man2/nanosleep.2

   1 .\" Hey Emacs! This file is -*- nroff -*- source.
   2 .\"
   3 .\" Copyright (C) Markus Kuhn, 1996
   4 .\"
   5 .\" This is free documentation; you can redistribute it and/or
   6 .\" modify it under the terms of the GNU General Public License as
   7 .\" published by the Free Software Foundation; either version 2 of
   8 .\" the License, or (at your option) any later version.
   9 .\"
  10 .\" The GNU General Public License's references to "object code"
  11 .\" and "executables" are to be interpreted as the output of any
  12 .\" document formatting or typesetting system, including
  13 .\" intermediate and printed output.
  14 .\"
  15 .\" This manual is distributed in the hope that it will be useful,
  16 .\" but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 .\" GNU General Public License for more details.
  19 .\"
  20 .\" You should have received a copy of the GNU General Public
  21 .\" License along with this manual; if not, write to the Free
  22 .\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
  23 .\" USA.
  24 .\"
  25 .\" 1996-04-10  Markus Kuhn <mskuhn@cip.informatik.uni-erlangen.de>
  26 .\"             First version written
  27 .\" Modified, 2004-10-24, aeb
  28 .TH NANOSLEEP 2 2007-07-26 "Linux" "Linux Programmer's Manual"
  29 .SH NAME
  30 nanosleep \- pause execution for a specified time
  31 .SH SYNOPSIS
  32 .B #include <time.h>
  33 .sp
  34 .BI "int nanosleep(const struct timespec *" req ", struct timespec *" rem );
  35 .sp
  36 .in -4n
  37 Feature Test Macro Requirements for glibc (see
  38 .BR feature_test_macros (7)):
  39 .in
  40 .sp
  41 .BR nanosleep ():
  42 _POSIX_C_SOURCE\ >=\ 199309L
  43 .SH DESCRIPTION
  44 .BR nanosleep ()
  45 delays the execution of the program for at least the time specified in
  46 .IR *req .
  47 The function can return earlier if a signal has been delivered to the
  48 process.
  49 In this case, it returns \-1, sets \fIerrno\fP to
  50 .BR EINTR ,
  51 and writes the
  52 remaining time into the structure pointed to by
  53 .I rem
  54 unless
  55 .I rem
  56 is NULL.
  57 The value of
  58 .I *rem
  59 can then be used to call
  60 .BR nanosleep ()
  61 again and complete the specified pause.
  62
  63 The structure
  64 .I timespec
  65 is used to specify intervals of time with nanosecond precision.
  66 It is
  67 specified in
  68 .I <time.h>
  69 and has the form
  70 .sp
  71 .RS
  72 .nf
  73 struct timespec {
  74     time_t tv_sec;        /* seconds */
  75     long   tv_nsec;       /* nanoseconds */
  76 };
  77 .fi
  78 .RE
  79 .PP
  80 The value of the nanoseconds field must be in the range 0 to 999999999.
  81
  82 Compared to
  83 .BR sleep  (3)
  84 and
  85 .BR usleep (3),
  86 .BR nanosleep ()
  87 has the advantage of not affecting any signals, it is standardized by
  88 POSIX, it provides higher timing resolution, and it allows to continue
  89 a sleep that has been interrupted by a signal more easily.
  90 .SH "RETURN VALUE"
  91 On successfully sleeping for the requested interval,
  92 .BR nanosleep ()
  93 returns 0.
  94 If the call is interrupted by a signal handler or encounters an error,
  95 then it returns \-1, with
  96 .I errno
  97 set to indicate the error.
  98 .SH ERRORS
  99 .TP
 100 .B EFAULT
 101 Problem with copying information from user space.
 102 .TP
 103 .B EINTR
 104 The pause has been interrupted by a non-blocked signal that was
 105 delivered to the process.
 106 The remaining sleep time has been written
 107 into *\fIrem\fP so that the process can easily call
 108 .BR nanosleep ()
 109 again and continue with the pause.
 110 .TP
 111 .B EINVAL
 112 The value in the
 113 .I tv_nsec
 114 field was not in the range 0 to 999999999 or
 115 .I tv_sec
 116 was negative.
 117 .SH "CONFORMING TO"
 118 POSIX.1-2001.
 119 .SH BUGS
 120 The current implementation of
 121 .BR nanosleep ()
 122 is based on the normal kernel timer mechanism, which has a resolution
 123 of 1/\fIHZ\fP\ s (see
 124 .BR time (7)).
 125 Therefore,
 126 .BR nanosleep ()
 127 pauses always for at least the specified time, however it can take up
 128 to 10 ms longer than specified until the process becomes runnable
 129 again.
 130 For the same reason, the value returned in case of a delivered
 131 signal in *\fIrem\fP is usually rounded to the next larger multiple of
 132 1/\fIHZ\fP\ s.
 133 .SS "Old behavior"
 134 In order to support applications requiring much more precise pauses
 135 (e.g., in order to control some time-critical hardware),
 136 .BR nanosleep ()
 137 would handle pauses of up to 2\ ms by busy waiting with microsecond
 138 precision when called from a process scheduled under a real-time policy
 139 like
 140 .B SCHED_FIFO
 141 or
 142 .BR SCHED_RR .
 143 This special extension was removed in kernel 2.5.39,
 144 hence is still present in
 145 current 2.4 kernels, but not in 2.6 kernels.
 146 .PP
 147 In Linux 2.4, if
 148 .BR nanosleep ()
 149 is stopped by a signal (e.g.,
 150 .BR SIGTSTP ),
 151 then the call fails with the error
 152 .B EINTR
 153 after the process is resumed by a
 154 .B SIGCONT
 155 signal.
 156 If the system call is subsequently restarted,
 157 then the time that the process spent in the stopped state is
 158 \fInot\fP counted against the sleep interval.
 159 .SH "SEE ALSO"
 160 .BR sched_setscheduler (2),
 161 .BR sleep (3),
 162 .BR timer_create (3),
 163 .BR usleep (3),
 164 .BR time (7)