timers(2)timers(2)NAME
timers: timer_create(), timer_delete(), timer_getoverrun(), timer_get‐
time(), timer_settime() - timer operations
SYNOPSISDESCRIPTIONtimer_create()
The function creates a per-process timer using the specified clock,
clock_id, as the timing base. The function returns, in the location
referenced by timerid, a timer ID of type timer_t used to identify the
timer in timer requests. This timer ID will be unique within the call‐
ing process until the timer is deleted. The particular clock,
clock_id, is defined in The timer whose ID is returned will be in a
disarmed state upon return from
The evp argument, if non-NULL, points to a sigevent structure. If the
sigev_notify member of evp is then the structure should also specify
the signal number to be sent to the process on timer expiration. The
signal to be sent is specified in the sigev_signo field of evp. If the
sigev_notify member of evp is no notification is sent. If evp is NULL,
then a default signal is sent to the process. The defaults for the
clocks and are and
Per-process timers are not inherited by a child process across a and
are disarmed and deleted by an
timer_delete()
The function deletes the specified timer, previously created by the
function. If the timer is armed when is called, the behavior is as if
the timer is automatically disarmed before removal. Any pending noti‐
fications from the timer remain.
timer_settime()
The function sets the time until the next expiration of the timer spec‐
ified by timerid from the it_value member of the value argument and
arms the timer if the it_value member of value is non-zero. If the
specified timer was already armed when 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. Any pending notifica‐
tions from the timer remain.
If the flag is not set in the argument flags, behaves as if the time
until next expiration is set equal to the interval specified by the
it_value member of value. That is, the timer will expire in it_value
nanoseconds from when the call is made.
If the flag is set in the argument flags, behaves as if the time until
next expiration is set 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 will expire when
the clock reaches the value specified by the it_value member of value.
If the specified time has already passed, the function will succeed 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 mul‐
tiples of the resolution of the specified timer are rounded up to the
larger multiple of the resolution. A quantization error will not cause
the timer to expire earlier than the rounded-up time value.
If the argument ovalue is not NULL, the function stores, in the loca‐
tion referenced by ovalue, a value representing the previous amount of
time before the timer would have expired or zero if the timer was dis‐
armed, together with the previous timer reload value. The members of
ovalue are subject to the resolution of the timer, and are the same
values that would be returned by a call at that point in time.
timer_gettime()
The function stores the amount of time until the specified timer,
timerid, expires and the timer's reload value into the space pointed to
by the value argument. The it_value member of this structure will con‐
tain the amount of time before the timer expires, or zero if the timer
is disarmed. This value is returned as the interval until timer expi‐
ration, even if the timer was armed with absolute time. The it_inter‐
val member of value will contain the reload value last set by
timer_getoverrun()
Only a single signal is delivered 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 delivered, and a timer overrun has occurred.
When a timer expiration signal is delivered to a process, the function
returns the timer expiration count for the specified timer. The over‐
run count returned contains the number of extra timer expirations which
occurred between the time the signal was generated and when it was
delivered, up to but not including an implementation defined maximum of
If the number of such extra expirations is greater than or equal to
then the overrun count is set to The value returned by applies to the
most recent expiration signal delivery for the timer. If no expiration
signal has been delivered for the timer, the meaning of the overrun
count returned is undefined.
RETURN VALUE
Upon successful completion, returns zero and updates the location ref‐
erenced by timerid to a timer_t which can be passed to the per-process
timer calls. Otherwise, returns −1 and sets to indicate the error.
The value of timerid is undefined if an error occurs.
Upon successful completion, returns zero. Otherwise, returns −1 and
sets to indicate the error.
Upon successful completion, returns zero and updates the location ref‐
erenced by ovalue, if ovalue is non-NULL.
Upon successful completion, returns zero and updates the location ref‐
erenced by value, if ovalue is non-NULL. Otherwise, returns −1 and
sets to indicate the error.
Upon successful completion, returns the timer expiration overrun count
as explained above. Otherwise, returns −1 and sets to indicate the
error.
ERRORS
If any of the following conditions occur, the function returns −1 and
sets (see errno(2)) to the corresponding value:
The system lacks sufficient signal queuing resources to honor
the request.
The calling process has already created all of the
timers it is allowed by this implementation.
The specified clock
ID is not defined.
The timerid or evp argument points to an invalid
address.
The function
is not supported by this implementation.
If any of the following conditions occur, the function returns −1 and
sets to the corresponding value:
The timer ID specified by timerid is not a valid timer ID.
The function
is not supported by this implementation.
If any of the following conditions occur, the and functions return −1
and set to the corresponding value:
The timerid argument does not correspond to an ID
returned by but not yet deleted by
The value structure passed to specified a nanosecond
value less than zero or greater than or equal to
1000 million.
The value or ovalue argument points to an invalid
address.
The and functions are not supported by this implementa‐
tion.
EXAMPLES
Create a timer, set it to go off in one minute, and deliver a signal:
AUTHOR
and were derived from the proposed IEEE POSIX P1003.4 standard, draft
14.
SEE ALSOclocks(2), getitimer(2).
STANDARDS CONFORMANCEtimers(2)
