src/core/lib/surface/server.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/lib/surface/server.h"

#include <limits.h>
#include <stdlib.h>
#include <string.h>

#include <grpc/support/alloc.h>
#include <grpc/support/log.h>
#include <grpc/support/string_util.h>
#include <grpc/support/useful.h>

#include "src/core/lib/channel/channel_args.h"
#include "src/core/lib/channel/connected_channel.h"
#include "src/core/lib/iomgr/iomgr.h"
#include "src/core/lib/support/stack_lockfree.h"
#include "src/core/lib/support/string.h"
#include "src/core/lib/surface/api_trace.h"
#include "src/core/lib/surface/call.h"
#include "src/core/lib/surface/channel.h"
#include "src/core/lib/surface/completion_queue.h"
#include "src/core/lib/surface/init.h"
#include "src/core/lib/transport/metadata.h"
#include "src/core/lib/transport/static_metadata.h"

typedef struct listener {
  void *arg;
  void (*start)(grpc_exec_ctx *exec_ctx, grpc_server *server, void *arg,
                grpc_pollset **pollsets, size_t pollset_count);
  void (*destroy)(grpc_exec_ctx *exec_ctx, grpc_server *server, void *arg,
                  grpc_closure *closure);
  struct listener *next;
  grpc_closure destroy_done;
} listener;

typedef struct call_data call_data;
typedef struct channel_data channel_data;
typedef struct registered_method registered_method;

typedef struct {
  call_data *next;
  call_data *prev;
} call_link;

typedef enum { BATCH_CALL, REGISTERED_CALL } requested_call_type;

typedef struct requested_call {
  requested_call_type type;
  void *tag;
  grpc_server *server;
  grpc_completion_queue *cq_bound_to_call;
  grpc_completion_queue *cq_for_notification;
  grpc_call **call;
  grpc_cq_completion completion;
  grpc_metadata_array *initial_metadata;
  union {
    struct {
      grpc_call_details *details;
    } batch;
    struct {
      registered_method *registered_method;
      gpr_timespec *deadline;
      grpc_byte_buffer **optional_payload;
    } registered;
  } data;
} requested_call;

typedef struct channel_registered_method {
  registered_method *server_registered_method;
  uint32_t flags;
  grpc_mdstr *method;
  grpc_mdstr *host;
} channel_registered_method;

struct channel_data {
  grpc_server *server;
  grpc_connectivity_state connectivity_state;
  grpc_channel *channel;
  /* linked list of all channels on a server */
  channel_data *next;
  channel_data *prev;
  channel_registered_method *registered_methods;
  uint32_t registered_method_slots;
  uint32_t registered_method_max_probes;
  grpc_closure finish_destroy_channel_closure;
  grpc_closure channel_connectivity_changed;
};

typedef struct shutdown_tag {
  void *tag;
  grpc_completion_queue *cq;
  grpc_cq_completion completion;
} shutdown_tag;

typedef enum {
  /* waiting for metadata */
  NOT_STARTED,
  /* inital metadata read, not flow controlled in yet */
  PENDING,
  /* flow controlled in, on completion queue */
  ACTIVATED,
  /* cancelled before being queued */
  ZOMBIED
} call_state;

typedef struct request_matcher request_matcher;

struct call_data {
  grpc_call *call;

  /** protects state */
  gpr_mu mu_state;
  /** the current state of a call - see call_state */
  call_state state;

  grpc_mdstr *path;
  grpc_mdstr *host;
  gpr_timespec deadline;

  grpc_completion_queue *cq_new;

  grpc_metadata_batch *recv_initial_metadata;
  bool recv_idempotent_request;
  grpc_metadata_array initial_metadata;

  request_matcher *request_matcher;
  grpc_byte_buffer *payload;

  grpc_closure got_initial_metadata;
  grpc_closure server_on_recv_initial_metadata;
  grpc_closure kill_zombie_closure;
  grpc_closure *on_done_recv_initial_metadata;

  grpc_closure publish;

  call_data *pending_next;
};

struct request_matcher {
  grpc_server *server;
  call_data *pending_head;
  call_data *pending_tail;
  gpr_stack_lockfree *requests;
};

struct registered_method {
  char *method;
  char *host;
  grpc_server_register_method_payload_handling payload_handling;
  uint32_t flags;
  request_matcher request_matcher;
  registered_method *next;
};

typedef struct {
  grpc_channel **channels;
  size_t num_channels;
} channel_broadcaster;

struct grpc_server {
  grpc_channel_args *channel_args;

  grpc_completion_queue **cqs;
  grpc_pollset **pollsets;
  size_t cq_count;

  /* The two following mutexes control access to server-state
     mu_global controls access to non-call-related state (e.g., channel state)
     mu_call controls access to call-related state (e.g., the call lists)

     If they are ever required to be nested, you must lock mu_global
     before mu_call. This is currently used in shutdown processing
     (grpc_server_shutdown_and_notify and maybe_finish_shutdown) */
  gpr_mu mu_global; /* mutex for server and channel state */
  gpr_mu mu_call;   /* mutex for call-specific state */

  registered_method *registered_methods;
  request_matcher unregistered_request_matcher;
  /** free list of available requested_calls indices */
  gpr_stack_lockfree *request_freelist;
  /** requested call backing data */
  requested_call *requested_calls;
  size_t max_requested_calls;

  gpr_atm shutdown_flag;
  uint8_t shutdown_published;
  size_t num_shutdown_tags;
  shutdown_tag *shutdown_tags;

  channel_data root_channel_data;

  listener *listeners;
  int listeners_destroyed;
  gpr_refcount internal_refcount;

  /** when did we print the last shutdown progress message */
  gpr_timespec last_shutdown_message_time;
};

#define SERVER_FROM_CALL_ELEM(elem) \
  (((channel_data *)(elem)->channel_data)->server)

static void publish_new_rpc(grpc_exec_ctx *exec_ctx, void *calld, bool success);
static void fail_call(grpc_exec_ctx *exec_ctx, grpc_server *server,
                      requested_call *rc);
/* Before calling maybe_finish_shutdown, we must hold mu_global and not
   hold mu_call */
static void maybe_finish_shutdown(grpc_exec_ctx *exec_ctx, grpc_server *server);

/*
 * channel broadcaster
 */

/* assumes server locked */
static void channel_broadcaster_init(grpc_server *s, channel_broadcaster *cb) {
  channel_data *c;
  size_t count = 0;
  for (c = s->root_channel_data.next; c != &s->root_channel_data; c = c->next) {
    count++;
  }
  cb->num_channels = count;
  cb->channels = gpr_malloc(sizeof(*cb->channels) * cb->num_channels);
  count = 0;
  for (c = s->root_channel_data.next; c != &s->root_channel_data; c = c->next) {
    cb->channels[count++] = c->channel;
    GRPC_CHANNEL_INTERNAL_REF(c->channel, "broadcast");
  }
}

struct shutdown_cleanup_args {
  grpc_closure closure;
  gpr_slice slice;
};

static void shutdown_cleanup(grpc_exec_ctx *exec_ctx, void *arg,
                             bool iomgr_status_ignored) {
  struct shutdown_cleanup_args *a = arg;
  gpr_slice_unref(a->slice);
  gpr_free(a);
}

static void send_shutdown(grpc_exec_ctx *exec_ctx, grpc_channel *channel,
                          int send_goaway, int send_disconnect) {
  grpc_transport_op op;
  struct shutdown_cleanup_args *sc;
  grpc_channel_element *elem;

  memset(&op, 0, sizeof(op));
  op.send_goaway = send_goaway;
  sc = gpr_malloc(sizeof(*sc));
  sc->slice = gpr_slice_from_copied_string("Server shutdown");
  op.goaway_message = &sc->slice;
  op.goaway_status = GRPC_STATUS_OK;
  op.disconnect = send_disconnect;
  grpc_closure_init(&sc->closure, shutdown_cleanup, sc);
  op.on_consumed = &sc->closure;

  elem = grpc_channel_stack_element(grpc_channel_get_channel_stack(channel), 0);
  elem->filter->start_transport_op(exec_ctx, elem, &op);
}

static void channel_broadcaster_shutdown(grpc_exec_ctx *exec_ctx,
                                         channel_broadcaster *cb,
                                         int send_goaway,
                                         int force_disconnect) {
  size_t i;

  for (i = 0; i < cb->num_channels; i++) {
    send_shutdown(exec_ctx, cb->channels[i], send_goaway, force_disconnect);
    GRPC_CHANNEL_INTERNAL_UNREF(exec_ctx, cb->channels[i], "broadcast");
  }
  gpr_free(cb->channels);
}

/*
 * request_matcher
 */

static void request_matcher_init(request_matcher *rm, size_t entries,
                                 grpc_server *server) {
  memset(rm, 0, sizeof(*rm));
  rm->server = server;
  rm->requests = gpr_stack_lockfree_create(entries);
}

static void request_matcher_destroy(request_matcher *rm) {
  GPR_ASSERT(gpr_stack_lockfree_pop(rm->requests) == -1);
  gpr_stack_lockfree_destroy(rm->requests);
}

static void kill_zombie(grpc_exec_ctx *exec_ctx, void *elem, bool success) {
  grpc_call_destroy(grpc_call_from_top_element(elem));
}

static void request_matcher_zombify_all_pending_calls(grpc_exec_ctx *exec_ctx,
                                                      request_matcher *rm) {
  while (rm->pending_head) {
    call_data *calld = rm->pending_head;
    rm->pending_head = calld->pending_next;
    gpr_mu_lock(&calld->mu_state);
    calld->state = ZOMBIED;
    gpr_mu_unlock(&calld->mu_state);
    grpc_closure_init(
        &calld->kill_zombie_closure, kill_zombie,
        grpc_call_stack_element(grpc_call_get_call_stack(calld->call), 0));
    grpc_exec_ctx_enqueue(exec_ctx, &calld->kill_zombie_closure, true, NULL);
  }
}

static void request_matcher_kill_requests(grpc_exec_ctx *exec_ctx,
                                          grpc_server *server,
                                          request_matcher *rm) {
  int request_id;
  while ((request_id = gpr_stack_lockfree_pop(rm->requests)) != -1) {
    fail_call(exec_ctx, server, &server->requested_calls[request_id]);
  }
}

/*
 * server proper
 */

static void server_ref(grpc_server *server) {
  gpr_ref(&server->internal_refcount);
}

static void server_delete(grpc_exec_ctx *exec_ctx, grpc_server *server) {
  registered_method *rm;
  size_t i;
  grpc_channel_args_destroy(server->channel_args);
  gpr_mu_destroy(&server->mu_global);
  gpr_mu_destroy(&server->mu_call);
  while ((rm = server->registered_methods) != NULL) {
    server->registered_methods = rm->next;
    request_matcher_destroy(&rm->request_matcher);
    gpr_free(rm->method);
    gpr_free(rm->host);
    gpr_free(rm);
  }
  for (i = 0; i < server->cq_count; i++) {
    GRPC_CQ_INTERNAL_UNREF(server->cqs[i], "server");
  }
  request_matcher_destroy(&server->unregistered_request_matcher);
  gpr_stack_lockfree_destroy(server->request_freelist);
  gpr_free(server->cqs);
  gpr_free(server->pollsets);
  gpr_free(server->shutdown_tags);
  gpr_free(server->requested_calls);
  gpr_free(server);
}

static void server_unref(grpc_exec_ctx *exec_ctx, grpc_server *server) {
  if (gpr_unref(&server->internal_refcount)) {
    server_delete(exec_ctx, server);
  }
}

static int is_channel_orphaned(channel_data *chand) {
  return chand->next == chand;
}

static void orphan_channel(channel_data *chand) {
  chand->next->prev = chand->prev;
  chand->prev->next = chand->next;
  chand->next = chand->prev = chand;
}

static void finish_destroy_channel(grpc_exec_ctx *exec_ctx, void *cd,
                                   bool success) {
  channel_data *chand = cd;
  grpc_server *server = chand->server;
  GRPC_CHANNEL_INTERNAL_UNREF(exec_ctx, chand->channel, "server");
  server_unref(exec_ctx, server);
}

static void destroy_channel(grpc_exec_ctx *exec_ctx, channel_data *chand) {
  if (is_channel_orphaned(chand)) return;
  GPR_ASSERT(chand->server != NULL);
  orphan_channel(chand);
  server_ref(chand->server);
  maybe_finish_shutdown(exec_ctx, chand->server);
  chand->finish_destroy_channel_closure.cb = finish_destroy_channel;
  chand->finish_destroy_channel_closure.cb_arg = chand;

  grpc_transport_op op;
  memset(&op, 0, sizeof(op));
  op.set_accept_stream = true;
  op.on_consumed = &chand->finish_destroy_channel_closure;
  grpc_channel_next_op(exec_ctx,
                       grpc_channel_stack_element(
                           grpc_channel_get_channel_stack(chand->channel), 0),
                       &op);
}

static void cpstr(char **dest, size_t *capacity, grpc_mdstr *value) {
  gpr_slice slice = value->slice;
  size_t len = GPR_SLICE_LENGTH(slice);

  if (len + 1 > *capacity) {
    *capacity = GPR_MAX(len + 1, *capacity * 2);
    *dest = gpr_realloc(*dest, *capacity);
  }
  memcpy(*dest, grpc_mdstr_as_c_string(value), len + 1);
}

static void done_request_event(grpc_exec_ctx *exec_ctx, void *req,
                               grpc_cq_completion *c) {
  requested_call *rc = req;
  grpc_server *server = rc->server;

  if (rc >= server->requested_calls &&
      rc < server->requested_calls + server->max_requested_calls) {
    GPR_ASSERT(rc - server->requested_calls <= INT_MAX);
    gpr_stack_lockfree_push(server->request_freelist,
                            (int)(rc - server->requested_calls));
  } else {
    gpr_free(req);
  }

  server_unref(exec_ctx, server);
}

static void publish_call(grpc_exec_ctx *exec_ctx, grpc_server *server,
                         call_data *calld, requested_call *rc) {
  grpc_call_set_completion_queue(exec_ctx, calld->call, rc->cq_bound_to_call);
  grpc_call *call = calld->call;
  *rc->call = call;
  calld->cq_new = rc->cq_for_notification;
  GPR_SWAP(grpc_metadata_array, *rc->initial_metadata, calld->initial_metadata);
  switch (rc->type) {
    case BATCH_CALL:
      GPR_ASSERT(calld->host != NULL);
      GPR_ASSERT(calld->path != NULL);
      cpstr(&rc->data.batch.details->host,
            &rc->data.batch.details->host_capacity, calld->host);
      cpstr(&rc->data.batch.details->method,
            &rc->data.batch.details->method_capacity, calld->path);
      rc->data.batch.details->deadline = calld->deadline;
      rc->data.batch.details->flags =
          0 | (calld->recv_idempotent_request
                   ? GRPC_INITIAL_METADATA_IDEMPOTENT_REQUEST
                   : 0);
      break;
    case REGISTERED_CALL:
      *rc->data.registered.deadline = calld->deadline;
      if (rc->data.registered.optional_payload) {
        *rc->data.registered.optional_payload = calld->payload;
      }
      break;
    default:
      GPR_UNREACHABLE_CODE(return );
  }

  grpc_call_element *elem =
      grpc_call_stack_element(grpc_call_get_call_stack(call), 0);
  channel_data *chand = elem->channel_data;
  server_ref(chand->server);
  grpc_cq_end_op(exec_ctx, calld->cq_new, rc->tag, true, done_request_event, rc,
                 &rc->completion);
}

static void publish_new_rpc(grpc_exec_ctx *exec_ctx, void *arg, bool success) {
  call_data *calld = arg;
  request_matcher *rm = calld->request_matcher;
  grpc_server *server = rm->server;

  if (!success || gpr_atm_acq_load(&server->shutdown_flag)) {
    gpr_mu_lock(&calld->mu_state);
    calld->state = ZOMBIED;
    gpr_mu_unlock(&calld->mu_state);
    grpc_closure_init(
        &calld->kill_zombie_closure, kill_zombie,
        grpc_call_stack_element(grpc_call_get_call_stack(calld->call), 0));
    grpc_exec_ctx_enqueue(exec_ctx, &calld->kill_zombie_closure, true, NULL);
    return;
  }

  int request_id = gpr_stack_lockfree_pop(rm->requests);
  if (request_id == -1) {
    gpr_mu_lock(&server->mu_call);
    gpr_mu_lock(&calld->mu_state);
    calld->state = PENDING;
    gpr_mu_unlock(&calld->mu_state);
    if (rm->pending_head == NULL) {
      rm->pending_tail = rm->pending_head = calld;
    } else {
      rm->pending_tail->pending_next = calld;
      rm->pending_tail = calld;
    }
    calld->pending_next = NULL;
    gpr_mu_unlock(&server->mu_call);
  } else {
    gpr_mu_lock(&calld->mu_state);
    calld->state = ACTIVATED;
    gpr_mu_unlock(&calld->mu_state);
    publish_call(exec_ctx, server, calld, &server->requested_calls[request_id]);
  }
}

static void finish_start_new_rpc(
    grpc_exec_ctx *exec_ctx, grpc_server *server, grpc_call_element *elem,
    request_matcher *rm,
    grpc_server_register_method_payload_handling payload_handling) {
  call_data *calld = elem->call_data;

  if (gpr_atm_acq_load(&server->shutdown_flag)) {
    gpr_mu_lock(&calld->mu_state);
    calld->state = ZOMBIED;
    gpr_mu_unlock(&calld->mu_state);
    grpc_closure_init(&calld->kill_zombie_closure, kill_zombie, elem);
    grpc_exec_ctx_enqueue(exec_ctx, &calld->kill_zombie_closure, true, NULL);
    return;
  }

  calld->request_matcher = rm;

  switch (payload_handling) {
    case GRPC_SRM_PAYLOAD_NONE:
      publish_new_rpc(exec_ctx, calld, true);
      break;
    case GRPC_SRM_PAYLOAD_READ_INITIAL_BYTE_BUFFER: {
      grpc_op op;
      memset(&op, 0, sizeof(op));
      op.op = GRPC_OP_RECV_MESSAGE;
      op.data.recv_message = &calld->payload;
      grpc_closure_init(&calld->publish, publish_new_rpc, calld);
      grpc_call_start_batch_and_execute(exec_ctx, calld->call, &op, 1,
                                        &calld->publish);
      break;
    }
  }
}

static void start_new_rpc(grpc_exec_ctx *exec_ctx, grpc_call_element *elem) {
  channel_data *chand = elem->channel_data;
  call_data *calld = elem->call_data;
  grpc_server *server = chand->server;
  uint32_t i;
  uint32_t hash;
  channel_registered_method *rm;

  if (chand->registered_methods && calld->path && calld->host) {
    /* TODO(ctiller): unify these two searches */
    /* check for an exact match with host */
    hash = GRPC_MDSTR_KV_HASH(calld->host->hash, calld->path->hash);
    for (i = 0; i <= chand->registered_method_max_probes; i++) {
      rm = &chand->registered_methods[(hash + i) %
                                      chand->registered_method_slots];
      if (!rm) break;
      if (rm->host != calld->host) continue;
      if (rm->method != calld->path) continue;
      if ((rm->flags & GRPC_INITIAL_METADATA_IDEMPOTENT_REQUEST) &&
          !calld->recv_idempotent_request)
        continue;
      finish_start_new_rpc(exec_ctx, server, elem,
                           &rm->server_registered_method->request_matcher,
                           rm->server_registered_method->payload_handling);
      return;
    }
    /* check for a wildcard method definition (no host set) */
    hash = GRPC_MDSTR_KV_HASH(0, calld->path->hash);
    for (i = 0; i <= chand->registered_method_max_probes; i++) {
      rm = &chand->registered_methods[(hash + i) %
                                      chand->registered_method_slots];
      if (!rm) break;
      if (rm->host != NULL) continue;
      if (rm->method != calld->path) continue;
      if ((rm->flags & GRPC_INITIAL_METADATA_IDEMPOTENT_REQUEST) &&
          !calld->recv_idempotent_request)
        continue;
      finish_start_new_rpc(exec_ctx, server, elem,
                           &rm->server_registered_method->request_matcher,
                           rm->server_registered_method->payload_handling);
      return;
    }
  }
  finish_start_new_rpc(exec_ctx, server, elem,
                       &server->unregistered_request_matcher,
                       GRPC_SRM_PAYLOAD_NONE);
}

static int num_listeners(grpc_server *server) {
  listener *l;
  int n = 0;
  for (l = server->listeners; l; l = l->next) {
    n++;
  }
  return n;
}

static void done_shutdown_event(grpc_exec_ctx *exec_ctx, void *server,
                                grpc_cq_completion *completion) {
  server_unref(exec_ctx, server);
}

static int num_channels(grpc_server *server) {
  channel_data *chand;
  int n = 0;
  for (chand = server->root_channel_data.next;
       chand != &server->root_channel_data; chand = chand->next) {
    n++;
  }
  return n;
}

static void kill_pending_work_locked(grpc_exec_ctx *exec_ctx,
                                     grpc_server *server) {
  registered_method *rm;
  request_matcher_kill_requests(exec_ctx, server,
                                &server->unregistered_request_matcher);
  request_matcher_zombify_all_pending_calls(
      exec_ctx, &server->unregistered_request_matcher);
  for (rm = server->registered_methods; rm; rm = rm->next) {
    request_matcher_kill_requests(exec_ctx, server, &rm->request_matcher);
    request_matcher_zombify_all_pending_calls(exec_ctx, &rm->request_matcher);
  }
}

static void maybe_finish_shutdown(grpc_exec_ctx *exec_ctx,
                                  grpc_server *server) {
  size_t i;
  if (!gpr_atm_acq_load(&server->shutdown_flag) || server->shutdown_published) {
    return;
  }

  kill_pending_work_locked(exec_ctx, server);

  if (server->root_channel_data.next != &server->root_channel_data ||
      server->listeners_destroyed < num_listeners(server)) {
    if (gpr_time_cmp(gpr_time_sub(gpr_now(GPR_CLOCK_REALTIME),
                                  server->last_shutdown_message_time),
                     gpr_time_from_seconds(1, GPR_TIMESPAN)) >= 0) {
      server->last_shutdown_message_time = gpr_now(GPR_CLOCK_REALTIME);
      gpr_log(GPR_DEBUG,
              "Waiting for %d channels and %d/%d listeners to be destroyed"
              " before shutting down server",
              num_channels(server),
              num_listeners(server) - server->listeners_destroyed,
              num_listeners(server));
    }
    return;
  }
  server->shutdown_published = 1;
  for (i = 0; i < server->num_shutdown_tags; i++) {
    server_ref(server);
    grpc_cq_end_op(exec_ctx, server->shutdown_tags[i].cq,
                   server->shutdown_tags[i].tag, 1, done_shutdown_event, server,
                   &server->shutdown_tags[i].completion);
  }
}

static grpc_mdelem *server_filter(void *user_data, grpc_mdelem *md) {
  grpc_call_element *elem = user_data;
  call_data *calld = elem->call_data;
  if (md->key == GRPC_MDSTR_PATH) {
    if (calld->path == NULL) {
      calld->path = GRPC_MDSTR_REF(md->value);
    }
    return NULL;
  } else if (md->key == GRPC_MDSTR_AUTHORITY) {
    if (calld->host == NULL) {
      calld->host = GRPC_MDSTR_REF(md->value);
    }
    return NULL;
  }
  return md;
}

static void server_on_recv_initial_metadata(grpc_exec_ctx *exec_ctx, void *ptr,
                                            bool success) {
  grpc_call_element *elem = ptr;
  call_data *calld = elem->call_data;
  gpr_timespec op_deadline;

  grpc_metadata_batch_filter(calld->recv_initial_metadata, server_filter, elem);
  op_deadline = calld->recv_initial_metadata->deadline;
  if (0 != gpr_time_cmp(op_deadline, gpr_inf_future(op_deadline.clock_type))) {
    calld->deadline = op_deadline;
  }
  if (calld->host && calld->path) {
    /* do nothing */
  } else {
    success = 0;
  }

  calld->on_done_recv_initial_metadata->cb(
      exec_ctx, calld->on_done_recv_initial_metadata->cb_arg, success);
}

static void server_mutate_op(grpc_call_element *elem,
                             grpc_transport_stream_op *op) {
  call_data *calld = elem->call_data;

  if (op->recv_initial_metadata != NULL) {
    GPR_ASSERT(op->recv_idempotent_request == NULL);
    calld->recv_initial_metadata = op->recv_initial_metadata;
    calld->on_done_recv_initial_metadata = op->recv_initial_metadata_ready;
    op->recv_initial_metadata_ready = &calld->server_on_recv_initial_metadata;
    op->recv_idempotent_request = &calld->recv_idempotent_request;
  }
}

static void server_start_transport_stream_op(grpc_exec_ctx *exec_ctx,
                                             grpc_call_element *elem,
                                             grpc_transport_stream_op *op) {
  GRPC_CALL_LOG_OP(GPR_INFO, elem, op);
  server_mutate_op(elem, op);
  grpc_call_next_op(exec_ctx, elem, op);
}

static void got_initial_metadata(grpc_exec_ctx *exec_ctx, void *ptr,
                                 bool success) {
  grpc_call_element *elem = ptr;
  call_data *calld = elem->call_data;
  if (success) {
    start_new_rpc(exec_ctx, elem);
  } else {
    gpr_mu_lock(&calld->mu_state);
    if (calld->state == NOT_STARTED) {
      calld->state = ZOMBIED;
      gpr_mu_unlock(&calld->mu_state);
      grpc_closure_init(&calld->kill_zombie_closure, kill_zombie, elem);
      grpc_exec_ctx_enqueue(exec_ctx, &calld->kill_zombie_closure, true, NULL);
    } else if (calld->state == PENDING) {
      calld->state = ZOMBIED;
      gpr_mu_unlock(&calld->mu_state);
      /* zombied call will be destroyed when it's removed from the pending
         queue... later */
    } else {
      gpr_mu_unlock(&calld->mu_state);
    }
  }
}

static void accept_stream(grpc_exec_ctx *exec_ctx, void *cd,
                          grpc_transport *transport,
                          const void *transport_server_data) {
  channel_data *chand = cd;
  /* create a call */
  grpc_call *call =
      grpc_call_create(chand->channel, NULL, 0, NULL, transport_server_data,
                       NULL, 0, gpr_inf_future(GPR_CLOCK_MONOTONIC));
  grpc_call_element *elem =
      grpc_call_stack_element(grpc_call_get_call_stack(call), 0);
  call_data *calld = elem->call_data;
  grpc_op op;
  memset(&op, 0, sizeof(op));
  op.op = GRPC_OP_RECV_INITIAL_METADATA;
  op.data.recv_initial_metadata = &calld->initial_metadata;
  grpc_closure_init(&calld->got_initial_metadata, got_initial_metadata, elem);
  grpc_call_start_batch_and_execute(exec_ctx, call, &op, 1,
                                    &calld->got_initial_metadata);
}

static void channel_connectivity_changed(grpc_exec_ctx *exec_ctx, void *cd,
                                         bool iomgr_status_ignored) {
  channel_data *chand = cd;
  grpc_server *server = chand->server;
  if (chand->connectivity_state != GRPC_CHANNEL_FATAL_FAILURE) {
    grpc_transport_op op;
    memset(&op, 0, sizeof(op));
    op.on_connectivity_state_change = &chand->channel_connectivity_changed,
    op.connectivity_state = &chand->connectivity_state;
    grpc_channel_next_op(exec_ctx,
                         grpc_channel_stack_element(
                             grpc_channel_get_channel_stack(chand->channel), 0),
                         &op);
  } else {
    gpr_mu_lock(&server->mu_global);
    destroy_channel(exec_ctx, chand);
    gpr_mu_unlock(&server->mu_global);
    GRPC_CHANNEL_INTERNAL_UNREF(exec_ctx, chand->channel, "connectivity");
  }
}

static void init_call_elem(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
                           grpc_call_element_args *args) {
  call_data *calld = elem->call_data;
  channel_data *chand = elem->channel_data;
  memset(calld, 0, sizeof(call_data));
  calld->deadline = gpr_inf_future(GPR_CLOCK_REALTIME);
  calld->call = grpc_call_from_top_element(elem);
  gpr_mu_init(&calld->mu_state);

  grpc_closure_init(&calld->server_on_recv_initial_metadata,
                    server_on_recv_initial_metadata, elem);

  server_ref(chand->server);
}

static void destroy_call_elem(grpc_exec_ctx *exec_ctx,
                              grpc_call_element *elem) {
  channel_data *chand = elem->channel_data;
  call_data *calld = elem->call_data;

  GPR_ASSERT(calld->state != PENDING);

  if (calld->host) {
    GRPC_MDSTR_UNREF(calld->host);
  }
  if (calld->path) {
    GRPC_MDSTR_UNREF(calld->path);
  }
  grpc_metadata_array_destroy(&calld->initial_metadata);

  gpr_mu_destroy(&calld->mu_state);

  server_unref(exec_ctx, chand->server);
}

static void init_channel_elem(grpc_exec_ctx *exec_ctx,
                              grpc_channel_element *elem,
                              grpc_channel_element_args *args) {
  channel_data *chand = elem->channel_data;
  GPR_ASSERT(args->is_first);
  GPR_ASSERT(!args->is_last);
  chand->server = NULL;
  chand->channel = NULL;
  chand->next = chand->prev = chand;
  chand->registered_methods = NULL;
  chand->connectivity_state = GRPC_CHANNEL_IDLE;
  grpc_closure_init(&chand->channel_connectivity_changed,
                    channel_connectivity_changed, chand);
}

static void destroy_channel_elem(grpc_exec_ctx *exec_ctx,
                                 grpc_channel_element *elem) {
  size_t i;
  channel_data *chand = elem->channel_data;
  if (chand->registered_methods) {
    for (i = 0; i < chand->registered_method_slots; i++) {
      if (chand->registered_methods[i].method) {
        GRPC_MDSTR_UNREF(chand->registered_methods[i].method);
      }
      if (chand->registered_methods[i].host) {
        GRPC_MDSTR_UNREF(chand->registered_methods[i].host);
      }
    }
    gpr_free(chand->registered_methods);
  }
  if (chand->server) {
    gpr_mu_lock(&chand->server->mu_global);
    chand->next->prev = chand->prev;
    chand->prev->next = chand->next;
    chand->next = chand->prev = chand;
    maybe_finish_shutdown(exec_ctx, chand->server);
    gpr_mu_unlock(&chand->server->mu_global);
    server_unref(exec_ctx, chand->server);
  }
}

const grpc_channel_filter grpc_server_top_filter = {
    server_start_transport_stream_op,
    grpc_channel_next_op,
    sizeof(call_data),
    init_call_elem,
    grpc_call_stack_ignore_set_pollset,
    destroy_call_elem,
    sizeof(channel_data),
    init_channel_elem,
    destroy_channel_elem,
    grpc_call_next_get_peer,
    "server",
};

static void register_completion_queue(grpc_server *server,
                                      grpc_completion_queue *cq,
                                      bool is_non_listening, void *reserved) {
  size_t i, n;
  GPR_ASSERT(!reserved);
  for (i = 0; i < server->cq_count; i++) {
    if (server->cqs[i] == cq) return;
  }

  grpc_cq_mark_server_cq(cq);

  /* Non-listening completion queues are not added to server->cqs */
  if (is_non_listening) {
    grpc_cq_mark_non_listening_server_cq(cq);
  } else {
    GRPC_CQ_INTERNAL_REF(cq, "server");
    n = server->cq_count++;
    server->cqs = gpr_realloc(
        server->cqs, server->cq_count * sizeof(grpc_completion_queue *));
    server->cqs[n] = cq;
  }
}

void grpc_server_register_completion_queue(grpc_server *server,
                                           grpc_completion_queue *cq,
                                           void *reserved) {
  GRPC_API_TRACE(
      "grpc_server_register_completion_queue(server=%p, cq=%p, reserved=%p)", 3,
      (server, cq, reserved));
  register_completion_queue(server, cq, false, reserved);
}

void grpc_server_register_non_listening_completion_queue(
    grpc_server *server, grpc_completion_queue *cq, void *reserved) {
  GRPC_API_TRACE(
      "grpc_server_register_non_listening_completion_queue(server=%p, cq=%p, "
      "reserved=%p)",
      3, (server, cq, reserved));
  register_completion_queue(server, cq, true, reserved);
}

grpc_server *grpc_server_create(const grpc_channel_args *args, void *reserved) {
  size_t i;

  GRPC_API_TRACE("grpc_server_create(%p, %p)", 2, (args, reserved));

  grpc_server *server = gpr_malloc(sizeof(grpc_server));

  GPR_ASSERT(grpc_is_initialized() && "call grpc_init()");

  memset(server, 0, sizeof(grpc_server));

  gpr_mu_init(&server->mu_global);
  gpr_mu_init(&server->mu_call);

  /* decremented by grpc_server_destroy */
  gpr_ref_init(&server->internal_refcount, 1);
  server->root_channel_data.next = server->root_channel_data.prev =
      &server->root_channel_data;

  /* TODO(ctiller): expose a channel_arg for this */
  server->max_requested_calls = 32768;
  server->request_freelist =
      gpr_stack_lockfree_create(server->max_requested_calls);
  for (i = 0; i < (size_t)server->max_requested_calls; i++) {
    gpr_stack_lockfree_push(server->request_freelist, (int)i);
  }
  request_matcher_init(&server->unregistered_request_matcher,
                       server->max_requested_calls, server);
  server->requested_calls = gpr_malloc(server->max_requested_calls *
                                       sizeof(*server->requested_calls));

  server->channel_args = grpc_channel_args_copy(args);

  return server;
}

static int streq(const char *a, const char *b) {
  if (a == NULL && b == NULL) return 1;
  if (a == NULL) return 0;
  if (b == NULL) return 0;
  return 0 == strcmp(a, b);
}

void *grpc_server_register_method(
    grpc_server *server, const char *method, const char *host,
    grpc_server_register_method_payload_handling payload_handling,
    uint32_t flags) {
  registered_method *m;
  GRPC_API_TRACE(
      "grpc_server_register_method(server=%p, method=%s, host=%s, "
      "flags=0x%08x)",
      4, (server, method, host, flags));
  if (!method) {
    gpr_log(GPR_ERROR,
            "grpc_server_register_method method string cannot be NULL");
    return NULL;
  }
  for (m = server->registered_methods; m; m = m->next) {
    if (streq(m->method, method) && streq(m->host, host)) {
      gpr_log(GPR_ERROR, "duplicate registration for %s@%s", method,
              host ? host : "*");
      return NULL;
    }
  }
  if ((flags & ~GRPC_INITIAL_METADATA_USED_MASK) != 0) {
    gpr_log(GPR_ERROR, "grpc_server_register_method invalid flags 0x%08x",
            flags);
    return NULL;
  }
  m = gpr_malloc(sizeof(registered_method));
  memset(m, 0, sizeof(*m));
  request_matcher_init(&m->request_matcher, server->max_requested_calls,
                       server);
  m->method = gpr_strdup(method);
  m->host = gpr_strdup(host);
  m->next = server->registered_methods;
  m->payload_handling = payload_handling;
  m->flags = flags;
  server->registered_methods = m;
  return m;
}

void grpc_server_start(grpc_server *server) {
  listener *l;
  size_t i;
  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;

  GRPC_API_TRACE("grpc_server_start(server=%p)", 1, (server));

  server->pollsets = gpr_malloc(sizeof(grpc_pollset *) * server->cq_count);
  for (i = 0; i < server->cq_count; i++) {
    server->pollsets[i] = grpc_cq_pollset(server->cqs[i]);
  }

  for (l = server->listeners; l; l = l->next) {
    l->start(&exec_ctx, server, l->arg, server->pollsets, server->cq_count);
  }

  grpc_exec_ctx_finish(&exec_ctx);
}

void grpc_server_setup_transport(grpc_exec_ctx *exec_ctx, grpc_server *s,
                                 grpc_transport *transport,
                                 const grpc_channel_args *args) {
  size_t num_registered_methods;
  size_t alloc;
  registered_method *rm;
  channel_registered_method *crm;
  grpc_channel *channel;
  channel_data *chand;
  grpc_mdstr *host;
  grpc_mdstr *method;
  uint32_t hash;
  size_t slots;
  uint32_t probes;
  uint32_t max_probes = 0;
  grpc_transport_op op;

  channel =
      grpc_channel_create(exec_ctx, NULL, args, GRPC_SERVER_CHANNEL, transport);
  chand = (channel_data *)grpc_channel_stack_element(
              grpc_channel_get_channel_stack(channel), 0)
              ->channel_data;
  chand->server = s;
  server_ref(s);
  chand->channel = channel;

  num_registered_methods = 0;
  for (rm = s->registered_methods; rm; rm = rm->next) {
    num_registered_methods++;
  }
  /* build a lookup table phrased in terms of mdstr's in this channels context
     to quickly find registered methods */
  if (num_registered_methods > 0) {
    slots = 2 * num_registered_methods;
    alloc = sizeof(channel_registered_method) * slots;
    chand->registered_methods = gpr_malloc(alloc);
    memset(chand->registered_methods, 0, alloc);
    for (rm = s->registered_methods; rm; rm = rm->next) {
      host = rm->host ? grpc_mdstr_from_string(rm->host) : NULL;
      method = grpc_mdstr_from_string(rm->method);
      hash = GRPC_MDSTR_KV_HASH(host ? host->hash : 0, method->hash);
      for (probes = 0; chand->registered_methods[(hash + probes) % slots]
                           .server_registered_method != NULL;
           probes++)
        ;
      if (probes > max_probes) max_probes = probes;
      crm = &chand->registered_methods[(hash + probes) % slots];
      crm->server_registered_method = rm;
      crm->flags = rm->flags;
      crm->host = host;
      crm->method = method;
    }
    GPR_ASSERT(slots <= UINT32_MAX);
    chand->registered_method_slots = (uint32_t)slots;
    chand->registered_method_max_probes = max_probes;
  }

  gpr_mu_lock(&s->mu_global);
  chand->next = &s->root_channel_data;
  chand->prev = chand->next->prev;
  chand->next->prev = chand->prev->next = chand;
  gpr_mu_unlock(&s->mu_global);

  GRPC_CHANNEL_INTERNAL_REF(channel, "connectivity");
  memset(&op, 0, sizeof(op));
  op.set_accept_stream = true;
  op.set_accept_stream_fn = accept_stream;
  op.set_accept_stream_user_data = chand;
  op.on_connectivity_state_change = &chand->channel_connectivity_changed;
  op.connectivity_state = &chand->connectivity_state;
  op.disconnect = gpr_atm_acq_load(&s->shutdown_flag) != 0;
  grpc_transport_perform_op(exec_ctx, transport, &op);
}

void done_published_shutdown(grpc_exec_ctx *exec_ctx, void *done_arg,
                             grpc_cq_completion *storage) {
  (void)done_arg;
  gpr_free(storage);
}

static void listener_destroy_done(grpc_exec_ctx *exec_ctx, void *s,
                                  bool success) {
  grpc_server *server = s;
  gpr_mu_lock(&server->mu_global);
  server->listeners_destroyed++;
  maybe_finish_shutdown(exec_ctx, server);
  gpr_mu_unlock(&server->mu_global);
}

void grpc_server_shutdown_and_notify(grpc_server *server,
                                     grpc_completion_queue *cq, void *tag) {
  listener *l;
  shutdown_tag *sdt;
  channel_broadcaster broadcaster;
  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;

  GRPC_API_TRACE("grpc_server_shutdown_and_notify(server=%p, cq=%p, tag=%p)", 3,
                 (server, cq, tag));

  /* lock, and gather up some stuff to do */
  gpr_mu_lock(&server->mu_global);
  grpc_cq_begin_op(cq, tag);
  if (server->shutdown_published) {
    grpc_cq_end_op(&exec_ctx, cq, tag, 1, done_published_shutdown, NULL,
                   gpr_malloc(sizeof(grpc_cq_completion)));
    gpr_mu_unlock(&server->mu_global);
    goto done;
  }
  server->shutdown_tags =
      gpr_realloc(server->shutdown_tags,
                  sizeof(shutdown_tag) * (server->num_shutdown_tags + 1));
  sdt = &server->shutdown_tags[server->num_shutdown_tags++];
  sdt->tag = tag;
  sdt->cq = cq;
  if (gpr_atm_acq_load(&server->shutdown_flag)) {
    gpr_mu_unlock(&server->mu_global);
    goto done;
  }

  server->last_shutdown_message_time = gpr_now(GPR_CLOCK_REALTIME);

  channel_broadcaster_init(server, &broadcaster);

  gpr_atm_rel_store(&server->shutdown_flag, 1);

  /* collect all unregistered then registered calls */
  gpr_mu_lock(&server->mu_call);
  kill_pending_work_locked(&exec_ctx, server);
  gpr_mu_unlock(&server->mu_call);

  maybe_finish_shutdown(&exec_ctx, server);
  gpr_mu_unlock(&server->mu_global);

  /* Shutdown listeners */
  for (l = server->listeners; l; l = l->next) {
    grpc_closure_init(&l->destroy_done, listener_destroy_done, server);
    l->destroy(&exec_ctx, server, l->arg, &l->destroy_done);
  }

  channel_broadcaster_shutdown(&exec_ctx, &broadcaster, 1, 0);

done:
  grpc_exec_ctx_finish(&exec_ctx);
}

void grpc_server_cancel_all_calls(grpc_server *server) {
  channel_broadcaster broadcaster;
  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;

  GRPC_API_TRACE("grpc_server_cancel_all_calls(server=%p)", 1, (server));

  gpr_mu_lock(&server->mu_global);
  channel_broadcaster_init(server, &broadcaster);
  gpr_mu_unlock(&server->mu_global);

  channel_broadcaster_shutdown(&exec_ctx, &broadcaster, 0, 1);
  grpc_exec_ctx_finish(&exec_ctx);
}

void grpc_server_destroy(grpc_server *server) {
  listener *l;
  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;

  GRPC_API_TRACE("grpc_server_destroy(server=%p)", 1, (server));

  gpr_mu_lock(&server->mu_global);
  GPR_ASSERT(gpr_atm_acq_load(&server->shutdown_flag) || !server->listeners);
  GPR_ASSERT(server->listeners_destroyed == num_listeners(server));

  while (server->listeners) {
    l = server->listeners;
    server->listeners = l->next;
    gpr_free(l);
  }

  gpr_mu_unlock(&server->mu_global);

  server_unref(&exec_ctx, server);
  grpc_exec_ctx_finish(&exec_ctx);
}

void grpc_server_add_listener(
    grpc_exec_ctx *exec_ctx, grpc_server *server, void *arg,
    void (*start)(grpc_exec_ctx *exec_ctx, grpc_server *server, void *arg,
                  grpc_pollset **pollsets, size_t pollset_count),
    void (*destroy)(grpc_exec_ctx *exec_ctx, grpc_server *server, void *arg,
                    grpc_closure *on_done)) {
  listener *l = gpr_malloc(sizeof(listener));
  l->arg = arg;
  l->start = start;
  l->destroy = destroy;
  l->next = server->listeners;
  server->listeners = l;
}

static grpc_call_error queue_call_request(grpc_exec_ctx *exec_ctx,
                                          grpc_server *server,
                                          requested_call *rc) {
  call_data *calld = NULL;
  request_matcher *rm = NULL;
  int request_id;
  if (gpr_atm_acq_load(&server->shutdown_flag)) {
    fail_call(exec_ctx, server, rc);
    return GRPC_CALL_OK;
  }
  request_id = gpr_stack_lockfree_pop(server->request_freelist);
  if (request_id == -1) {
    /* out of request ids: just fail this one */
    fail_call(exec_ctx, server, rc);
    return GRPC_CALL_OK;
  }
  switch (rc->type) {
    case BATCH_CALL:
      rm = &server->unregistered_request_matcher;
      break;
    case REGISTERED_CALL:
      rm = &rc->data.registered.registered_method->request_matcher;
      break;
  }
  server->requested_calls[request_id] = *rc;
  gpr_free(rc);
  if (gpr_stack_lockfree_push(rm->requests, request_id)) {
    /* this was the first queued request: we need to lock and start
       matching calls */
    gpr_mu_lock(&server->mu_call);
    while ((calld = rm->pending_head) != NULL) {
      request_id = gpr_stack_lockfree_pop(rm->requests);
      if (request_id == -1) break;
      rm->pending_head = calld->pending_next;
      gpr_mu_unlock(&server->mu_call);
      gpr_mu_lock(&calld->mu_state);
      if (calld->state == ZOMBIED) {
        gpr_mu_unlock(&calld->mu_state);
        grpc_closure_init(
            &calld->kill_zombie_closure, kill_zombie,
            grpc_call_stack_element(grpc_call_get_call_stack(calld->call), 0));
        grpc_exec_ctx_enqueue(exec_ctx, &calld->kill_zombie_closure, true,
                              NULL);
      } else {
        GPR_ASSERT(calld->state == PENDING);
        calld->state = ACTIVATED;
        gpr_mu_unlock(&calld->mu_state);
        publish_call(exec_ctx, server, calld,
                     &server->requested_calls[request_id]);
      }
      gpr_mu_lock(&server->mu_call);
    }
    gpr_mu_unlock(&server->mu_call);
  }
  return GRPC_CALL_OK;
}

grpc_call_error grpc_server_request_call(
    grpc_server *server, grpc_call **call, grpc_call_details *details,
    grpc_metadata_array *initial_metadata,
    grpc_completion_queue *cq_bound_to_call,
    grpc_completion_queue *cq_for_notification, void *tag) {
  grpc_call_error error;
  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
  requested_call *rc = gpr_malloc(sizeof(*rc));
  GRPC_API_TRACE(
      "grpc_server_request_call("
      "server=%p, call=%p, details=%p, initial_metadata=%p, "
      "cq_bound_to_call=%p, cq_for_notification=%p, tag=%p)",
      7, (server, call, details, initial_metadata, cq_bound_to_call,
          cq_for_notification, tag));
  if (!grpc_cq_is_server_cq(cq_for_notification)) {
    gpr_free(rc);
    error = GRPC_CALL_ERROR_NOT_SERVER_COMPLETION_QUEUE;
    goto done;
  }
  grpc_cq_begin_op(cq_for_notification, tag);
  details->reserved = NULL;
  rc->type = BATCH_CALL;
  rc->server = server;
  rc->tag = tag;
  rc->cq_bound_to_call = cq_bound_to_call;
  rc->cq_for_notification = cq_for_notification;
  rc->call = call;
  rc->data.batch.details = details;
  rc->initial_metadata = initial_metadata;
  error = queue_call_request(&exec_ctx, server, rc);
done:
  grpc_exec_ctx_finish(&exec_ctx);
  return error;
}

grpc_call_error grpc_server_request_registered_call(
    grpc_server *server, void *rmp, grpc_call **call, gpr_timespec *deadline,
    grpc_metadata_array *initial_metadata, grpc_byte_buffer **optional_payload,
    grpc_completion_queue *cq_bound_to_call,
    grpc_completion_queue *cq_for_notification, void *tag) {
  grpc_call_error error;
  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
  requested_call *rc = gpr_malloc(sizeof(*rc));
  registered_method *rm = rmp;
  GRPC_API_TRACE(
      "grpc_server_request_registered_call("
      "server=%p, rmp=%p, call=%p, deadline=%p, initial_metadata=%p, "
      "optional_payload=%p, cq_bound_to_call=%p, cq_for_notification=%p, "
      "tag=%p)",
      9, (server, rmp, call, deadline, initial_metadata, optional_payload,
          cq_bound_to_call, cq_for_notification, tag));
  if (!grpc_cq_is_server_cq(cq_for_notification)) {
    gpr_free(rc);
    error = GRPC_CALL_ERROR_NOT_SERVER_COMPLETION_QUEUE;
    goto done;
  }
  if ((optional_payload == NULL) !=
      (rm->payload_handling == GRPC_SRM_PAYLOAD_NONE)) {
    gpr_free(rc);
    error = GRPC_CALL_ERROR_PAYLOAD_TYPE_MISMATCH;
    goto done;
  }
  grpc_cq_begin_op(cq_for_notification, tag);
  rc->type = REGISTERED_CALL;
  rc->server = server;
  rc->tag = tag;
  rc->cq_bound_to_call = cq_bound_to_call;
  rc->cq_for_notification = cq_for_notification;
  rc->call = call;
  rc->data.registered.registered_method = rm;
  rc->data.registered.deadline = deadline;
  rc->initial_metadata = initial_metadata;
  rc->data.registered.optional_payload = optional_payload;
  error = queue_call_request(&exec_ctx, server, rc);
done:
  grpc_exec_ctx_finish(&exec_ctx);
  return error;
}

static void fail_call(grpc_exec_ctx *exec_ctx, grpc_server *server,
                      requested_call *rc) {
  *rc->call = NULL;
  rc->initial_metadata->count = 0;

  server_ref(server);
  grpc_cq_end_op(exec_ctx, rc->cq_for_notification, rc->tag, 0,
                 done_request_event, rc, &rc->completion);
}

const grpc_channel_args *grpc_server_get_channel_args(grpc_server *server) {
  return server->channel_args;
}

int grpc_server_has_open_connections(grpc_server *server) {
  int r;
  gpr_mu_lock(&server->mu_global);
  r = server->root_channel_data.next != &server->root_channel_data;
  gpr_mu_unlock(&server->mu_global);
  return r;
}