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authorrpj <rpj>2005-05-05 14:18:27 +0000
committerrpj <rpj>2005-05-05 14:18:27 +0000
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+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
+<HTML>
+<HEAD>
+ <META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=utf-8">
+ <TITLE>&quot;PTHREAD_RWLOCK_RDLOCK&quot;(P) manual page</TITLE>
+ <META NAME="GENERATOR" CONTENT="OpenOffice.org 1.1.3 (Linux)">
+ <META NAME="CREATED" CONTENT="20050505;10352600">
+ <META NAME="CHANGED" CONTENT="20050505;12554200">
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+<BODY LANG="en-GB" BGCOLOR="#ffffff" DIR="LTR">
+<P><A HREF="#toc">Table of Contents</A></P>
+<H2><A HREF="#toc0" NAME="sect0">Name</A></H2>
+<P>pthread_rwlock_rdlock, pthread_rwlock_tryrdlock - lock a
+read-write lock object for reading
+</P>
+<H2><A HREF="#toc1" NAME="sect1">Synopsis</A></H2>
+<P><B>#include &lt;pthread.h&gt; </B>
+</P>
+<P><B>int pthread_rwlock_rdlock(pthread_rwlock_t <I>*</I></B><I>rwlock</I><B>);
+<BR></B>i<B>nt pthread_rwlock_tryrdlock(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_rdlock</B> function shall apply a read lock
+to the read-write lock referenced by <I>rwlock</I>. The calling
+thread acquires the read lock if a writer does not hold the lock and
+there are no writers blocked on the 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>A thread may hold multiple concurrent read locks on <I>rwlock</I>
+(that is, successfully call the <B>pthread_rwlock_rdlock</B> function
+<I>n</I> times). If so, the application shall ensure that the thread
+performs matching unlocks (that is, it calls the
+<A HREF="pthread_rwlock_unlock.html"><B>pthread_rwlock_unlock</B>(3)</A>
+function <I>n</I> times).
+</P>
+<P>The <B>pthread_rwlock_tryrdlock</B> function shall apply a read
+lock as in the <B>pthread_rwlock_rdlock</B> function, with the
+exception that the function shall fail if the equivalent
+<B>pthread_rwlock_rdlock</B> call would have blocked the calling
+thread. In no case shall the <B>pthread_rwlock_tryrdlock</B> function
+ever block; it always either acquires the lock or fails and returns
+immediately.
+</P>
+<P>Results are undefined if any of these functions are called with an
+uninitialized read-write lock.
+</P>
+<P><B>Pthreads-w32</B> does not detect deadlock if the thread already
+owns the lock for writing.</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>If successful, the <B>pthread_rwlock_rdlock</B> function shall
+return zero; otherwise, an error number shall be returned to indicate
+the error.
+</P>
+<P>The <B>pthread_rwlock_tryrdlock</B> function shall return zero if
+the lock for reading 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>
+<H2><A HREF="#toc4" NAME="sect4">Errors</A></H2>
+<P>The <B>pthread_rwlock_tryrdlock</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 reading because a
+ writer holds the lock or a writer with the appropriate priority was
+ blocked on it.
+ </DD></DL>
+<P>
+The <B>pthread_rwlock_rdlock</B> and <B>pthread_rwlock_tryrdlock</B>
+functions may fail if:
+</P>
+<DL>
+ <DT><B>EINVAL</B>
+ </DT><DD>
+ The value specified by <I>rwlock</I> does not refer to an
+ initialized read-write lock object.
+ </DD><DT>
+ <B>EAGAIN</B>
+ </DT><DD STYLE="margin-bottom: 0.5cm">
+ The read lock could not be acquired because the maximum number of
+ read locks for <I>rwlock</I> has been exceeded.
+ </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&nbsp;Std&nbsp;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_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_wrlock.html"><B>pthread_rwlock_trywrlock</B>(3)</A>
+<B>,</B> <A HREF="pthread_rwlock_unlock.html"><B>pthread_rwlock_unlock</B>(3)</A>
+<B>,</B> <A HREF="pthread_rwlock_wrlock.html"><B>pthread_rwlock_wrlock</B>(3)</A>
+<B>,</B> the Base Definitions volume of IEEE&nbsp;Std&nbsp;1003.1-2001,
+<I>&lt;pthread.h&gt;</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>
+</BODY>
+</HTML>