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PTHREAD_SETSCHEDPARAM(3) Linux Programmer's Manual PTHREAD_SETSCHEDPARAM(3)
pthread_setschedparam, pthread_getschedparam - set/get scheduling policy and
parameters of a thread
#include <pthread.h>
pthread_setschedparam(pthread_t thread, int policy,
const struct sched_param *param);
pthread_getschedparam(pthread_t thread, int *policy,
struct sched_param *param);
Compile and link with -pthread.
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_setscheduler(2).
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_setscheduler(2).
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.1-2001 also documents an ENOTSUP ("attempt was made to set the policy or
scheduling parameters to an unsupported value") error for
pthread_setschedparam().
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_setscheduler(2).
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.
/* pthreads_sched_test.c */
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.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|s} 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;
}
int
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 (-s)\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;
else
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);
s = 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 */
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), sched_setscheduler(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)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2008-11-17 PTHREAD_SETSCHEDPARAM(3)
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