man3/usleep.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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  25 .\" References consulted:
  26 .\"     Linux libc source code
  27 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  28 .\"     386BSD man pages
  29 .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
  30 .\" Modified 2001-04-01 by aeb
  31 .\" Modified 2003-07-23 by aeb
  32 .\"
  33 .TH USLEEP 3  2017-09-15 "" "Linux Programmer's Manual"
  34 .SH NAME
  35 usleep \- suspend execution for microsecond intervals
  36 .SH SYNOPSIS
  37 .nf
  38 .B "#include <unistd.h>"
  39 .PP
  40 .BI "int usleep(useconds_t " usec );
  41 .fi
  42 .PP
  43 .in -4n
  44 Feature Test Macro Requirements for glibc (see
  45 .BR feature_test_macros (7)):
  46 .in
  47 .PP
  48 .BR usleep ():
  49 .ad l
  50 .RS 4
  51 .PD 0
  52 .TP 4
  53 Since glibc 2.12:
  54 .nf
  55 (_XOPEN_SOURCE\ >=\ 500) && ! (_POSIX_C_SOURCE\ >=\ 200809L)
  56     || /* Glibc since 2.19: */ _DEFAULT_SOURCE
  57     || /* Glibc versions <= 2.19: */ _BSD_SOURCE
  58 .TP 4
  59 .fi
  60 Before glibc 2.12:
  61 _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
  62 .\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  63 .PD
  64 .RE
  65 .ad b
  66 .SH DESCRIPTION
  67 The
  68 .BR usleep ()
  69 function suspends execution of the calling thread for
  70 (at least) \fIusec\fP microseconds.
  71 The sleep may be lengthened slightly
  72 by any system activity or by the time spent processing the call or by the
  73 granularity of system timers.
  74 .SH RETURN VALUE
  75 The
  76 .BR usleep ()
  77 function returns 0 on success.
  78 On error, \-1 is returned, with
  79 .I errno
  80 set to indicate the cause of the error.
  81 .SH ERRORS
  82 .TP
  83 .B EINTR
  84 Interrupted by a signal; see
  85 .BR signal (7).
  86 .TP
  87 .B EINVAL
  88 \fIusec\fP is greater than or equal to 1000000.
  89 (On systems where that is considered an error.)
  90 .SH ATTRIBUTES
  91 For an explanation of the terms used in this section, see
  92 .BR attributes (7).
  93 .TS
  94 allbox;
  95 lb lb lb
  96 l l l.
  97 Interface       Attribute       Value
  98 T{
  99 .BR usleep ()
 100 T}      Thread safety   MT-Safe
 101 .TE
 102 .SH CONFORMING TO
 103 4.3BSD, POSIX.1-2001.
 104 POSIX.1-2001 declares this function obsolete; use
 105 .BR nanosleep (2)
 106 instead.
 107 POSIX.1-2008 removes the specification of
 108 .BR usleep ().
 109 .PP
 110 On the original BSD implementation,
 111 and in glibc before version 2.2.2, the return type of this function is
 112 .IR void .
 113 The POSIX version returns
 114 .IR int ,
 115 and this is also the prototype used since glibc 2.2.2.
 116 .PP
 117 Only the
 118 .B EINVAL
 119 error return is documented by SUSv2 and POSIX.1-2001.
 120 .SH NOTES
 121 The type
 122 .I useconds_t
 123 is an unsigned integer type capable of holding integers
 124 in the range [0,1000000].
 125 Programs will be more portable
 126 if they never mention this type explicitly.
 127 Use
 128 .PP
 129 .in +4n
 130 .EX
 131 #include <unistd.h>
 132 \&...
 133     unsigned int usecs;
 134 \&...
 135     usleep(usecs);
 136 .EE
 137 .in
 138 .PP
 139 The interaction of this function with the
 140 .B SIGALRM
 141 signal, and with other timer functions such as
 142 .BR alarm (2),
 143 .BR sleep (3),
 144 .BR nanosleep (2),
 145 .BR setitimer (2),
 146 .BR timer_create (2),
 147 .BR timer_delete (2),
 148 .BR timer_getoverrun (2),
 149 .BR timer_gettime (2),
 150 .BR timer_settime (2),
 151 .BR ualarm (3)
 152 is unspecified.
 153 .SH SEE ALSO
 154 .BR alarm (2),
 155 .BR getitimer (2),
 156 .BR nanosleep (2),
 157 .BR select (2),
 158 .BR setitimer (2),
 159 .BR sleep (3),
 160 .BR ualarm (3),
 161 .BR time (7)