kqueue_timers.cc

/* Copyright (c) 2014, 2023, Oracle and/or its affiliates.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

   This program is also distributed with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have included with MySQL.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

/**
  @file mysys/kqueue_timers.cc
*/

#include <assert.h>
#include <errno.h>
#include <sys/types.h> /* Must be before <sys/event.h> on FreeBSD. */
#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#endif

#include <sys/event.h>

#include "my_sys.h"    /* my_message_local */
#include "my_thread.h" /* my_thread_init, my_thread_end */
#include "my_timer.h"  /* my_timer_t */
#include "mysql/psi/mysql_thread.h"
#include "mysys_err.h"
#include "mysys_priv.h" /* key_thread_timer_notifier */

/* Kernel event queue file descriptor. */
static int kq_fd = -1;

/* Timer thread object. */
static my_thread_handle timer_notify_thread;

/**
  Timer expiration notification thread.

  @param  arg   Unused.
*/

static void *timer_notify_thread_func(void *arg [[maybe_unused]]) {
  my_timer_t *timer;
  struct kevent kev;

  my_thread_init();

  while (1) {
    if (kevent(kq_fd, NULL, 0, &kev, 1, NULL) < 0) {
      if (errno == EINTR)
        continue;
      else {
        my_message_local(ERROR_LEVEL, EE_EXITING_TIMER_NOTIFY_THREAD, errno);
        break;
      }
    }

    if (kev.filter == EVFILT_TIMER) {
      timer = static_cast<my_timer_t *>(kev.udata);
      assert(timer->id == kev.ident);
      timer->notify_function(timer);
    } else if (kev.filter == EVFILT_USER)
      break;
  }

  close(kq_fd);
  my_thread_end();

  return NULL;
}

/**
  Create a helper thread to dispatch timer expiration notifications.

  @return On success, 0. On error, -1 is returned.
*/

static int start_helper_thread(void) {
  struct kevent kev;

  EV_SET(&kev, 0, EVFILT_USER, EV_ADD, 0, 0, 0);

  if (kevent(kq_fd, &kev, 1, NULL, 0, NULL) < 0) {
    my_message_local(ERROR_LEVEL, EE_FAILED_TO_CREATE_TIMER, errno);
    return -1;
  }

  return mysql_thread_create(key_thread_timer_notifier, &timer_notify_thread,
                             NULL, timer_notify_thread_func, NULL);
}

/**
  Initialize internal components.

  @return On success, 0.
          On error, -1 is returned, and errno is set to indicate the error.
*/

int my_timer_initialize(void) {
  int rc;

  /* Create a file descriptor for event notification. */
  if ((kq_fd = kqueue()) < 0) {
    my_message_local(ERROR_LEVEL, EE_FAILED_TO_CREATE_TIMER_QUEUE, errno);
    return -1;
  }

  /* Create a helper thread. */
  if ((rc = start_helper_thread())) {
    my_message_local(ERROR_LEVEL, EE_FAILED_TO_START_TIMER_NOTIFY_THREAD);
    close(kq_fd);
  }

  return rc;
}

/**
  Release any resources that were allocated as part of initialization.
*/

void my_timer_deinitialize(void) {
  struct kevent kev;

  EV_SET(&kev, 0, EVFILT_USER, 0, NOTE_TRIGGER, 0, 0);

  if (kevent(kq_fd, &kev, 1, NULL, 0, NULL) < 0)
    my_message_local(ERROR_LEVEL,
                     EE_FAILED_TO_CREATE_TIMER_NOTIFY_THREAD_INTERRUPT_EVENT,
                     errno);

  my_thread_join(&timer_notify_thread, NULL);
}

int my_timer_create(my_timer_t *timer) {
  assert(kq_fd >= 0);

  timer->id = (uintptr_t)timer;

  return 0;
}

/**
  Set the time until the next expiration of the timer.

  @param  timer   Timer object.
  @param  time    Amount of time (in milliseconds) before the timer expires.

  @return On success, 0.
          On error, -1 is returned, and errno is set to indicate the error.
*/

int my_timer_set(my_timer_t *timer, unsigned long time) {
  struct kevent kev;

  EV_SET(&kev, timer->id, EVFILT_TIMER, EV_ADD | EV_ONESHOT, 0, time, timer);

  return kevent(kq_fd, &kev, 1, NULL, 0, NULL);
}

/**
  Cancel the timer.

  @param  timer   Timer object.
  @param  state   The state of the timer at the time of cancellation, either
                  signaled (false) or nonsignaled (true).

  @return On success, 0.
          On error, -1 is returned, and errno is set to indicate the error.
*/

int my_timer_cancel(my_timer_t *timer, int *state) {
  int status;
  struct kevent kev;

  EV_SET(&kev, timer->id, EVFILT_TIMER, EV_DELETE, 0, 0, NULL);

  status = kevent(kq_fd, &kev, 1, NULL, 0, NULL);

  /*
    If the event was retrieved from the kqueue (at which point we
    consider it to be signaled), the timer was automatically deleted.
  */
  if (!status)
    *state = 1;
  else if (errno == ENOENT) {
    *state = 0;
    status = 0;
  }

  return status;
}

/**
  Delete a timer object.

  @param  timer   Timer object.
*/

void my_timer_delete(my_timer_t *timer) {
  struct kevent kev;

  EV_SET(&kev, timer->id, EVFILT_TIMER, EV_DELETE, 0, 0, NULL);

  kevent(kq_fd, &kev, 1, NULL, 0, NULL);
}