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TIMER_GETOVERRUN(3P) POSIX Programmer's Manual TIMER_GETOVERRUN(3P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
timer_getoverrun, timer_gettime, timer_settime — per-process timers
#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);
The timer_gettime() function shall store 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 shall contain 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 shall contain the
reload value last set by timer_settime().
The timer_settime() function shall set 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 shall reset the time until next
expiration to the value specified. If the it_value member of value is
zero, the timer shall be disarmed. The effect of disarming or
resetting a timer with pending expiration notifications is
unspecified.
If the flag TIMER_ABSTIME is not set in the argument flags,
timer_settime() shall behave 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 shall expire in it_value nanoseconds from
when the call is made. If the flag TIMER_ABSTIME is set in the
argument flags, timer_settime() shall behave 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 shall expire when the clock reaches the value specified by the
it_value member of value. If the specified time has already passed,
the function shall succeed and the expiration notification shall be
made.
The reload value of the timer shall be 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 shall be rounded
up to the larger multiple of the resolution. Quantization error shall
not cause the timer to expire earlier than the rounded time value.
If the argument ovalue is not NULL, the timer_settime() function
shall store, 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 shall not expire before their
scheduled time.
Only a single signal shall 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 shall be queued, and a timer overrun shall
occur. When a timer expiration signal is delivered to or accepted by
a process, the timer_getoverrun() function shall return 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-
defined maximum of {DELAYTIMER_MAX}. If the number of such extra
expirations is greater than or equal to {DELAYTIMER_MAX}, then the
overrun count shall be set to {DELAYTIMER_MAX}. The value returned
by timer_getoverrun() shall apply to the most recent expiration
signal delivery or acceptance for the timer. If no expiration signal
has been delivered for the timer, the return value of
timer_getoverrun() is unspecified.
If the timer_getoverrun() function succeeds, it shall return the
timer expiration overrun count as explained above.
If the timer_gettime() or timer_settime() functions succeed, a value
of 0 shall be returned.
If an error occurs for any of these functions, the value −1 shall be
returned, and errno set to indicate the error.
The timer_settime() function shall 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.
These functions may fail if:
EINVAL The timerid argument does not correspond to an ID returned by
timer_create() but not yet deleted by timer_delete().
The timer_settime() function 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.
The following sections are informative.
None.
Using fixed stack addresses is problematic when timer expiration is
signaled by the creation of a new thread. Since it cannot be assumed
that the thread created for one expiration is finished before the
next expiration of the timer, it could happen that two threads use
the same memory as a stack at the same time. This is invalid and
produces undefined results.
Practical clocks tick at a finite rate, with rates of 100 hertz and
1000 hertz being common. The inverse of this tick rate is the clock
resolution, also called the clock granularity, which in either case
is expressed as a time duration, being 10 milliseconds and 1
millisecond respectively for these common rates. The granularity of
practical clocks implies that if one reads a given clock twice in
rapid succession, one may get the same time value twice; and that
timers must wait for the next clock tick after the theoretical
expiration time, to ensure that a timer never returns too soon. Note
also that the granularity of the clock may be significantly coarser
than the resolution of the data format used to set and get time and
interval values. Also note that some implementations may choose to
adjust time and/or interval values to exactly match the ticks of the
underlying clock.
This volume of POSIX.1‐2008 defines functions that allow an
application to determine the implementation-supported resolution for
the clocks and requires an implementation to document the resolution
supported for timers and nanosleep() if they differ from the
supported clock resolution. This is more of a procurement issue than
a runtime application issue.
None.
clock_getres(3p), timer_create(3p)
The Base Definitions volume of POSIX.1‐2008, time.h(0p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 TIMER_GETOVERRUN(3P)
Pages that refer to this page: time.h(0p), clock_getres(3p), getitimer(3p), timer_create(3p)