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timerfd_create.2: Document TFD_TIMER_CANCEL_ON_SET 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2016-11-21 16:13:29 +01:00
parent 510625764c
commit e9477548b0
1 changed files with 35 additions and 0 deletions
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35
man2/timerfd_create.2
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@ -209,6 +209,23 @@ as an absolute value on the timer's clock.
The timer will expire when the value of the timer's
clock reaches the value specified in
.IR new_value.it_value .
.TP
.BR TFD_TIMER_CANCEL_ON_SET
If this flag is specified along with
.B TFD_TIMER_ABSTIME
and the clock for this timer is
.BR CLOCK_REALTIME
or
.BR CLOCK_REALTIME_ALARM ,
then mark this timer as cancelable if the real-time clock
undergoes a discontinuous change
.RB ( settimeofday (2),
.BR clock_settime (2),
or similar).
When such changes occur, a current or future
.BR read (2)
from the file descriptor will fail with the error
.BR ECANCELED .
.PP
If the
.I old_value
@ -283,6 +300,24 @@ A
will fail with the error
.B EINVAL
if the size of the supplied buffer is less than 8 bytes.
If the associated clock is either
.BR CLOCK_REALTIME
or
.BR CLOCK_REALTIME_ALARM ,
the timer is absolute
.RB ( TFD_TIMER_ABSTIME ),
and the flag
.BR TFD_TIMER_CANCEL_ON_SET
was specified when calling
.BR timerfd_settime (),
then
.BR read (2)
will fail with the error
.BR ECANCELED
if the real-time clock undergoes a discontinuous change.
(This allows the reading application to discover
such discontinuous changes to the clock.)
.TP
.BR poll "(2), " select "(2) (and similar)"
The file descriptor is readable