man2/alarm.2

   1 .\" Hey Emacs! This file is -*- nroff -*- source.
   2 .\"
   3 .\" This manpage is Copyright (C) 1992 Drew Eckhardt;
   4 .\"                               1993 Michael Haardt, Ian Jackson.
   5 .\"
   6 .\" Permission is granted to make and distribute verbatim copies of this
   7 .\" manual provided the copyright notice and this permission notice are
   8 .\" preserved on all copies.
   9 .\"
  10 .\" Permission is granted to copy and distribute modified versions of this
  11 .\" manual under the conditions for verbatim copying, provided that the
  12 .\" entire resulting derived work is distributed under the terms of a
  13 .\" permission notice identical to this one.
  14 .\"
  15 .\" Since the Linux kernel and libraries are constantly changing, this
  16 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  17 .\" responsibility for errors or omissions, or for damages resulting from
  18 .\" the use of the information contained herein.  The author(s) may not
  19 .\" have taken the same level of care in the production of this manual,
  20 .\" which is licensed free of charge, as they might when working
  21 .\" professionally.
  22 .\"
  23 .\" Formatted or processed versions of this manual, if unaccompanied by
  24 .\" the source, must acknowledge the copyright and authors of this work.
  25 .\"
  26 .\" Modified Wed Jul 21 19:42:57 1993 by Rik Faith <faith@cs.unc.edu>
  27 .\" Modified Sun Jul 21 21:25:26 1996 by Andries Brouwer <aeb@cwi.nl>
  28 .\" Modified Wed Nov  6 03:46:05 1996 by Eric S. Raymond <esr@thyrsus.com>
  29 .\"
  30 .TH ALARM 2 1993-07-21 Linux "Linux Programmer's Manual"
  31 .SH NAME
  32 alarm \- set an alarm clock for delivery of a signal
  33 .SH SYNOPSIS
  34 .nf
  35 .B #include <unistd.h>
  36 .sp
  37 .BI "unsigned int alarm(unsigned int " seconds );
  38 .fi
  39 .SH DESCRIPTION
  40 .BR alarm ()
  41 arranges for a
  42 .B SIGALRM
  43 signal to be delivered to the process in
  44 .I seconds
  45 seconds.
  46
  47 If
  48 .I seconds
  49 is zero, no new
  50 .BR alarm ()
  51 is scheduled.
  52
  53 In any event any previously set
  54 .BR alarm ()
  55 is cancelled.
  56 .SH "RETURN VALUE"
  57 .BR alarm ()
  58 returns the number of seconds remaining until any previously scheduled
  59 alarm was due to be delivered, or zero if there was no previously
  60 scheduled alarm.
  61 .SH NOTES
  62 .BR alarm ()
  63 and
  64 .BR setitimer (2)
  65 share the same timer; calls to one will interfere with use of the
  66 other.
  67 .PP
  68 .BR sleep (3)
  69 may be implemented using
  70 .BR SIGALRM ;
  71 mixing calls to
  72 .BR alarm ()
  73 and
  74 .BR sleep (3)
  75 is a bad idea.
  76
  77 Scheduling delays can, as ever, cause the execution of the process to
  78 be delayed by an arbitrary amount of time.
  79 .SH "CONFORMING TO"
  80 SVr4, POSIX.1-2001, 4.3BSD
  81 .SH "SEE ALSO"
  82 .BR gettimeofday (2),
  83 .BR pause (2),
  84 .BR select (2),
  85 .BR setitimer (2),
  86 .BR sigaction (2),
  87 .BR signal (2),
  88 .BR sleep (3),
  89 .BR time (7)