Tribblix: 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.