.\"     $NetBSD: proc_compare.3,v 1.1 2011/10/21 12:10:31 christos Exp $
.\"
.\" Copyright (c) 2011 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Christos Zoulas.
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.Dd October 20, 2011
.Dt PROC_COMPARE 3
.Os
.Sh NAME
.Nm proc_compare
.Nd compare two processes interactivity
.Sh LIBRARY
.Lb libutil
.Sh SYNOPSIS
.In sys/sysctl.h
.Ft int
.Fn "proc_compare" "const struct kinfo_proc2 *p1" "const struct kinfo_lwp *l1" \
"const struct kinfo_proc2 *p2" "const struct kinfo_lwp *l2"
.Sh DESCRIPTION
The
.Fn proc_compare
function compares two processes that are on the same terminal for their
interactivity.
This means that the process returned is the one that has a better chance
being the active foreground process on that tty.
This algorithm is used in the kernel for
.Dv SIGINFO
reporting and in userland by
.Xr w 1 .
.Pp
The algorithm used is as follows:
.Bl -bullet -compact -offset indent
.It
If one of them is runnable, it is preferred.
.It
If both are runnable, the one with the largest cpu percent is preferred.
.It
In a cpu percent tie, the one started more recently wins.
.It 
If none are runnable, and one of them is a zombie, the non zombie is preferred
.It
If both are zombies, the one started more recently wins.
.It
If neither is a zombie, the one with the smaller sleep time wins.
.It
In a tie, and one is sleeping in non interruptible sleep, we prefer that one.
.It
If both are in the same state, the one started more recently is preferred.
.El
In all cases where the most recently started wins, if there was no winner,
the one with the largest pid wins.
.Sh RETURN VALUES
The
.Fn proc_compare
function returns
.Dv 0
if
.Fa p1
is to be preferred
and
.Dv 1
if
.Fa p2
is to be preferred.
.Sh SEE ALSO
.Xr w 1
.Sh HISTORY
The
.Fn proc_compare
was extracted from src/sys/kern/tty.c and src/usr.bin/w/proc_compare.c
and merged in
.Nx 6.