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1 .\" Copyright (c) 1998 Alex Nash
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25 .\" $FreeBSD: src/lib/libc_r/man/pthread_rwlock_wrlock.3,v 1.4 2001/10/01 16:09:09 ru Exp $
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27 .Dd August 4, 1998
28 .Dt PTHREAD_RWLOCK_WRLOCK 3
29 .Os
30 .Sh NAME
31 .Nm pthread_rwlock_trywrlock ,
32 .Nm pthread_rwlock_wrlock
33 .Nd acquire a read/write lock for writing
34 .Sh SYNOPSIS
35 .In pthread.h
36 .Ft int
37 .Fo pthread_rwlock_trywrlock
38 .Fa "pthread_rwlock_t *rwlock"
39 .Fc
40 .Ft int
41 .Fo pthread_rwlock_wrlock
42 .Fa "pthread_rwlock_t *rwlock"
43 .Fc
44 .Sh DESCRIPTION
45 The
46 .Fn pthread_rwlock_wrlock
47 function blocks until a write lock can be acquired against
48 .Fa rwlock .
49 The
50 .Fn pthread_rwlock_trywrlock
51 function performs the same action, but does not block if the lock
52 cannot be immediately obtained.
53 .Pp
54 The results are undefined if the calling thread already holds the
55 lock at the time the call is made.
56 .Sh IMPLEMENTATION NOTES
57 To prevent writer starvation, writers are favored over readers.
58 .Sh RETURN VALUES
59 If successful, the
60 .Fn pthread_rwlock_wrlock
61 and
62 .Fn pthread_rwlock_trywrlock
63 functions will return zero.
64 Otherwise, an error number will be returned to indicate the error.
65 .Sh SEE ALSO
66 .Xr pthread_rwlock_trywrlock 3 ,
67 .Xr pthread_rwlock_unlock 3 ,
68 .Xr pthread_rwlock_wrlock 3
69 .Sh STANDARDS
70 The
71 .Fn pthread_rwlock_wrlock
72 and
73 .Fn pthread_rwlock_trywrlock
74 functions are expected to conform to
75 .St -susv2 .
76 .Sh ERRORS
77 The
78 .Fn pthread_rwlock_trywrlock
79 function will fail if:
80 .Bl -tag -width Er
81 .It Bq Er EBUSY
82 The calling thread is not able to acquire the lock without blocking.
83 .El
84 .Pp
85 The
86 .Fn pthread_rwlock_wrlock
87 and
88 .Fn pthread_rwlock_trywrlock
89 functions may fail if:
90 .Bl -tag -width Er
91 .It Bq Er EDEADLK
92 The calling thread already owns the read/write lock (for reading
93 or writing).
94 .It Bq Er EINVAL
95 The value specified by
96 .Fa rwlock
97 is invalid.
98 .It Bq Er ENOMEM
99 Insufficient memory exists to initialize the lock (applies to
100 statically initialized locks only).
101 .El
102 .Sh HISTORY
103 The
104 .Fn pthread_rwlock_wrlock
105 function first appeared in
106 .Fx 3.0 .