illumos: manual page: timer

TIMER_SETTIME(3C) Standard C Library Functions TIMER_SETTIME(3C)

NAME

timer_settime, timer_gettime, timer_getoverrun - per-process timers

SYNOPSIS

#include <time.h>

int timer_settime(timer_t timerid, int flags,
const struct itimerspec *restrict value,
struct itimerspec *restrict ovalue);

int timer_gettime(timer_t timerid, struct itimerspec *value);

int timer_getoverrun(timer_t timerid);

DESCRIPTION

The timer_settime() function sets the time until the next expiration of
the timer specified by 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 timer_settime() is called,
this call resets the time until next expiration to the value specified.
If the it_value member of value is 0, the timer is disarmed. The effect
of disarming or resetting a timer on pending expiration notifications is
unspecified.

If the flag TIMER_ABSTIME is not set in the argument flags,
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, 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 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.

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.

Time values that are between two consecutive non-negative integer
multiples of the resolution of the specified timer will be rounded up to
the larger multiple of the resolution. Quantization error will not cause
the timer to expire earlier than the rounded time value.

If the argument ovalue is not NULL, the function timer_settime() stores,
in the location referenced by ovalue, a value representing the previous
amount of time before the timer would have expired or 0 if the timer was
disarmed, together with the previous timer reload value. The members of
ovalue are subject to the resolution of the timer, and they are the same
values that would be returned by a timer_gettime() call at that point in
time.

The timer_gettime() function stores the amount of time until the
specified timer, timerid, expires and the reload value of the timer into
the space pointed to by the value argument. The it_value member of this
structure contains the amount of time before the timer expires, or 0 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
timer_settime().

Only a single signal will be 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 will be queued, and a timer overrun occurs. When a
timer expiration signal is delivered to or accepted by a process, the
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 delivered or accepted, up to but not
including an implementation-dependent maximum of DELAYTIMER_MAX. If the
number of such extra expirations is greater than or equal to
DELAYTIMER_MAX, then the overrun count will be set to DELAYTIMER_MAX. The
value returned by timer_getoverrun() applies to the most recent
expiration signal delivery or acceptance for the timer. If no expiration
signal has been delivered for the timer, the meaning of the overrun count
returned is undefined.

If the specified timer is of type CLOCK_HIGHRES and the time value is
smaller than a system defined threshold, then {PRIV_PROC_CLOCK_HIGHRES}
must be asserted in the effective set of the calling process or the time
values will be adjusted up to the threshold value.

RETURN VALUES

If the timer_settime() or timer_gettime() functions succeed, 0 is
returned. If an error occurs for either of these functions, -1 is
returned, and errno is set to indicate the error. If the
timer_getoverrun() function succeeds, it returns the timer expiration
overrun count as explained above.

ERRORS

The timer_settime(), timer_gettime() and timer_getoverrun() functions
will fail if:

EINVAL
The timerid argument does not correspond to a timer returned
by timer_create(3C) but not yet deleted by timer_delete(3C).

ENOSYS
The timer_settime(), timer_gettime(), and timer_getoverrun()
functions are not supported by the system. The timer_settime()
function will fail if:

EINVAL
A value structure specified a nanosecond value less than zero
or greater than or equal to 1000 million.