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<H4>POSIX Threads for Windows – REFERENCE - <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A></H4>
<P><A HREF="index.html">Reference Index</A></P>
<P><A HREF="#toc">Table of Contents</A></P>
<H2><A HREF="#toc0" NAME="sect0">Name</A></H2>
<P>pthread_rwlock_trywrlock, pthread_rwlock_wrlock - lock a
read-write lock object for writing
</P>
<H2><A HREF="#toc1" NAME="sect1">Synopsis</A></H2>
<P><B>#include <pthread.h> </B>
</P>
<P><B>int pthread_rwlock_trywrlock(pthread_rwlock_t <I>*</I></B><I>rwlock</I><B>);
<BR>int pthread_rwlock_wrlock(pthread_rwlock_t <I>*</I></B><I>rwlock</I><B>);
</B>
</P>
<H2><A HREF="#toc2" NAME="sect2">Description</A></H2>
<P>The <B>pthread_rwlock_trywrlock</B> function shall apply a write
lock like the <B>pthread_rwlock_wrlock</B> function, with the
exception that the function shall fail if any thread currently holds
<I>rwlock</I> (for reading or writing).
</P>
<P>The <B>pthread_rwlock_wrlock</B> function shall apply a write lock
to the read-write lock referenced by <I>rwlock</I>. The calling
thread acquires the write lock if no other thread (reader or writer)
holds the read-write lock <I>rwlock</I>. 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).
</P>
<P><B>Pthreads-win32</B> does not prefer either writers or readers in
acquiring the lock – all threads enter a single prioritised FIFO
queue. While this may not be optimally efficient for some
applications, it does ensure that one type does not starve the other.</P>
<P>Results are undefined if any of these functions are called with an
uninitialized read-write lock.
</P>
<P><B>Pthreads-w32</B> defines <B>_POSIX_READER_WRITER_LOCKS</B> in
pthread.h as 200112L to indicate that the reader/writer routines are
implemented and may be used.</P>
<H2><A HREF="#toc3" NAME="sect3">Return Value</A></H2>
<P>The <B>pthread_rwlock_trywrlock</B> function shall return zero if
the lock for writing on the read-write lock object referenced by
<I>rwlock</I> is acquired. Otherwise, an error number shall be
returned to indicate the error.
</P>
<P>If successful, the <B>pthread_rwlock_wrlock</B> function shall
return zero; otherwise, an error number shall be returned to indicate
the error.
</P>
<H2><A HREF="#toc4" NAME="sect4">Errors</A></H2>
<P>The <B>pthread_rwlock_trywrlock</B> function shall fail if:
</P>
<DL>
<DT><B>EBUSY</B>
</DT><DD STYLE="margin-bottom: 0.5cm">
The read-write lock could not be acquired for writing because it was
already locked for reading or writing.
</DD></DL>
<P>
The <B>pthread_rwlock_trywrlock</B> and <B>pthread_rwlock_wrlock</B>
functions may fail if:
</P>
<DL>
<DT><B>EINVAL</B>
</DT><DD STYLE="margin-bottom: 0.5cm">
The value specified by <I>rwlock</I> does not refer to an
initialized read-write lock object.
</DD></DL>
<P>
These functions shall not return an error code of [EINTR].
</P>
<P><I>The following sections are informative.</I>
</P>
<H2><A HREF="#toc5" NAME="sect5">Examples</A></H2>
<P>None.
</P>
<H2><A HREF="#toc6" NAME="sect6">Application Usage</A></H2>
<P>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.
</P>
<H2><A HREF="#toc7" NAME="sect7">Rationale</A></H2>
<P>None.
</P>
<H2><A HREF="#toc8" NAME="sect8">Future Directions</A></H2>
<P>None.
</P>
<H2><A HREF="#toc9" NAME="sect9">See Also</A></H2>
<P><A HREF="pthread_rwlock_init.html"><B>pthread_rwlock_destroy</B>(3)</A>
<B>,</B> <A HREF="pthread_rwlock_rdlock.html"><B>pthread_rwlock_rdlock</B>(3)</A>
<B>,</B> <A HREF="pthread_rwlock_timedrdlock.html"><B>pthread_rwlock_timedrdlock</B>(3)</A>
<B>,</B> <A HREF="pthread_rwlock_timedwrlock.html"><B>pthread_rwlock_timedwrlock</B>(3)</A>
<B>,</B> <A HREF="pthread_rwlock_rdlock.html"><B>pthread_rwlock_tryrdlock</B>(3)</A>
<B>,</B> <A HREF="pthread_rwlock_unlock.html"><B>pthread_rwlock_unlock</B>(3)</A>
<B>,</B> the Base Definitions volume of IEEE Std 1003.1-2001,
<I><pthread.h></I>
</P>
<H2><A HREF="#toc10" NAME="sect10">Copyright</A></H2>
<P>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 <A HREF="http://www.opengroup.org/unix/online.html">http://www.opengroup.org/unix/online.html</A>
.
</P>
<P>Modified by Ross Johnson for use with <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A>.</P>
<HR>
<P><A NAME="toc"></A><B>Table of Contents</B></P>
<UL>
<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect0" NAME="toc0">Name</A>
</P>
<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect1" NAME="toc1">Synopsis</A>
</P>
<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect2" NAME="toc2">Description</A>
</P>
<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect3" NAME="toc3">Return
Value</A>
</P>
<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect4" NAME="toc4">Errors</A>
</P>
<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect5" NAME="toc5">Examples</A>
</P>
<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect6" NAME="toc6">Application
Usage</A>
</P>
<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect7" NAME="toc7">Rationale</A>
</P>
<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect8" NAME="toc8">Future
Directions</A>
</P>
<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect9" NAME="toc9">See
Also</A>
</P>
<LI><P><A HREF="#sect10" NAME="toc10">Copyright</A>
</P>
</UL>
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