getpriority¶

Synopsis¶

#include <sys/resource.h>

int getpriority(int which, id_t who);

int setpriority(int which, id_t who, int value);

Status¶

Implemented

Conformance¶

IEEE Std 1003.1-2017

Description¶

The getpriority() function shall obtain the nice value of a process, process group, or user. The setpriority() function shall set the nice value of a process, process group, or user to value+{NZERO}.

Target processes are specified by the values of the which and who arguments. The which argument may be one of the following values: PRIO_PROCESS, PRIO_PGRP, or PRIO_USER, indicating that the who argument is to be interpreted as a process ID, a process group ID, or an effective user ID, respectively. A 0 value for the who argument specifies the current process, process group, or user. Phoenix-RTOS has no user accounts, so for PRIO_USER only a who value of 0 is accepted; any other value is rejected with EINVAL.

The nice value set with setpriority() shall be applied to the process. If the process is multithreaded, the nice value shall affect all system scope threads in the process.

If more than one process is specified, getpriority() shall return value {NZERO} less than the lowest nice value pertaining to any of the specified processes, and setpriority() shall set the nice values of all the specified processes to value+{NZERO}.

The default nice value is {NZERO}; lower nice values shall cause more favorable scheduling. Only a process with appropriate privileges can lower its nice value.

Any processes or threads using SCHED_FIFO or SCHED_RR shall be unaffected by a call to setpriority(). This is not considered an error. Phoenix-RTOS supports only the SCHED_RR policy, so setpriority() changes nothing and getpriority() always returns 0, the default nice value less {NZERO}. Both functions only validate which and check that the process or process group specified by who exists. To change the priority of a thread, use sched_setparam() or pthread_setschedprio(), see Scheduling priorities.

Since getpriority() can return the value -1 upon successful completion, it is necessary to set errno to 0 prior to a call to getpriority(). If getpriority() returns the value -1, then errno can be checked to see if an error occurred or if the value is a legitimate nice value.

Return value¶

Upon successful completion, getpriority() shall return an integer in the range -{NZERO} to {NZERO}-1. Otherwise, -1 shall be returned and errno set to indicate the error.

Upon successful completion, setpriority() shall return 0; otherwise, -1 shall be returned and errno set to indicate the error.

Errors¶

The getpriority() and setpriority() functions shall fail if:

ESRCH - No process could be located using the which and who argument values specified.
EINVAL - The value of the which argument was not recognized, or the value of the who argument is not a valid process ID, process group ID, or user ID.

In addition, setpriority() may fail if:

EPERM - A process was located, but neither the real nor effective user ID of the executing process match the effective user ID of the process whose nice value is being changed.
EACCES - A request was made to change the nice value to a lower numeric value and the current process does not have appropriate privileges.

POSIX deviations¶

No POSIX deviations discovered.