.\" Copyright (c) 2009 Linux Foundation, written by Michael Kerrisk
.\" <mtk.manpages@gmail.com>
.\"
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+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
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-.TH TIMER_GETOVERRUN 2 2009-02-16 Linux "Linux Programmer's Manual"
+.TH TIMER_GETOVERRUN 2 2021-03-22 "Linux man-pages (unreleased)" "Linux Programmer's Manual"
.SH NAME
timer_getoverrun \- get overrun count for a POSIX per-process timer
+.SH LIBRARY
+Real-time library
+.RI ( librt ", " \-lrt )
.SH SYNOPSIS
.nf
.B #include <time.h>
-
+.PP
.BI "int timer_getoverrun(timer_t " timerid );
.fi
-
-Link with
-.IR \-lrt .
-.sp
-.in -4n
+.PP
+.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
-.in
-.sp
+.RE
+.PP
.BR timer_getoverrun ():
-_POSIX_C_SOURCE >= 199309
+.nf
+ _POSIX_C_SOURCE >= 199309L
+.fi
.SH DESCRIPTION
.BR timer_getoverrun ()
returns the "overrun count" for the timer referred to by
.RB ( SIGEV_SIGNAL ),
and via threads
.RB ( SIGEV_THREAD ).
-
+.PP
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.
+(This is the behavior specified by POSIX.1.
The alternative, queuing one signal for each timer expiration,
could easily result in overflowing the allowed limits for
queued signals on the system.)
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.
-
+.PP
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
+and in that delay interval, additional timer expirations may occur.
.SH RETURN VALUE
On success,
.BR timer_getoverrun ()
is not a valid timer ID.
.SH VERSIONS
This system call is available since Linux 2.6.
-.SH CONFORMING TO
-POSIX.1-2001
+.SH STANDARDS
+POSIX.1-2001, POSIX.1-2008.
.SH NOTES
When timer notifications are delivered via signals
.RB ( SIGEV_SIGNAL ),
.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
+but is a nonportable extension to POSIX.1.
+.PP
+POSIX.1 discusses timer overruns only in the context of
timer notifications using signals.
.\" FIXME . Austin bug filed, 11 Feb 09
+.\" https://www.austingroupbugs.net/view.php?id=95
.SH BUGS
-POSIX.1-2001 specifies that if the timer overrun count
+POSIX.1 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,
+However, before Linux 4.19,
+.\" http://bugzilla.kernel.org/show_bug.cgi?id=12665
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 EXAMPLE
+Since Linux 4.19,
+.\" commit 78c9c4dfbf8c04883941445a195276bb4bb92c76
+.BR timer_getoverrun ()
+returns
+.B DELAYTIMER_MAX
+(defined as
+.B INT_MAX
+in
+.IR <limits.h> )
+in this case (and the overrun value is reset to 0).
+.SH EXAMPLES
See
.BR timer_create (2).
.SH SEE ALSO
projects / thirdparty / man-pages.git / blobdiff