sched_getparam man page on FreeBSD

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SCHED_SETPARAM(2)	    BSD System Calls Manual	     SCHED_SETPARAM(2)

NAME
     sched_setparam, sched_getparam — set/get scheduling parameters

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sched.h>

     int
     sched_setparam(pid_t pid, const struct sched_param *param);

     int
     sched_getparam(pid_t pid, struct sched_param *param);

DESCRIPTION
     The sched_setparam() system call 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 param structure must be any integer within the inclusive priority
     range for the current scheduling policy of the process specified by pid.
     Higher numerical values for the priority represent higher priorities.

     In this implementation, if the value of pid is negative the system call
     will fail.

     If a process specified by pid exists and if the calling process has per‐
     mission, the scheduling parameters are set for the process whose process
     ID is equal to pid.

     If pid is zero, the scheduling parameters are set for the calling
     process.

     In this implementation, the policy of when a process can affect the
     scheduling parameters of another process is specified in IEEE Std
     1003.1b-1993 (“POSIX.1”) as a write-style operation.

     The target process, whether it is running or not running, will resume
     execution 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 speci‐
     fied process is ready to run, the process specified by the pid argument
     will preempt a lowest priority running process.  Similarly, if the
     process calling sched_setparam() sets its own priority lower than that of
     one or more other nonempty process lists, then the process that is the
     head of the highest priority list will also preempt the calling process.
     Thus, in either case, the originating process might not receive notifica‐
     tion of the completion of the requested priority change until the higher
     priority process has executed.

     In this implementation, when the current scheduling policy for the
     process specified by pid is normal timesharing (SCHED_OTHER, aka
     SCHED_NORMAL when not POSIX-source) or the idle policy (SCHED_IDLE when
     not POSIX-source) then the behavior is as if the process had been running
     under SCHED_RR with a priority lower than any actual realtime priority.

     The sched_getparam() system call will return the scheduling parameters of
     a process specified by pid in the sched_param structure pointed to by
     param.

     If a process specified by pid exists and if the calling process has per‐
     mission, the scheduling parameters for the process whose process ID is
     equal to pid are returned.

     In this implementation, the policy of when a process can obtain the
     scheduling parameters of another process are detailed in IEEE Std
     1003.1b-1993 (“POSIX.1”) as a read-style operation.

     If pid is zero, the scheduling parameters for the calling process will be
     returned.	In this implementation, the sched_getparam system call will
     fail if pid is negative.

RETURN VALUES
     Upon successful completion, the value 0 is returned; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS
     On failure errno will be set to the corresponding value:

     [ENOSYS]		The system is not configured to support this function‐
			ality.

     [EPERM]		The requesting process doesn not have permission as
			detailed in IEEE Std 1003.1b-1993 (“POSIX.1”).

     [ESRCH]		No process can be found corresponding to that speci‐
			fied by pid.

     [EINVAL]		For sched_setparam(): one or more of the requested
			scheduling parameters is outside the range defined for
			the scheduling policy of the specified pid.

SEE ALSO
     sched_get_priority_max(2), sched_get_priority_min(2),
     sched_getscheduler(2), sched_rr_get_interval(2), sched_setscheduler(2),
     sched_yield(2)

STANDARDS
     The sched_setparam() and sched_getparam() system calls conform to IEEE
     Std 1003.1b-1993 (“POSIX.1”).

BSD				March 12, 1998				   BSD
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