pthread_setschedparam(3)Library Functions Manualpthread_setschedparam(3)
pthread_setschedparam, pthread_getschedparam - set/get scheduling
policy and parameters of a thread
POSIX threads library (libpthread, -lpthread)
#include <pthread.h>
int pthread_setschedparam(pthread_t thread, int policy,
const struct sched_param *param);
int pthread_getschedparam(pthread_t thread, int *restrict policy,
struct sched_param *restrict param);
The pthread_setschedparam() function sets the scheduling policy
and parameters of the thread thread.
policy specifies the new scheduling policy for thread. The
supported values for policy, and their semantics, are described
in sched(7).
The structure pointed to by param specifies the new scheduling
parameters for thread. Scheduling parameters are maintained in
the following structure:
struct sched_param {
int sched_priority; /* Scheduling priority */
As can be seen, only one scheduling parameter is supported. For
details of the permitted ranges for scheduling priorities in each
scheduling policy, see sched(7).
The pthread_getschedparam() function returns the scheduling
policy and parameters of the thread thread, in the buffers
pointed to by policy and param, respectively. The returned
priority value is that set by the most recent
pthread_setschedparam(), pthread_setschedprio(3), or
pthread_create(3) call that affected thread. The returned
priority does not reflect any temporary priority adjustments as a
result of calls to any priority inheritance or priority ceiling
functions (see, for example, pthread_mutexattr_setprioceiling(3)
and pthread_mutexattr_setprotocol(3)).
On success, these functions return 0; on error, they return a
nonzero error number. If pthread_setschedparam() fails, the
scheduling policy and parameters of thread are not changed.
Both of these functions can fail with the following error:
ESRCH No thread with the ID thread could be found.
pthread_setschedparam() may additionally fail with the following
errors:
EINVAL policy is not a recognized policy, or param does not make
sense for the policy.
EPERM The caller does not have appropriate privileges to set the
specified scheduling policy and parameters.
POSIX.1 also documents an ENOTSUP ("attempt was made to set the
policy or scheduling parameters to an unsupported value") error
for pthread_setschedparam().
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│pthread_setschedparam(), │ Thread safety │ MT-Safe │
│pthread_getschedparam() │ │ │
└──────────────────────────────────────┴───────────────┴─────────┘
POSIX.1-2008.
glibc 2.0 POSIX.1-2001.
For a description of the permissions required to, and the effect
of, changing a thread's scheduling policy and priority, and
details of the permitted ranges for priorities in each scheduling
policy, see sched(7).
The program below demonstrates the use of pthread_setschedparam()
and pthread_getschedparam(), as well as the use of a number of
other scheduling-related pthreads functions.
In the following run, the main thread sets its scheduling policy
to SCHED_FIFO with a priority of 10, and initializes a thread
attributes object with a scheduling policy attribute of SCHED_RR
and a scheduling priority attribute of 20. The program then sets
(using pthread_attr_setinheritsched(3)) the inherit scheduler
attribute of the thread attributes object to
PTHREAD_EXPLICIT_SCHED, meaning that threads created using this
attributes object should take their scheduling attributes from
the thread attributes object. The program then creates a thread
using the thread attributes object, and that thread displays its
scheduling policy and priority.
$ su # Need privilege to set real-time scheduling policies
Password:
# ./a.out -mf10 -ar20 -i e
Scheduler settings of main thread
policy=SCHED_FIFO, priority=10
Scheduler settings in 'attr'
policy=SCHED_RR, priority=20
inheritsched is EXPLICIT
Scheduler attributes of new thread
policy=SCHED_RR, priority=20
In the above output, one can see that the scheduling policy and
priority were taken from the values specified in the thread
attributes object.
The next run is the same as the previous, except that the inherit
scheduler attribute is set to PTHREAD_INHERIT_SCHED, meaning that
threads created using the thread attributes object should ignore
the scheduling attributes specified in the attributes object and
instead take their scheduling attributes from the creating
thread.
# ./a.out -mf10 -ar20 -i i
Scheduler settings of main thread
policy=SCHED_FIFO, priority=10
Scheduler settings in 'attr'
policy=SCHED_RR, priority=20
inheritsched is INHERIT
Scheduler attributes of new thread
policy=SCHED_FIFO, priority=10
In the above output, one can see that the scheduling policy and
priority were taken from the creating thread, rather than the
thread attributes object.
Note that if we had omitted the -i i option, the output would
have been the same, since PTHREAD_INHERIT_SCHED is the default
for the inherit scheduler attribute.
Program source
/* pthreads_sched_test.c */
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define handle_error_en(en, msg) \
do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
static void
usage(char *prog_name, char *msg)
if (msg != NULL)
fputs(msg, stderr);
fprintf(stderr, "Usage: %s [options]\n", prog_name);
fprintf(stderr, "Options are:\n");
#define fpe(msg) fprintf(stderr, "\t%s", msg) /* Shorter */
fpe("-a<policy><prio> Set scheduling policy and priority in\n");
fpe(" thread attributes object\n");
fpe(" <policy> can be\n");
fpe(" f SCHED_FIFO\n");
fpe(" r SCHED_RR\n");
fpe(" o SCHED_OTHER\n");
fpe("-A Use default thread attributes object\n");
fpe("-i {e|i} Set inherit scheduler attribute to\n");
fpe(" 'explicit' or 'inherit'\n");
fpe("-m<policy><prio> Set scheduling policy and priority on\n");
fpe(" main thread before pthread_create() call\n");
exit(EXIT_FAILURE);
static int
get_policy(char p, int *policy)
switch (p) {
case 'f': *policy = SCHED_FIFO; return 1;
case 'r': *policy = SCHED_RR; return 1;
case 'o': *policy = SCHED_OTHER; return 1;
default: return 0;
static void
display_sched_attr(int policy, struct sched_param *param)
printf(" policy=%s, priority=%d\n",
(policy == SCHED_FIFO) ? "SCHED_FIFO" :
(policy == SCHED_RR) ? "SCHED_RR" :
(policy == SCHED_OTHER) ? "SCHED_OTHER" :
"???",
param->sched_priority);
static void
display_thread_sched_attr(char *msg)
int policy, s;
struct sched_param param;
s = pthread_getschedparam(pthread_self(), &policy, ¶m);
if (s != 0)
handle_error_en(s, "pthread_getschedparam");
printf("%s\n", msg);
display_sched_attr(policy, ¶m);
static void *
thread_start(void *arg)
display_thread_sched_attr("Scheduler attributes of new thread");
return NULL;
main(int argc, char *argv[])
int s, opt, inheritsched, use_null_attrib, policy;
pthread_t thread;
pthread_attr_t attr;
pthread_attr_t *attrp;
char *attr_sched_str, *main_sched_str, *inheritsched_str;
struct sched_param param;
/* Process command-line options. */
use_null_attrib = 0;
attr_sched_str = NULL;
main_sched_str = NULL;
inheritsched_str = NULL;
while ((opt = getopt(argc, argv, "a:Ai:m:")) != -1) {
switch (opt) {
case 'a': attr_sched_str = optarg; break;
case 'A': use_null_attrib = 1; break;
case 'i': inheritsched_str = optarg; break;
case 'm': main_sched_str = optarg; break;
default: usage(argv[0], "Unrecognized option\n");
if (use_null_attrib
&& (inheritsched_str != NULL || attr_sched_str != NULL))
usage(argv[0], "Can't specify -A with -i or -a\n");
/* Optionally set scheduling attributes of main thread,
and display the attributes. */
if (main_sched_str != NULL) {
if (!get_policy(main_sched_str[0], &policy))
usage(argv[0], "Bad policy for main thread (-m)\n");
param.sched_priority = strtol(&main_sched_str[1], NULL, 0);
s = pthread_setschedparam(pthread_self(), policy, ¶m);
if (s != 0)
handle_error_en(s, "pthread_setschedparam");
display_thread_sched_attr("Scheduler settings of main thread");
printf("\n");
/* Initialize thread attributes object according to options. */
attrp = NULL;
if (!use_null_attrib) {
s = pthread_attr_init(&attr);
if (s != 0)
handle_error_en(s, "pthread_attr_init");
attrp = &attr;
if (inheritsched_str != NULL) {
if (inheritsched_str[0] == 'e')
inheritsched = PTHREAD_EXPLICIT_SCHED;
else if (inheritsched_str[0] == 'i')
inheritsched = PTHREAD_INHERIT_SCHED;
usage(argv[0], "Value for -i must be 'e' or 'i'\n");
s = pthread_attr_setinheritsched(&attr, inheritsched);
if (s != 0)
handle_error_en(s, "pthread_attr_setinheritsched");
if (attr_sched_str != NULL) {
if (!get_policy(attr_sched_str[0], &policy))
usage(argv[0], "Bad policy for 'attr' (-a)\n");
param.sched_priority = strtol(&attr_sched_str[1], NULL, 0);
s = pthread_attr_setschedpolicy(&attr, policy);
if (s != 0)
handle_error_en(s, "pthread_attr_setschedpolicy");
s = pthread_attr_setschedparam(&attr, ¶m);
if (s != 0)
handle_error_en(s, "pthread_attr_setschedparam");
/* If we initialized a thread attributes object, display
the scheduling attributes that were set in the object. */
if (attrp != NULL) {
s = pthread_attr_getschedparam(&attr, ¶m);
if (s != 0)
handle_error_en(s, "pthread_attr_getschedparam");
s = pthread_attr_getschedpolicy(&attr, &policy);
if (s != 0)
handle_error_en(s, "pthread_attr_getschedpolicy");
printf("Scheduler settings in 'attr'\n");
display_sched_attr(policy, ¶m);
pthread_attr_getinheritsched(&attr, &inheritsched);
printf(" inheritsched is %s\n",
(inheritsched == PTHREAD_INHERIT_SCHED) ? "INHERIT" :
(inheritsched == PTHREAD_EXPLICIT_SCHED) ? "EXPLICIT" :
"???");
printf("\n");
/* Create a thread that will display its scheduling attributes. */
s = pthread_create(&thread, attrp, &thread_start, NULL);
if (s != 0)
handle_error_en(s, "pthread_create");
/* Destroy unneeded thread attributes object. */
if (!use_null_attrib) {
s = pthread_attr_destroy(&attr);
if (s != 0)
handle_error_en(s, "pthread_attr_destroy");
s = pthread_join(thread, NULL);
if (s != 0)
handle_error_en(s, "pthread_join");
exit(EXIT_SUCCESS);
getrlimit(2), sched_get_priority_min(2), pthread_attr_init(3),
pthread_attr_setinheritsched(3), pthread_attr_setschedparam(3),
pthread_attr_setschedpolicy(3), pthread_create(3),
pthread_self(3), pthread_setschedprio(3), pthreads(7), sched(7)
Pages that refer to this page:
sched_setattr(2),
sched_setscheduler(2),
pthread_attr_setinheritsched(3),
pthread_attr_setschedparam(3),
pthread_attr_setschedpolicy(3),
pthread_setschedprio(3),
aio(7),
sched(7)
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