mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-23 11:18:54 +00:00
f56be64fb2
a "null pointer".'' Making good use of the excellent explanations sent to me by Ruslan Ermilov, Garrett Wollman and Bruce Evans, correct the descriptions of null pointers. They are just "null pointers", not nil, not NULL or ".Dv NULL". Suggested by: ru, wollman, bde Reviewed by: ru, wollman Pointy hat: keramida
185 lines
4.8 KiB
Groff
185 lines
4.8 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the University of
|
|
.\" California, Berkeley and its contributors.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" @(#)getitimer.2 8.3 (Berkeley) 5/16/95
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd May 16, 1995
|
|
.Dt GETITIMER 2
|
|
.Os
|
|
.Sh NAME
|
|
.Nm getitimer ,
|
|
.Nm setitimer
|
|
.Nd get/set value of interval timer
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In sys/time.h
|
|
.Fd "#define ITIMER_REAL 0"
|
|
.Fd "#define ITIMER_VIRTUAL 1"
|
|
.Fd "#define ITIMER_PROF 2"
|
|
.Ft int
|
|
.Fn getitimer "int which" "struct itimerval *value"
|
|
.Ft int
|
|
.Fn setitimer "int which" "const struct itimerval *value" "struct itimerval *ovalue"
|
|
.Sh DESCRIPTION
|
|
The system provides each process with three interval timers,
|
|
defined in
|
|
.In sys/time.h .
|
|
The
|
|
.Fn getitimer
|
|
system call returns the current value for the timer specified in
|
|
.Fa which
|
|
in the structure at
|
|
.Fa value .
|
|
The
|
|
.Fn setitimer
|
|
system call sets a timer to the specified
|
|
.Fa value
|
|
(returning the previous value of the timer if
|
|
.Fa ovalue
|
|
is not a null pointer).
|
|
.Pp
|
|
A timer value is defined by the
|
|
.Fa itimerval
|
|
structure:
|
|
.Bd -literal -offset indent
|
|
struct itimerval {
|
|
struct timeval it_interval; /* timer interval */
|
|
struct timeval it_value; /* current value */
|
|
};
|
|
.Ed
|
|
.Pp
|
|
If
|
|
.Fa it_value
|
|
is non-zero, it indicates the time to the next timer expiration.
|
|
If
|
|
.Fa it_interval
|
|
is non-zero, it specifies a value to be used in reloading
|
|
.Fa it_value
|
|
when the timer expires.
|
|
Setting
|
|
.Fa it_value
|
|
to 0 disables a timer, regardless of the value of
|
|
.Fa it_interval .
|
|
Setting
|
|
.Fa it_interval
|
|
to 0 causes a timer to be disabled after its next expiration (assuming
|
|
.Fa it_value
|
|
is non-zero).
|
|
.Pp
|
|
Time values smaller than the resolution of the
|
|
system clock are rounded up to this resolution
|
|
(typically 10 milliseconds).
|
|
.Pp
|
|
The
|
|
.Dv ITIMER_REAL
|
|
timer decrements in real time.
|
|
A
|
|
.Dv SIGALRM
|
|
signal is
|
|
delivered when this timer expires.
|
|
.Pp
|
|
The
|
|
.Dv ITIMER_VIRTUAL
|
|
timer decrements in process virtual time.
|
|
It runs only when the process is executing.
|
|
A
|
|
.Dv SIGVTALRM
|
|
signal
|
|
is delivered when it expires.
|
|
.Pp
|
|
The
|
|
.Dv ITIMER_PROF
|
|
timer decrements both in process virtual time and
|
|
when the system is running on behalf of the process.
|
|
It is designed
|
|
to be used by interpreters in statistically profiling the execution
|
|
of interpreted programs.
|
|
Each time the
|
|
.Dv ITIMER_PROF
|
|
timer expires, the
|
|
.Dv SIGPROF
|
|
signal is
|
|
delivered.
|
|
Because this signal may interrupt in-progress
|
|
system calls, programs using this timer must be prepared to
|
|
restart interrupted system calls.
|
|
.Pp
|
|
The maximum number of seconds allowed for
|
|
.Fa it_interval
|
|
and
|
|
.Fa it_value
|
|
in
|
|
.Fn setitimer
|
|
is 100000000.
|
|
.Sh NOTES
|
|
Three macros for manipulating time values are defined in
|
|
.In sys/time.h .
|
|
The
|
|
.Fn timerclear
|
|
macro
|
|
sets a time value to zero,
|
|
.Fn timerisset
|
|
tests if a time value is non-zero, and
|
|
.Fn timercmp
|
|
compares two time values.
|
|
.Sh RETURN VALUES
|
|
.Rv -std
|
|
.Sh ERRORS
|
|
The
|
|
.Fn getitimer
|
|
and
|
|
.Fn setitimer
|
|
system calls
|
|
will fail if:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EFAULT
|
|
The
|
|
.Fa value
|
|
argument specified a bad address.
|
|
.It Bq Er EINVAL
|
|
The
|
|
.Fa value
|
|
argument specified a time that was too large
|
|
to be handled.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr gettimeofday 2 ,
|
|
.Xr select 2 ,
|
|
.Xr sigvec 2 ,
|
|
.Xr clocks 7
|
|
.Sh HISTORY
|
|
The
|
|
.Fn getitimer
|
|
system call appeared in
|
|
.Bx 4.2 .
|