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