src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_ev_driver_posix.cc - third_party/grpc - Git at Google

 /*
  *
  * Copyright 2016 gRPC authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  *
  */
 #include <grpc/support/port_platform.h>
 #include "src/core/lib/iomgr/port.h"
 #if GRPC_ARES == 1 && defined(GRPC_POSIX_SOCKET)

 #include <ares.h>
 #include <sys/ioctl.h>

 #include "src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_ev_driver.h"

 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 #include <grpc/support/string_util.h>
 #include <grpc/support/time.h>
 #include <grpc/support/useful.h>
 #include "src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.h"
 #include "src/core/lib/iomgr/ev_posix.h"
 #include "src/core/lib/iomgr/iomgr_internal.h"
 #include "src/core/lib/iomgr/sockaddr_utils.h"
 #include "src/core/lib/support/string.h"

 typedef struct fd_node {
   /** the owner of this fd node */
   grpc_ares_ev_driver* ev_driver;
   /** a closure wrapping on_readable_cb, which should be invoked when the
       grpc_fd in this node becomes readable. */
   grpc_closure read_closure;
   /** a closure wrapping on_writable_cb, which should be invoked when the
       grpc_fd in this node becomes writable. */
   grpc_closure write_closure;
   /** next fd node in the list */
   struct fd_node* next;

   /** mutex guarding the rest of the state */
   gpr_mu mu;
   /** the grpc_fd owned by this fd node */
   grpc_fd* fd;
   /** if the readable closure has been registered */
   bool readable_registered;
   /** if the writable closure has been registered */
   bool writable_registered;
   /** if the fd is being shut down */
   bool shutting_down;
 } fd_node;

 struct grpc_ares_ev_driver {
   /** the ares_channel owned by this event driver */
   ares_channel channel;
   /** pollset set for driving the IO events of the channel */
   grpc_pollset_set* pollset_set;
   /** refcount of the event driver */
   gpr_refcount refs;

   /** mutex guarding the rest of the state */
   gpr_mu mu;
   /** a list of grpc_fd that this event driver is currently using. */
   fd_node* fds;
   /** is this event driver currently working? */
   bool working;
   /** is this event driver being shut down */
   bool shutting_down;
 };

 static void grpc_ares_notify_on_event_locked(grpc_ares_ev_driver* ev_driver);

 static grpc_ares_ev_driver* grpc_ares_ev_driver_ref(
     grpc_ares_ev_driver* ev_driver) {
   gpr_log(GPR_DEBUG, "Ref ev_driver %" PRIuPTR, (uintptr_t)ev_driver);
   gpr_ref(&ev_driver->refs);
   return ev_driver;
 }

 static void grpc_ares_ev_driver_unref(grpc_ares_ev_driver* ev_driver) {
   gpr_log(GPR_DEBUG, "Unref ev_driver %" PRIuPTR, (uintptr_t)ev_driver);
   if (gpr_unref(&ev_driver->refs)) {
     gpr_log(GPR_DEBUG, "destroy ev_driver %" PRIuPTR, (uintptr_t)ev_driver);
     GPR_ASSERT(ev_driver->fds == nullptr);
     gpr_mu_destroy(&ev_driver->mu);
     ares_destroy(ev_driver->channel);
     gpr_free(ev_driver);
   }
 }

 static void fd_node_destroy(fd_node* fdn) {
   gpr_log(GPR_DEBUG, "delete fd: %d", grpc_fd_wrapped_fd(fdn->fd));
   GPR_ASSERT(!fdn->readable_registered);
   GPR_ASSERT(!fdn->writable_registered);
   gpr_mu_destroy(&fdn->mu);
   /* c-ares library has closed the fd inside grpc_fd. This fd may be picked up
      immediately by another thread, and should not be closed by the following
      grpc_fd_orphan. */
   grpc_fd_orphan(fdn->fd, nullptr, nullptr, true /* already_closed */,
                  "c-ares query finished");
   gpr_free(fdn);
 }

 static void fd_node_shutdown(fd_node* fdn) {
   gpr_mu_lock(&fdn->mu);
   fdn->shutting_down = true;
   if (!fdn->readable_registered && !fdn->writable_registered) {
     gpr_mu_unlock(&fdn->mu);
     fd_node_destroy(fdn);
   } else {
     grpc_fd_shutdown(
         fdn->fd, GRPC_ERROR_CREATE_FROM_STATIC_STRING("c-ares fd shutdown"));
     gpr_mu_unlock(&fdn->mu);
   }
 }

 grpc_error* grpc_ares_ev_driver_create(grpc_ares_ev_driver** ev_driver,
                                        grpc_pollset_set* pollset_set) {
   *ev_driver = (grpc_ares_ev_driver*)gpr_malloc(sizeof(grpc_ares_ev_driver));
   int status = ares_init(&(*ev_driver)->channel);
   gpr_log(GPR_DEBUG, "grpc_ares_ev_driver_create");
   if (status != ARES_SUCCESS) {
     char* err_msg;
     gpr_asprintf(&err_msg, "Failed to init ares channel. C-ares error: %s",
                  ares_strerror(status));
     grpc_error* err = GRPC_ERROR_CREATE_FROM_COPIED_STRING(err_msg);
     gpr_free(err_msg);
     gpr_free(*ev_driver);
     return err;
   }
   gpr_mu_init(&(*ev_driver)->mu);
   gpr_ref_init(&(*ev_driver)->refs, 1);
   (*ev_driver)->pollset_set = pollset_set;
   (*ev_driver)->fds = nullptr;
   (*ev_driver)->working = false;
   (*ev_driver)->shutting_down = false;
   return GRPC_ERROR_NONE;
 }

 void grpc_ares_ev_driver_destroy(grpc_ares_ev_driver* ev_driver) {
   // It's not safe to shut down remaining fds here directly, becauses
   // ares_host_callback does not provide an exec_ctx. We mark the event driver
   // as being shut down. If the event driver is working,
   // grpc_ares_notify_on_event_locked will shut down the fds; if it's not
   // working, there are no fds to shut down.
   gpr_mu_lock(&ev_driver->mu);
   ev_driver->shutting_down = true;
   gpr_mu_unlock(&ev_driver->mu);
   grpc_ares_ev_driver_unref(ev_driver);
 }

 void grpc_ares_ev_driver_shutdown(grpc_ares_ev_driver* ev_driver) {
   gpr_mu_lock(&ev_driver->mu);
   ev_driver->shutting_down = true;
   fd_node* fn = ev_driver->fds;
   while (fn != nullptr) {
     grpc_fd_shutdown(fn->fd, GRPC_ERROR_CREATE_FROM_STATIC_STRING(
                                  "grpc_ares_ev_driver_shutdown"));
     fn = fn->next;
   }
   gpr_mu_unlock(&ev_driver->mu);
 }

 // Search fd in the fd_node list head. This is an O(n) search, the max possible
 // value of n is ARES_GETSOCK_MAXNUM (16). n is typically 1 - 2 in our tests.
 static fd_node* pop_fd_node(fd_node** head, int fd) {
   fd_node dummy_head;
   dummy_head.next = *head;
   fd_node* node = &dummy_head;
   while (node->next != nullptr) {
     if (grpc_fd_wrapped_fd(node->next->fd) == fd) {
       fd_node* ret = node->next;
       node->next = node->next->next;
       *head = dummy_head.next;
       return ret;
     }
     node = node->next;
   }
   return nullptr;
 }

 /* Check if \a fd is still readable */
 static bool grpc_ares_is_fd_still_readable(grpc_ares_ev_driver* ev_driver,
                                            int fd) {
   size_t bytes_available = 0;
   return ioctl(fd, FIONREAD, &bytes_available) == 0 && bytes_available > 0;
 }

 static void on_readable_cb(void* arg, grpc_error* error) {
   fd_node* fdn = (fd_node*)arg;
   grpc_ares_ev_driver* ev_driver = fdn->ev_driver;
   gpr_mu_lock(&fdn->mu);
   const int fd = grpc_fd_wrapped_fd(fdn->fd);
   fdn->readable_registered = false;
   if (fdn->shutting_down && !fdn->writable_registered) {
     gpr_mu_unlock(&fdn->mu);
     fd_node_destroy(fdn);
     grpc_ares_ev_driver_unref(ev_driver);
     return;
   }
   gpr_mu_unlock(&fdn->mu);

   gpr_log(GPR_DEBUG, "readable on %d", fd);
   if (error == GRPC_ERROR_NONE) {
     do {
       ares_process_fd(ev_driver->channel, fd, ARES_SOCKET_BAD);
     } while (grpc_ares_is_fd_still_readable(ev_driver, fd));
   } else {
     // If error is not GRPC_ERROR_NONE, it means the fd has been shutdown or
     // timed out. The pending lookups made on this ev_driver will be cancelled
     // by the following ares_cancel() and the on_done callbacks will be invoked
     // with a status of ARES_ECANCELLED. The remaining file descriptors in this
     // ev_driver will be cleaned up in the follwing
     // grpc_ares_notify_on_event_locked().
     ares_cancel(ev_driver->channel);
   }
   gpr_mu_lock(&ev_driver->mu);
   grpc_ares_notify_on_event_locked(ev_driver);
   gpr_mu_unlock(&ev_driver->mu);
   grpc_ares_ev_driver_unref(ev_driver);
 }

 static void on_writable_cb(void* arg, grpc_error* error) {
   fd_node* fdn = (fd_node*)arg;
   grpc_ares_ev_driver* ev_driver = fdn->ev_driver;
   gpr_mu_lock(&fdn->mu);
   const int fd = grpc_fd_wrapped_fd(fdn->fd);
   fdn->writable_registered = false;
   if (fdn->shutting_down && !fdn->readable_registered) {
     gpr_mu_unlock(&fdn->mu);
     fd_node_destroy(fdn);
     grpc_ares_ev_driver_unref(ev_driver);
     return;
   }
   gpr_mu_unlock(&fdn->mu);

   gpr_log(GPR_DEBUG, "writable on %d", fd);
   if (error == GRPC_ERROR_NONE) {
     ares_process_fd(ev_driver->channel, ARES_SOCKET_BAD, fd);
   } else {
     // If error is not GRPC_ERROR_NONE, it means the fd has been shutdown or
     // timed out. The pending lookups made on this ev_driver will be cancelled
     // by the following ares_cancel() and the on_done callbacks will be invoked
     // with a status of ARES_ECANCELLED. The remaining file descriptors in this
     // ev_driver will be cleaned up in the follwing
     // grpc_ares_notify_on_event_locked().
     ares_cancel(ev_driver->channel);
   }
   gpr_mu_lock(&ev_driver->mu);
   grpc_ares_notify_on_event_locked(ev_driver);
   gpr_mu_unlock(&ev_driver->mu);
   grpc_ares_ev_driver_unref(ev_driver);
 }

 ares_channel* grpc_ares_ev_driver_get_channel(grpc_ares_ev_driver* ev_driver) {
   return &ev_driver->channel;
 }

 // Get the file descriptors used by the ev_driver's ares channel, register
 // driver_closure with these filedescriptors.
 static void grpc_ares_notify_on_event_locked(grpc_ares_ev_driver* ev_driver) {
   fd_node* new_list = nullptr;
   if (!ev_driver->shutting_down) {
     ares_socket_t socks[ARES_GETSOCK_MAXNUM];
     int socks_bitmask =
         ares_getsock(ev_driver->channel, socks, ARES_GETSOCK_MAXNUM);
     for (size_t i = 0; i < ARES_GETSOCK_MAXNUM; i++) {
       if (ARES_GETSOCK_READABLE(socks_bitmask, i) ||
           ARES_GETSOCK_WRITABLE(socks_bitmask, i)) {
         fd_node* fdn = pop_fd_node(&ev_driver->fds, socks[i]);
         // Create a new fd_node if sock[i] is not in the fd_node list.
         if (fdn == nullptr) {
           char* fd_name;
           gpr_asprintf(&fd_name, "ares_ev_driver-%" PRIuPTR, i);
           fdn = (fd_node*)gpr_malloc(sizeof(fd_node));
           gpr_log(GPR_DEBUG, "new fd: %d", socks[i]);
           fdn->fd = grpc_fd_create(socks[i], fd_name);
           fdn->ev_driver = ev_driver;
           fdn->readable_registered = false;
           fdn->writable_registered = false;
           fdn->shutting_down = false;
           gpr_mu_init(&fdn->mu);
           GRPC_CLOSURE_INIT(&fdn->read_closure, on_readable_cb, fdn,
                             grpc_schedule_on_exec_ctx);
           GRPC_CLOSURE_INIT(&fdn->write_closure, on_writable_cb, fdn,
                             grpc_schedule_on_exec_ctx);
           grpc_pollset_set_add_fd(ev_driver->pollset_set, fdn->fd);
           gpr_free(fd_name);
         }
         fdn->next = new_list;
         new_list = fdn;
         gpr_mu_lock(&fdn->mu);
         // Register read_closure if the socket is readable and read_closure has
         // not been registered with this socket.
         if (ARES_GETSOCK_READABLE(socks_bitmask, i) &&
             !fdn->readable_registered) {
           grpc_ares_ev_driver_ref(ev_driver);
           gpr_log(GPR_DEBUG, "notify read on: %d", grpc_fd_wrapped_fd(fdn->fd));
           grpc_fd_notify_on_read(fdn->fd, &fdn->read_closure);
           fdn->readable_registered = true;
         }
         // Register write_closure if the socket is writable and write_closure
         // has not been registered with this socket.
         if (ARES_GETSOCK_WRITABLE(socks_bitmask, i) &&
             !fdn->writable_registered) {
           gpr_log(GPR_DEBUG, "notify write on: %d",
                   grpc_fd_wrapped_fd(fdn->fd));
           grpc_ares_ev_driver_ref(ev_driver);
           grpc_fd_notify_on_write(fdn->fd, &fdn->write_closure);
           fdn->writable_registered = true;
         }
         gpr_mu_unlock(&fdn->mu);
       }
     }
   }
   // Any remaining fds in ev_driver->fds were not returned by ares_getsock() and
   // are therefore no longer in use, so they can be shut down and removed from
   // the list.
   while (ev_driver->fds != nullptr) {
     fd_node* cur = ev_driver->fds;
     ev_driver->fds = ev_driver->fds->next;
     fd_node_shutdown(cur);
   }
   ev_driver->fds = new_list;
   // If the ev driver has no working fd, all the tasks are done.
   if (new_list == nullptr) {
     ev_driver->working = false;
     gpr_log(GPR_DEBUG, "ev driver stop working");
   }
 }

 void grpc_ares_ev_driver_start(grpc_ares_ev_driver* ev_driver) {
   gpr_mu_lock(&ev_driver->mu);
   if (!ev_driver->working) {
     ev_driver->working = true;
     grpc_ares_notify_on_event_locked(ev_driver);
   }
   gpr_mu_unlock(&ev_driver->mu);
 }

 #endif /* GRPC_ARES == 1 && defined(GRPC_POSIX_SOCKET) */
	/*
	*
	* Copyright 2016 gRPC authors.
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*
	*/
	#include <grpc/support/port_platform.h>
	#include "src/core/lib/iomgr/port.h"
	#if GRPC_ARES == 1 && defined(GRPC_POSIX_SOCKET)

	#include <ares.h>
	#include <sys/ioctl.h>

	#include "src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_ev_driver.h"

	#include <grpc/support/alloc.h>
	#include <grpc/support/log.h>
	#include <grpc/support/string_util.h>
	#include <grpc/support/time.h>
	#include <grpc/support/useful.h>
	#include "src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.h"
	#include "src/core/lib/iomgr/ev_posix.h"
	#include "src/core/lib/iomgr/iomgr_internal.h"
	#include "src/core/lib/iomgr/sockaddr_utils.h"
	#include "src/core/lib/support/string.h"

	typedef struct fd_node {
	/** the owner of this fd node */
	grpc_ares_ev_driver* ev_driver;
	/** a closure wrapping on_readable_cb, which should be invoked when the
	grpc_fd in this node becomes readable. */
	grpc_closure read_closure;
	/** a closure wrapping on_writable_cb, which should be invoked when the
	grpc_fd in this node becomes writable. */
	grpc_closure write_closure;
	/** next fd node in the list */
	struct fd_node* next;

	/** mutex guarding the rest of the state */
	gpr_mu mu;
	/** the grpc_fd owned by this fd node */
	grpc_fd* fd;
	/** if the readable closure has been registered */
	bool readable_registered;
	/** if the writable closure has been registered */
	bool writable_registered;
	/** if the fd is being shut down */
	bool shutting_down;
	} fd_node;

	struct grpc_ares_ev_driver {
	/** the ares_channel owned by this event driver */
	ares_channel channel;
	/** pollset set for driving the IO events of the channel */
	grpc_pollset_set* pollset_set;
	/** refcount of the event driver */
	gpr_refcount refs;

	/** mutex guarding the rest of the state */
	gpr_mu mu;
	/** a list of grpc_fd that this event driver is currently using. */
	fd_node* fds;
	/** is this event driver currently working? */
	bool working;
	/** is this event driver being shut down */
	bool shutting_down;
	};

	static void grpc_ares_notify_on_event_locked(grpc_ares_ev_driver* ev_driver);

	static grpc_ares_ev_driver* grpc_ares_ev_driver_ref(
	grpc_ares_ev_driver* ev_driver) {
	gpr_log(GPR_DEBUG, "Ref ev_driver %" PRIuPTR, (uintptr_t)ev_driver);
	gpr_ref(&ev_driver->refs);
	return ev_driver;
	}

	static void grpc_ares_ev_driver_unref(grpc_ares_ev_driver* ev_driver) {
	gpr_log(GPR_DEBUG, "Unref ev_driver %" PRIuPTR, (uintptr_t)ev_driver);
	if (gpr_unref(&ev_driver->refs)) {
	gpr_log(GPR_DEBUG, "destroy ev_driver %" PRIuPTR, (uintptr_t)ev_driver);
	GPR_ASSERT(ev_driver->fds == nullptr);
	gpr_mu_destroy(&ev_driver->mu);
	ares_destroy(ev_driver->channel);
	gpr_free(ev_driver);
	}
	}

	static void fd_node_destroy(fd_node* fdn) {
	gpr_log(GPR_DEBUG, "delete fd: %d", grpc_fd_wrapped_fd(fdn->fd));
	GPR_ASSERT(!fdn->readable_registered);
	GPR_ASSERT(!fdn->writable_registered);
	gpr_mu_destroy(&fdn->mu);
	/* c-ares library has closed the fd inside grpc_fd. This fd may be picked up
	immediately by another thread, and should not be closed by the following
	grpc_fd_orphan. */
	grpc_fd_orphan(fdn->fd, nullptr, nullptr, true /* already_closed */,
	"c-ares query finished");
	gpr_free(fdn);
	}

	static void fd_node_shutdown(fd_node* fdn) {
	gpr_mu_lock(&fdn->mu);
	fdn->shutting_down = true;
	if (!fdn->readable_registered && !fdn->writable_registered) {
	gpr_mu_unlock(&fdn->mu);
	fd_node_destroy(fdn);
	} else {
	grpc_fd_shutdown(
	fdn->fd, GRPC_ERROR_CREATE_FROM_STATIC_STRING("c-ares fd shutdown"));
	gpr_mu_unlock(&fdn->mu);
	}
	}

	grpc_error* grpc_ares_ev_driver_create(grpc_ares_ev_driver** ev_driver,
	grpc_pollset_set* pollset_set) {
	ev_driver = (grpc_ares_ev_driver)gpr_malloc(sizeof(grpc_ares_ev_driver));
	int status = ares_init(&(*ev_driver)->channel);
	gpr_log(GPR_DEBUG, "grpc_ares_ev_driver_create");
	if (status != ARES_SUCCESS) {
	char* err_msg;
	gpr_asprintf(&err_msg, "Failed to init ares channel. C-ares error: %s",
	ares_strerror(status));
	grpc_error* err = GRPC_ERROR_CREATE_FROM_COPIED_STRING(err_msg);
	gpr_free(err_msg);
	gpr_free(*ev_driver);
	return err;
	}
	gpr_mu_init(&(*ev_driver)->mu);
	gpr_ref_init(&(*ev_driver)->refs, 1);
	(*ev_driver)->pollset_set = pollset_set;
	(*ev_driver)->fds = nullptr;
	(*ev_driver)->working = false;
	(*ev_driver)->shutting_down = false;
	return GRPC_ERROR_NONE;
	}

	void grpc_ares_ev_driver_destroy(grpc_ares_ev_driver* ev_driver) {
	// It's not safe to shut down remaining fds here directly, becauses
	// ares_host_callback does not provide an exec_ctx. We mark the event driver
	// as being shut down. If the event driver is working,
	// grpc_ares_notify_on_event_locked will shut down the fds; if it's not
	// working, there are no fds to shut down.
	gpr_mu_lock(&ev_driver->mu);
	ev_driver->shutting_down = true;
	gpr_mu_unlock(&ev_driver->mu);
	grpc_ares_ev_driver_unref(ev_driver);
	}

	void grpc_ares_ev_driver_shutdown(grpc_ares_ev_driver* ev_driver) {
	gpr_mu_lock(&ev_driver->mu);
	ev_driver->shutting_down = true;
	fd_node* fn = ev_driver->fds;
	while (fn != nullptr) {
	grpc_fd_shutdown(fn->fd, GRPC_ERROR_CREATE_FROM_STATIC_STRING(
	"grpc_ares_ev_driver_shutdown"));
	fn = fn->next;
	}
	gpr_mu_unlock(&ev_driver->mu);
	}

	// Search fd in the fd_node list head. This is an O(n) search, the max possible
	// value of n is ARES_GETSOCK_MAXNUM (16). n is typically 1 - 2 in our tests.
	static fd_node* pop_fd_node(fd_node** head, int fd) {
	fd_node dummy_head;
	dummy_head.next = *head;
	fd_node* node = &dummy_head;
	while (node->next != nullptr) {
	if (grpc_fd_wrapped_fd(node->next->fd) == fd) {
	fd_node* ret = node->next;
	node->next = node->next->next;
	*head = dummy_head.next;
	return ret;
	}
	node = node->next;
	}
	return nullptr;
	}

	/* Check if \a fd is still readable */
	static bool grpc_ares_is_fd_still_readable(grpc_ares_ev_driver* ev_driver,
	int fd) {
	size_t bytes_available = 0;
	return ioctl(fd, FIONREAD, &bytes_available) == 0 && bytes_available > 0;
	}

	static void on_readable_cb(void* arg, grpc_error* error) {
	fd_node* fdn = (fd_node*)arg;
	grpc_ares_ev_driver* ev_driver = fdn->ev_driver;
	gpr_mu_lock(&fdn->mu);
	const int fd = grpc_fd_wrapped_fd(fdn->fd);
	fdn->readable_registered = false;
	if (fdn->shutting_down && !fdn->writable_registered) {
	gpr_mu_unlock(&fdn->mu);
	fd_node_destroy(fdn);
	grpc_ares_ev_driver_unref(ev_driver);
	return;
	}
	gpr_mu_unlock(&fdn->mu);

	gpr_log(GPR_DEBUG, "readable on %d", fd);
	if (error == GRPC_ERROR_NONE) {
	do {
	ares_process_fd(ev_driver->channel, fd, ARES_SOCKET_BAD);
	} while (grpc_ares_is_fd_still_readable(ev_driver, fd));
	} else {
	// If error is not GRPC_ERROR_NONE, it means the fd has been shutdown or
	// timed out. The pending lookups made on this ev_driver will be cancelled
	// by the following ares_cancel() and the on_done callbacks will be invoked
	// with a status of ARES_ECANCELLED. The remaining file descriptors in this
	// ev_driver will be cleaned up in the follwing
	// grpc_ares_notify_on_event_locked().
	ares_cancel(ev_driver->channel);
	}
	gpr_mu_lock(&ev_driver->mu);
	grpc_ares_notify_on_event_locked(ev_driver);
	gpr_mu_unlock(&ev_driver->mu);
	grpc_ares_ev_driver_unref(ev_driver);
	}

	static void on_writable_cb(void* arg, grpc_error* error) {
	fd_node* fdn = (fd_node*)arg;
	grpc_ares_ev_driver* ev_driver = fdn->ev_driver;
	gpr_mu_lock(&fdn->mu);
	const int fd = grpc_fd_wrapped_fd(fdn->fd);
	fdn->writable_registered = false;
	if (fdn->shutting_down && !fdn->readable_registered) {
	gpr_mu_unlock(&fdn->mu);
	fd_node_destroy(fdn);
	grpc_ares_ev_driver_unref(ev_driver);
	return;
	}
	gpr_mu_unlock(&fdn->mu);

	gpr_log(GPR_DEBUG, "writable on %d", fd);
	if (error == GRPC_ERROR_NONE) {
	ares_process_fd(ev_driver->channel, ARES_SOCKET_BAD, fd);
	} else {
	// If error is not GRPC_ERROR_NONE, it means the fd has been shutdown or
	// timed out. The pending lookups made on this ev_driver will be cancelled
	// by the following ares_cancel() and the on_done callbacks will be invoked
	// with a status of ARES_ECANCELLED. The remaining file descriptors in this
	// ev_driver will be cleaned up in the follwing
	// grpc_ares_notify_on_event_locked().
	ares_cancel(ev_driver->channel);
	}
	gpr_mu_lock(&ev_driver->mu);
	grpc_ares_notify_on_event_locked(ev_driver);
	gpr_mu_unlock(&ev_driver->mu);
	grpc_ares_ev_driver_unref(ev_driver);
	}

	ares_channel* grpc_ares_ev_driver_get_channel(grpc_ares_ev_driver* ev_driver) {
	return &ev_driver->channel;
	}

	// Get the file descriptors used by the ev_driver's ares channel, register
	// driver_closure with these filedescriptors.
	static void grpc_ares_notify_on_event_locked(grpc_ares_ev_driver* ev_driver) {
	fd_node* new_list = nullptr;
	if (!ev_driver->shutting_down) {
	ares_socket_t socks[ARES_GETSOCK_MAXNUM];
	int socks_bitmask =
	ares_getsock(ev_driver->channel, socks, ARES_GETSOCK_MAXNUM);
	for (size_t i = 0; i < ARES_GETSOCK_MAXNUM; i++) {
	if (ARES_GETSOCK_READABLE(socks_bitmask, i) \|\|
	ARES_GETSOCK_WRITABLE(socks_bitmask, i)) {
	fd_node* fdn = pop_fd_node(&ev_driver->fds, socks[i]);
	// Create a new fd_node if sock[i] is not in the fd_node list.
	if (fdn == nullptr) {
	char* fd_name;
	gpr_asprintf(&fd_name, "ares_ev_driver-%" PRIuPTR, i);
	fdn = (fd_node*)gpr_malloc(sizeof(fd_node));
	gpr_log(GPR_DEBUG, "new fd: %d", socks[i]);
	fdn->fd = grpc_fd_create(socks[i], fd_name);
	fdn->ev_driver = ev_driver;
	fdn->readable_registered = false;
	fdn->writable_registered = false;
	fdn->shutting_down = false;
	gpr_mu_init(&fdn->mu);
	GRPC_CLOSURE_INIT(&fdn->read_closure, on_readable_cb, fdn,
	grpc_schedule_on_exec_ctx);
	GRPC_CLOSURE_INIT(&fdn->write_closure, on_writable_cb, fdn,
	grpc_schedule_on_exec_ctx);
	grpc_pollset_set_add_fd(ev_driver->pollset_set, fdn->fd);
	gpr_free(fd_name);
	}
	fdn->next = new_list;
	new_list = fdn;
	gpr_mu_lock(&fdn->mu);
	// Register read_closure if the socket is readable and read_closure has
	// not been registered with this socket.
	if (ARES_GETSOCK_READABLE(socks_bitmask, i) &&
	!fdn->readable_registered) {
	grpc_ares_ev_driver_ref(ev_driver);
	gpr_log(GPR_DEBUG, "notify read on: %d", grpc_fd_wrapped_fd(fdn->fd));
	grpc_fd_notify_on_read(fdn->fd, &fdn->read_closure);
	fdn->readable_registered = true;
	}
	// Register write_closure if the socket is writable and write_closure
	// has not been registered with this socket.
	if (ARES_GETSOCK_WRITABLE(socks_bitmask, i) &&
	!fdn->writable_registered) {
	gpr_log(GPR_DEBUG, "notify write on: %d",
	grpc_fd_wrapped_fd(fdn->fd));
	grpc_ares_ev_driver_ref(ev_driver);
	grpc_fd_notify_on_write(fdn->fd, &fdn->write_closure);
	fdn->writable_registered = true;
	}
	gpr_mu_unlock(&fdn->mu);
	}
	}
	}
	// Any remaining fds in ev_driver->fds were not returned by ares_getsock() and
	// are therefore no longer in use, so they can be shut down and removed from
	// the list.
	while (ev_driver->fds != nullptr) {
	fd_node* cur = ev_driver->fds;
	ev_driver->fds = ev_driver->fds->next;
	fd_node_shutdown(cur);
	}
	ev_driver->fds = new_list;
	// If the ev driver has no working fd, all the tasks are done.
	if (new_list == nullptr) {
	ev_driver->working = false;
	gpr_log(GPR_DEBUG, "ev driver stop working");
	}
	}

	void grpc_ares_ev_driver_start(grpc_ares_ev_driver* ev_driver) {
	gpr_mu_lock(&ev_driver->mu);
	if (!ev_driver->working) {
	ev_driver->working = true;
	grpc_ares_notify_on_event_locked(ev_driver);
	}
	gpr_mu_unlock(&ev_driver->mu);
	}

	#endif /* GRPC_ARES == 1 && defined(GRPC_POSIX_SOCKET) */