xref: /freebsd/share/man/man3/pthread_once.3 (revision ae83180158c4c937f170e31eff311b18c0286a93)
1.\" Copyright (c) 1996 John Birrell <jb@cimlogic.com.au>.
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31.\" $FreeBSD$
32.\"
33.Dd April 4, 1996
34.Dt PTHREAD_ONCE 3
35.Os
36.Sh NAME
37.Nm pthread_once
38.Nd dynamic package initialization
39.Sh LIBRARY
40.Lb libc_r
41.Sh SYNOPSIS
42.In pthread.h
43.Pp
44pthread_once_t
45.Fa once_control
46= PTHREAD_ONCE_INIT;
47.Ft int
48.Fn pthread_once "pthread_once_t *once_control" "void (*init_routine)(void)"
49.Sh DESCRIPTION
50The first call to
51.Fn pthread_once
52by any thread in a process, with a given
53.Fa once_control ,
54will call the
55.Fn init_routine
56with no arguments.
57Subsequent calls to
58.Fn pthread_once
59with the same
60.Fa once_control
61will not call the
62.Fn init_routine .
63On return from
64.Fn pthread_once ,
65it is guaranteed that
66.Fn init_routine
67has completed.
68The
69.Fa once_control
70parameter is used to determine whether the associated initialization
71routine has been called.
72.Pp
73The function
74.Fn pthread_once
75is not a cancellation point.
76However, if
77.Fn init_routine
78is a cancellation point and is cancelled, the effect on
79.Fa once_control is as if
80.Fn pthread_once
81was never called.
82.Pp
83The constant
84.Fa PTHREAD_ONCE_INIT
85is defined by header
86.Aq Pa pthread.h .
87.Pp
88The behavior of
89.Fn pthread_once
90is undefined if
91.Fa once_control
92has automatic storage duration or is not initialized by
93.Fa PTHREAD_ONCE_INIT .
94.Sh RETURN VALUES
95If successful,  the
96.Fn pthread_once
97function will return zero.
98Otherwise an error number will be returned to
99indicate the error.
100.Sh ERRORS
101None.
102.Sh STANDARDS
103.Fn pthread_once
104conforms to
105.St -p1003.1-96 .
106