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+.\"
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+.\" $FreeBSD$
+.\"
+.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 .