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.TH PTHREAD_RWLOCK_DESTROY "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.

.SH NAME
pthread_rwlock_destroy,
pthread_rwlock_init
\(em destroy and initialize a read-write lock object
.SH SYNOPSIS
.LP
.nf
#include <pthread.h>
.P
int pthread_rwlock_destroy(pthread_rwlock_t *\fIrwlock\fP);
int pthread_rwlock_init(pthread_rwlock_t *restrict \fIrwlock\fP,
    const pthread_rwlockattr_t *restrict \fIattr\fP);
pthread_rwlock_t \fIrwlock\fR = PTHREAD_RWLOCK_INITIALIZER;
.fi
.SH DESCRIPTION
The
\fIpthread_rwlock_destroy\fR()
function shall destroy the read-write lock object referenced by
.IR rwlock
and release any resources used by the lock. The effect of subsequent
use of the lock is undefined until the lock is reinitialized by
another call to
\fIpthread_rwlock_init\fR().
An implementation may cause
\fIpthread_rwlock_destroy\fR()
to set the object referenced by
.IR rwlock
to an invalid value. Results are undefined if
\fIpthread_rwlock_destroy\fR()
is called when any thread holds
.IR rwlock .
Attempting to destroy an uninitialized read-write lock results in
undefined behavior.
.P
The
\fIpthread_rwlock_init\fR()
function shall allocate any resources required to use the read-write
lock referenced by
.IR rwlock
and initializes the lock to an unlocked state with attributes
referenced by
.IR attr .
If
.IR attr
is NULL, the default read-write lock attributes shall be used; the
effect is the same as passing the address of a default read-write lock
attributes object. Once initialized, the lock can be used any number of
times without being reinitialized. Results are undefined if
\fIpthread_rwlock_init\fR()
is called specifying an already initialized read-write lock. Results
are undefined if a read-write lock is used without first being
initialized.
.P
If the
\fIpthread_rwlock_init\fR()
function fails,
.IR rwlock
shall not be initialized and the contents of
.IR rwlock
are undefined.
.P
Only the object referenced by
.IR rwlock
may be used for performing synchronization. The result of referring to
copies of that object in calls to
\fIpthread_rwlock_destroy\fR(),
\fIpthread_rwlock_rdlock\fR(),
\fIpthread_rwlock_timedrdlock\fR(),
\fIpthread_rwlock_timedwrlock\fR(),
\fIpthread_rwlock_tryrdlock\fR(),
\fIpthread_rwlock_trywrlock\fR(),
\fIpthread_rwlock_unlock\fR(),
or
\fIpthread_rwlock_wrlock\fR()
is undefined.
.P
In cases where default read-write lock attributes are appropriate, the
macro PTHREAD_RWLOCK_INITIALIZER can be used to initialize read-write
locks. The effect shall be equivalent to dynamic initialization by a
call to
\fIpthread_rwlock_init\fR()
with the
.IR attr
parameter specified as NULL, except that no error checks are performed.
.P
The behavior is undefined if the value specified by the
.IR attr
argument to
\fIpthread_rwlock_init\fR()
does not refer to an initialized read-write lock attributes object.
.SH "RETURN VALUE"
If successful, the
\fIpthread_rwlock_destroy\fR()
and
\fIpthread_rwlock_init\fR()
functions shall return zero; otherwise, an error number shall be
returned to indicate the error.
.SH ERRORS
The
\fIpthread_rwlock_init\fR()
function shall fail if:
.TP
.BR EAGAIN
The system lacked the necessary resources (other than memory) to
initialize another read-write lock.
.TP
.BR ENOMEM
Insufficient memory exists to initialize the read-write lock.
.TP
.BR EPERM
The caller does not have the privilege to perform the operation.
.P
These functions shall not return an error code of
.BR [EINTR] .
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
Applications using these and related read-write lock functions may be
subject to priority inversion, as discussed in the Base Definitions volume of POSIX.1\(hy2008,
.IR "Section 3.287" ", " "Priority Inversion".
.SH RATIONALE
If an implementation detects that the value specified by the
.IR rwlock
argument to
\fIpthread_rwlock_destroy\fR()
does not refer to an initialized read-write lock object, it is
recommended that the function should fail and report an
.BR [EINVAL] 
error.
.P
If an implementation detects that the value specified by the
.IR attr
argument to
\fIpthread_rwlockr_init\fR()
does not refer to an initialized read-write lock attributes object,
it is recommended that the function should fail and report an
.BR [EINVAL] 
error.
.P
If an implementation detects that the value specified by the
.IR rwlock
argument to
\fIpthread_rwlock_destroy\fR()
or
\fIpthread_rwlock_init\fR()
refers to a locked read-write lock object, or detects that the value
specified by the
.IR rwlock
argument to
\fIpthread_rwlock_init\fR()
refers to an already initialized read-write lock object, it is recommended
that the function should fail and report an
.BR [EBUSY] 
error.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.ad l
.IR "\fIpthread_rwlock_rdlock\fR\^(\|)",
.IR "\fIpthread_rwlock_timedrdlock\fR\^(\|)",
.IR "\fIpthread_rwlock_timedwrlock\fR\^(\|)",
.IR "\fIpthread_rwlock_trywrlock\fR\^(\|)",
.IR "\fIpthread_rwlock_unlock\fR\^(\|)"
.ad b
.P
The Base Definitions volume of POSIX.1\(hy2008,
.IR "Section 3.287" ", " "Priority Inversion",
.IR "\fB<pthread.h>\fP"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.unix.org/online.html .

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