HP-UX Reference (11i v1 05/09) - 2 System Calls (vol 5)

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rtsched(2) rtsched(2)

Note: If the target process is multi-threaded, this change will only affect a child process that is created later

and inherits its parent’s scheduling policy and priority. The priority returned is the old priority of the tar-

get process, though individual threads or lightweight processes may have a different value if some other

interface is used to change an individual thread or lightweight process’ priority.

Appropriate privileges are required to change the scheduling parameters of another process.

The calling process must have appropriate privileges or be a member of a group having

PRIV_RTSCHED

access to successfully call sched_setscheduler()

The

sched_setscheduler()

function is considered successful if it succeeds in setting the scheduling

policy and scheduling parameters of the process speciﬁed by pid to the values speciﬁed by policy and the

structure param, respectively.

sched_getscheduler()

The

sched_getscheduler()

function returns the scheduling policy of the process speciﬁed by pid.

The values that can be returned by

sched_getscheduler()

are deﬁned in the header ﬁle

<sched.h> (see sched_setscheduler()

If a process described by pid exists, the scheduling policy is returned for the process whose process ID is

equal to pid.

If pid is zero, the scheduling policy is returned for the calling process.

If the process pid contains more than one thread or lightweight process (that is, the process is multi-

threaded), this function shall only return the process scheduling policy and priority. Individual threads or

lightweight processes in the target process will have their own scheduling policies and priorities which may

be different from the scheduling policy and priority of their process.

sched_yield()

The

sched_yield() function forces the running process to relinquish the processor until it again

becomes the head of its process list. It takes no arguments.

sched_get_priority_max()

sched_get_priority_min()

The sched_get_priority_max()

and sched_get_priority_min()

functions return the

appropriate maximum or minimum, respectively, for the scheduling policy speciﬁed by policy.

The value of policy must be one of the scheduling policy values deﬁned in

<sched.h>.

sched_rr_get_interval()

The

sched_rr_get_interval()

function updates the timespec structure referenced by the interval

argument to contain the current execution time limit (that is, time quantum) for the process indicated by

pid under the

SCHED_RR policy, at which a scheduling decision will be made when another process at the

same priority is ready to execute. If pid is zero, the current execution time limit for the calling process is

returned.

PRI_HPUX_TO_POSIX()

PRI_POSIX_TO_HPUX()

These two functions serve to map (translate) the range of HP-UX priorities into the POSIX.4 model. These

translations are necessary because the POSIX.4 standard chose larger numbers to represent stronger prior-

ities and the existing HP-UX behavior, which must be maintained for backward compatibility, uses smaller

numbers for stronger priorities.

The PRI_HPUX_TO_POSIX() function returns the POSIX.4 scheduling priority corresponding to the

HP-UX priority passed in the argument pri. The value of pri can be any integer.

The PRI_POSIX_TO_HPUX() function returns an HP-UX process priority corresponding to the priority

passed in the argument pri. The value of pri can be any integer. The HP-UX priority returned is compar-

able to the values returned by getpriority() (see getpriority (2)).

Scheduling Policies

The scheduling policies described are deﬁned in terms of a conceptual model, which contains a set of pro-

cess lists. There is, conceptually, one process list for each priority. Any runnable process may be in any

process list. Multiple scheduling policies are provided. Each nonempty list is ordered, and contains a head

as one end of its order, and a tail as the other. The purpose of a scheduling policy is to deﬁne the allowable

operations on this set of lists (for example, moving processes between and within lists).

HP-UX 11i Version 1: September 2005 − 3 − Hewlett-Packard Company Section 2−−289