table of contents
|TIMER_SETTIME(2)||System Calls Manual||TIMER_SETTIME(2)|
— per-process timers (REALTIME)
POSIX Real-time Library (librt, -lrt)
int flags, const struct itimerspec
*restrict value, struct itimerspec *restrict
system call 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 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
system call sets the time until the next expiration of the timer specified
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
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
If the flag
TIMER_ABSTIME is not set in the argument
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
TIMER_ABSTIME is set in the argument
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 system call 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 are 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
system call 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 do not expire before
their scheduled time.
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
system call 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
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
timer_getoverrun() is unspecified.
timer_getoverrun() system call
succeeds, it returns the timer expiration overrun count as explained above.
Otherwise the value -1 is returned, and the global variable
errno is set to indicate the error.
timer_settime() functions return the value 0
if successful; otherwise the value -1 is returned and the global
variable errno is set to indicate the error.
timer_settime() system call will fail
- 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.
These system calls may fail if:
- The timerid argument does not correspond to an ID
timer_create() but not yet deleted by
timer_settime() system call may fail
- The it_interval member of
value is not zero and the timer was created with
notification by creation of a new thread
SIGEV_THREAD) and a fixed stack address has been set in the thread attribute pointed to by sigev_notify_attributes.
timer_settime() system calls may fail if:
- Any arguments point outside the allocated address space or there is a memory protection fault.
timer_settime() system calls conform to
IEEE Std 1003.1-2004 (“POSIX.1”).
Support for POSIX per-process timer first appeared in FreeBSD 7.0.
|September 11, 2000||Debian|