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<title>guard - Auto-lock/unlock-er</title>
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<img src="../../../../boost.png" width="276" height="86" alt="C++ Boost">
<h1 align="center">guard - Auto-lock/unlock-er</h1>
<h2>Introduction</h2>
<p>detail/guard.hpp provides a type <span class=
"code">guard<Mutex></span> that allows scoped access to the
<span class="code">Mutex</span>'s locking and unlocking operations. It is
used to ensure that a <span class="code">Mutex</span> is unlocked, even if
an exception is thrown.</p>
<h2>Synopsis</h2>
<pre class="code">
namespace details {
namespace pool {
template <typename Mutex>
class guard
{
private:
guard(const guard &);
void operator=(const guard &);
public:
explicit guard(Mutex & mtx);
~guard();
};
} // namespace pool
} // namespace details
</pre>
<h2>Semantics</h2>
<table border align="center" summary="">
<caption>
<em>Symbol Table</em>
</caption>
<tr>
<th>Symbol</th>
<th>Meaning</th>
</tr>
<tr>
<td class="code">T</td>
<td><span class="code">guard<Mutex></span></td>
</tr>
<tr>
<td class="code">m</td>
<td>value of type <span class="code">Mutex &</span></td>
</tr>
<tr>
<td class="code">g</td>
<td>value of type <span class="code">guard<Mutex></span></td>
</tr>
</table><br>
<table border align="center" summary="">
<caption>
<em>Requirements on <span class="code">Mutex</span></em>
</caption>
<tr>
<th>Expression</th>
<th>Return Type</th>
<th>Assertion/Note/Pre/Post-Condition</th>
</tr>
<tr>
<td class="code">m.lock()</td>
<td>not used</td>
<td>Locks the mutex referred to by <span class="code">m</span></td>
</tr>
<tr>
<td class="code">m.unlock()</td>
<td>not used</td>
<td>Unlocks the mutex referred to by <span class="code">m</span></td>
</tr>
</table><br>
<table border align="center" summary="">
<caption>
<em>Requirements satisfied by <span class="code">guard</span></em>
</caption>
<tr>
<th>Expression</th>
<th>Assertion/Note/Pre/Post-Condition</th>
</tr>
<tr>
<td class="code">T(m)</td>
<td>Locks the mutex referred to by <span class="code">m</span>; binds
<span class="code">T(m)</span> to <span class="code">m</span></td>
</tr>
<tr>
<td class="code">(&g)->~T()</td>
<td>Unlocks the mutex that <span class="code">g</span> is bound to</td>
</tr>
</table>
<h2>Example</h2>
<p>Given a (platform-specific) <span class="code">mutex</span> class, we
can wrap code as follows:</p>
<pre class="code">
extern mutex global_lock;
static void f()
{
boost::details::pool::guard<mutex> g(global_lock);
// g's constructor locks "global_lock"
... // do anything:
// throw exceptions
// return
// or just fall through
} // g's destructor unlocks "global_lock"
</pre>
<h2>Dependencies</h2>
<p>None.</p>
<h2>Future Directions</h2>
<p>This header will eventually be replaced by a Boost multithreading
library.</p>
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<p>Revised
<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->05
December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38516" --></p>
<p><i>Copyright © 2000, 2001 Stephen Cleary (scleary AT jerviswebb DOT
com)</i></p>
<p><i>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>)</i></p>
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