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.\" Copyright (c) 2005 David Xu <davidxu@FreeBSD.org>
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.\" $FreeBSD: release/9.1.0/lib/libc/sys/timer_settime.2 235580 2012-05-18 01:04:03Z gjb $
.\"
.Dd September 11, 2000
.Dt TIMER_SETTIME 2
.Os
.Sh NAME
.Nm timer_getoverrun ,
.Nm timer_gettime ,
.Nm timer_settime
.Nd "per-process timers (REALTIME)"
.Sh LIBRARY
.Lb librt
.Sh SYNOPSIS
.In time.h
.Ft int
.Fn timer_getoverrun "timer_t timerid"
.Ft int
.Fn timer_gettime "timer_t timerid" "struct itimerspec *value"
.Ft int
.Fo timer_settime
.Fa "timer_t timerid" "int flags" "const struct itimerspec *restrict value"
.Fa "struct itimerspec *restrict ovalue"
.Fc
.Sh DESCRIPTION
The
.Fn timer_gettime
system call stores the amount of time until the specified timer,
.Fa timerid ,
expires and the reload value of the timer into the space pointed to by the
.Fa value
argument.
The
.Va it_value
member of this structure contains the amount of time
before the timer expires, or zero if the timer is disarmed.
This value is
returned as the interval until timer expiration, even if the timer was armed
with absolute time.
The
.Va it_interval
member of
.Fa value
contains the reload
value last set by
.Fn timer_settime .
.Pp
The
.Fn timer_settime
system call sets the time until the next expiration of the timer specified
by
.Fa timerid
from the
.Va it_value
member of the
.Fa value
argument and arms the timer if the
.Va it_value
member of
.Fa value
is non-zero.
If the specified timer was already
armed when
.Fn timer_settime
is called, this call resets the time until next expiration to the value
specified.
If the
.Va it_value
member of
.Fa value
is zero, the timer is disarmed.
If the timer is disarmed, then pending signal is removed.
.Pp
If the flag
.Dv TIMER_ABSTIME
is not set in the argument
.Fa flags ,
.Fn timer_settime
behaves as if the time until next expiration is set to
be equal to the interval specified by the
.Va it_value
member of
.Fa value .
That is,
the timer expires in
.Va it_value
nanoseconds from when the call is made.
If the flag
.Dv TIMER_ABSTIME
is set in the argument
.Fa flags ,
.Fn timer_settime
behaves as if the time until next expiration is set to be equal to the
difference between the absolute time specified by the it_value member of
value and the current value of the clock associated with
.Fa timerid .
That is, the timer expires when the clock reaches the value specified by the
.Va it_value
member of
.Fa value .
If the specified time has already passed, the
system call succeeds and the expiration notification is made.
.Pp
The reload value of the timer is set to the value specified by the
.Va it_interval
member of
.Fa value .
When a timer is armed with a non-zero
.Va it_interval ,
a periodic
(or repetitive) timer is specified.
.Pp
Time values that are between two consecutive non-negative integer multiples of
the resolution of the specified timer are rounded up to the larger multiple of
the resolution.
Quantization error will not cause the timer to expire earlier
than the rounded time value.
.Pp
If the argument
.Fa ovalue
is not
.Dv NULL ,
the
.Fn timer_settime
system call stores, in the location referenced by
.Fa ovalue ,
a value representing
the previous amount of time before the timer would have expired, or zero if the
timer was disarmed, together with the previous timer reload value.
Timers do not
expire before their scheduled time.
.Pp
Only a single signal is queued to the process for a given timer at any point in
time.
When a timer for which a signal is still pending expires, no signal is
queued, and a timer overrun will occur.
When a timer expiration signal is
accepted by a process, the
.Fn timer_getoverrun
system call returns the timer expiration overrun count for the specified timer.
The overrun count returned contains the number of extra timer expirations that
occurred between the time the signal was generated (queued) and when it was
accepted, up to but not including an maximum of
.Brq Dv DELAYTIMER_MAX .
If the number of
such extra expirations is greater than or equal to
.Brq Dv DELAYTIMER_MAX ,
then the overrun count is set to
.Brq Dv DELAYTIMER_MAX .
The value returned by
.Fn timer_getoverrun
applies to the most recent expiration signal acceptance for the timer.
If no
expiration signal has been delivered for the timer, the return value of
.Fn timer_getoverrun
is unspecified.
.Sh RETURN VALUES
If the
.Fn timer_getoverrun
system call succeeds, it returns the timer expiration overrun count as explained
above.
Otherwise the value \-1 is returned, and the global variable
.Va errno
is set to indicate the error.
.Pp
.Rv -std timer_gettime timer_settime
.Sh ERRORS
The
.Fn timer_settime
system call
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
A
.Fa value
structure specified a nanosecond value less than zero or greater than
or equal to 1000 million, and the
.Va it_value
member of that structure did not
specify zero seconds and nanoseconds.
.El
.Pp
These system calls may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa timerid
argument does not correspond to an ID returned by
.Fn timer_create
but not yet deleted by
.Fn timer_delete .
.El
.Pp
The
.Fn timer_settime
system call may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Va it_interval
member of
.Fa value
is not zero and the timer was created with
notification by creation of a new thread
.Va ( sigev_sigev_notify
was
.Dv SIGEV_THREAD )
and a fixed stack address has been set in the thread attribute pointed to by
.Va sigev_notify_attributes .
.El
.Pp
The
.Fn timer_gettime
and
.Fn timer_settime
system calls
may fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
Any arguments point outside the allocated address space or there is a
memory protection fault.
.El
.Sh SEE ALSO
.Xr clock_getres 2 ,
.Xr timer_create 2 ,
.Xr siginfo 3
.Sh STANDARDS
The
.Fn timer_getoverrun ,
.Fn timer_gettime ,
and
.Fn timer_settime
system calls conform to
.St -p1003.1-2004 .
.Sh HISTORY
Support for
.Tn POSIX
per-process timer first appeared in
.Fx 7.0 .