Programming with POSIX® Threads

103  thread_param.sched_priority);

104  status = pthread_attr_setschedparam (

105  &thread_attr, &thread_param);

106  if (status != 0)

107  err_abort (status, "Set params");

108  printf (

109  "Creating thread at RR/%d\n",

110  thread_param.sched_priority);

111  status = pthread_attr_setinheritsched (

112  &thread_attr, PTHREAD_EXPLICIT_SCHED);

113  if (status != 0)

114  err_abort (status, "Set inherit");

115 }

116 #else

117  printf ("Priority scheduling not supported\n");

118 #endif

119  status = pthread_create (

120  &thread_id, &thread_attr, thread_routine, NULL);

121  if (status != 0)

122  err_abort (status, "Create thread");

123  status = pthread_join (thread_id, NULL);

124  if (status != 0)

125  err_abort (status, "Join thread");

126  printf ("Main exiting\n");

127 return 0;

128 }

The next program, sched_thread.c, shows how to modify the realtime scheduling policy and parameters for a running thread. When changing the scheduling policy and parameters in a thread attributes object, remember, you use two separate operations: one to modify the scheduling policy and the other to modify the scheduling parameters.

You cannot modify the scheduling policy of a running thread separately from the thread's parameters, because the policy and parameters must always be consistent for scheduling to operate correctly. Each scheduling policy may have a unique range of valid scheduling priorities, and a thread cannot operate at a priority that isn't valid for its current policy. To ensure consistency of the policy and parameters, they are set with a single call.

55 Unlike sched_attr.c, sched_thread.c does not check the compile-time feature macro _POSIX_THREAD_PRIORITY_SCHEDULING. That means it will probably not compile, and almost certainly won't run correctly, on a system that does not support the option. There's nothing wrong with writing a program that way — in fact, that's what you are likely to do most of the time. If you need priority scheduling, you would document that your application requires the _POSIX_THREAD_ PRIORITY_SCHEDULING option, and use it.

57-62 Solaris 2.5, despite defining _POSIX_THREAD_PRIORITY_SCHEDULING, does not support realtime scheduling policies. For this reason, the ENOSYS from sched_get_priority_min is handled as a special case.

■ sched_thread.c

1 #include

2 #include

3 #include

4 #include "errors.h" 5

6 #define THREADS 5 7

8 /*

9 * Structure describing each thread.

10 */

11 typedef struct thread_tag {

12  int index;

13  pthread_t id;

14 } thread_t;

15

16 thread_t threads[THREADS];

17 int rr_min_priority; 18

19 /*

20 * Thread start routine that willset its own priority.

21 */

22 void *thread_routine (void *arg)

23 {

24  thread_t *self = (thread_t*)arg;

25  int my_policy;

26  struct sched_param my_param;

27  int status;

28

29  my_param.sched_priority = rr_min_priority + self->index;

30  DPRINTF ((

31  "Thread %d will set SCHED_FIFO, priority %d\n",

32  self->index, my_param.sched_priority));

33  status = pthread_setschedparam (

34  self->id, SCHED_RR, &my_param);

35  if (status != 0) 

36  err_abort (status, "Set sched");

37  status = pthread_getschedparam (

38  self->id, &my_policy, &my_param);

39  if (status != 0)

40  err_abort (status, "Get sched");

41  printf ("thread_routine %d running at %s/%d\n",