBCHANNEL_REF(con, "subchannel_call");
+  grpc_call_stack_init(exec_ctx, chanstk, 1, subchannel_call_destroy, call,
+                       NULL, NULL, callstk);
+  grpc_call_stack_set_pollset(exec_ctx, callstk, pollset);
+  return call;
+}
+
+grpc_call_stack *grpc_subchannel_call_get_call_stack(
+    grpc_subchannel_call *subchannel_call) {
+  return SUBCHANNEL_CALL_TO_CALL_STACK(subchannel_call);
+}