getpriority.2

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)getpriority.2	8.1	9/11/90
.TH getpriority 2
.SH Name
getpriority, setpriority \- get or set program scheduling priority
.SH Syntax
.nf
.ft B
#include <sys/time.h>
#include <sys/resource.h>
.PP
.ft B
#define PRIO_PROCESS	0	/* process */
#define PRIO_PGRP		1	/* process group */
#define PRIO_USER		2	/* user id */
.PP
.ft B
prio = getpriority(which, who)
int prio, which, who;
.PP
.ft B
setpriority(which, who, prio)
int which, who, prio;
.fi
.SH Description
.NXR "getpriority system call"
.NXR "setpriority system call"
.NXR "process" "getting scheduling priority"
.NXR "process" "setting scheduling priority"
The scheduling
priority of the process, process group, or user, as indicated by
.I which
and
.I who,
is obtained with the
.PN getpriority
call and set with the
.PN setpriority
call.
The
.I which
is one of PRIO_PROCESS, PRIO_PGRP, or PRIO_USER, and 
.I who
is interpreted relative to 
.I which
(a process identifier for PRIO_PROCESS, process group
identifier for PRIO_PGRP, and a user ID for PRIO_USER).
The
.I prio
is a value in the range \-20 to 20.  The default priority is 0;
lower priorities cause more favorable scheduling.
.PP
The
.PN getpriority
call returns the highest priority (lowest numerical value)
enjoyed by any of the specified processes.  The
.PN setpriority
call sets the priorities of all of the specified processes
to the specified value.  Only the superuser may lower priorities.
.SH Return Values
Since
.PN getpriority
can legitimately return the value \-1, it is necessary
to clear the external variable \fIerrno\fP prior to the
call, then check it afterward to determine
if a \-1 is an error or a legitimate value.
The
.PN setpriority
call returns 0 if there is no error or
\-1 if there is.
.SH Diagnostics
The
.PN getpriority
and
.PN setpriority
system calls fail under the following conditions:
.TP 15
[ESRCH]
No processes were located using the 
.I which
and
.I who
values specified.
.TP 15
[EINVAL]
The
.I which
was not one of PRIO_PROCESS, PRIO_PGRP, or PRIO_USER.
.PP
In addition to the errors indicated above,
.I setpriority
can fail under the following conditions:
.TP 15
[EPERM]
A process was located, but neither its effective nor real
user ID matched the effective user ID of the caller.
.TP 15
[EACCES]
A user other than the superuser attempted to change a process
priority to a negative value.
.SH See Also
nice(1), fork(2), renice(8)