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. In this case, it returns \-1, sets \fIerrno\fR to
  43 .BR EINTR ,
  44 and writes the
  45 remaining time into the structure pointed to by
  46 .IR rem
  47 unless
  48 .I rem
  49 is
  50 .BR 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. It is
  60 specified in
  61 .I <time.h>
  62 and has the form
  63 .sp
  64 .RS
  65 .nf
  66 .ne 12
  67 .ta 8n 16n 32n
  68 struct timespec
  69 {
  70         time_t  tv_sec;                 /* seconds */
  71         long    tv_nsec;                /* nanoseconds */
  72 };
  73 .ta
  74 .fi
  75 .RE
  76 .PP
  77 The value of the nanoseconds field must be in the range 0 to 999999999.
  78
  79 Compared to
  80 .BR sleep  (3)
  81 and
  82 .BR usleep (3),
  83 .BR nanosleep ()
  84 has the advantage of not affecting any signals, it is standardized by
  85 POSIX, it provides higher timing resolution, and it allows to continue
  86 a sleep that has been interrupted by a signal more easily.
  87 .SH ERRORS
  88 In case of an error or exception, the
  89 .BR nanosleep ()
  90 system call returns \-1 instead of 0 and sets
  91 .I errno
  92 to one of the following values:
  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. The remaining sleep time has been written
 100 into *\fIrem\fR so that the process can easily call
 101 .BR nanosleep ()
 102 again and continue with the pause.
 103 .TP
 104 .B EINVAL
 105 The value in the
 106 .I tv_nsec
 107 field was not in the range 0 to 999999999 or
 108 .I tv_sec
 109 was negative.
 110 .SH BUGS
 111 The current implementation of
 112 .BR nanosleep ()
 113 is based on the normal kernel timer mechanism, which has a resolution
 114 of 1/\fIHZ\fR\ s (i.e, 10\ ms on Linux/i386 and 1\ ms on Linux/Alpha).
 115 Therefore,
 116 .BR nanosleep ()
 117 pauses always for at least the specified time, however it can take up
 118 to 10 ms longer than specified until the process becomes runnable
 119 again. For the same reason, the value returned in case of a delivered
 120 signal in *\fIrem\fR is usually rounded to the next larger multiple of
 121 1/\fIHZ\fR\ s.
 122
 123 .SS "Old behaviour"
 124 In order to support applications requiring much more precise pauses
 125 (e.g., in order to control some time-critical hardware),
 126 .BR nanosleep ()
 127 would handle pauses of up to 2\ ms by busy waiting with microsecond
 128 precision when called from a process scheduled under a real-time policy
 129 like
 130 .I SCHED_FIFO
 131 or
 132 .IR SCHED_RR .
 133 This special extension was removed in kernel 2.5.39, hence is still present in
 134 current 2.4 kernels, but not in 2.6 kernels.
 135 .SH "CONFORMING TO"
 136 POSIX.1b (formerly POSIX.4).
 137 .SH "SEE ALSO"
 138 .BR sched_setscheduler (2),
 139 .BR timer_create (2),
 140 .BR sleep (3),
 141 .BR usleep (3)