UALARM
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
Page Index
NAME
ualarm - schedule signal after given number of microseconds
SYNOPSIS
#include <unistd.h>
useconds_t ualarm(useconds_t usecs, useconds_t interval);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
ualarm():
-
- Since glibc 2.12:
-
(_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200809L)
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE
- Before glibc 2.12:
-
_BSD_SOURCE || _XOPEN_SOURCE >= 500
DESCRIPTION
The
ualarm()
function causes the signal
SIGALRM
to be sent to the invoking process after (not less than)
usecs
microseconds.
The delay may be lengthened slightly by any system activity
or by the time spent processing the call or by the
granularity of system timers.
Unless caught or ignored, the
SIGALRM
signal will terminate the process.
If the
interval
argument is nonzero, further
SIGALRM
signals will be sent every
interval
microseconds after the first.
RETURN VALUE
This function returns the number of microseconds remaining for
any alarm that was previously set, or 0 if no alarm was pending.
ERRORS
- EINTR
-
Interrupted by a signal; see
signal(7).
- EINVAL
-
usecs or interval is not smaller than 1000000.
(On systems where that is considered an error.)
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
ualarm()
| Thread safety | MT-Safe
|
CONFORMING TO
4.3BSD, POSIX.1-2001.
POSIX.1-2001 marks
ualarm()
as obsolete.
POSIX.1-2008 removes the specification of
ualarm().
4.3BSD, SUSv2, and POSIX do not define any errors.
NOTES
POSIX.1-2001 does not specify what happens if the
usecs
argument is 0.
On Linux (and probably most other systems),
the effect is to cancel any pending alarm.
The type
useconds_t
is an unsigned integer type capable of holding integers
in the range [0,1000000].
On the original BSD implementation, and in glibc before version 2.1,
the arguments to
ualarm()
were instead typed as
unsigned int.
Programs will be more portable if they never mention
useconds_t
explicitly.
The interaction of this function with
other timer functions such as
alarm(2),
sleep(3),
nanosleep(2),
setitimer(2),
timer_create(2),
timer_delete(2),
timer_getoverrun(2),
timer_gettime(2),
timer_settime(2),
usleep(3)
is unspecified.
This function is obsolete.
Use
setitimer(2)
or POSIX interval timers
(timer_create(2),
etc.)
instead.
SEE ALSO
alarm(2),
getitimer(2),
nanosleep(2),
select(2),
setitimer(2),
usleep(3),
time(7)
COLOPHON
This page is part of release 5.10 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.