1.\" Copyright (c) 2003 Sergey Osokin <osa@FreeBSD.org.ru>
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25.\" $FreeBSD: src/share/man/man3/pthread_getconcurrency.3,v 1.6 2007/10/22 10:08:00 ru Exp $
26.\" $DragonFly: src/lib/libc_r/man/pthread_getconcurrency.3,v 1.2 2003/06/17 04:26:48 dillon Exp $
27.Dd July 10, 2009
28.Dt PTHREAD_GETCONCURRENCY 3
29.Os
30.Sh NAME
31.Nm pthread_getconcurrency ,
32.Nm pthread_setconcurrency
33.Nd get or set level of concurrency
34.Sh LIBRARY
35.Lb libpthread
36.Sh SYNOPSIS
37.In pthread.h
38.Ft int
39.Fn pthread_getconcurrency void
40.Ft int
41.Fn pthread_setconcurrency "int new_level"
42.Sh DESCRIPTION
43The
44.Fn pthread_getconcurrency
45function allows an application to inform the threads implementation
46of its desired concurrency level,
47.Fa new_level .
48The actual level of concurrency provided by the implementation
49as a result of this function call is unspecified.
50If
51.Fa new_level
52is zero, it causes the implementation to maintain the concurrency
53level at its discretion as if
54.Fn pthread_setconcurrency
55was never called.
56The
57.Fn pthread_getconcurrency
58function returns the value set by a previous call to the
59.Fn pthread_setconcurrency
60function.
61If the
62.Fn pthread_setconcurrency
63function was not previously called, this function returns zero to
64indicate that the implementation is maintaining the concurrency
65level.
66When an application calls
67.Fn pthread_setconcurrency ,
68it is informing the implementation of its desired concurrency
69level.
70The implementation uses this as a hint, not a requirement.
71.Sh RETURN VALUES
72If successful, the
73.Fn pthread_setconcurrency
74function returns zero.
75Otherwise, an error number is returned
76to indicate the error.
77The
78.Fn pthread_getconcurrency
79function always returns the concurrency level set by a previous
80call to
81.Fn pthread_setconcurrency .
82If the
83.Fn pthread_setconcurrency
84function has never been called,
85.Fn pthread_getconcurrency
86returns zero.
87.Sh ERRORS
88The
89.Fn pthread_setconcurrency
90function will fail if:
91.Bl -tag -width Er
92.It Bq Er EINVAL
93The value specified by
94.Fa new_level
95is negative.
96.It Bq Er EAGAIN
97The value specified by
98.Fa new_level
99would cause a system resource to be exceeded.
100.El
101.Sh APPLICATION USAGE
102Use of these functions changes the state of the underlying
103concurrency upon which the application depends.
104Library developers are advised to not use the
105.Fn pthread_getconcurrency
106and
107.Fn pthread_setconcurrency
108functions since their use may conflict with an application's
109use of these functions.
110.Sh STANDARDS
111The
112.Fn pthread_getconcurrency
113and
114.Fn pthread_setconcurrency
115functions conform to
116.St -susv2 .
117