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25.\" $FreeBSD: src/share/man/man3/pthread_rwlock_wrlock.3,v 1.11 2007/10/22 10:08:00 ru Exp $
26.\"
27.Dd July 10, 2009
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 LIBRARY
35.Lb libpthread
36.Sh SYNOPSIS
37.In pthread.h
38.Ft int
39.Fn pthread_rwlock_wrlock "pthread_rwlock_t *lock"
40.Ft int
41.Fn pthread_rwlock_trywrlock "pthread_rwlock_t *lock"
42.Sh DESCRIPTION
43The
44.Fn pthread_rwlock_wrlock
45function blocks until a write lock can be acquired against
46.Fa lock .
47The
48.Fn pthread_rwlock_trywrlock
49function performs the same action, but does not block if the lock
50cannot be immediately obtained.
51.Pp
52The results are undefined if the calling thread already holds the
53lock at the time the call is made.
54.Sh IMPLEMENTATION NOTES
55To prevent writer starvation, writers are favored over readers.
56.Sh RETURN VALUES
57If successful, the
58.Fn pthread_rwlock_wrlock
59and
60.Fn pthread_rwlock_trywrlock
61functions will return zero.
62Otherwise an error number will be returned
63to indicate the error.
64.Sh ERRORS
65The
66.Fn pthread_rwlock_trywrlock
67function will fail if:
68.Bl -tag -width Er
69.It Bq Er EBUSY
70The calling thread is not able to acquire the lock without blocking.
71.El
72.Pp
73The
74.Fn pthread_rwlock_wrlock
75and
76.Fn pthread_rwlock_trywrlock
77functions may fail if:
78.Bl -tag -width Er
79.It Bq Er EDEADLK
80The calling thread already owns the read/write lock (for reading
81or writing).
82.It Bq Er EINVAL
83The value specified by
84.Fa lock
85is invalid.
86.It Bq Er ENOMEM
87Insufficient memory exists to initialize the lock (applies to
88statically initialized locks only).
89.El
90.Sh SEE ALSO
91.Xr pthread_rwlock_init 3 ,
92.Xr pthread_rwlock_rdlock 3 ,
93.Xr pthread_rwlock_tryrdlock 3 ,
94.Xr pthread_rwlock_unlock 3
95.Sh STANDARDS
96The
97.Fn pthread_rwlock_wrlock
98and
99.Fn pthread_rwlock_trywrlock
100functions are expected to conform to
101.St -susv2 .
102.Sh HISTORY
103The
104.Fn pthread_rwlock_wrlock
105function first appeared in
106.Fx 3.0 .
107