Originální popis anglicky:
getpriority, setpriority - get and set the nice value
Návod, kniha: POSIX Programmer's Manual
#include <sys/resource.h>
int getpriority(int
which, id_t
who);
int setpriority(int
which, id_t
who, int value);
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.
The nice value set with
setpriority() shall be applied to the process. If
the process is multi-threaded, 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 of the
specified processes to
value+ {NZERO}.
The default nice value is {NZERO}; lower nice values shall cause more favorable
scheduling. While the range of valid nice values is [0,{NZERO}*2-1],
implementations may enforce more restrictive limits. If
value+ {NZERO}
is less than the system's lowest supported nice value,
setpriority()
shall set the nice value to the lowest supported value; if
value+
{NZERO} is greater than the system's highest supported nice value,
setpriority() shall set the nice value to the highest supported value.
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. A process which
subsequently reverts to SCHED_OTHER need not have its priority affected by
such a
setpriority() call.
The effect of changing the nice value may vary depending on the
process-scheduling algorithm in effect.
Since
getpriority() can return the value -1 on 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.
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.
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.
The following sections are informative.
The following example returns the current scheduling priority for the process ID
returned by the call to
getpid().
#include <sys/resource.h>
...
int which = PRIO_PROCESS;
id_t pid;
int ret;
pid = getpid();
ret = getpriority(which, pid);
The following example sets the priority for the current process ID to -20.
#include <sys/resource.h>
...
int which = PRIO_PROCESS;
id_t pid;
int priority = -20;
int ret;
pid = getpid();
ret = setpriority(which, pid, priority);
The
getpriority() and
setpriority() functions work with an offset
nice value (nice value -{NZERO}). The nice value is in the range [0,2*{NZERO}
-1], while the return value for
getpriority() and the third parameter
for
setpriority() are in the range [-{NZERO},{NZERO} -1].
None.
None.
nice() ,
sched_get_priority_max() ,
sched_setscheduler() ,
the Base Definitions volume of IEEE Std 1003.1-2001,
<sys/resource.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
