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25.Dd August 4, 1998
26.Dt PTHREAD_RWLOCK_WRLOCK 3
27.Os
28.Sh NAME
29.Nm pthread_rwlock_wrlock ,
30.Nm pthread_rwlock_trywrlock
31.Nd acquire a read/write lock for writing
32.Sh LIBRARY
33.Lb libpthread
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
41The
42.Fn pthread_rwlock_wrlock
43function blocks until a write lock can be acquired against
44.Fa lock .
45The
46.Fn pthread_rwlock_trywrlock
47function performs the same action, but does not block if the lock
48cannot be immediately obtained.
49.Pp
50The results are undefined if the calling thread already holds the
51lock at the time the call is made.
52.Sh IMPLEMENTATION NOTES
53To prevent writer starvation, writers are favored over readers.
54.Sh RETURN VALUES
55If successful, the
56.Fn pthread_rwlock_wrlock
57and
58.Fn pthread_rwlock_trywrlock
59functions will return zero.
60Otherwise an error number will be returned
61to indicate the error.
62.Sh ERRORS
63The
64.Fn pthread_rwlock_trywrlock
65function will fail if:
66.Bl -tag -width Er
67.It Bq Er EBUSY
68The calling thread is not able to acquire the lock without blocking.
69.El
70.Pp
71The
72.Fn pthread_rwlock_wrlock
73and
74.Fn pthread_rwlock_trywrlock
75functions may fail if:
76.Bl -tag -width Er
77.It Bq Er EDEADLK
78The calling thread already owns the read/write lock (for reading
79or writing).
80.It Bq Er EINVAL
81The value specified by
82.Fa lock
83is invalid.
84.It Bq Er ENOMEM
85Insufficient memory exists to initialize the lock (applies to
86statically 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
94The
95.Fn pthread_rwlock_wrlock
96and
97.Fn pthread_rwlock_trywrlock
98functions are expected to conform to
99.St -susv2 .
100.Sh HISTORY
101The
102.Fn pthread_rwlock_wrlock
103function first appeared in
104.Fx 3.0 .
105