man2/nanosleep.2

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  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 2004-10-24 "Linux 2.6.9" "Linux Programmer's Manual"
  29 .SH NAME
  30 nanosleep \- pause execution for a specified time
  31 .SH SYNOPSIS
  32 .B #define _POSIX_C_SOURCE 199309
  33 .B #include <time.h>
  34 .sp
  35 \fBint nanosleep(const struct timespec *\fIreq\fB, struct timespec *\fIrem\fB);
  36 .fi
  37 .SH DESCRIPTION
  38 .BR nanosleep ()
  39 delays the execution of the program for at least the time specified in
  40 .IR *req .
  41 The function can return earlier if a signal has been delivered to the
  42 process.
  43 In this case, it returns \-1, sets \fIerrno\fR to
  44 .BR EINTR ,
  45 and writes the
  46 remaining time into the structure pointed to by
  47 .IR rem
  48 unless
  49 .I rem
  50 is NULL.
  51 The value of
  52 .I *rem
  53 can then be used to call
  54 .BR nanosleep ()
  55 again and complete the specified pause.
  56
  57 The structure
  58 .I timespec
  59 is used to specify intervals of time with nanosecond precision.
  60 It is
  61 specified in
  62 .I <time.h>
  63 and has the form
  64 .sp
  65 .RS
  66 .nf
  67 struct timespec {
  68     time_t tv_sec;        /* seconds */
  69     long   tv_nsec;       /* nanoseconds */
  70 };
  71 .fi
  72 .RE
  73 .PP
  74 The value of the nanoseconds field must be in the range 0 to 999999999.
  75
  76 Compared to
  77 .BR sleep  (3)
  78 and
  79 .BR usleep (3),
  80 .BR nanosleep ()
  81 has the advantage of not affecting any signals, it is standardized by
  82 POSIX, it provides higher timing resolution, and it allows to continue
  83 a sleep that has been interrupted by a signal more easily.
  84 .SH "RETURN VALUE"
  85 On successfully sleeping for the requested interval,
  86 .BR nanosleep ()
  87 returns 0.
  88 If the call is interrupted by a signal handler or encounters an error,
  89 then it returns \-1, with
  90 .I errno
  91 set to indicate the error.
  92 .SH ERRORS
  93 .TP
  94 .B EFAULT
  95 Problem with copying information from user space.
  96 .TP
  97 .B EINTR
  98 The pause has been interrupted by a non-blocked signal that was
  99 delivered to the process.
 100 The remaining sleep time has been written
 101 into *\fIrem\fR so that the process can easily call
 102 .BR nanosleep ()
 103 again and continue with the pause.
 104 .TP
 105 .B EINVAL
 106 The value in the
 107 .I tv_nsec
 108 field was not in the range 0 to 999999999 or
 109 .I tv_sec
 110 was negative.
 111 .SH BUGS
 112 The current implementation of
 113 .BR nanosleep ()
 114 is based on the normal kernel timer mechanism, which has a resolution
 115 of 1/\fIHZ\fR\ s (see
 116 .BR time (7)).
 117 Therefore,
 118 .BR nanosleep ()
 119 pauses always for at least the specified time, however it can take up
 120 to 10 ms longer than specified until the process becomes runnable
 121 again.
 122 For the same reason, the value returned in case of a delivered
 123 signal in *\fIrem\fR is usually rounded to the next larger multiple of
 124 1/\fIHZ\fR\ s.
 125 .SS "Old behaviour"
 126 In order to support applications requiring much more precise pauses
 127 (e.g., in order to control some time-critical hardware),
 128 .BR nanosleep ()
 129 would handle pauses of up to 2\ ms by busy waiting with microsecond
 130 precision when called from a process scheduled under a real-time policy
 131 like
 132 .I SCHED_FIFO
 133 or
 134 .IR SCHED_RR .
 135 This special extension was removed in kernel 2.5.39,
 136 hence is still present in
 137 current 2.4 kernels, but not in 2.6 kernels.
 138 .PP
 139 In Linux 2.4, if
 140 .BR nanosleep ()
 141 is stopped by a signal (e.g., SIGTSTP),
 142 then the call fails with the error
 143 .BR EINTR
 144 after the process is resumed by a SIGCONT signal.
 145 If the system call is subsequently restarted,
 146 then the time that the process spent in the stopped state is
 147 \fInot\fP counted against the sleep interval.
 148 .SH "CONFORMING TO"
 149 POSIX.1-2001.
 150 .SH "SEE ALSO"
 151 .BR sched_setscheduler (2),
 152 .BR timer_create (2),
 153 .BR sleep (3),
 154 .BR usleep (3),
 155 .BR feature_test_macros (7),
 156 .BR time (7)