src/core/channel/client_channel.c

/*
 *
 * 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/channel/client_channel.h"

#include <stdio.h>
#include <string.h>

#include "src/core/channel/channel_args.h"
#include "src/core/channel/connected_channel.h"
#include "src/core/surface/channel.h"
#include "src/core/iomgr/iomgr.h"
#include "src/core/support/string.h"
#include "src/core/transport/connectivity_state.h"
#include <grpc/support/alloc.h>
#include <grpc/support/log.h>
#include <grpc/support/sync.h>
#include <grpc/support/useful.h>

/* Client channel implementation */

typedef struct call_data call_data;

typedef struct
{
  /** metadata context for this channel */
  grpc_mdctx *mdctx;
  /** resolver for this channel */
  grpc_resolver *resolver;
  /** have we started resolving this channel */
  int started_resolving;
  /** master channel - the grpc_channel instance that ultimately owns
      this channel_data via its channel stack.
      We occasionally use this to bump the refcount on the master channel
      to keep ourselves alive through an asynchronous operation. */
  grpc_channel *master;

  /** mutex protecting client configuration, including all
      variables below in this data structure */
  gpr_mu mu_config;
  /** currently active load balancer - guarded by mu_config */
  grpc_lb_policy *lb_policy;
  /** incoming configuration - set by resolver.next
      guarded by mu_config */
  grpc_client_config *incoming_configuration;
  /** a list of closures that are all waiting for config to come in */
  grpc_closure_list waiting_for_config_closures;
  /** resolver callback */
  grpc_closure on_config_changed;
  /** connectivity state being tracked */
  grpc_connectivity_state_tracker state_tracker;
  /** when an lb_policy arrives, should we try to exit idle */
  int exit_idle_when_lb_policy_arrives;
  /** pollset_set of interested parties in a new connection */
  grpc_pollset_set pollset_set;
} channel_data;

/** We create one watcher for each new lb_policy that is returned from a
   resolver,
    to watch for state changes from the lb_policy. When a state change is seen,
   we
    update the channel, and create a new watcher */
typedef struct
{
  channel_data *chand;
  grpc_closure on_changed;
  grpc_connectivity_state state;
  grpc_lb_policy *lb_policy;
} lb_policy_connectivity_watcher;

typedef enum
{
  CALL_CREATED,
  CALL_WAITING_FOR_SEND,
  CALL_WAITING_FOR_CONFIG,
  CALL_WAITING_FOR_PICK,
  CALL_WAITING_FOR_CALL,
  CALL_ACTIVE,
  CALL_CANCELLED
} call_state;

struct call_data
{
  /* owning element */
  grpc_call_element *elem;

  gpr_mu mu_state;

  call_state state;
  gpr_timespec deadline;
  grpc_subchannel *picked_channel;
  grpc_closure async_setup_task;
  grpc_transport_stream_op waiting_op;
  /* our child call stack */
  grpc_subchannel_call *subchannel_call;
  grpc_linked_mdelem status;
  grpc_linked_mdelem details;
};

static grpc_closure *
merge_into_waiting_op (grpc_call_element * elem, grpc_transport_stream_op * new_op)
  GRPC_MUST_USE_RESULT;

     static void handle_op_after_cancellation (grpc_exec_ctx * exec_ctx, grpc_call_element * elem, grpc_transport_stream_op * op)
{
  call_data *calld = elem->call_data;
  channel_data *chand = elem->channel_data;
  if (op->send_ops)
    {
      grpc_stream_ops_unref_owned_objects (op->send_ops->ops, op->send_ops->nops);
      op->on_done_send->cb (exec_ctx, op->on_done_send->cb_arg, 0);
    }
  if (op->recv_ops)
    {
      char status[GPR_LTOA_MIN_BUFSIZE];
      grpc_metadata_batch mdb;
      gpr_ltoa (GRPC_STATUS_CANCELLED, status);
      calld->status.md = grpc_mdelem_from_strings (chand->mdctx, "grpc-status", status);
      calld->details.md = grpc_mdelem_from_strings (chand->mdctx, "grpc-message", "Cancelled");
      calld->status.prev = calld->details.next = NULL;
      calld->status.next = &calld->details;
      calld->details.prev = &calld->status;
      mdb.list.head = &calld->status;
      mdb.list.tail = &calld->details;
      mdb.garbage.head = mdb.garbage.tail = NULL;
      mdb.deadline = gpr_inf_future (GPR_CLOCK_REALTIME);
      grpc_sopb_add_metadata (op->recv_ops, mdb);
      *op->recv_state = GRPC_STREAM_CLOSED;
      op->on_done_recv->cb (exec_ctx, op->on_done_recv->cb_arg, 1);
    }
  if (op->on_consumed)
    {
      op->on_consumed->cb (exec_ctx, op->on_consumed->cb_arg, 0);
    }
}

typedef struct
{
  grpc_closure closure;
  grpc_call_element *elem;
} waiting_call;

static void perform_transport_stream_op (grpc_exec_ctx * exec_ctx, grpc_call_element * elem, grpc_transport_stream_op * op, int continuation);

static void
continue_with_pick (grpc_exec_ctx * exec_ctx, void *arg, int iomgr_success)
{
  waiting_call *wc = arg;
  call_data *calld = wc->elem->call_data;
  perform_transport_stream_op (exec_ctx, wc->elem, &calld->waiting_op, 1);
  gpr_free (wc);
}

static void
add_to_lb_policy_wait_queue_locked_state_config (grpc_call_element * elem)
{
  channel_data *chand = elem->channel_data;
  waiting_call *wc = gpr_malloc (sizeof (*wc));
  grpc_closure_init (&wc->closure, continue_with_pick, wc);
  wc->elem = elem;
  grpc_closure_list_add (&chand->waiting_for_config_closures, &wc->closure, 1);
}

static int
is_empty (void *p, int len)
{
  char *ptr = p;
  int i;
  for (i = 0; i < len; i++)
    {
      if (ptr[i] != 0)
	return 0;
    }
  return 1;
}

static void
started_call (grpc_exec_ctx * exec_ctx, void *arg, int iomgr_success)
{
  call_data *calld = arg;
  grpc_transport_stream_op op;
  int have_waiting;

  gpr_mu_lock (&calld->mu_state);
  if (calld->state == CALL_CANCELLED && calld->subchannel_call != NULL)
    {
      memset (&op, 0, sizeof (op));
      op.cancel_with_status = GRPC_STATUS_CANCELLED;
      gpr_mu_unlock (&calld->mu_state);
      grpc_subchannel_call_process_op (exec_ctx, calld->subchannel_call, &op);
    }
  else if (calld->state == CALL_WAITING_FOR_CALL)
    {
      have_waiting = !is_empty (&calld->waiting_op, sizeof (calld->waiting_op));
      if (calld->subchannel_call != NULL)
	{
	  calld->state = CALL_ACTIVE;
	  gpr_mu_unlock (&calld->mu_state);
	  if (have_waiting)
	    {
	      grpc_subchannel_call_process_op (exec_ctx, calld->subchannel_call, &calld->waiting_op);
	    }
	}
      else
	{
	  calld->state = CALL_CANCELLED;
	  gpr_mu_unlock (&calld->mu_state);
	  if (have_waiting)
	    {
	      handle_op_after_cancellation (exec_ctx, calld->elem, &calld->waiting_op);
	    }
	}
    }
  else
    {
      GPR_ASSERT (calld->state == CALL_CANCELLED);
      gpr_mu_unlock (&calld->mu_state);
    }
}

static void
picked_target (grpc_exec_ctx * exec_ctx, void *arg, int iomgr_success)
{
  call_data *calld = arg;
  grpc_pollset *pollset;

  if (calld->picked_channel == NULL)
    {
      /* treat this like a cancellation */
      calld->waiting_op.cancel_with_status = GRPC_STATUS_UNAVAILABLE;
      perform_transport_stream_op (exec_ctx, calld->elem, &calld->waiting_op, 1);
    }
  else
    {
      gpr_mu_lock (&calld->mu_state);
      if (calld->state == CALL_CANCELLED)
	{
	  gpr_mu_unlock (&calld->mu_state);
	  handle_op_after_cancellation (exec_ctx, calld->elem, &calld->waiting_op);
	}
      else
	{
	  GPR_ASSERT (calld->state == CALL_WAITING_FOR_PICK);
	  calld->state = CALL_WAITING_FOR_CALL;
	  pollset = calld->waiting_op.bind_pollset;
	  gpr_mu_unlock (&calld->mu_state);
	  grpc_closure_init (&calld->async_setup_task, started_call, calld);
	  grpc_subchannel_create_call (exec_ctx, calld->picked_channel, pollset, &calld->subchannel_call, &calld->async_setup_task);
	}
    }
}

static grpc_closure *
merge_into_waiting_op (grpc_call_element * elem, grpc_transport_stream_op * new_op)
{
  call_data *calld = elem->call_data;
  grpc_closure *consumed_op = NULL;
  grpc_transport_stream_op *waiting_op = &calld->waiting_op;
  GPR_ASSERT ((waiting_op->send_ops != NULL) + (new_op->send_ops != NULL) <= 1);
  GPR_ASSERT ((waiting_op->recv_ops != NULL) + (new_op->recv_ops != NULL) <= 1);
  if (new_op->send_ops != NULL)
    {
      waiting_op->send_ops = new_op->send_ops;
      waiting_op->is_last_send = new_op->is_last_send;
      waiting_op->on_done_send = new_op->on_done_send;
    }
  if (new_op->recv_ops != NULL)
    {
      waiting_op->recv_ops = new_op->recv_ops;
      waiting_op->recv_state = new_op->recv_state;
      waiting_op->on_done_recv = new_op->on_done_recv;
    }
  if (new_op->on_consumed != NULL)
    {
      if (waiting_op->on_consumed != NULL)
	{
	  consumed_op = waiting_op->on_consumed;
	}
      waiting_op->on_consumed = new_op->on_consumed;
    }
  if (new_op->cancel_with_status != GRPC_STATUS_OK)
    {
      waiting_op->cancel_with_status = new_op->cancel_with_status;
    }
  return consumed_op;
}

static char *
cc_get_peer (grpc_exec_ctx * exec_ctx, grpc_call_element * elem)
{
  call_data *calld = elem->call_data;
  channel_data *chand = elem->channel_data;
  grpc_subchannel_call *subchannel_call;
  char *result;

  gpr_mu_lock (&calld->mu_state);
  if (calld->state == CALL_ACTIVE)
    {
      subchannel_call = calld->subchannel_call;
      GRPC_SUBCHANNEL_CALL_REF (subchannel_call, "get_peer");
      gpr_mu_unlock (&calld->mu_state);
      result = grpc_subchannel_call_get_peer (exec_ctx, subchannel_call);
      GRPC_SUBCHANNEL_CALL_UNREF (exec_ctx, subchannel_call, "get_peer");
      return result;
    }
  else
    {
      gpr_mu_unlock (&calld->mu_state);
      return grpc_channel_get_target (chand->master);
    }
}

static void
perform_transport_stream_op (grpc_exec_ctx * exec_ctx, grpc_call_element * elem, grpc_transport_stream_op * op, int continuation)
{
  call_data *calld = elem->call_data;
  channel_data *chand = elem->channel_data;
  grpc_subchannel_call *subchannel_call;
  grpc_lb_policy *lb_policy;
  grpc_transport_stream_op op2;
  GPR_ASSERT (elem->filter == &grpc_client_channel_filter);
  GRPC_CALL_LOG_OP (GPR_INFO, elem, op);

  gpr_mu_lock (&calld->mu_state);
  switch (calld->state)
    {
    case CALL_ACTIVE:
      GPR_ASSERT (!continuation);
      subchannel_call = calld->subchannel_call;
      gpr_mu_unlock (&calld->mu_state);
      grpc_subchannel_call_process_op (exec_ctx, subchannel_call, op);
      break;
    case CALL_CANCELLED:
      gpr_mu_unlock (&calld->mu_state);
      handle_op_after_cancellation (exec_ctx, elem, op);
      break;
    case CALL_WAITING_FOR_SEND:
      GPR_ASSERT (!continuation);
      grpc_closure_list_add (closure_list, merge_into_waiting_op (elem, op), 1);
      if (!calld->waiting_op.send_ops && calld->waiting_op.cancel_with_status == GRPC_STATUS_OK)
	{
	  gpr_mu_unlock (&calld->mu_state);
	  break;
	}
      *op = calld->waiting_op;
      memset (&calld->waiting_op, 0, sizeof (calld->waiting_op));
      continuation = 1;
      /* fall through */
    case CALL_WAITING_FOR_CONFIG:
    case CALL_WAITING_FOR_PICK:
    case CALL_WAITING_FOR_CALL:
      if (!continuation)
	{
	  if (op->cancel_with_status != GRPC_STATUS_OK)
	    {
	      calld->state = CALL_CANCELLED;
	      op2 = calld->waiting_op;
	      memset (&calld->waiting_op, 0, sizeof (calld->waiting_op));
	      if (op->on_consumed)
		{
		  calld->waiting_op.on_consumed = op->on_consumed;
		  op->on_consumed = NULL;
		}
	      else if (op2.on_consumed)
		{
		  calld->waiting_op.on_consumed = op2.on_consumed;
		  op2.on_consumed = NULL;
		}
	      gpr_mu_unlock (&calld->mu_state);
	      handle_op_after_cancellation (exec_ctx, elem, op);
	      handle_op_after_cancellation (exec_ctx, elem, &op2);
	    }
	  else
	    {
	      grpc_closure_list_add (closure_list, merge_into_waiting_op (elem, op), 1);
	      gpr_mu_unlock (&calld->mu_state);
	    }
	  break;
	}
      /* fall through */
    case CALL_CREATED:
      if (op->cancel_with_status != GRPC_STATUS_OK)
	{
	  calld->state = CALL_CANCELLED;
	  gpr_mu_unlock (&calld->mu_state);
	  handle_op_after_cancellation (exec_ctx, elem, op);
	}
      else
	{
	  calld->waiting_op = *op;

	  if (op->send_ops == NULL)
	    {
	      /* need to have some send ops before we can select the
	         lb target */
	      calld->state = CALL_WAITING_FOR_SEND;
	      gpr_mu_unlock (&calld->mu_state);
	    }
	  else
	    {
	      gpr_mu_lock (&chand->mu_config);
	      lb_policy = chand->lb_policy;
	      if (lb_policy)
		{
		  grpc_transport_stream_op *op = &calld->waiting_op;
		  grpc_pollset *bind_pollset = op->bind_pollset;
		  grpc_metadata_batch *initial_metadata = &op->send_ops->ops[0].data.metadata;
		  GRPC_LB_POLICY_REF (lb_policy, "pick");
		  gpr_mu_unlock (&chand->mu_config);
		  calld->state = CALL_WAITING_FOR_PICK;

		  GPR_ASSERT (op->bind_pollset);
		  GPR_ASSERT (op->send_ops);
		  GPR_ASSERT (op->send_ops->nops >= 1);
		  GPR_ASSERT (op->send_ops->ops[0].type == GRPC_OP_METADATA);
		  gpr_mu_unlock (&calld->mu_state);

		  grpc_closure_init (&calld->async_setup_task, picked_target, calld);
		  grpc_lb_policy_pick (exec_ctx, lb_policy, bind_pollset, initial_metadata, &calld->picked_channel, &calld->async_setup_task);

		  GRPC_LB_POLICY_UNREF (exec_ctx, lb_policy, "pick");
		}
	      else if (chand->resolver != NULL)
		{
		  calld->state = CALL_WAITING_FOR_CONFIG;
		  add_to_lb_policy_wait_queue_locked_state_config (elem);
		  if (!chand->started_resolving && chand->resolver != NULL)
		    {
		      GRPC_CHANNEL_INTERNAL_REF (chand->master, "resolver");
		      chand->started_resolving = 1;
		      grpc_resolver_next (exec_ctx, chand->resolver, &chand->incoming_configuration, &chand->on_config_changed);
		    }
		  gpr_mu_unlock (&chand->mu_config);
		  gpr_mu_unlock (&calld->mu_state);
		}
	      else
		{
		  calld->state = CALL_CANCELLED;
		  gpr_mu_unlock (&chand->mu_config);
		  gpr_mu_unlock (&calld->mu_state);
		  handle_op_after_cancellation (exec_ctx, elem, op);
		}
	    }
	}
      break;
    }
}

static void
cc_start_transport_stream_op (grpc_exec_ctx * exec_ctx, grpc_call_element * elem, grpc_transport_stream_op * op)
{
  perform_transport_stream_op (exec_ctx, elem, op, 0);
}

static void watch_lb_policy (channel_data * chand, grpc_lb_policy * lb_policy, grpc_connectivity_state current_state, grpc_closure_list * cl);

static void
on_lb_policy_state_changed_locked (lb_policy_connectivity_watcher * w, grpc_closure_list * cl)
{
  /* check if the notification is for a stale policy */
  if (w->lb_policy != w->chand->lb_policy)
    return;

  grpc_connectivity_state_set (&w->chand->state_tracker, w->state, "lb_changed", cl);
  if (w->state != GRPC_CHANNEL_FATAL_FAILURE)
    {
      watch_lb_policy (w->chand, w->lb_policy, w->state, cl);
    }
}

static void
on_lb_policy_state_changed (grpc_exec_ctx * exec_ctx, void *arg, int iomgr_success)
{
  lb_policy_connectivity_watcher *w = arg;

  gpr_mu_lock (&w->chand->mu_config);
  on_lb_policy_state_changed_locked (exec_ctx, w);
  gpr_mu_unlock (&w->chand->mu_config);

  GRPC_CHANNEL_INTERNAL_UNREF (exec_ctx, w->chand->master, "watch_lb_policy");
  gpr_free (w);
}

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_INTERNAL_REF (chand->master, "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);
}

static void
cc_on_config_changed (grpc_exec_ctx * exec_ctx, void *arg, int iomgr_success)
{
  channel_data *chand = arg;
  grpc_lb_policy *lb_policy = NULL;
  grpc_lb_policy *old_lb_policy;
  grpc_resolver *old_resolver;
  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;

  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_closure_list_move (exec_ctx, &chand->waiting_for_config_closures);
    }
  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)
    {
      grpc_resolver *resolver = chand->resolver;
      GRPC_RESOLVER_REF (resolver, "channel-next");
      grpc_connectivity_state_set (exec_ctx, &chand->state_tracker, state, "new_lb+resolver");
      if (lb_policy != NULL)
	{
	  watch_lb_policy (exec_ctx, chand, lb_policy, state);
	}
      gpr_mu_unlock (&chand->mu_config);
      GRPC_CHANNEL_INTERNAL_REF (chand->master, "resolver");
      grpc_resolver_next (exec_ctx, resolver, &chand->incoming_configuration, &chand->on_config_changed);
      GRPC_RESOLVER_UNREF (exec_ctx, resolver, "channel-next");
    }
  else
    {
      old_resolver = chand->resolver;
      chand->resolver = NULL;
      grpc_connectivity_state_set (exec_ctx, &chand->state_tracker, GRPC_CHANNEL_FATAL_FAILURE, "resolver_gone");
      gpr_mu_unlock (&chand->mu_config);
      if (old_resolver != NULL)
	{
	  grpc_resolver_shutdown (exec_ctx, old_resolver);
	  GRPC_RESOLVER_UNREF (exec_ctx, old_resolver, "channel");
	}
    }

  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_lb_policy_shutdown (exec_ctx, old_lb_policy);
      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_INTERNAL_UNREF (exec_ctx, chand->master, "resolver");
}

static void
cc_start_transport_op (grpc_exec_ctx * exec_ctx, grpc_channel_element * elem, grpc_transport_op * op)
{
  grpc_lb_policy *lb_policy = NULL;
  channel_data *chand = elem->channel_data;
  grpc_resolver *destroy_resolver = NULL;

  grpc_closure_list_add (closure_list, op->on_consumed, 1);

  GPR_ASSERT (op->set_accept_stream == NULL);
  GPR_ASSERT (op->bind_pollset == NULL);

  gpr_mu_lock (&chand->mu_config);
  if (op->on_connectivity_state_change != NULL)
    {
      grpc_connectivity_state_notify_on_state_change (exec_ctx, &chand->state_tracker, op->connectivity_state, op->on_connectivity_state_change);
      op->on_connectivity_state_change = NULL;
      op->connectivity_state = NULL;
    }

  if (!is_empty (op, sizeof (*op)))
    {
      lb_policy = chand->lb_policy;
      if (lb_policy)
	{
	  GRPC_LB_POLICY_REF (lb_policy, "broadcast");
	}
    }

  if (op->disconnect && chand->resolver != NULL)
    {
      grpc_connectivity_state_set (exec_ctx, &chand->state_tracker, GRPC_CHANNEL_FATAL_FAILURE, "disconnect");
      destroy_resolver = chand->resolver;
      chand->resolver = NULL;
      if (chand->lb_policy != NULL)
	{
	  grpc_lb_policy_shutdown (exec_ctx, chand->lb_policy);
	  GRPC_LB_POLICY_UNREF (exec_ctx, chand->lb_policy, "channel");
	  chand->lb_policy = NULL;
	}
    }
  gpr_mu_unlock (&chand->mu_config);

  if (destroy_resolver)
    {
      grpc_resolver_shutdown (exec_ctx, destroy_resolver);
      GRPC_RESOLVER_UNREF (exec_ctx, destroy_resolver, "channel");
    }

  if (lb_policy)
    {
      grpc_lb_policy_broadcast (exec_ctx, lb_policy, op);
      GRPC_LB_POLICY_UNREF (exec_ctx, lb_policy, "broadcast");
    }
}

/* Constructor for call_data */
static void
init_call_elem (grpc_exec_ctx * exec_ctx, grpc_call_element * elem, const void *server_transport_data, grpc_transport_stream_op * initial_op)
{
  call_data *calld = elem->call_data;

  /* TODO(ctiller): is there something useful we can do here? */
  GPR_ASSERT (initial_op == NULL);

  GPR_ASSERT (elem->filter == &grpc_client_channel_filter);
  GPR_ASSERT (server_transport_data == NULL);
  gpr_mu_init (&calld->mu_state);
  calld->elem = elem;
  calld->state = CALL_CREATED;
  calld->deadline = gpr_inf_future (GPR_CLOCK_REALTIME);
}

/* Destructor for call_data */
static void
destroy_call_elem (grpc_exec_ctx * exec_ctx, grpc_call_element * elem)
{
  call_data *calld = elem->call_data;
  grpc_subchannel_call *subchannel_call;

  /* if the call got activated, we need to destroy the child stack also, and
     remove it from the in-flight requests tracked by the child_entry we
     picked */
  gpr_mu_lock (&calld->mu_state);
  switch (calld->state)
    {
    case CALL_ACTIVE:
      subchannel_call = calld->subchannel_call;
      gpr_mu_unlock (&calld->mu_state);
      GRPC_SUBCHANNEL_CALL_UNREF (exec_ctx, subchannel_call, "client_channel");
      break;
    case CALL_CREATED:
    case CALL_CANCELLED:
      gpr_mu_unlock (&calld->mu_state);
      break;
    case CALL_WAITING_FOR_PICK:
    case CALL_WAITING_FOR_CONFIG:
    case CALL_WAITING_FOR_CALL:
    case CALL_WAITING_FOR_SEND:
      gpr_log (GPR_ERROR, "should never reach here");
      abort ();
      break;
    }
}

/* Constructor for channel_data */
static void
init_channel_elem (grpc_exec_ctx * exec_ctx, grpc_channel_element * elem, grpc_channel * master, const grpc_channel_args * args, grpc_mdctx * metadata_context, int is_first, int is_last)
{
  channel_data *chand = elem->channel_data;

  memset (chand, 0, sizeof (*chand));

  GPR_ASSERT (is_last);
  GPR_ASSERT (elem->filter == &grpc_client_channel_filter);

  gpr_mu_init (&chand->mu_config);
  chand->mdctx = metadata_context;
  chand->master = master;
  grpc_pollset_set_init (&chand->pollset_set);
  grpc_closure_init (&chand->on_config_changed, cc_on_config_changed, chand);

  grpc_connectivity_state_init (&chand->state_tracker, GRPC_CHANNEL_IDLE, "client_channel");
}

/* Destructor for channel_data */
static void
destroy_channel_elem (grpc_exec_ctx * exec_ctx, grpc_channel_element * elem)
{
  channel_data *chand = elem->channel_data;

  if (chand->resolver != NULL)
    {
      grpc_resolver_shutdown (exec_ctx, chand->resolver);
      GRPC_RESOLVER_UNREF (exec_ctx, chand->resolver, "channel");
    }
  if (chand->lb_policy != NULL)
    {
      GRPC_LB_POLICY_UNREF (exec_ctx, chand->lb_policy, "channel");
    }
  grpc_connectivity_state_destroy (exec_ctx, &chand->state_tracker);
  grpc_pollset_set_destroy (&chand->pollset_set);
  gpr_mu_destroy (&chand->mu_config);
}

const grpc_channel_filter grpc_client_channel_filter = {
  cc_start_transport_stream_op,
  cc_start_transport_op,
  sizeof (call_data),
  init_call_elem,
  destroy_call_elem,
  sizeof (channel_data),
  init_channel_elem,
  destroy_channel_elem,
  cc_get_peer,
  "client-channel",
};

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_config);
  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 = 1;
      GRPC_CHANNEL_INTERNAL_REF (chand->master, "resolver");
      grpc_resolver_next (exec_ctx, resolver, &chand->incoming_configuration, &chand->on_config_changed);
    }
  gpr_mu_unlock (&chand->mu_config);
}

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_config);
  out = grpc_connectivity_state_check (&chand->state_tracker);
  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 = 1;
	  if (!chand->started_resolving && chand->resolver != NULL)
	    {
	      GRPC_CHANNEL_INTERNAL_REF (chand->master, "resolver");
	      chand->started_resolving = 1;
	      grpc_resolver_next (exec_ctx, chand->resolver, &chand->incoming_configuration, &chand->on_config_changed);
	    }
	}
    }
  gpr_mu_unlock (&chand->mu_config);
  return out;
}

void
grpc_client_channel_watch_connectivity_state (grpc_exec_ctx * exec_ctx, grpc_channel_element * elem, grpc_connectivity_state * state, grpc_closure * on_complete)
{
  channel_data *chand = elem->channel_data;
  gpr_mu_lock (&chand->mu_config);
  grpc_connectivity_state_notify_on_state_change (exec_ctx, &chand->state_tracker, state, on_complete);
  gpr_mu_unlock (&chand->mu_config);
}

grpc_pollset_set *
grpc_client_channel_get_connecting_pollset_set (grpc_channel_element * elem)
{
  channel_data *chand = elem->channel_data;
  return &chand->pollset_set;
}

void
grpc_client_channel_add_interested_party (grpc_exec_ctx * exec_ctx, grpc_channel_element * elem, grpc_pollset * pollset)
{
  channel_data *chand = elem->channel_data;
  grpc_pollset_set_add_pollset (exec_ctx, &chand->pollset_set, pollset);
}

void
grpc_client_channel_del_interested_party (grpc_exec_ctx * exec_ctx, grpc_channel_element * elem, grpc_pollset * pollset)
{
  channel_data *chand = elem->channel_data;
  grpc_pollset_set_del_pollset (exec_ctx, &chand->pollset_set, pollset);
}