libpthread-218.51.1.tar.gz
[apple/libpthread.git] / man / pthread_rwlock_wrlock.3
1 .\" Copyright (c) 1998 Alex Nash
2 .\" All rights reserved.
3 .\"
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
6 .\" are met:
7 .\" 1. Redistributions of source code must retain the above copyright
8 .\" notice, this list of conditions and the following disclaimer.
9 .\" 2. Redistributions in binary form must reproduce the above copyright
10 .\" notice, this list of conditions and the following disclaimer in the
11 .\" documentation and/or other materials provided with the distribution.
12 .\"
13 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
14 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
16 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
17 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
18 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
19 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
20 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
21 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
22 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
23 .\" SUCH DAMAGE.
24 .\"
25 .\" $FreeBSD$
26 .\"
27 .Dd August 4, 1998
28 .Dt PTHREAD_RWLOCK_WRLOCK 3
29 .Os
30 .Sh NAME
31 .Nm pthread_rwlock_wrlock ,
32 .Nm pthread_rwlock_trywrlock
33 .Nd acquire a read/write lock for writing
34 .Sh SYNOPSIS
35 .In pthread.h
36 .Ft int
37 .Fn pthread_rwlock_wrlock "pthread_rwlock_t *lock"
38 .Ft int
39 .Fn pthread_rwlock_trywrlock "pthread_rwlock_t *lock"
40 .Sh DESCRIPTION
41 The
42 .Fn pthread_rwlock_wrlock
43 function blocks until a write lock can be acquired against
44 .Fa lock .
45 The
46 .Fn pthread_rwlock_trywrlock
47 function performs the same action, but does not block if the lock
48 cannot be immediately obtained.
49 .Pp
50 The results are undefined if the calling thread already holds the
51 lock at the time the call is made.
52 .Sh IMPLEMENTATION NOTES
53 To prevent writer starvation, writers are favored over readers.
54 .Sh RETURN VALUES
55 If successful, the
56 .Fn pthread_rwlock_wrlock
57 and
58 .Fn pthread_rwlock_trywrlock
59 functions will return zero.
60 Otherwise an error number will be returned
61 to indicate the error.
62 .Sh ERRORS
63 The
64 .Fn pthread_rwlock_trywrlock
65 function will fail if:
66 .Bl -tag -width Er
67 .It Bq Er EBUSY
68 The calling thread is not able to acquire the lock without blocking.
69 .El
70 .Pp
71 The
72 .Fn pthread_rwlock_wrlock
73 and
74 .Fn pthread_rwlock_trywrlock
75 functions may fail if:
76 .Bl -tag -width Er
77 .It Bq Er EDEADLK
78 The calling thread already owns the read/write lock (for reading
79 or writing).
80 .It Bq Er EINVAL
81 The value specified by
82 .Fa lock
83 is invalid.
84 .It Bq Er ENOMEM
85 Insufficient memory exists to initialize the lock (applies to
86 statically initialized locks only).
87 .El
88 .Sh SEE ALSO
89 .Xr pthread_rwlock_init 3 ,
90 .Xr pthread_rwlock_rdlock 3 ,
91 .Xr pthread_rwlock_tryrdlock 3 ,
92 .Xr pthread_rwlock_unlock 3
93 .Sh STANDARDS
94 The
95 .Fn pthread_rwlock_wrlock
96 and
97 .Fn pthread_rwlock_trywrlock
98 functions are expected to conform to
99 .St -susv2 .
100 .Sh HISTORY
101 The
102 .Fn pthread_rwlock_wrlock
103 function first appeared in
104 .Fx 3.0 .