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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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| <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> |
| |
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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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