TIMER_GETOVERRUN
Section: POSIX Programmer's Manual (3P)
Updated: 2013
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PROLOG
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.
NAME
timer_getoverrun,
timer_gettime,
timer_settime
--- per-process timers
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
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.
RETURN VALUE
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.
ERRORS
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.
EXAMPLES
None.
APPLICATION USAGE
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.
RATIONALE
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.
FUTURE DIRECTIONS
None.
SEE ALSO
clock_getres(),
timer_create()
The Base Definitions volume of POSIX.1-2008,
<time.h>
COPYRIGHT
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 .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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