Programming with POSIX® Threads

22 * If the alarm list is empty, wait until an alarm is

23 * added. Setting current_alarm to 0 informs the insert

24 * routine that the thread is not busy.

25 */

26  current_alarm = 0;

27  while (alarm_list == NULL) {

28  status = pthread_cond_wait (&alarm_cond, &alarm_mutex);

29  if (status != 0)

30  err_abort (status, "Wait on cond");

31  }

32  alarm = alarm_list;

33  alarm_list = alarm->link;

34  now = time (NULL);

35  expired = 0;

36  if (alarm->time > now) {

37 #ifdef DEBUG

38  printf ("[waiting: %d(%d)\"%s\"]\n", alarm->time,

39  alarm->time - time (NULL), alarm->message);

40 #endif

41  cond_time.tv_sec = alarm->time;

42  cond_time.tv_nsec = 0;

43  current_alarm = alarm->time;

44  while (current_alarm == alarm->time) {

45  status = pthread_cond_timedwait (

46  &alarm_cond, &alarm_mutex, &cond_time);

47  if (Status == ETIMEDOUT) {

48  expired = 1;

49  break;

50  }

51  if (status != 0)

52  err_abort (status, "Cond timedwait");

53  }

54  if (!expired)

55  alarm_insert (alarm);

56  } else

57  expired = 1;

58  if (expired) {

59  printf ("(%d) %s\n", alarm->seconds, alarm->message);

60  free (alarm);

61  }

62 }

63 }

Part 4 shows the final section of alarm_cond.c, the main program. It is nearly identical to the main function from alarm_mutex.c.

38 Because the condition variable signal operation is built into the new alarm_ insert function, we call alarm_insert rather than inserting a new alarm directly.

■ alarm_cond.c part 4 main

1 int main (int argc, char *argv[])

2 {

3 int status;

4 char line[128];

5 alarm_t *alarm;

6 pthread_t thread; 7

8 status = pthread_create (

9 &thread, NULL, alarm thread, NULL);

10 if (status != 0)

11  err_abort (status, "Create alarm thread");

12 while (1) {

13  printf ("Alarm> ");

14  if (fgets (line, sizeof (line), stdin) == NULL) exit (0);

15  if (strlen (line) <= 1) continue;

16  alarm = (alarm_t*)malloc (sizeof (alarm_t));

17  if (alarm == NULL)

18  errno_abort ("Allocate alarm");

19

20 /*

21 * Parse input line into seconds (%d) and a message

22 * (%64[^\n]), consisting of up to 64 characters

23 * separated from the seconds by whitespace.

24 */

25  if (sscanf (line, "%d %64[^\n]",

26  &alarm->seconds, alarm->message) < 2) {

27  fprintf (stderr, "Bad command\n");

28  free (alarm);

29  } else {

30  status = pthread_mutex_lock (&alarm_mutex);

31  if (status != 0)

32  err_abort (status, "Lock mutex");

33  alarm->time = time (NULL) + alarm->seconds;

34 /*

35 * Insert the new alarm into the list of alarms,

36 * sorted by expiration time.

37 */

38  alarm_insert (alarm);

39  status = pthread_mutex_unlock (&alarm_mutex);

40  if (status != 0)

41  err_abort (status, "Unlock mutex");

42  }

43 }

44 }