sched_setparam(3RT) Realtime Library Functions sched_setparam(3RT)NAMEsched_setparam - set scheduling parameters
SYNOPSIS
cc [ flag... ] file... -lrt [ library... ]
#include <sched.h>
int sched_setparam(pid_t pid, const struct sched_param *param);
DESCRIPTION
The sched_setparam() function sets the scheduling parameters of the
process specified by pid to the values specified by the sched_param
structure pointed to by param. The value of the sched_priority member
in the sched_param structure is any integer within the inclusive prior‐
ity range for the current scheduling policy of the process specified by
pid. Higher numerical values for the priority represent higher priori‐
ties. If the value of pid is negative, the behavior of the sched_set‐
param() function is unspecified.
If a process specified by pid exists and if the calling process has
permission, the scheduling parameters will be set for the process whose
process ID is equal to pid. The real or effective user ID of the call‐
ing process must match the real or saved (from exec(2)) user ID of the
target process unless the effective user ID of the calling process is
0. See intro(2).
If pid is zero, the scheduling parameters will be set for the calling
process.
The target process, whether it is running or not running, resumes exe‐
cution after all other runnable processes of equal or greater priority
have been scheduled to run.
If the priority of the process specified by the pid argument is set
higher than that of the lowest priority running process and if the
specified process is ready to run, the process specified by the pid
argument preempts a lowest priority running process. Similarly, if the
process calling sched_setparam() sets its own priority lower than that
of one or more other non-empty process lists, then the process that is
the head of the highest priority list also preempts the calling
process. Thus, in either case, the originating process might not
receive notification of the completion of the requested priority change
until the higher priority process has executed.
If the current scheduling policy for the process specified by pid is
not SCHED_FIFO or SCHED_RR, including SCHED_OTHER, the result is equal
to priocntl(P_PID, pid, PC_SETPARMS, &pcparam), where pcparam is an
image of *param.
The effect of this function on individual threads is dependent on the
scheduling contention scope of the threads:
· For threads with system scheduling contention scope, these func‐
tions have no effect on their scheduling.
· For threads with process scheduling contention scope, the threads'
scheduling parameters will not be affected. However, the schedul‐
ing of these threads with respect to threads in other processes
may be dependent on the scheduling parameters of their process,
which are governed using these functions.
If an implementation supports a two-level scheduling model in which
library threads are multiplexed on top of several kernel scheduled
entities, then the underlying kernel scheduled entities for the system
contention scope threads will not be affected by these functions.
The underlying kernel scheduled entities for the process contention
scope threads will have their scheduling parameters changed to the
value specified in param. Kernel scheduled entities for use by process
contention scope threads that are created after this call completes
inherit their scheduling policy and associated scheduling parameters
from the process.
This function is not atomic with respect to other threads in the
process. Threads are allowed to continue to execute while this function
call is in the process of changing the scheduling policy for the under‐
lying kernel scheduled entities used by the process contention scope
threads.
RETURN VALUES
If successful, the sched_setparam() function returns 0.
If the call to sched_setparam() is unsuccessful, the priority remains
unchanged, and the function returns −1 and sets errno to indicate the
error.
ERRORS
The sched_setparam() function will fail if:
EINVAL One or more of the requested scheduling parameters is
outside the range defined for the scheduling policy of
the specified pid.
ENOSYS The sched_setparam() function is not supported by the
system.
EPERM The requesting process does not have permission to set
the scheduling parameters for the specified process, or
does not have the appropriate privilege to invoke
sched_setparam().
ESRCH No process can be found corresponding to that specified
by pid.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Standard │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │MT-Safe │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOintro(2), exec(2), librt(3LIB), sched.h(3HEAD), sched_getparam(3RT),
sched_getscheduler(3RT), sched_setscheduler(3RT), attributes(5)NOTES
Solaris 2.6 was the first release to support libposix4/librt. Prior to
this release, this function always returned −1 and set errno to ENOSYS.
SunOS 5.10 5 Oct 2001 sched_setparam(3RT)
