minix/lib/libc/sys/getitimer.2
Ben Gras 2fe8fb192f Full switch to clang/ELF. Drop ack. Simplify.
There is important information about booting non-ack images in
docs/UPDATING. ack/aout-format images can't be built any more, and
booting clang/ELF-format ones is a little different. Updating to the
new boot monitor is recommended.

Changes in this commit:

	. drop boot monitor -> allowing dropping ack support
	. facility to copy ELF boot files to /boot so that old boot monitor
	  can still boot fairly easily, see UPDATING
	. no more ack-format libraries -> single-case libraries
	. some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases
	. drop several ack toolchain commands, but not all support
	  commands (e.g. aal is gone but acksize is not yet).
	. a few libc files moved to netbsd libc dir
	. new /bin/date as minix date used code in libc/
	. test compile fix
	. harmonize includes
	. /usr/lib is no longer special: without ack, /usr/lib plays no
	  kind of special bootstrapping role any more and bootstrapping
	  is done exclusively through packages, so releases depend even
	  less on the state of the machine making them now.
	. rename nbsd_lib* to lib*
	. reduce mtree
2012-02-14 14:52:02 +01:00

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.\" $NetBSD: getitimer.2,v 1.24 2010/04/30 04:17:45 jruoho Exp $
.\"
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.\" @(#)getitimer.2 8.3 (Berkeley) 5/16/95
.\"
.Dd April 30, 2010
.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 * restrict value" "struct itimerval * restrict ovalue"
.Sh DESCRIPTION
The system provides each process with three interval timers,
defined in
.Ao Pa sys/time.h Ac .
The
.Fn getitimer
call returns the current value for the timer specified in
.Fa which
in the structure at
.Fa value .
The
.Fn setitimer
call sets a timer to the specified
.Fa value
(returning the previous value of the timer if
.Fa ovalue
is non-nil).
.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.
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.
.Sh NOTES
Macros for manipulating time values are defined in the
.In sys/time.h
header;
.Fn timerclear
sets a time value to zero,
.Fn timerisset
tests if a time value is non-zero,
.Fn timercmp
compares two time values,
.Fn timeradd
adds a time value to another time value,
.Fn timersub
computes the time difference between two time values.
For additional details, see
.Xr timeradd 3 .
.Sh RETURN VALUES
If the calls succeed, a value of 0 is returned.
If an error occurs, the value \-1 is returned, and a more precise error
code is placed in the global variable
.Va errno .
.Sh ERRORS
.Fn getitimer
and
.Fn setitimer
will fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
The
.Fa value
parameter specified a bad address.
.It Bq Er EINVAL
A
.Fa value
parameter specified a time that was too large
to be handled.
.El
.Sh SEE ALSO
.Xr gettimeofday 2 ,
.Xr poll 2 ,
.Xr select 2 ,
.Xr sigaction 2
.Sh STANDARDS
The
.Fn getitimer
and
.Fn setitimer
functions conform to
.St -p1003.1-2001 .
The later
.St -p1003.1-2008
revision however marked both functions as obsolescent,
recommending the use of
.Xr timer_gettime 2
and
.Xr timer_settime 2
instead.
.Sh HISTORY
The
.Fn getitimer
function call appeared in
.Bx 4.2 .