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TIMER_SETTIME(2) | System Calls Manual | TIMER_SETTIME(2) |
NAME¶
timer_getoverrun
,
timer_gettime
,
timer_settime
—
per-process timers (REALTIME)
LIBRARY¶
POSIX Real-time Library (librt, -lrt)SYNOPSIS¶
#include
<time.h>
int
timer_getoverrun
(timer_t
timerid);
int
timer_gettime
(timer_t
timerid, struct
itimerspec *value);
int
timer_settime
(timer_t
timerid, int flags,
const struct itimerspec *restrict value,
struct itimerspec *restrict ovalue);
DESCRIPTION¶
Thetimer_gettime
() 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
timer_settime
().
The timer_settime
() 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 is removed.
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 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 is not
NULL
, the
timer_settime
() 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
timer_getoverrun
() 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.
RETURN VALUES¶
If thetimer_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.
The
timer_gettime
() and
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.
ERRORS¶
Thetimer_settime
() system call will fail if:
- [
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.
- [
EINVAL
] - The timerid argument does not correspond
to an ID returned by
timer_create
() but not yet deleted bytimer_delete
().
timer_settime
() system call may fail if:
- [
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.
timer_gettime
() and
timer_settime
() system calls may fail if:
- [
EFAULT
] - Any arguments point outside the allocated address space or there is a memory protection fault.
SEE ALSO¶
clock_getres(2), timer_create(2), siginfo(3)STANDARDS¶
Thetimer_getoverrun
(),
timer_gettime
(), and
timer_settime
() system calls conform to
IEEE Std 1003.1-2004
(“POSIX.1”).
HISTORY¶
Support for POSIX per-process timer first appeared in FreeBSD 7.0.September 11, 2000 | Debian |