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30.Dd $Mdocdate: June 5 2013 $
31.Dt USLEEP 3
32.Os
33.Sh NAME
34.Nm usleep
35.Nd suspend process execution for interval measured in microseconds
36.Sh SYNOPSIS
37.In unistd.h
38.Ft int
39.Fn usleep "useconds_t microseconds"
40.Sh DESCRIPTION
41.Bf -symbolic
42This interface is obsoleted by
43.Xr nanosleep 2 .
44.Ef
45.Pp
46The
47.Fn usleep
48function suspends execution of the calling process until either
49.Fa microseconds
50microseconds have elapsed or a signal is delivered to the process and its
51action is to invoke a signal-catching function or to terminate the
52process.
53The suspension time may be longer than requested due to the
54scheduling of other activity by the system.
55.Pp
56This function is implemented using
57.Xr nanosleep 2
58by pausing for
59.Fa microseconds
60microseconds or until a signal occurs.
61Consequently, in this implementation,
62sleeping has no effect on the state of process timers,
63and there is no special handling for
64.Dv SIGALRM .
65.Sh RETURN VALUES
66.Rv -std usleep
67.Sh ERRORS
68The
69.Fn usleep
70function
71will fail if:
72.Bl -tag -width Er
73.It Bq Er EINTR
74A signal was delivered to the process and its
75action was to invoke a signal-catching function.
76.El
77.Sh NOTES
78A microsecond is 0.000001 seconds.
79.Sh SEE ALSO
80.Xr sleep 1 ,
81.Xr nanosleep 2 ,
82.Xr sleep 3
83.Sh STANDARDS
84The
85.Fn usleep
86function conforms to
87.St -xpg4.2 .
88.Sh HISTORY
89The
90.Fn usleep
91function appeared in
92.Bx 4.3 .
93.Sh CAVEATS
94Some implementations of
95.Fn usleep
96return an error if
97.Fa microseconds
98is greater than or equal to 1,000,000.
99Portable applications should be written with this limitation in mind.
100