Originální popis anglicky:
timer_getoverrun, timer_gettime, timer_settime - per-process timers (
REALTIME)
Návod, kniha: POSIX Programmer's Manual
#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, if the
implementation supports the Realtime Signals Extension, 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, or if the Realtime Signals Extension is not
supported, 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_getoverrun(),
timer_gettime(), and
timer_settime() functions shall 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 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.
The following sections are informative.
None.
None.
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 IEEE Std 1003.1-2001 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() ,
timer_create() , the Base Definitions volume of
IEEE Std 1003.1-2001,
<time.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html
.
