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#include <sched.h>
int sched_setscheduler(pid_t pid, int policy, const struct sched_param *param);
int sched_getscheduler(pid_t pid);
struct
sched_param {
int sched_priority; /* process execution
scheduling priority */
...
}
param->sched_priority must be any integer within the inclusive priority range for the scheduling policy specified by policy.
The possible values for the policy parameter are defined in the
header file <sched.h>:
SCHED_FIFO,
SCHED_RR,
or SCHED_OTHER.
If pid is zero, the scheduling policy and scheduling parameters are set for the calling process. Otherwise, if a process specified by pid exists and if the calling process has permission, the scheduling policy and scheduling parameters are set for the process whose process ID is equal to pid. The real or effective user ID of the calling 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 super-user. See intro(2) .
To change the policy of any process to either of the real time policies SCHED_FIFO or SCHED_RR, the calling process must either have the SCHED_FIFO, or SCHED_RR policy or have an effective user ID of 0.
sched_getscheduler() returns the scheduling policy of the process specified by pid. If pid is zero, the scheduling policy is returned for the calling process. Otherwise, if a process specified by pid exists and if the calling process has permission, the scheduling policy is returned for the process whose process ID is equal to pid.
SCHED_FIFO (realtime), First-In-First-Out; processes scheduled to this policy, if not pre-empted by a higher priority or interrupted by a signal, will proceed until completion.
SCHED_RR (realtime), Round-Robin; processes scheduled to this policy, if not pre-empted by a higher priority or interrupted by a signal, will execute for a time period, returned by sched_rr_get_interval(3R) or by the system.
or
SCHED_OTHER (time-sharing).
Otherwise, the policy and sheduling parameters remain unchanged, sched_setscheduler() returns -1, and sets errno to indicate the error condition.
If successful, sched_getscheduler() returns the scheduling policy of the specified processr; otherwise, it returns -1, and sets errno to indicate the error condition.