.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "PTHREAD_RWLOCK_TRYWRLOCK" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" pthread_rwlock_trywrlock 
.SH NAME
pthread_rwlock_trywrlock, pthread_rwlock_wrlock \- lock a read-write
lock object for writing
.SH SYNOPSIS
.LP
\fB#include <pthread.h>
.br
.sp
int pthread_rwlock_trywrlock(pthread_rwlock_t\fP \fI*rwlock\fP\fB);
.br
int pthread_rwlock_wrlock(pthread_rwlock_t\fP \fI*rwlock\fP\fB); \fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIpthread_rwlock_trywrlock\fP() function shall apply a write
lock like the \fIpthread_rwlock_wrlock\fP() function, with
the exception that the function shall fail if any thread currently
holds \fIrwlock\fP (for reading or writing).
.LP
The \fIpthread_rwlock_wrlock\fP() function shall apply a write lock
to the read-write lock referenced by \fIrwlock\fP. The
calling thread acquires the write lock if no other thread (reader
or writer) holds the read-write lock \fIrwlock\fP. Otherwise,
the thread shall block until it can acquire the lock. The calling
thread may deadlock if at the time the call is made it holds the
read-write lock (whether a read or write lock).
.LP
Implementations may favor writers over readers to avoid writer starvation.
.LP
Results are undefined if any of these functions are called with an
uninitialized read-write lock.
.LP
If a signal is delivered to a thread waiting for a read-write lock
for writing, upon return from the signal handler the thread
resumes waiting for the read-write lock for writing as if it was not
interrupted.
.SH RETURN VALUE
.LP
The \fIpthread_rwlock_trywrlock\fP() function shall return zero if
the lock for writing on the read-write lock object
referenced by \fIrwlock\fP is acquired. Otherwise, an error number
shall be returned to indicate the error.
.LP
If successful, the \fIpthread_rwlock_wrlock\fP() function shall return
zero; otherwise, an error number shall be returned to
indicate the error.
.SH ERRORS
.LP
The \fIpthread_rwlock_trywrlock\fP() function shall fail if:
.TP 7
.B EBUSY
The read-write lock could not be acquired for writing because it was
already locked for reading or writing.
.sp
.LP
The \fIpthread_rwlock_trywrlock\fP() and \fIpthread_rwlock_wrlock\fP()
functions may fail if:
.TP 7
.B EINVAL
The value specified by \fIrwlock\fP does not refer to an initialized
read-write lock object.
.sp
.LP
The \fIpthread_rwlock_wrlock\fP() function may fail if:
.TP 7
.B EDEADLK
The current thread already owns the read-write lock for writing or
reading.
.sp
.LP
These functions shall not return an error code of [EINTR].
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
Applications using these functions may be subject to priority inversion,
as discussed in the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 3.285, Priority Inversion.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIpthread_rwlock_destroy\fP() , \fIpthread_rwlock_rdlock\fP() , \fIpthread_rwlock_timedrdlock\fP()
, \fIpthread_rwlock_timedwrlock\fP() , \fIpthread_rwlock_tryrdlock\fP()
, \fIpthread_rwlock_unlock\fP() , the Base Definitions volume of IEEE\ Std\ 1003.1-2001,
\fI<pthread.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .