Move pthread* manpages to lib/libpthread as they are not libc_r specific.
[dragonfly.git] / lib / libpthread / sem_wait.3
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28.\" $FreeBSD: src/lib/libc_r/man/sem_wait.3,v 1.1.2.7 2001/12/17 10:08:26 ru Exp $
1de703da 29.\" $DragonFly: src/lib/libc_r/man/sem_wait.3,v 1.2 2003/06/17 04:26:48 dillon Exp $
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30.Dd February 15, 2000
31.Dt SEM_WAIT 3
32.Os
33.Sh NAME
34.Nm sem_wait ,
35.Nm sem_trywait
36.Nd decrement (lock) a semaphore
37.Sh LIBRARY
38.Lb libc_r
39.Sh SYNOPSIS
40.In semaphore.h
41.Ft int
42.Fn sem_wait "sem_t *sem"
43.Ft int
44.Fn sem_trywait "sem_t *sem"
45.Sh DESCRIPTION
46The
47.Fn sem_wait
48function decrements (locks) the semaphore pointed to by
49.Fa sem ,
50but blocks if the value of
51.Fa sem
52is zero, until the value is non-zero and the value can be decremented.
53.Pp
54The
55.Fn sem_trywait
56function decrements (locks) the semaphore pointed to by
57.Fa sem
58only if the value is non-zero. Otherwise, the semaphore is not decremented and
59an error is returned.
60.Sh RETURN VALUES
61.Rv -std
62.Sh ERRORS
63.Fn sem_wait
64and
65.Fn sem_trywait
66will fail if:
67.Bl -tag -width Er
68.It Bq Er EINVAL
69.Fa sem
70points to an invalid semaphore.
71.El
72.Pp
73Additionally,
74.Fn sem_trywait
75will fail if:
76.Bl -tag -width Er
77.It Bq Er EAGAIN
78The semaphore value was zero, and thus could not be decremented.
79.El
80.Sh SEE ALSO
81.Xr sem_post 3
82.Sh STANDARDS
83.Fn sem_wait
84and
85.Fn sem_trywait
86conform to
87.St -p1003.1-96 .