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26<a name="boost.read_write_mutex"></a><div class="titlepage"></div>
27<div class="refnamediv">
28<h2><span class="refentrytitle">Class read_write_mutex</span></h2>
29<p>boost::read_write_mutex &#8212; <p>The <a href="read_write_mutex.html" title="Class read_write_mutex">read_write_mutex</a> class is a model of the
30                        <a href="../thread/concepts.html#thread.concepts.ReadWriteMutex" title="ReadWriteMutex Concept">ReadWriteMutex</a> concept.</p><div class="note"><table border="0" summary="Note">
31<tr>
32<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../images/note.png"></td>
33<th align="left">Note</th>
34</tr>
35<tr><td align="left" valign="top"> Unfortunately it turned out that the current implementation of Read/Write Mutex has     
36            some serious problems. So it was decided not to put this implementation into
37            release grade code. Also discussions on the mailing list led to the
38            conclusion that the current concepts need to be rethought. In particular
39            the schedulings <a href="../thread/concepts.html#thread.concepts.read-write-scheduling-policies.inter-class" title="Inter-Class Scheduling Policies">
40                Inter-Class Scheduling Policies</a> are deemed unnecessary.
41            There seems to be common belief that a fair scheme suffices.
42            The following documentation has been retained however, to give
43            readers of this document the opportunity to study the original design.
44    </td></tr>
45</table></div></p>
46</div>
47<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
48<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis">
49<span class="bold"><strong>class</strong></span> read_write_mutex : <span class="bold"><strong>private</strong></span> boost::noncopyable,  <span class="emphasis"><em>// Exposition only</em></span>
50                         <span class="bold"><strong>private</strong></span> boost::noncopyable   <span class="emphasis"><em>// Exposition only</em></span>
51{
52<span class="bold"><strong>public</strong></span>:
53  <span class="emphasis"><em>// types</em></span>
54  <span class="bold"><strong>typedef</strong></span> <span class="emphasis"><em>implementation-defined</em></span> scoped_read_write_lock;
55  <span class="bold"><strong>typedef</strong></span> <span class="emphasis"><em>implementation-defined</em></span> scoped_read_lock;      
56  <span class="bold"><strong>typedef</strong></span> <span class="emphasis"><em>implementation-defined</em></span> scoped_write_lock;     
57
58  <span class="emphasis"><em>// <a href="read_write_mutex.html#boost.read_write_mutexconstruct-copy-destruct">construct/copy/destruct</a></em></span>
59  <a href="read_write_mutex.html#id1275854-bb">read_write_mutex</a>(boost::read_write_scheduling_policy);
60  <a href="read_write_mutex.html#id1289193-bb">~read_write_mutex</a>();
61};</pre></div>
62<div class="refsect1" lang="en">
63<a name="id1741938"></a><h2>Description</h2>
64<p>The <a href="read_write_mutex.html" title="Class read_write_mutex">read_write_mutex</a> class is a model of the
65                        <a href="../thread/concepts.html#thread.concepts.ReadWriteMutex" title="ReadWriteMutex Concept">ReadWriteMutex</a> concept.
66                        It should be used to synchronize access to shared resources using
67                        <a href="../thread/concepts.html#thread.concepts.read-write-locking-strategies.unspecified" title="Unspecified Locking Strategy">Unspecified</a>
68                        locking mechanics.</p>
69<p>For classes that model related mutex concepts, see
70                        <a href="try_read_write_mutex.html" title="Class try_read_write_mutex">try_read_write_mutex</a> and <a href="timed_read_write_mutex.html" title="Class timed_read_write_mutex">timed_read_write_mutex</a>.</p>
71<p>The <a href="read_write_mutex.html" title="Class read_write_mutex">read_write_mutex</a> class supplies the following typedefs,
72                        which <a href="../thread/concepts.html#thread.concepts.read-write-lock-models" title="Lock Models">model</a>
73                        the specified locking strategies:
74
75                        </p>
76<div class="informaltable"><table class="table">
77<colgroup>
78<col>
79<col>
80</colgroup>
81<thead><tr>
82<th align="left">Lock Name</th>
83<th align="left">Lock Concept</th>
84</tr></thead>
85<tbody>
86<tr>
87<td align="left">scoped_read_write_lock</td>
88<td align="left"><a href="../thread/concepts.html#thread.concepts.ScopedReadWriteLock" title="ScopedReadWriteLock Concept">ScopedReadWriteLock</a></td>
89</tr>
90<tr>
91<td align="left">scoped_read_lock</td>
92<td align="left"><a href="../thread/concepts.html#thread.concepts.ScopedLock" title="ScopedLock Concept">ScopedLock</a></td>
93</tr>
94<tr>
95<td align="left">scoped_write_lock</td>
96<td align="left"><a href="../thread/concepts.html#thread.concepts.ScopedLock" title="ScopedLock Concept">ScopedLock</a></td>
97</tr>
98</tbody>
99</table></div>
100<p>                     
101                        </p>
102<p>The <a href="read_write_mutex.html" title="Class read_write_mutex">read_write_mutex</a> class uses an
103                        <a href="../thread/concepts.html#thread.concepts.read-write-locking-strategies.unspecified" title="Unspecified Locking Strategy">Unspecified</a>
104                        locking strategy, so attempts to recursively lock a <a href="read_write_mutex.html" title="Class read_write_mutex">read_write_mutex</a>
105                        object or attempts to unlock one by threads that don't own a lock on it result in
106                        <span class="bold"><strong>undefined behavior</strong></span>.
107                        This strategy allows implementations to be as efficient as possible
108                        on any given platform. It is, however, recommended that
109                        implementations include debugging support to detect misuse when
110                        <code class="computeroutput">NDEBUG</code> is not defined.</p>
111<p>Like all
112                        <a href="../thread/concepts.html#thread.concepts.read-write-mutex-models" title="Mutex Models">read/write mutex models</a>
113                        in <span class="bold"><strong>Boost.Thread</strong></span>, <a href="read_write_mutex.html" title="Class read_write_mutex">read_write_mutex</a> has two types of
114                        <a href="../thread/concepts.html#thread.concepts.read-write-scheduling-policies" title="Scheduling Policies">scheduling policies</a>, an
115                        <a href="../thread/concepts.html#thread.concepts.read-write-scheduling-policies.inter-class" title="Inter-Class Scheduling Policies">inter-class sheduling policy</a>
116                        between threads trying to obtain different types of locks and an
117                        <a href="../thread/concepts.html#thread.concepts.read-write-scheduling-policies.intra-class" title="Intra-Class Scheduling Policies">intra-class sheduling policy</a>
118                        between threads trying to obtain the same type of lock.
119                        The <a href="read_write_mutex.html" title="Class read_write_mutex">read_write_mutex</a> class allows the
120                        programmer to choose what
121                        <a href="../thread/concepts.html#thread.concepts.read-write-scheduling-policies.inter-class" title="Inter-Class Scheduling Policies">inter-class sheduling policy</a>
122                        will be used; however, like all read/write mutex models,
123                        <a href="read_write_mutex.html" title="Class read_write_mutex">read_write_mutex</a> leaves the
124                        <a href="../thread/concepts.html#thread.concepts.read-write-scheduling-policies.intra-class" title="Intra-Class Scheduling Policies">intra-class sheduling policy</a> as
125                        <a href="../thread/concepts.html#thread.concepts.read-write-locking-strategies.unspecified" title="Unspecified Locking Strategy">Unspecified</a>.                       
126                        </p>
127<div class="note"><table border="0" summary="Note">
128<tr>
129<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../images/note.png"></td>
130<th align="left">Note</th>
131</tr>
132<tr><td align="left" valign="top">Self-deadlock is virtually guaranteed if a thread tries to
133                        lock the same <a href="read_write_mutex.html" title="Class read_write_mutex">read_write_mutex</a> multiple times
134                        unless all locks are read-locks (but see below)</td></tr>
135</table></div>
136<div class="refsect2" lang="en">
137<a name="id1742245"></a><h3>
138<a name="boost.read_write_mutexconstruct-copy-destruct"></a><code class="computeroutput">read_write_mutex</code> construct/copy/destruct</h3>
139<div class="orderedlist"><ol type="1">
140<li>
141<pre class="literallayout"><a name="id1275854-bb"></a>read_write_mutex(boost::read_write_scheduling_policy count);</pre>
142<div class="variablelist"><table border="0">
143<col align="left" valign="top">
144<tbody>
145<tr>
146<td>
147<span class="term">Effects:</span></td>
148<td>Constructs a <a href="read_write_mutex.html" title="Class read_write_mutex">read_write_mutex</a> object.
149                        </td>
150</tr>
151<tr>
152<td>
153<span class="term">Postconditions:</span></td>
154<td>
155<code class="computeroutput">*this</code> is in an unlocked state.
156                        </td>
157</tr>
158</tbody>
159</table></div>
160</li>
161<li>
162<pre class="literallayout"><a name="id1289193-bb"></a>~read_write_mutex();</pre>
163<div class="variablelist"><table border="0">
164<col align="left" valign="top">
165<tbody>
166<tr>
167<td>
168<span class="term">Effects:</span></td>
169<td>Destroys a <a href="read_write_mutex.html" title="Class read_write_mutex">read_write_mutex</a> object.</td>
170</tr>
171<tr>
172<td>
173<span class="term">Requires:</span></td>
174<td>
175<code class="computeroutput">*this</code> is in an unlocked state.</td>
176</tr>
177<tr>
178<td>
179<span class="term">Notes:</span></td>
180<td>
181<span class="bold"><strong>Danger:</strong></span> Destruction of a
182                        locked mutex is a serious programming error resulting in undefined
183                        behavior such as a program crash.</td>
184</tr>
185</tbody>
186</table></div>
187</li>
188</ol></div>
189</div>
190</div>
191</div>
192<table width="100%"><tr>
193<td align="left"></td>
194<td align="right"><small>Copyright © 2001-2003 William E. Kempf</small></td>
195</tr></table>
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