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.Dd Sep 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 libc
.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
.Fn timer_settime "timer_t timerid" "int flags" "const struct itimerspec *restrict value" "struct itimerspec *restrict ovalue"
.Sh DESCRIPTION
The
.Fn timer_gettime
function 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 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 it_interval member of value contains the reload
value last set by
.Fn timer_settime .
.Pp
The
.Fn timer_settime
function sets the time until the next expiration of the timer specified
by
.Fa timerid
from the it_value member of the value argument and arm the timer if the
it_value member of 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 it_value member of value is zero, the timer is disarmed.
If the timer is disarmed, then pending signal is removed.
.Pp
If the flag 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 it_value member of value. That is,
the timer expires in it_value nanoseconds from when the call is made. If the
flag TIMER_ABSTIME is set in the argument 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
it_value member of value. If the specified time has already passed, the
function succeeds and the expiration notification is made.
.Pp
The reload value of the timer is set to the value specified by the it_interval
member of value. When a timer is armed with a non-zero 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 is 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 ovalue is not NULL, the
.Fn timer_settime
function stores, in the location referenced by 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 is 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
function 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 {DELAYTIMER_MAX}. If the number of
such extra expirations is greater than or equal to {DELAYTIMER_MAX}, then the
overrun count is set to {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
function succeeds, it returns the timer expiration overrun count as explained
above.
.Pp
If the
.Fn timer_gettime
or
.Fn timer_settime
functions succeed, a value of 0 is returned.
.Pp
If an error occurs for any of these functions, the value -1 is returned, and
errno set to indicate the error.
.Sh ERRORS
The
.Fn timer_settime
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
A value structure specified a nanosecond value less than zero or greater than
or equal to 1000 million, and the it_value member of that structure did not
specify zero seconds and nanoseconds.
.El
.Pp
These functions 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 timer_settime() function may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The it_interval member of value is not zero and the timer was created with
notification by creation of a new thread ( sigev_sigev_notify was SIGEV_THREAD)
and a fixed stack address has been set in the thread attribute pointed to by
sigev_notify_attributes.
.El
.Pp
The
.Fn timer_gettime
and
.Fn timer_settime
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
.Sh STANDARDS
The
.Fn timer_getoverrun ,
.Fn timer_gettime ,
and
.Fn timer_settime
function conform to
.St -p1003.1-96 .