.\" $OpenBSD: pthread_rwlock_wrlock.3,v 1.6 2003/06/02 11:19:48 jmc Exp $
.\" Copyright (c) 1998 Alex Nash
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.\" $FreeBSD: pthread_rwlock_wrlock.3,v 1.2 1999/08/28 00:03:10 peter Exp $
.\"
.Dd August 4, 1998
.Dt PTHREAD_RWLOCK_WRLOCK 3
.Os
.Sh NAME
.Nm pthread_rwlock_wrlock ,
.Nm pthread_rwlock_trywrlock
.Nd acquire a read/write lock for writing
.Sh SYNOPSIS
.Fd #include <pthread.h>
.Ft int
.Fn pthread_rwlock_wrlock "pthread_rwlock_t *lock"
.Ft int
.Fn pthread_rwlock_trywrlock "pthread_rwlock_t *lock"
.Sh DESCRIPTION
The
.Fn pthread_rwlock_wrlock
function blocks until a write lock can be acquired against
.Fa lock .
The
.Fn pthread_rwlock_trywrlock
function performs the same action, but does not block if the lock
cannot be immediately obtained.
.Pp
The results are undefined if the calling thread already holds the
lock at the time the call is made.
.Sh IMPLEMENTATION NOTES
To prevent writer starvation, writers are favored over readers.
.Sh RETURN VALUES
If successful, the
.Fn pthread_rwlock_wrlock
and
.Fn pthread_rwlock_trywrlock
functions will return zero.
Otherwise an error number will be returned to indicate the error.
.Sh ERRORS
The
.Fn pthread_rwlock_trywrlock
function will fail if:
.Bl -tag -width Er
.It Bq Er EBUSY
The calling thread is not able to acquire the lock without blocking.
.El
.Pp
The
.Fn pthread_rwlock_wrlock
and
.Fn pthread_rwlock_trywrlock
functions may fail if:
.Bl -tag -width Er
.It Bq Er EDEADLK
The calling thread already owns the read/write lock (for reading
or writing).
.It Bq Er EINVAL
The value specified by
.Fa lock
is invalid.
.It Bq Er ENOMEM
Insufficient memory exists to initialize the lock (applies to
statically initialized locks only).
.El
.Sh SEE ALSO
.Xr pthread_rwlock_unlock 3
.Sh STANDARDS
The
.Fn pthread_rwlock_wrlock
and
.Fn pthread_rwlock_trywrlock
functions are expected to conform to
.St -susv2 .
.Sh HISTORY
The
.Fn pthread_rwlock_wrlock
function first appeared in
.Fx 3.0
and
.Ox 2.5 .