mirror of https://github.com/mkerrisk/man-pages
timer_getoverrun.2: New page documenting timer_getoverrun(2)
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
parent
167f7e62e1
commit
c6f51a127e
|
@ -0,0 +1,135 @@
|
|||
.\" Copyright (c) 2009 Linux Foundation, written by Michael Kerrisk
|
||||
.\" <mtk.manpages@gmail.com>
|
||||
.\"
|
||||
.\" Permission is granted to make and distribute verbatim copies of this
|
||||
.\" manual provided the copyright notice and this permission notice are
|
||||
.\" preserved on all copies.
|
||||
.\"
|
||||
.\" Permission is granted to copy and distribute modified versions of this
|
||||
.\" manual under the conditions for verbatim copying, provided that the
|
||||
.\" entire resulting derived work is distributed under the terms of a
|
||||
.\" permission notice identical to this one.
|
||||
.\"
|
||||
.\" Since the Linux kernel and libraries are constantly changing, this
|
||||
.\" manual page may be incorrect or out-of-date. The author(s) assume no
|
||||
.\" responsibility for errors or omissions, or for damages resulting from
|
||||
.\" the use of the information contained herein. The author(s) may not
|
||||
.\" have taken the same level of care in the production of this manual,
|
||||
.\" which is licensed free of charge, as they might when working
|
||||
.\" professionally.
|
||||
.\"
|
||||
.\" Formatted or processed versions of this manual, if unaccompanied by
|
||||
.\" the source, must acknowledge the copyright and authors of this work.
|
||||
.TH TIMER_GETOVERRUN 2 2009-02-16 Linux "Linux Programmer's Manual"
|
||||
.SH NAME
|
||||
timer_getoverrun \- get overrun count for a POSIX per-process timer
|
||||
.SH SYNOPSIS
|
||||
.nf
|
||||
.B #include <time.h>
|
||||
|
||||
.BI "int timer_getoverrun(timer_t " timerid );
|
||||
.fi
|
||||
|
||||
Link with
|
||||
.IR \-lrt .
|
||||
.sp
|
||||
.in -4n
|
||||
Feature Test Macro Requirements for glibc (see
|
||||
.BR feature_test_macros (7)):
|
||||
.in
|
||||
.sp
|
||||
.BR timer_getoverrun ():
|
||||
_POSIX_C_SOURCE >= 199309
|
||||
.SH DESCRIPTION
|
||||
.BR timer_getoverrun ()
|
||||
returns the "overrun count" for the timer referred to by
|
||||
.IR timerid .
|
||||
An application can use the overrun count to accurately calculate the number
|
||||
of timer expirations that would have occurred over a given time interval.
|
||||
Timer overruns can occur both when receiving expiration notifications
|
||||
via signals
|
||||
.RB ( SIGEV_SIGNAL ),
|
||||
and via threads
|
||||
.RB ( SIGEV_THREAD ).
|
||||
|
||||
When expiration notifications are delivered via a signal,
|
||||
overruns can occur as follows.
|
||||
Regardless of whether or not a real-time signal is used for
|
||||
timer notifications,
|
||||
the system queues at most one signal per timer.
|
||||
(This is the behavior specified by POSIX.1-2001.
|
||||
The alternative, queuing one signal for each timer expiration,
|
||||
could easily result in overflowing the allowed limits for
|
||||
queued signals on the system.)
|
||||
Because of system scheduling delays,
|
||||
or because the signal may be temporarily blocked,
|
||||
there can be a delay between the time when the notification
|
||||
signal is generated and the time when it
|
||||
is delivered (e.g., caught by a signal handler) or accepted (e.g., using
|
||||
.BR sigwaitinfo (2)).
|
||||
In this interval, further timer expirations may occur.
|
||||
The timer overrun count is the number of additional
|
||||
timer expirations that occurred between the time when the signal
|
||||
was generated and when it was delivered or accepted.
|
||||
|
||||
Timer overruns can also occur when expiration notifications
|
||||
are delivered via invocation of a thread,
|
||||
since there may be an arbitrary delay between an expiration of the timer
|
||||
and the invocation of the notification thread,
|
||||
and in that delay interval, additional timer expirations may occur
|
||||
.SH RETURN VALUE
|
||||
On success,
|
||||
.BR timer_getoverrun ()
|
||||
returns the overrun count of the specified timer;
|
||||
this count may be 0 if no overruns have occurred.
|
||||
On failure, \-1 is returned, and
|
||||
.I errno
|
||||
is set to indicate the error.
|
||||
.SH ERRORS
|
||||
.TP
|
||||
.B EINVAL
|
||||
.I timerid
|
||||
is not a valid timer ID.
|
||||
.SH VERSIONS
|
||||
This system call is available since Linux 2.6.
|
||||
.SH CONFORMING TO
|
||||
POSIX.1-2001
|
||||
.SH NOTES
|
||||
When timer notifications are delivered via signals
|
||||
.RB ( SIGEV_SIGNAL ),
|
||||
on Linux it is also possible to obtain the overrun count via the
|
||||
.I si_overrun
|
||||
field of the
|
||||
.I siginfo_t
|
||||
structure (see
|
||||
.BR sigaction (2)).
|
||||
This allows an application to avoid the overhead of making
|
||||
a system call to obtain the overrun count,
|
||||
but is a non-portable extension POSIX.1-2001.
|
||||
|
||||
POSIX.1-2001 only discusses timer overruns in the context of
|
||||
timer notifications using signals.
|
||||
.\" FIXME . Austin bug filed, 11 Feb 09
|
||||
.SH BUGS
|
||||
POSIX.1-2001 specifies that if the timer overrun count
|
||||
is equal to or greater than an implementation-defined maximum,
|
||||
.BR DELAYTIMER_MAX ,
|
||||
then
|
||||
.BR timer_getoverrun ()
|
||||
should return
|
||||
.BR DELAYTIMER_MAX .
|
||||
However, Linux does not implement this feature: instead,
|
||||
if the timer overrun value exceeds the maximum representable integer,
|
||||
the counter cycles, starting once more from low values.
|
||||
.\" Bug filed: http://bugzilla.kernel.org/show_bug.cgi?id=12665
|
||||
.\" http://thread.gmane.org/gmane.linux.kernel/113276/
|
||||
.SH SEE ALSO
|
||||
.BR clock_gettime (2),
|
||||
.BR sigaction (2),
|
||||
.BR signalfd (2),
|
||||
.BR sigwaitinfo (2),
|
||||
.BR timer_create (2),
|
||||
.BR timer_delete (2),
|
||||
.BR timer_settime (2),
|
||||
.BR signal (7),
|
||||
.BR time (7)
|
Loading…
Reference in New Issue