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- <h1><img src="../../../../boost.png" alt="Boost logo" align=
- "middle" width="277" height="86">Boost.Flyweight
- Locking policies reference</h1>
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- <hr>
- <h2>Contents</h2>
- <ul>
- <li><a href="#preliminary">Preliminary concepts</a></li>
- <li><a href="#locking">Locking policies</a></li>
- <li><a href="#locking_tag_synopsis">Header
- <code>"boost/flyweight/locking_tag.hpp"</code> synopsis</a>
- <ul>
- <li><a href="#is_locking">Class template <code>is_locking</code></a></li>
- <li><a href="#locking_construct">Class template <code>locking</code></a></li>
- </ul>
- </li>
- <li><a href="#simple_locking_fwd_synopsis">Header
- <code>"boost/flyweight/simple_locking_fwd.hpp"</code> synopsis</a>
- </li>
- <li><a href="#simple_locking_synopsis">Header
- <code>"boost/flyweight/simple_locking.hpp"</code> synopsis</a>
- <ul>
- <li><a href="#simple_locking">Class <code>simple_locking</code></a></li>
- </ul>
- </li>
- <li><a href="#no_locking_fwd_synopsis">Header
- <code>"boost/flyweight/no_locking_fwd.hpp"</code> synopsis</a>
- </li>
- <li><a href="#no_locking_synopsis">Header
- <code>"boost/flyweight/no_locking.hpp"</code> synopsis</a>
- <ul>
- <li><a href="#no_locking">Class <code>no_locking</code></a></li>
- </ul>
- </li>
- </ul>
- <h2><a name="preliminary">Preliminary concepts</a></h2>
- <p>
- A <i>mutex</i> is a type whose objects can be in either of two states, called
- locked and unlocked, with the property that when a thread A has locked a
- mutex <code>m</code> and a different thread B tries to lock <code>m</code>,
- B is blocked until A unlocks <code>m</code>. Additionally, a mutex is said to
- support <i>recursive locking</i> if a thread can succesfully invoke the locking
- operation for a mutex already locked by this same thread; in this case, it is
- required that the thread execute as many unlock operations as lock
- operations it has performed for the mutex to become effectively unlocked.
- A <i>scoped lock</i> is a
- type associated to some mutex type whose objects do the locking/unlocking
- of a mutex on construction/destruction time.
- </p>
- <p>
- In the following table, <code>Mutex</code> is a mutex type, <code>m</code>
- is an object of type <code>Mutex</code>, <code>Lock</code> is a scoped lock
- associated to <code>Mutex</code> and <code>lk</code> is a value of
- <code>Lock</code>.
- <p align="center">
- <table cellspacing="0">
- <caption><b>Mutex and Scoped Lock requirements.</b></caption>
- <tr>
- <th align="center">expression</th>
- <th align="center">return type</th>
- <th align="center">assertion/note<br>pre/post-condition</th>
- </tr>
- <tr>
- <td><code>Mutex m;</code></td>
- <td> </td>
- <td>Post: <code>m</code> is unlocked.
- </td>
- </tr>
- <tr class="odd_tr">
- <td><code>(&m)->~Mutex();</code></td>
- <td><code>void</code></td>
- <td>Pre: <code>m</code> is unlocked.</td>
- </tr>
- <tr>
- <td><code>Lock lk(m);</code></td>
- <td> </td>
- <td>Associates <code>m</code> to <code>lk</code> and locks <code>m</code>.</td>
- </tr>
- <tr class="odd_tr">
- <td><code>(&lk)->~Lock();</code></td>
- <td><code>void</code></td>
- <td>Unlocks the mutex associated to <code>lk</code>.</td>
- </tr>
- </table>
- </p>
- <p>
- These concepts are very similar, but not entirely equivalent, to
- the homonym ones described in the
- <a href="../../../../doc/html/thread/synchronization.html#thread.synchronization.mutex_concepts">Boost Thread
- Library</a>.
- </p>
- <h2><a name="locking">Locking policies</a></h2>
- <p>
- <i>Locking policies</i> describe a mutex type and an associated
- scoped lock type.
- <a href="flyweight.html#flyweight"><code>flyweight</code></a> uses a given locking
- policy to synchronize the access to its internal
- <a href="factories.html#factory">factory</a>.
- </p>
- <p>
- A type <code>Locking</code> is a locking policy if:
- <ul>
- <li>One of the following conditions is satisfied:
- <ol type="a">
- <li><a href="#is_locking"><code>is_locking<Locking>::type</code></a> is
- <a href="../../../mpl/doc/refmanual/bool.html"><code>boost::mpl::true_</code></a>,</li>
- <li><code>Locking</code> is of the form
- <a href="#locking_construct"><code>locking<Locking'></code></a>.</li>
- </ol>
- </li>
- <li>The type <code>Locking::mutex_type</code> (or
- <code>Locking'::mutex_type</code> if (b) applies) is a
- model of <a href="#preliminary"><code>Mutex</code></a>
- and supports recursive locking.
- </li>
- <li>The type <code>Locking::lock_type</code> (or
- <code>Locking'::lock_type</code> if (b) applies) is a
- <a href="#preliminary"><code>Scoped Lock</code></a> of
- the mutex referred to above.
- </li>
- </ul>
- </p>
- <h2><a name="locking_tag_synopsis">Header
- <a href="../../../../boost/flyweight/locking_tag.hpp"><code>"boost/flyweight/locking_tag.hpp"</code></a> synopsis</a></h2>
- <blockquote><pre>
- <span class=keyword>namespace</span> <span class=identifier>boost</span><span class=special>{</span>
- <span class=keyword>namespace</span> <span class=identifier>flyweights</span><span class=special>{</span>
- <span class=keyword>struct</span> <span class=identifier>locking_marker</span><span class=special>;</span>
- <span class=keyword>template</span><span class=special><</span><span class=keyword>typename</span> <span class=identifier>T</span><span class=special>></span>
- <span class=keyword>struct</span> <span class=identifier>is_locking</span>
- <span class=keyword>template</span><span class=special><</span><span class=keyword>typename</span> <span class=identifier>T</span><span class=special>></span>
- <span class=keyword>struct</span> <span class=identifier>locking</span><span class=special>;</span>
- <span class=special>}</span> <span class=comment>// namespace boost::flyweights</span>
- <span class=special>}</span> <span class=comment>// namespace boost</span>
- </pre></blockquote>
- <h3><a name="is_locking">Class template <code>is_locking</code></a></h3>
- <p>
- Unless specialized by the user, <code>is_locking<T>::type</code> is
- <a href="../../../mpl/doc/refmanual/bool.html"><code>boost::mpl::true_</code></a>
- if <code>T</code> is derived from <code>locking_marker</code>, and it is
- <a href="../../../mpl/doc/refmanual/bool.html"><code>boost::mpl::false_</code></a>
- otherwise.
- </p>
- <h3><a name="locking_construct">Class template <code>locking</code></a></h3>
- <p>
- <code>locking<T></code> is a syntactic construct meant to indicate
- that <code>T</code> is a locking policy without resorting to the
- mechanisms provided by the <code>is_locking</code> class template.
- </p>
- <h2><a name="simple_locking_fwd_synopsis">Header
- <a href="../../../../boost/flyweight/simple_locking_fwd.hpp"><code>"boost/flyweight/simple_locking_fwd.hpp"</code></a> synopsis</a></h2>
- <blockquote><pre>
- <span class=keyword>namespace</span> <span class=identifier>boost</span><span class=special>{</span>
- <span class=keyword>namespace</span> <span class=identifier>flyweights</span><span class=special>{</span>
- <span class=keyword>struct</span> <span class=identifier>simple_locking</span><span class=special>;</span>
- <span class=special>}</span> <span class=comment>// namespace boost::flyweights</span>
- <span class=special>}</span> <span class=comment>// namespace boost</span>
- </pre></blockquote>
- <p>
- <code>simple_locking_fwd.hpp</code> forward declares the class
- <a href="#simple_locking"><code>simple_locking</code></a>.
- </p>
- <h2><a name="simple_locking_synopsis">Header
- <a href="../../../../boost/flyweight/simple_locking.hpp"><code>"boost/flyweight/simple_locking.hpp"</code></a> synopsis</a></h2>
- <h3><a name="simple_locking">Class <code>simple_locking</code></a></h3>
- <p>
- <a href="#locking"><code>Locking Policy</code></a> that specifies a basic
- mutex type based on the simplest synchronization mechanisms provided by
- the environment; When no threading capabilities are available,
- <code>simple_locking</code> specifies a dummy type without actual
- synchronization capabilities.
- </p>
- <h2><a name="no_locking_fwd_synopsis">Header
- <a href="../../../../boost/flyweight/no_locking_fwd.hpp"><code>"boost/flyweight/no_locking_fwd.hpp"</code></a> synopsis</a></h2>
- <blockquote><pre>
- <span class=keyword>namespace</span> <span class=identifier>boost</span><span class=special>{</span>
- <span class=keyword>namespace</span> <span class=identifier>flyweights</span><span class=special>{</span>
- <span class=keyword>struct</span> <span class=identifier>no_locking</span><span class=special>;</span>
- <span class=special>}</span> <span class=comment>// namespace boost::flyweights</span>
- <span class=special>}</span> <span class=comment>// namespace boost</span>
- </pre></blockquote>
- <p>
- <code>no_locking_fwd.hpp</code> forward declares the class
- <a href="#no_locking"><code>no_locking</code></a>.
- </p>
- <h2><a name="no_locking_synopsis">Header
- <a href="../../../../boost/flyweight/no_locking.hpp"><code>"boost/flyweight/no_locking.hpp"</code></a> synopsis</a></h2>
- <h3><a name="no_locking">Class <code>no_locking</code></a></h3>
- <p>
- Null <a href="#locking"><code>Locking Policy</code></a>: it specifies a dummy
- type that satisfies the formal requirements for the
- <a href="#preliminary"><code>Mutex</code></a> concept but does not perform
- thread blocking. <code>no_locking</code> should only be used in single-threaded
- environments.
- </p>
- <hr>
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- <br>
- <p>Revised March 9th 2010</p>
- <p>© Copyright 2006-2010 Joaquín M López Muñoz.
- Distributed under the Boost Software
- License, Version 1.0. (See accompanying file <a href="../../../../LICENSE_1_0.txt">
- LICENSE_1_0.txt</a> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt">
- http://www.boost.org/LICENSE_1_0.txt</a>)
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