.\" Copyright (c) 2003 Andries Brouwer (aeb@cwi.nl)
.\"
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.TH UALARM 3  2017-09-15 "" "Linux Programmer's Manual"
.SH NAME
ualarm \- schedule signal after given number of microseconds
.SH SYNOPSIS
.nf
.B "#include <unistd.h>"
.PP
.BI "useconds_t ualarm(useconds_t " usecs ", useconds_t " interval );
.fi
.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.PP
.BR ualarm ():
.ad l
.RS 4
.PD 0
.TP 4
Since glibc 2.12:
.nf
(_XOPEN_SOURCE\ >=\ 500) && ! (_POSIX_C_SOURCE\ >=\ 200809L)
    || /* Glibc since 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE
.TP 4
.fi
Before glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
.\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
.PD
.RE
.ad b
.SH DESCRIPTION
The
.BR ualarm ()
function causes the signal
.B SIGALRM
to be sent to the invoking process after (not less than)
.I 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.
.PP
Unless caught or ignored, the
.B SIGALRM
signal will terminate the process.
.PP
If the
.I interval
argument is nonzero, further
.B SIGALRM
signals will be sent every
.I interval
microseconds after the first.
.SH RETURN VALUE
This function returns the number of microseconds remaining for
any alarm that was previously set, or 0 if no alarm was pending.
.SH ERRORS
.TP
.B EINTR
Interrupted by a signal; see
.BR signal (7).
.TP
.B EINVAL
\fIusecs\fP or \fIinterval\fP is not smaller than 1000000.
(On systems where that is considered an error.)
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lb lb lb
l l l.
Interface	Attribute	Value
T{
.BR ualarm ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
4.3BSD, POSIX.1-2001.
POSIX.1-2001 marks
.BR ualarm ()
as obsolete.
POSIX.1-2008 removes the specification of
.BR ualarm ().
4.3BSD, SUSv2, and POSIX do not define any errors.
.SH NOTES
POSIX.1-2001 does not specify what happens if the
.I usecs
argument is 0.
.\" This case is not documented in HP-US, Solar, FreeBSD, NetBSD, or OpenBSD!
On Linux (and probably most other systems),
the effect is to cancel any pending alarm.
.PP
The type
.I 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
.BR ualarm ()
were instead typed as
.IR "unsigned int" .
Programs will be more portable if they never mention
.I useconds_t
explicitly.
.PP
The interaction of this function with
other timer functions such as
.BR alarm (2),
.BR sleep (3),
.BR nanosleep (2),
.BR setitimer (2),
.BR timer_create (2),
.BR timer_delete (2),
.BR timer_getoverrun (2),
.BR timer_gettime (2),
.BR timer_settime (2),
.BR usleep (3)
is unspecified.
.PP
This function is obsolete.
Use
.BR setitimer (2)
or POSIX interval timers
.RB ( timer_create (2),
etc.)
instead.
.SH SEE ALSO
.BR alarm (2),
.BR getitimer (2),
.BR nanosleep (2),
.BR select (2),
.BR setitimer (2),
.BR usleep (3),
.BR time (7)
.SH COLOPHON
This page is part of release 4.16 of the Linux
.I 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/.