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.\" Copyright (c) 2003 Andries Brouwer (aeb@cwi.nl)
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.\"
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.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
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.\" This is free documentation; you can redistribute it and/or
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.\" modify it under the terms of the GNU General Public License as
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.\" published by the Free Software Foundation; either version 2 of
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.\" the License, or (at your option) any later version.
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.\"
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.\" The GNU General Public License's references to "object code"
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.\" and "executables" are to be interpreted as the output of any
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.\" document formatting or typesetting system, including
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.\" intermediate and printed output.
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.\"
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.\" This manual is distributed in the hope that it will be useful,
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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" GNU General Public License for more details.
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.\"
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.\" You should have received a copy of the GNU General Public
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.\" License along with this manual; if not, see
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.\" <http://www.gnu.org/licenses/>.
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.\" %%%LICENSE_END
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.\"
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.TH UALARM 3 2017-09-15 "" "Linux Programmer's Manual"
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.SH NAME
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ualarm \- schedule signal after given number of microseconds
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.SH SYNOPSIS
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.nf
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.B "#include <unistd.h>"
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.PP
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.BI "useconds_t ualarm(useconds_t " usecs ", useconds_t " interval );
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.fi
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.PP
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.PP
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.BR ualarm ():
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.ad l
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.RS 4
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.PD 0
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.TP 4
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Since glibc 2.12:
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.nf
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(_XOPEN_SOURCE\ >=\ 500) && ! (_POSIX_C_SOURCE\ >=\ 200809L)
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|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
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|| /* Glibc versions <= 2.19: */ _BSD_SOURCE
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.TP 4
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.fi
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Before glibc 2.12:
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_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
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.\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
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.PD
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.RE
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.ad b
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.SH DESCRIPTION
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The
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.BR ualarm ()
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function causes the signal
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.B SIGALRM
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to be sent to the invoking process after (not less than)
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.I usecs
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microseconds.
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The delay may be lengthened slightly by any system activity
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or by the time spent processing the call or by the
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granularity of system timers.
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.PP
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Unless caught or ignored, the
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.B SIGALRM
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signal will terminate the process.
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.PP
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If the
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.I interval
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argument is nonzero, further
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.B SIGALRM
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signals will be sent every
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.I interval
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microseconds after the first.
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.SH RETURN VALUE
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This function returns the number of microseconds remaining for
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any alarm that was previously set, or 0 if no alarm was pending.
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.SH ERRORS
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.TP
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.B EINTR
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Interrupted by a signal; see
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.BR signal (7).
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.TP
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.B EINVAL
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\fIusecs\fP or \fIinterval\fP is not smaller than 1000000.
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(On systems where that is considered an error.)
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.SH ATTRIBUTES
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For an explanation of the terms used in this section, see
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.BR attributes (7).
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.TS
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allbox;
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lb lb lb
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l l l.
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Interface Attribute Value
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T{
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.BR ualarm ()
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T} Thread safety MT-Safe
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.TE
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.SH CONFORMING TO
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4.3BSD, POSIX.1-2001.
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POSIX.1-2001 marks
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.BR ualarm ()
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as obsolete.
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POSIX.1-2008 removes the specification of
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.BR ualarm ().
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4.3BSD, SUSv2, and POSIX do not define any errors.
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.SH NOTES
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POSIX.1-2001 does not specify what happens if the
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.I usecs
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argument is 0.
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.\" This case is not documented in HP-US, Solar, FreeBSD, NetBSD, or OpenBSD!
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On Linux (and probably most other systems),
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the effect is to cancel any pending alarm.
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.PP
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The type
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.I useconds_t
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is an unsigned integer type capable of holding integers
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in the range [0,1000000].
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On the original BSD implementation, and in glibc before version 2.1,
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the arguments to
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.BR ualarm ()
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were instead typed as
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.IR "unsigned int" .
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Programs will be more portable if they never mention
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.I useconds_t
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explicitly.
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.PP
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The interaction of this function with
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other timer functions such as
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.BR alarm (2),
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.BR sleep (3),
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.BR nanosleep (2),
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.BR setitimer (2),
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.BR timer_create (2),
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.BR timer_delete (2),
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.BR timer_getoverrun (2),
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.BR timer_gettime (2),
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.BR timer_settime (2),
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.BR usleep (3)
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is unspecified.
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.PP
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This function is obsolete.
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Use
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.BR setitimer (2)
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or POSIX interval timers
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.RB ( timer_create (2),
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etc.)
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instead.
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.SH SEE ALSO
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.BR alarm (2),
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.BR getitimer (2),
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.BR nanosleep (2),
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.BR select (2),
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.BR setitimer (2),
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.BR usleep (3),
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.BR time (7)
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.SH COLOPHON
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This page is part of release 4.15 of the Linux
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.I man-pages
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project.
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A description of the project,
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information about reporting bugs,
|
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and the latest version of this page,
|
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can be found at
|
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\%https://www.kernel.org/doc/man\-pages/.
|