227 lines
9.1 KiB
HTML
227 lines
9.1 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
|
|
<html>
|
|
<head>
|
|
<meta name="generator" content="HTML Tidy, see www.w3.org">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
|
|
<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
|
|
<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
|
|
<title>pthread_rwlock_rdlock</title>
|
|
</head>
|
|
<body bgcolor="white">
|
|
<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
|
|
</script>
|
|
|
|
<basefont size="3"> <a name="pthread_rwlock_rdlock"></a> <a name="tag_03_556"></a><!-- pthread_rwlock_rdlock -->
|
|
<!--header start-->
|
|
<center><font size="2">The Open Group Base Specifications Issue 6<br>
|
|
IEEE Std 1003.1-2001<br>
|
|
Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
|
|
|
|
<!--header end-->
|
|
<hr size="2" noshade>
|
|
<h4><a name="tag_03_556_01"></a>NAME</h4>
|
|
|
|
<blockquote>pthread_rwlock_rdlock, pthread_rwlock_tryrdlock - lock a read-write lock object for reading</blockquote>
|
|
|
|
<h4><a name="tag_03_556_02"></a>SYNOPSIS</h4>
|
|
|
|
<blockquote class="synopsis">
|
|
<div class="box"><code><tt><sup>[<a href="javascript:open_code('THR')">THR</a>]</sup> <img src="../images/opt-start.gif" alt=
|
|
"[Option Start]" border="0"> #include <<a href="../basedefs/pthread.h.html">pthread.h</a>><br>
|
|
<br>
|
|
int pthread_rwlock_rdlock(pthread_rwlock_t</tt> <i>*rwlock</i><tt>);<br>
|
|
int pthread_rwlock_tryrdlock(pthread_rwlock_t</tt> <i>*rwlock</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]"
|
|
border="0"></tt></code></div>
|
|
|
|
<tt><br>
|
|
</tt></blockquote>
|
|
|
|
<h4><a name="tag_03_556_03"></a>DESCRIPTION</h4>
|
|
|
|
<blockquote>
|
|
<p>The <i>pthread_rwlock_rdlock</i>() 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><sup>[<a href="javascript:open_code('TPS')">TPS</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
|
|
If the Thread Execution Scheduling option is supported, and the threads involved in the lock are executing with the scheduling
|
|
policies SCHED_FIFO or SCHED_RR, the calling thread shall not acquire the lock if a writer holds the lock or if writers of higher
|
|
or equal priority are blocked on the lock; otherwise, the calling thread shall acquire the lock. <img src="../images/opt-end.gif"
|
|
alt="[Option End]" border="0"></p>
|
|
|
|
<p><sup>[<a href="javascript:open_code('TPS TSP')">TPS TSP</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"
|
|
border="0"> If the Threads Execution Scheduling option is supported, and the threads involved in the lock are executing with the
|
|
SCHED_SPORADIC scheduling policy, the calling thread shall not acquire the lock if a writer holds the lock or if writers of higher
|
|
or equal priority are blocked on the lock; otherwise, the calling thread shall acquire the lock. <img src="../images/opt-end.gif"
|
|
alt="[Option End]" border="0"></p>
|
|
|
|
<p>If the Thread Execution Scheduling option is not supported, it is implementation-defined whether the calling thread acquires the
|
|
lock when a writer does not hold the lock and there are writers blocked on the lock. If a writer holds the lock, the calling thread
|
|
shall not acquire the read lock. If the read lock is not acquired, the calling thread shall block until it can acquire the lock.
|
|
The calling thread may deadlock if at the time the call is made it holds a write lock.</p>
|
|
|
|
<p>A thread may hold multiple concurrent read locks on <i>rwlock</i> (that is, successfully call the <i>pthread_rwlock_rdlock</i>()
|
|
function <i>n</i> times). If so, the application shall ensure that the thread performs matching unlocks (that is, it calls the <a
|
|
href="../functions/pthread_rwlock_unlock.html"><i>pthread_rwlock_unlock</i>()</a> function <i>n</i> times).</p>
|
|
|
|
<p>The maximum number of simultaneous read locks that an implementation guarantees can be applied to a read-write lock shall be
|
|
implementation-defined. The <i>pthread_rwlock_rdlock</i>() function may fail if this maximum would be exceeded.</p>
|
|
|
|
<p>The <i>pthread_rwlock_tryrdlock</i>() function shall apply a read lock as in the <i>pthread_rwlock_rdlock</i>() function, with
|
|
the exception that the function shall fail if the equivalent <i>pthread_rwlock_rdlock</i>() call would have blocked the calling
|
|
thread. In no case shall the <i>pthread_rwlock_tryrdlock</i>() 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>If a signal is delivered to a thread waiting for a read-write lock for reading, upon return from the signal handler the thread
|
|
resumes waiting for the read-write lock for reading as if it was not interrupted.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_556_04"></a>RETURN VALUE</h4>
|
|
|
|
<blockquote>
|
|
<p>If successful, the <i>pthread_rwlock_rdlock</i>() function shall return zero; otherwise, an error number shall be returned to
|
|
indicate the error.</p>
|
|
|
|
<p>The <i>pthread_rwlock_tryrdlock</i>() 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>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_556_05"></a>ERRORS</h4>
|
|
|
|
<blockquote>
|
|
<p>The <i>pthread_rwlock_tryrdlock</i>() function shall fail if:</p>
|
|
|
|
<dl compact>
|
|
<dt>[EBUSY]</dt>
|
|
|
|
<dd>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 <i>pthread_rwlock_rdlock</i>() and <i>pthread_rwlock_tryrdlock</i>() functions may fail if:</p>
|
|
|
|
<dl compact>
|
|
<dt>[EINVAL]</dt>
|
|
|
|
<dd>The value specified by <i>rwlock</i> does not refer to an initialized read-write lock object.</dd>
|
|
|
|
<dt>[EAGAIN]</dt>
|
|
|
|
<dd>The read lock could not be acquired because the maximum number of read locks for <i>rwlock</i> has been exceeded.</dd>
|
|
</dl>
|
|
|
|
<p>The <i>pthread_rwlock_rdlock</i>() function may fail if:</p>
|
|
|
|
<dl compact>
|
|
<dt>[EDEADLK]</dt>
|
|
|
|
<dd>The current thread already owns the read-write lock for writing.</dd>
|
|
</dl>
|
|
|
|
<p>These functions shall not return an error code of [EINTR].</p>
|
|
</blockquote>
|
|
|
|
<hr>
|
|
<div class="box"><em>The following sections are informative.</em></div>
|
|
|
|
<h4><a name="tag_03_556_06"></a>EXAMPLES</h4>
|
|
|
|
<blockquote>
|
|
<p>None.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_556_07"></a>APPLICATION USAGE</h4>
|
|
|
|
<blockquote>
|
|
<p>Applications using these functions may be subject to priority inversion, as discussed in the Base Definitions volume of
|
|
IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap03.html#tag_03_285">Section 3.285, Priority Inversion</a>.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_556_08"></a>RATIONALE</h4>
|
|
|
|
<blockquote>
|
|
<p>None.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_556_09"></a>FUTURE DIRECTIONS</h4>
|
|
|
|
<blockquote>
|
|
<p>None.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_556_10"></a>SEE ALSO</h4>
|
|
|
|
<blockquote>
|
|
<p><a href="pthread_rwlock_destroy.html"><i>pthread_rwlock_destroy</i>()</a> , <a href=
|
|
"pthread_rwlock_timedrdlock.html"><i>pthread_rwlock_timedrdlock</i>()</a> , <a href=
|
|
"pthread_rwlock_timedwrlock.html"><i>pthread_rwlock_timedwrlock</i>()</a> , <a href=
|
|
"pthread_rwlock_trywrlock.html"><i>pthread_rwlock_trywrlock</i>()</a> , <a href=
|
|
"pthread_rwlock_unlock.html"><i>pthread_rwlock_unlock</i>()</a> , <a href=
|
|
"pthread_rwlock_wrlock.html"><i>pthread_rwlock_wrlock</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a
|
|
href="../basedefs/pthread.h.html"><i><pthread.h></i></a></p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_556_11"></a>CHANGE HISTORY</h4>
|
|
|
|
<blockquote>
|
|
<p>First released in Issue 5.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_556_12"></a>Issue 6</h4>
|
|
|
|
<blockquote>
|
|
<p>The following changes are made for alignment with IEEE Std 1003.1j-2000:</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>The margin code in the SYNOPSIS is changed to THR to indicate that the functionality is now part of the Threads option
|
|
(previously it was part of the Read-Write Locks option in IEEE Std 1003.1j-2000 and also part of the XSI extension).</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p>The DESCRIPTION is updated as follows:</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>Conditions under which writers have precedence over readers are specified.</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p>Failure of <i>pthread_rwlock_tryrdlock</i>() is clarified.</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p>A paragraph on the maximum number of read locks is added.</p>
|
|
</li>
|
|
</ul>
|
|
</li>
|
|
|
|
<li>
|
|
<p>In the ERRORS sections, [EBUSY] is modified to take into account write priority, and [EDEADLK] is deleted as a
|
|
<i>pthread_rwlock_tryrdlock</i>() error.</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p>The SEE ALSO section is updated.</p>
|
|
</li>
|
|
</ul>
|
|
</blockquote>
|
|
|
|
<div class="box"><em>End of informative text.</em></div>
|
|
|
|
<hr>
|
|
<hr size="2" noshade>
|
|
<center><font size="2"><!--footer start-->
|
|
UNIX ® is a registered Trademark of The Open Group.<br>
|
|
POSIX ® is a registered Trademark of The IEEE.<br>
|
|
[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
|
|
"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
|
|
]</font></center>
|
|
|
|
<!--footer end-->
|
|
<hr size="2" noshade>
|
|
</body>
|
|
</html>
|
|
|