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<div class="section" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="threads.concepts"></a>Concepts</h3></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="concepts.html#threads.concepts.mutexes">Mutexes</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-mutexes">Read/Write Mutexes</a></span></dt>
</dl></div>
<p> currently supports two types of mutex concepts:
	ordinary <a href="concepts.html#threads.concepts.mutexes" title="Mutexes">Mutexes</a>,
	which allow only one thread at a time to access a resource, and
	<a href="concepts.html#threads.concepts.read-write-mutexes" title="Read/Write Mutexes">Read/Write Mutexes</a>,
	which allow only one thread at a time to access a resource when it is
	being modified (the "Write" part of Read/Write), but allows multiple threads
	to access a resource when it is only being referenced (the "Read" part of
	Read/Write).</p>
<div class="section" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="threads.concepts.mutexes"></a>Mutexes</h4></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="concepts.html#threads.concepts.locking-strategies">Locking Strategies</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.sheduling-policies">Scheduling Policies</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.mutex-concepts">Mutex Concepts</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.mutex-models">Mutex Models</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.lock-concepts">Lock Concepts</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.lock-models">Lock Models</a></span></dt>
</dl></div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>Certain changes to the mutexes and lock concepts are
		currently under discussion. In particular, the combination of
		the multiple lock concepts into a single lock concept
		is likely, and the combination of the multiple mutex
		concepts into a single mutex concept is also possible.</div>
<p>A mutex (short for mutual-exclusion) object is used to serialize
		access to a resource shared between multiple threads. The
		<a href="concepts.html#threads.concepts.Mutex" title="Mutex Concept">Mutex</a> concept, with
		<a href="concepts.html#threads.concepts.TryMutex" title="TryMutex Concept">TryMutex</a> and
		<a href="concepts.html#threads.concepts.TimedMutex" title="TimedMutex Concept">TimedMutex</a> refinements,
		formalize the requirements. A model that implements Mutex and its
		refinements has two states: <span class="bold"><strong>locked</strong></span> and
		<span class="bold"><strong>unlocked</strong></span>. Before using a shared resource, a
		thread locks a  mutex object
		(an object whose type is a model of
		<a href="concepts.html#threads.concepts.Mutex" title="Mutex Concept">Mutex</a> or one of it's
		refinements), ensuring
		<a href="../threads.html#threads.glossary.thread-safe">thread-safe</a> access to
		the shared resource. When use of the shared resource is complete, the thread
		unlocks the mutex object, allowing another thread to acquire the lock and
		use the shared resource.</p>
<p>Traditional C thread APIs, like POSIX threads or the Windows thread
		APIs, expose functions to lock and unlock a mutex object. This is dangerous
		since it's easy to forget to unlock a locked mutex. When the flow of control
		is complex, with multiple return points, the likelihood of forgetting to
		unlock a mutex object becomes even greater. When exceptions are thrown,
		it becomes nearly impossible to ensure that the mutex object is unlocked
		properly when using these traditional API's. The result is
		<a href="../threads.html#threads.glossary.deadlock">deadlock</a>.</p>
<p>Many C++ threading libraries use a pattern known as <span class="emphasis"><em>Scoped
		Locking</em></span> to free the programmer from
		the need to explicitly lock and unlock mutex objects. With this pattern, a
		<a href="concepts.html#threads.concepts.lock-concepts" title="Lock Concepts">Lock</a> concept is employed where
		the lock object's constructor locks the associated mutex object and the
		destructor automatically does the unlocking. The
		 library takes this pattern to
		the extreme in that Lock concepts are the only way to lock and unlock a
		mutex object: lock and unlock functions are not exposed by any
		 mutex objects. This helps to
		ensure safe usage patterns, especially when code throws exceptions.</p>
<div class="section" lang="en">
<div class="titlepage"><div><div><h5 class="title">
<a name="threads.concepts.locking-strategies"></a>Locking Strategies</h5></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="concepts.html#threads.concepts.recursive-locking-strategy">Recursive Locking Strategy</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.checked-locking-strategy">Checked Locking Strategy</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.unchecked-locking-strategy">Unchecked Locking Strategy</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.unspecified-locking-strategy">Unspecified Locking Strategy</a></span></dt>
</dl></div>
<p>Every mutex object follows one of several locking strategies. These
			strategies define the semantics for the locking operation when the calling
			thread already owns a lock on the mutex object.</p>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.recursive-locking-strategy"></a>Recursive Locking Strategy</h6></div></div></div>
<p>With a recursive locking strategy, when a thread attempts to acquire
				a lock on the mutex object for which it already owns a lock, the operation
				is successful. Note the distinction between a thread, which may have
				multiple locks outstanding on a recursive mutex object, and a lock object,
				which even for a recursive mutex object cannot have any of its lock
				functions called multiple times without first calling unlock.</p>
<p>Internally a lock count is maintained and the owning thread must
				unlock the mutex object the same number of times that it locked it before
				the mutex object's state returns to unlocked. Since mutex objects in
				 expose locking
				functionality only through lock concepts, a thread will always unlock a
				mutex object the same number of times that it locked it. This helps to
				eliminate a whole set of errors typically found in traditional C style
				thread APIs.</p>
<p>Classes <code class="computeroutput"><a href="../recursive_mutex.html" title="Class recursive_mutex">boost::recursive_mutex</a></code>,
				<code class="computeroutput"><a href="../recursive_try_mutex.html" title="Class recursive_try_mutex">boost::recursive_try_mutex</a></code> and
				<code class="computeroutput"><a href="../recursive_timed_mutex.html" title="Class recursive_timed_mutex">boost::recursive_timed_mutex</a></code> use this locking
				strategy.</p>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.checked-locking-strategy"></a>Checked Locking Strategy</h6></div></div></div>
<p>With a checked locking strategy, when a thread attempts to acquire a
				lock on the mutex object for which the thread already owns a lock, the
				operation will fail with some sort of error indication. Further, attempts
				by a thread to unlock a mutex object that was not locked by the thread
				will also return some sort of error indication. In
				, an exception of type
				<code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code> 
				would be thrown in these cases.</p>
<p> does not currently
				provide any mutex objects that use this strategy.</p>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.unchecked-locking-strategy"></a>Unchecked Locking Strategy</h6></div></div></div>
<p>With an unchecked locking strategy, when a thread attempts to acquire
				a lock on a mutex object for which the thread already owns a lock the
				operation will
				<a href="../threads.html#threads.glossary.deadlock">deadlock</a>. In general
				this locking strategy is less safe than a checked or recursive strategy,
				but it's also a faster strategy and so is employed by many libraries.</p>
<p> does not currently
				provide any mutex objects that use this strategy.</p>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.unspecified-locking-strategy"></a>Unspecified Locking Strategy</h6></div></div></div>
<p>With an unspecified locking strategy, when a thread attempts to
				acquire a lock on a mutex object for which the thread already owns a lock
				the operation results in 
				<a href="../threads.html#threads.glossary.undefined-behavior">undefined behavior</a>.
				</p>
<p>In general a mutex object with an unspecified locking strategy is
				unsafe, and it requires programmer discipline to use the mutex object
				properly. However, this strategy allows an implementation to be as fast as
				possible with no restrictions on its implementation. This is especially
				true for portable implementations that wrap the native threading support
				of a platform. For this reason, the classes
				<code class="computeroutput"><a href="../mutex.html" title="Class mutex">boost::mutex</a></code>,
				<code class="computeroutput"><a href="../try_mutex.html" title="Class try_mutex">boost::try_mutex</a></code> and
				<code class="computeroutput"><a href="../timed_mutex.html" title="Class timed_mutex">boost::timed_mutex</a></code> use this locking strategy
				despite the lack of safety.</p>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h5 class="title">
<a name="threads.concepts.sheduling-policies"></a>Scheduling Policies</h5></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="concepts.html#threads.concepts.FIFO-scheduling-policy">FIFO Scheduling Policy</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.priority-driven-scheduling-policy">Priority Driven Policy</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.unspecified-scheduling-policy">Unspecified Policy</a></span></dt>
</dl></div>
<p>Every mutex object follows one of several scheduling policies. These
			policies define the semantics when the mutex object is unlocked and there is
			more than one thread waiting to acquire a lock. In other words, the policy
			defines which waiting thread shall acquire the lock.</p>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.FIFO-scheduling-policy"></a>FIFO Scheduling Policy</h6></div></div></div>
<p>With a FIFO ("First In First Out") scheduling policy, threads waiting 
				for the lock will acquire it in a first-come-first-served order.
				This can help prevent a high priority thread from starving lower priority
				threads that are also waiting on the mutex object's lock.</p>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.priority-driven-scheduling-policy"></a>Priority Driven Policy</h6></div></div></div>
<p>With a Priority Driven scheduling policy, the thread with the
				highest priority acquires the lock. Note that this means that low-priority
				threads may never acquire the lock if the mutex object has high contention
				and there is always at least one high-priority thread waiting. This is
				known as thread starvation. When multiple threads of the same priority are
				waiting on the mutex object's lock one of the other scheduling priorities
				will determine which thread shall acquire the lock.</p>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.unspecified-scheduling-policy"></a>Unspecified Policy</h6></div></div></div>
<p>The mutex object does not specify a scheduling policy. In order to
				ensure portability, all 
				mutex objects use an unspecified scheduling policy.</p>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h5 class="title">
<a name="threads.concepts.mutex-concepts"></a>Mutex Concepts</h5></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="concepts.html#threads.concepts.Mutex">Mutex Concept</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.TryMutex">TryMutex Concept</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.TimedMutex">TimedMutex Concept</a></span></dt>
</dl></div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.Mutex"></a>Mutex Concept</h6></div></div></div>
<p>A Mutex object has two states: locked and unlocked. Mutex object
				state can only be determined by a lock object meeting the
				appropriate lock concept requirements
				and constructed for the Mutex object.</p>
<p>A Mutex is
				<a href="../../../libs/utility/utility.htm#Class%20noncopyable" target="_top">
				NonCopyable</a>.</p>
<p>For a Mutex type <code class="computeroutput">M</code>
				and an object <code class="computeroutput">m</code> of that type, 
				the following expressions must be well-formed
				and have the indicated effects.</p>
<div class="table">
<a name="id1358355"></a><p class="title"><b>Table 12.1. Mutex Expressions</b></p>
<table class="table" summary="Mutex Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody>
<tr>
<td>M m;</td>
<td>
<p>Constructs a mutex object m.</p>
<p>Postcondition: m is unlocked.</p>
</td>
</tr>
<tr>
<td>(&amp;m)-&gt;~M();</td>
<td>Precondition: m is unlocked. Destroys a mutex object
								m.</td>
</tr>
<tr>
<td>M::scoped_lock</td>
<td>A model of
								<a href="concepts.html#threads.concepts.ScopedLock" title="ScopedLock Concept">ScopedLock</a>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.TryMutex"></a>TryMutex Concept</h6></div></div></div>
<p>A TryMutex is a refinement of
				<a href="concepts.html#threads.concepts.Mutex" title="Mutex Concept">Mutex</a>. 
				For a TryMutex type <code class="computeroutput">M</code>
				and an object <code class="computeroutput">m</code> of that type, 
				the following expressions must be well-formed 
				and have the indicated effects.</p>
<div class="table">
<a name="id1358432"></a><p class="title"><b>Table 12.2. TryMutex Expressions</b></p>
<table class="table" summary="TryMutex Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody><tr>
<td>M::scoped_try_lock</td>
<td>A model of
								<a href="concepts.html#threads.concepts.ScopedTryLock" title="ScopedTryLock Concept">ScopedTryLock</a>
</td>
</tr></tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.TimedMutex"></a>TimedMutex Concept</h6></div></div></div>
<p>A TimedMutex is a refinement of
				<a href="concepts.html#threads.concepts.TryMutex" title="TryMutex Concept">TryMutex</a>. 
				For a TimedMutex type <code class="computeroutput">M</code>
				and an object <code class="computeroutput">m</code> of that type, 
				the following expressions must be well-formed
				and have the indicated effects.</p>
<div class="table">
<a name="id1358492"></a><p class="title"><b>Table 12.3. TimedMutex Expressions</b></p>
<table class="table" summary="TimedMutex Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody><tr>
<td>M::scoped_timed_lock</td>
<td>A model of
								<a href="concepts.html#threads.concepts.ScopedTimedLock" title="ScopedTimedLock Concept">ScopedTimedLock</a>
</td>
</tr></tbody>
</table>
</div>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h5 class="title">
<a name="threads.concepts.mutex-models"></a>Mutex Models</h5></div></div></div>
<p> currently supplies six models of
			<a href="concepts.html#threads.concepts.Mutex" title="Mutex Concept">Mutex</a>
			and its refinements.</p>
<div class="table">
<a name="id1358540"></a><p class="title"><b>Table 12.4. Mutex Models</b></p>
<table class="table" summary="Mutex Models">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Concept</th>
<th>Refines</th>
<th>Models</th>
</tr></thead>
<tbody>
<tr>
<td><a href="concepts.html#threads.concepts.Mutex" title="Mutex Concept">Mutex</a></td>
<td> </td>
<td>
<p><code class="computeroutput"><a href="../mutex.html" title="Class mutex">boost::mutex</a></code></p>
<p><code class="computeroutput"><a href="../recursive_mutex.html" title="Class recursive_mutex">boost::recursive_mutex</a></code></p>
</td>
</tr>
<tr>
<td><a href="concepts.html#threads.concepts.TryMutex" title="TryMutex Concept">TryMutex</a></td>
<td><a href="concepts.html#threads.concepts.Mutex" title="Mutex Concept">Mutex</a></td>
<td>
<p><code class="computeroutput"><a href="../try_mutex.html" title="Class try_mutex">boost::try_mutex</a></code></p>
<p><code class="computeroutput"><a href="../recursive_try_mutex.html" title="Class recursive_try_mutex">boost::recursive_try_mutex</a></code></p>
</td>
</tr>
<tr>
<td><a href="concepts.html#threads.concepts.TimedMutex" title="TimedMutex Concept">TimedMutex</a></td>
<td><a href="concepts.html#threads.concepts.TryMutex" title="TryMutex Concept">TryMutex</a></td>
<td>
<p><code class="computeroutput"><a href="../timed_mutex.html" title="Class timed_mutex">boost::timed_mutex</a></code></p>
<p><code class="computeroutput"><a href="../recursive_timed_mutex.html" title="Class recursive_timed_mutex">boost::recursive_timed_mutex</a></code></p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h5 class="title">
<a name="threads.concepts.lock-concepts"></a>Lock Concepts</h5></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="concepts.html#threads.concepts.Lock">Lock Concept</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.ScopedLock">ScopedLock Concept</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.TryLock">TryLock Concept</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.ScopedTryLock">ScopedTryLock Concept</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.TimedLock">TimedLock Concept</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.ScopedTimedLock">ScopedTimedLock Concept</a></span></dt>
</dl></div>
<p>A lock object provides a safe means for locking and unlocking a mutex
			object (an object whose type is a model of <a href="concepts.html#threads.concepts.Mutex" title="Mutex Concept">Mutex</a> or one of its refinements). In
			other words they are an implementation of the <span class="emphasis"><em>Scoped
			Locking</em></span> pattern. The <a href="concepts.html#threads.concepts.ScopedLock" title="ScopedLock Concept">ScopedLock</a>,
			<a href="concepts.html#threads.concepts.ScopedTryLock" title="ScopedTryLock Concept">ScopedTryLock</a>, and 
			<a href="concepts.html#threads.concepts.ScopedTimedLock" title="ScopedTimedLock Concept">ScopedTimedLock</a>
			concepts formalize the requirements.</p>
<p>Lock objects are constructed with a reference to a mutex object and
			typically acquire ownership of the mutex object by setting its state to
			locked. They also ensure ownership is relinquished in the destructor. Lock
			objects also expose functions to query the lock status and to manually lock
			and unlock the mutex object.</p>
<p>Lock objects are meant to be short lived, expected to be used at block
			scope only. The lock objects are not <a href="../threads.html#threads.glossary.thread-safe">thread-safe</a>. Lock objects must
			maintain state to indicate whether or not they've been locked and this state
			is not protected by any synchronization concepts. For this reason a lock
			object should never be shared between multiple threads.</p>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.Lock"></a>Lock Concept</h6></div></div></div>
<p>For a Lock type <code class="computeroutput">L</code> 
				and an object <code class="computeroutput">lk</code> 
				and const object <code class="computeroutput">clk</code> of that type, 
				the following expressions must be well-formed
				and have the indicated effects.</p>
<div class="table">
<a name="id1358762"></a><p class="title"><b>Table 12.5. Lock Expressions</b></p>
<table class="table" summary="Lock Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody>
<tr>
<td><code class="computeroutput">(&amp;lk)-&gt;~L();</code></td>
<td><code class="computeroutput">if (locked()) unlock();</code></td>
</tr>
<tr>
<td><code class="computeroutput">(&amp;clk)-&gt;operator const void*()</code></td>
<td>Returns type void*, non-zero if the associated mutex
								object has been locked by <code class="computeroutput">clk</code>, otherwise 0.</td>
</tr>
<tr>
<td><code class="computeroutput">clk.locked()</code></td>
<td>Returns a <code class="computeroutput">bool</code>, <code class="computeroutput">(&amp;clk)-&gt;operator
								const void*() != 0</code>
</td>
</tr>
<tr>
<td><code class="computeroutput">lk.lock()</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
									if <code class="computeroutput">locked()</code>.</p>
<p>If the associated mutex object is
									already locked by some other thread, places the current thread in the 
									<a href="../threads.html#threads.glossary.thread-state">Blocked</a> state until
									the associated mutex is unlocked, after which the current thread
									is placed in the <a href="../threads.html#threads.glossary.thread-state">Ready</a> state,
									eventually to be returned to the <a href="../threads.html#threads.glossary.thread-state">Running</a> state. If
									the associated mutex object is already locked by the same thread
									the behavior is dependent on the <a href="concepts.html#threads.concepts.locking-strategies" title="Locking Strategies">locking
									strategy</a> of the associated mutex object.</p>
<p>Postcondition: <code class="computeroutput">locked() == true</code></p>
</td>
</tr>
<tr>
<td><code class="computeroutput">lk.unlock()</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
									if <code class="computeroutput">!locked()</code>.</p>
<p>Unlocks the associated mutex.</p>
<p>Postcondition: <code class="computeroutput">!locked()</code></p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.ScopedLock"></a>ScopedLock Concept</h6></div></div></div>
<p>A ScopedLock is a refinement of <a href="concepts.html#threads.concepts.Lock" title="Lock Concept">Lock</a>. 
				For a ScopedLock type <code class="computeroutput">L</code> 
				and an object <code class="computeroutput">lk</code> of that type, 
				and an object <code class="computeroutput">m</code> of a type meeting the 
				<a href="concepts.html#threads.concepts.Mutex" title="Mutex Concept">Mutex</a> requirements, 
				and an object <code class="computeroutput">b</code> of type <code class="computeroutput">bool</code>, 
				the following expressions must be well-formed 
				and have the indicated effects.</p>
<div class="table">
<a name="id1358999"></a><p class="title"><b>Table 12.6. ScopedLock Expressions</b></p>
<table class="table" summary="ScopedLock Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody>
<tr>
<td><code class="computeroutput">L lk(m);</code></td>
<td>Constructs an object <code class="computeroutput">lk</code>, and associates mutex
								object <code class="computeroutput">m</code> with it, then calls
								<code class="computeroutput">lock()</code>
</td>
</tr>
<tr>
<td><code class="computeroutput">L lk(m,b);</code></td>
<td>Constructs an object <code class="computeroutput">lk</code>, and associates mutex
								object <code class="computeroutput">m</code> with it, then if <code class="computeroutput">b</code>, calls
								<code class="computeroutput">lock()</code>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.TryLock"></a>TryLock Concept</h6></div></div></div>
<p>A TryLock is a refinement of <a href="concepts.html#threads.concepts.Lock" title="Lock Concept">Lock</a>. 
				For a TryLock type <code class="computeroutput">L</code> 
				and an object <code class="computeroutput">lk</code> of that type, 
				the following expressions must be well-formed 
				and have the indicated effects.</p>
<div class="table">
<a name="id1359102"></a><p class="title"><b>Table 12.7. TryLock Expressions</b></p>
<table class="table" summary="TryLock Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody><tr>
<td><code class="computeroutput">lk.try_lock()</code></td>
<td>
<p>Throws  <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
									if locked().</p>
<p>Makes a
									non-blocking attempt to lock the associated mutex object,
									returning <code class="computeroutput">true</code> if the lock attempt is successful,
									otherwise <code class="computeroutput">false</code>. If the associated mutex object is
									already locked by the same thread the behavior is dependent on the
									<a href="concepts.html#threads.concepts.locking-strategies" title="Locking Strategies">locking
									strategy</a> of the associated mutex object.</p>
</td>
</tr></tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.ScopedTryLock"></a>ScopedTryLock Concept</h6></div></div></div>
<p>A ScopedTryLock is a refinement of <a href="concepts.html#threads.concepts.TryLock" title="TryLock Concept">TryLock</a>. 
				For a ScopedTryLock type <code class="computeroutput">L</code> 
				and an object <code class="computeroutput">lk</code> of that type, 
				and an object <code class="computeroutput">m</code> of a type meeting the 
				<a href="concepts.html#threads.concepts.TryMutex" title="TryMutex Concept">TryMutex</a> requirements, 
				and an object <code class="computeroutput">b</code> of type <code class="computeroutput">bool</code>, 
				the following expressions must be well-formed 
				and have the indicated effects.</p>
<div class="table">
<a name="id1359223"></a><p class="title"><b>Table 12.8. ScopedTryLock Expressions</b></p>
<table class="table" summary="ScopedTryLock Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody>
<tr>
<td><code class="computeroutput">L lk(m);</code></td>
<td>Constructs an object <code class="computeroutput">lk</code>, and associates mutex
								object <code class="computeroutput">m</code> with it, then calls
								<code class="computeroutput">try_lock()</code>
</td>
</tr>
<tr>
<td><code class="computeroutput">L lk(m,b);</code></td>
<td>Constructs an object <code class="computeroutput">lk</code>, and associates mutex
								object <code class="computeroutput">m</code> with it, then if <code class="computeroutput">b</code>, calls
								<code class="computeroutput">lock()</code>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.TimedLock"></a>TimedLock Concept</h6></div></div></div>
<p>A TimedLock is a refinement of <a href="concepts.html#threads.concepts.TryLock" title="TryLock Concept">TryLock</a>. 
				For a TimedLock type <code class="computeroutput">L</code> 
				and an object <code class="computeroutput">lk</code> of that type, 
				and an object <code class="computeroutput">t</code> of type <code class="computeroutput"><a href="../xtime.html" title="Struct xtime">boost::xtime</a></code>, 
				the following expressions must be well-formed 
				and have the indicated effects.</p>
<div class="table">
<a name="id1359344"></a><p class="title"><b>Table 12.9. TimedLock Expressions</b></p>
<table class="table" summary="TimedLock Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody><tr>
<td><code class="computeroutput">lk.timed_lock(t)</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
									if locked().</p>
<p>Makes a blocking attempt
									to lock the associated mutex object, and returns <code class="computeroutput">true</code>
									if successful within the specified time <code class="computeroutput">t</code>, otherwise
									<code class="computeroutput">false</code>. If the associated mutex object is already
									locked by the same thread the behavior is dependent on the <a href="concepts.html#threads.concepts.locking-strategies" title="Locking Strategies">locking
									strategy</a> of the associated mutex object.</p>
</td>
</tr></tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.ScopedTimedLock"></a>ScopedTimedLock Concept</h6></div></div></div>
<p>A ScopedTimedLock is a refinement of <a href="concepts.html#threads.concepts.TimedLock" title="TimedLock Concept">TimedLock</a>. 
				For a ScopedTimedLock type <code class="computeroutput">L</code> 
				and an object <code class="computeroutput">lk</code> of that type, 
				and an object <code class="computeroutput">m</code> of a type meeting the 
				<a href="concepts.html#threads.concepts.TimedMutex" title="TimedMutex Concept">TimedMutex</a> requirements, 
				and an object <code class="computeroutput">b</code> of type <code class="computeroutput">bool</code>, 
				and an object <code class="computeroutput">t</code> of type <code class="computeroutput"><a href="../xtime.html" title="Struct xtime">boost::xtime</a></code>, 
				the following expressions must be well-formed 
				and have the indicated effects.</p>
<div class="table">
<a name="id1359488"></a><p class="title"><b>Table 12.10. ScopedTimedLock Expressions</b></p>
<table class="table" summary="ScopedTimedLock Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody>
<tr>
<td><code class="computeroutput">L lk(m,t);</code></td>
<td>Constructs an object <code class="computeroutput">lk</code>, and associates mutex
								object <code class="computeroutput">m</code> with it, then calls
								<code class="computeroutput">timed_lock(t)</code>
</td>
</tr>
<tr>
<td><code class="computeroutput">L lk(m,b);</code></td>
<td>Constructs an object <code class="computeroutput">lk</code>, and associates mutex
								object <code class="computeroutput">m</code> with it, then if <code class="computeroutput">b</code>, calls
								<code class="computeroutput">lock()</code>
</td>
</tr>
</tbody>
</table>
</div>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h5 class="title">
<a name="threads.concepts.lock-models"></a>Lock Models</h5></div></div></div>
<p> currently supplies twelve models of
			<a href="concepts.html#threads.concepts.Lock" title="Lock Concept">Lock</a>
			and its refinements.</p>
<div class="table">
<a name="id1359578"></a><p class="title"><b>Table 12.11. Lock Models</b></p>
<table class="table" summary="Lock Models">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Concept</th>
<th>Refines</th>
<th>Models</th>
</tr></thead>
<tbody>
<tr>
<td><a href="concepts.html#threads.concepts.Lock" title="Lock Concept">Lock</a></td>
<td> </td>
<td> </td>
</tr>
<tr>
<td><a href="concepts.html#threads.concepts.ScopedLock" title="ScopedLock Concept">ScopedLock</a></td>
<td><a href="concepts.html#threads.concepts.Lock" title="Lock Concept">Lock</a></td>
<td>
<p><code class="computeroutput">boost::mutex::scoped_lock</code></p>
<p><code class="computeroutput">boost::recursive_mutex::scoped_lock</code></p>
<p><code class="computeroutput">boost::try_mutex::scoped_lock</code></p>
<p><code class="computeroutput">boost::recursive_try_mutex::scoped_lock</code></p>
<p><code class="computeroutput">boost::timed_mutex::scoped_lock</code></p>
<p><code class="computeroutput">boost::recursive_timed_mutex::scoped_lock</code></p>
</td>
</tr>
<tr>
<td><a href="concepts.html#threads.concepts.TryLock" title="TryLock Concept">TryLock</a></td>
<td><a href="concepts.html#threads.concepts.Lock" title="Lock Concept">Lock</a></td>
<td> </td>
</tr>
<tr>
<td><a href="concepts.html#threads.concepts.ScopedTryLock" title="ScopedTryLock Concept">ScopedTryLock</a></td>
<td><a href="concepts.html#threads.concepts.TryLock" title="TryLock Concept">TryLock</a></td>
<td>
<p><code class="computeroutput">boost::try_mutex::scoped_try_lock</code></p>
<p><code class="computeroutput">boost::recursive_try_mutex::scoped_try_lock</code></p>
<p><code class="computeroutput">boost::timed_mutex::scoped_try_lock</code></p>
<p><code class="computeroutput">boost::recursive_timed_mutex::scoped_try_lock</code></p>
</td>
</tr>
<tr>
<td><a href="concepts.html#threads.concepts.TimedLock" title="TimedLock Concept">TimedLock</a></td>
<td><a href="concepts.html#threads.concepts.TryLock" title="TryLock Concept">TryLock</a></td>
<td> </td>
</tr>
<tr>
<td><a href="concepts.html#threads.concepts.ScopedTimedLock" title="ScopedTimedLock Concept">ScopedTimedLock</a></td>
<td><a href="concepts.html#threads.concepts.TimedLock" title="TimedLock Concept">TimedLock</a></td>
<td>
<p><code class="computeroutput">boost::timed_mutex::scoped_timed_lock</code></p>
<p><code class="computeroutput">boost::recursive_timed_mutex::scoped_timed_lock</code></p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="threads.concepts.read-write-mutexes"></a>Read/Write Mutexes</h4></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-locking-strategies">Locking Strategies</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-scheduling-policies">Scheduling Policies</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-mutex-concepts">Mutex Concepts</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-mutex-models">Mutex Models</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-lock-concepts">Lock Concepts</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-lock-models">Lock Models</a></span></dt>
</dl></div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>Since the read/write mutex and related classes are new,
		both interface and implementation are liable to change
		in future releases of .
		The lock concepts and lock promotion and demotion in particular 
		are still under discussion and very likely to change.</div>
<p>A read/write mutex (short for reader/writer mutual-exclusion) object
		is used to serialize access to a resource shared between multiple 
		threads, where multiple "readers" can share simultaneous access, but 
		"writers" require exclusive access. The
		<a href="concepts.html#threads.concepts.ReadWriteMutex" title="ReadWriteMutex Concept">ReadWriteMutex</a> concept, with 
		<a href="concepts.html#threads.concepts.TryReadWriteMutex" title="TryReadWriteMutex Concept">TryReadWriteMutex</a> and 
		<a href="concepts.html#threads.concepts.TimedReadWriteMutex" title="TimedReadWriteMutex Concept"> TimedReadWriteMutex</a>
		refinements formalize the requirements. A model that implements 
		ReadWriteMutex and its refinements has three states: 
		<span class="bold"><strong>read-locked</strong></span>,
		<span class="bold"><strong>write-locked</strong></span>, and 
		<span class="bold"><strong>unlocked</strong></span>.
		Before reading from a shared resource, a thread 
		<span class="bold"><strong>read-locks</strong></span> 
		a  read/write mutex object
		(an object whose type is a model of
		<a href="concepts.html#threads.concepts.ReadWriteMutex" title="ReadWriteMutex Concept">ReadWriteMutex</a>
		or one of it's refinements), ensuring 
		<a href="../threads.html#threads.glossary.thread-safe">thread-safe</a>
		access for reading from the shared resource. Before writing 
		to a shared resource, a thread 
		<span class="bold"><strong>write-locks</strong></span> a  
		read/write mutex object
		(an object whose type is a model of
		<a href="concepts.html#threads.concepts.ReadWriteMutex" title="ReadWriteMutex Concept">ReadWriteMutex</a>
		or one of it's refinements), ensuring 
		<a href="../threads.html#threads.glossary.thread-safe">thread-safe</a>
		access for altering the shared resource. When use of the shared 
		resource is complete, the thread unlocks the mutex object, 
		allowing another thread to acquire the lock and use the shared 
		resource.</p>
<p>Traditional C thread APIs that provide read/write mutex
		primitives (like POSIX threads) expose functions to lock and unlock a
		mutex object. This is dangerous since it's easy to forget to unlock a
		locked mutex. When the flow of control is complex, with multiple
		return points, the likelihood of forgetting to unlock a mutex object
		becomes even greater. When exceptions are thrown, it becomes nearly
		impossible to ensure that the mutex object is unlocked
		properly when using these traditional API's. The result is
		<a href="../threads.html#threads.glossary.deadlock">deadlock</a>.</p>
<p>Many C++ threading libraries use a pattern known as <span class="emphasis"><em>Scoped
		Locking</em></span> to free the
		programmer from the need to explicitly lock and unlock
		read/write mutex objects. With this  pattern, a 
		<a href="concepts.html#threads.concepts.read-write-lock-concepts" title="Lock Concepts">Read/Write Lock</a>
		concept is employed where the lock object's constructor locks
		the associated read/write mutex object
		and the destructor automatically does the unlocking. The
		 library takes this pattern to
		the extreme in that 
		<a href="concepts.html#threads.concepts.read-write-lock-concepts" title="Lock Concepts">Read/Write Lock</a>
		concepts are the only way to lock and unlock a read/write mutex
		object: lock and unlock functions are not exposed by any
		 read/write mutex objects. This helps to
		ensure safe usage patterns, especially when code throws exceptions.</p>
<div class="section" lang="en">
<div class="titlepage"><div><div><h5 class="title">
<a name="threads.concepts.read-write-locking-strategies"></a>Locking Strategies</h5></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-locking-strategies.recursive">Recursive Locking Strategy</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-locking-strategies.checked">Checked Locking Strategy</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-locking-strategies.unchecked">Unchecked Locking Strategy</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-locking-strategies.unspecified">Unspecified Locking Strategy</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-locking-strategies.thread-identification">Thread Identification</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-locking-strategies.promotion">Lock Promotion</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-locking-strategies.demotion">Lock Demotion</a></span></dt>
</dl></div>
<p>Every read/write mutex object follows one of several locking
			strategies. These strategies define the semantics for the locking
			operation when the calling thread already owns a lock on the 
			read/write mutex object.</p>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.read-write-locking-strategies.recursive"></a>Recursive Locking Strategy</h6></div></div></div>
<p>With a recursive locking strategy, when a thread attempts
				to acquire a lock on a read/write mutex object
				for which it already owns a lock, the operation is successful,
				except in the case where a thread holding a read-lock 
				attempts to obtain a write lock, in which case a
				<code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code> exception will
				be thrown. Note the distinction between a thread, which may have
				multiple locks outstanding on a recursive read/write mutex object,
				and a lock object, which even for a recursive read/write mutex
				object cannot have any of its lock functions called multiple
				times without first calling unlock.</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Lock Type Held</th>
<th>Lock Type Requested</th>
<th>Action</th>
</tr></thead>
<tbody>
<tr>
<td>read-lock</td>
<td>read-lock</td>
<td>Grant the read-lock immediately</td>
</tr>
<tr>
<td>read-lock</td>
<td>write-lock</td>
<td>If this thread is the only holder of the read-lock,
								grants the write lock immediately. Otherwise throws a
								<code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code> exception.</td>
</tr>
<tr>
<td>write-locked</td>
<td>read-lock</td>
<td>Grants the (additional) read-lock immediately.</td>
</tr>
<tr>
<td>write-locked</td>
<td>write-lock</td>
<td> Grant the write-lock immediately</td>
</tr>
</tbody>
</table></div>
<p>Internally a lock count is maintained and the owning
				thread must unlock the mutex object the same number of times
				that it locked it before the mutex object's state returns
				to unlocked. Since mutex objects in  expose
				locking functionality only through lock concepts, a thread
				will always unlock a mutex object the same number of times
				that it locked it. This helps to eliminate a whole set of
				errors typically found in traditional C style thread APIs.
				</p>
<p> does not currently provide any read/write mutex objects 
				that use this strategy.  A successful implementation of this locking strategy
				may require
				<a href="concepts.html#threads.concepts.read-write-locking-strategies.thread-identification" title="Thread Identification">thread identification</a>.
				</p>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.read-write-locking-strategies.checked"></a>Checked Locking Strategy</h6></div></div></div>
<p>With a checked locking strategy, when a thread attempts
				to acquire a lock on the mutex object for which the thread
				already owns a lock, the operation will fail with some sort of
				error indication, except in the case of multiple read-lock 
				acquisition which is a normal operation for ANY ReadWriteMutex.
				Further, attempts by a thread to unlock a mutex that was not
				locked by the thread will also return some sort of error
				indication. In , an exception of type 
				<code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code> would be thrown in
				these cases.</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Lock Type Held</th>
<th>Lock Type Requested</th>
<th>Action</th>
</tr></thead>
<tbody>
<tr>
<td>read-lock</td>
<td>read-lock</td>
<td>Grant the read-lock immediately</td>
</tr>
<tr>
<td>read-lock</td>
<td>write-lock</td>
<td>Throw <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
</td>
</tr>
<tr>
<td>write-locked</td>
<td>read-lock</td>
<td>Throw <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
</td>
</tr>
<tr>
<td>write-locked</td>
<td>write-lock</td>
<td> Throw <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
</td>
</tr>
</tbody>
</table></div>
<p> does not currently provide any read/write mutex objects 
				that use this strategy.  A successful implementation of this locking strategy
				may require
				<a href="concepts.html#threads.concepts.read-write-locking-strategies.thread-identification" title="Thread Identification">thread identification</a>.
				</p>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.read-write-locking-strategies.unchecked"></a>Unchecked Locking Strategy</h6></div></div></div>
<p>With an unchecked locking strategy, when a thread
				attempts to acquire a lock on the read/write mutex object
				for which the thread already owns a lock, the operation 
				will <a href="../threads.html#threads.glossary.deadlock">deadlock</a>.
				In general this locking strategy is less safe than a checked
				or recursive strategy, but it can be a faster strategy and so
				is employed by many libraries.</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Lock Type Held</th>
<th>Lock Type Requested</th>
<th>Action</th>
</tr></thead>
<tbody>
<tr>
<td>read-lock</td>
<td>read-lock</td>
<td>Grant the read-lock immediately</td>
</tr>
<tr>
<td>read-lock</td>
<td>write-lock</td>
<td><a href="../threads.html#threads.glossary.deadlock">Deadlock</a></td>
</tr>
<tr>
<td>write-locked</td>
<td>read-lock</td>
<td><a href="../threads.html#threads.glossary.deadlock">Deadlock</a></td>
</tr>
<tr>
<td>write-locked</td>
<td>write-lock</td>
<td><a href="../threads.html#threads.glossary.deadlock">Deadlock</a></td>
</tr>
</tbody>
</table></div>
<p> does not currently provide any mutex
				objects that use this strategy.  For ReadWriteMutexes on
				platforms that contain natively recursive synchronization
				primitives, implementing a guaranteed-deadlock can actually
				involve extra work, and would likely require 
				<a href="concepts.html#threads.concepts.read-write-locking-strategies.thread-identification" title="Thread Identification">thread identification</a>.
				</p>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.read-write-locking-strategies.unspecified"></a>Unspecified Locking Strategy</h6></div></div></div>
<p>With an unspecified locking strategy, when a thread
				attempts to acquire a lock on a read/write mutex object for
				which the thread already owns a lock, the operation results 
				in <a href="../threads.html#threads.glossary.undefined-behavior">undefined behavior</a>.
				When a read/write mutex object has an unspecified locking 
				strategy the programmer must assume that the read/write mutex
				object instead uses an unchecked strategy as the worse case,
				although some platforms may exhibit a mix of unchecked and
				recursive behavior.</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Lock Type Held</th>
<th>Lock Type Requested</th>
<th>Action</th>
</tr></thead>
<tbody>
<tr>
<td>read-lock</td>
<td>read-lock</td>
<td>Grant the read-lock immediately</td>
</tr>
<tr>
<td>read-lock</td>
<td>write-lock</td>
<td>
<a href="../threads.html#threads.glossary.undefined-behavior">Undefined</a>, but generally <a href="../threads.html#threads.glossary.deadlock">deadlock</a>
</td>
</tr>
<tr>
<td>write-locked</td>
<td>read-lock</td>
<td>
<a href="../threads.html#threads.glossary.undefined-behavior">Undefined</a>, but generally <a href="../threads.html#threads.glossary.deadlock">deadlock</a>
</td>
</tr>
<tr>
<td>write-locked</td>
<td>write-lock</td>
<td>
<a href="../threads.html#threads.glossary.undefined-behavior">Undefined</a>, but generally <a href="../threads.html#threads.glossary.deadlock">deadlock</a>
</td>
</tr>
</tbody>
</table></div>
<p>In general a read/write mutex object with an unspecified
				locking strategy is unsafe, and it requires programmer discipline
				to use the read/write mutex object properly. However, this strategy
				allows an implementation to be as fast as possible with no restrictions 
				on its implementation. This is especially true for portable implementations
				that wrap the native threading support of a platform. For this reason, the
				classes 
				<code class="computeroutput">read_write_mutex</code>,
				<code class="computeroutput">try_read_write_mutex</code>, and
				<code class="computeroutput">timed_read_write_mutex</code>
				use this locking strategy despite the lack of safety.</p>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.read-write-locking-strategies.thread-identification"></a>Thread Identification</h6></div></div></div>
<p>ReadWriteMutexes can support specific Locking Strategies 
				(recursive and checked) which help to detect and protect against
				self-deadlock.  Self-deadlock can occur when a holder of a locked
				ReadWriteMutex attempts to obtain another lock.  Given an
				implemention <span class="emphasis"><em>I</em></span> which is susceptible to
				self-deadlock but otherwise correct and efficient, a recursive or
				checked implementation <span class="emphasis"><em>Ir</em></span> or 
				<span class="emphasis"><em>Ic</em></span> can use the same basic implementation,
				but make special checks against self-deadlock by tracking the
				identities of thread(s) currently holding locks.  This approach 
				makes deadlock detection othrogonal to the basic ReadWriteMutex
				implementaion.</p>
<p>Alternatively, a different basic implementation for 
				ReadWriteMutex concepts, 
				<span class="emphasis"><em>I'</em></span> (I-Prime) may exist which uses recursive
				or checked versions of synchronization primitives to produce
				a recursive or checked ReadWriteMutex while still providing
				flexibility in terms of Scheduling Policies. </p>
<p>Please refer to the <a href="concepts.html#threads.concepts.read-write-mutex-concepts" title="Mutex Concepts">read/write mutex concept</a> 
				documentation for a discussion of locking strategies.
				The read/write mutex supports only the
				<a href="concepts.html#threads.concepts.read-write-locking-strategies.unspecified" title="Unspecified Locking Strategy">unspecified</a>
				locking strategy. ReadWriteMutexes are parameterized on a
				Mutex type which they use to control write-locking 
				and access to internal state.</p>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.read-write-locking-strategies.promotion"></a>Lock Promotion</h6></div></div></div>
<p>ReadWriteMutexes can support lock promotion, where a
				mutex which is in the read-locked state transitions to a
				write-locked state without releasing the lock. Lock
				promotion can be tricky to implement; for instance,
				extra care must be taken to ensure that only one thread holding a
				read-lock can block awaiting promotion at any given time.  If
				more than one read-lock holder is allowed to enter a blocked
				state while waiting to be promoted, deadlock will result since
				both threads will be waiting for the other to release their read-lock.
				</p>
<p>Currently,  supports lock promotion
				through <code class="computeroutput">promote()</code>, <code class="computeroutput">try_promote()</code>,
				and <code class="computeroutput">timed_promote()</code> operations.</p>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.read-write-locking-strategies.demotion"></a>Lock Demotion</h6></div></div></div>
<p>ReadWriteMutexes can support lock demotion, where a
				mutex which is in the write-locked state transitions to a
				read-locked state without releasing the lock.
				Since by definition only one thread at a time may hold
				a write-lock, the problem with deadlock that can occur
				during lock promotion is not a problem for lock
				demotion.</p>
<p>Currently,  supports lock demotion
				through <code class="computeroutput">demote()</code>, <code class="computeroutput">try_demote()</code>,
				and <code class="computeroutput">timed_demote()</code> operations.</p>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h5 class="title">
<a name="threads.concepts.read-write-scheduling-policies"></a>Scheduling Policies</h5></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-scheduling-policies.inter-class">Inter-Class Scheduling Policies</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.read-write-scheduling-policies.intra-class">Intra-Class Scheduling Policies</a></span></dt>
</dl></div>
<p>Every read/write mutex object follows one of several scheduling
			policies. These policies define the semantics when the mutex object
			is unlocked and there is more than one thread waiting to acquire a
			lock. In other words, the policy defines which waiting thread shall
			acquire the lock. For a read/write mutex, it is particularly important
			to define the behavior when threads are requesting both read and
			write access simultaneously. This will be referred to as "inter-class 
			scheduling" because it describes the scheduling between two
			classes of threads (those waiting for a read lock and those
			waiting for a write lock).</p>
<p>For some types of inter-class scheduling, an "intra-class"
			scheduling policy can also be defined that will describe the order
			in which waiting threads of the same class (i.e., those
			waiting for the same type of lock) will acquire the thread.
			</p>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.read-write-scheduling-policies.inter-class"></a>Inter-Class Scheduling Policies</h6></div></div></div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.read-write-scheduling-policies.reader-priority"></a>ReaderPriority</h6></div></div></div>
<p>With ReaderPriority scheduling, any pending request for
					a read-lock will have priority over a pending request for a
					write-lock, irrespective of the current lock state of the 
					read/write mutex, and irrespective of the relative order
					that the pending requests arrive.</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Current mutex state</th>
<th>Request Type</th>
<th>Action</th>
</tr></thead>
<tbody>
<tr>
<td>unlocked</td>
<td>read-lock</td>
<td>Grant the read-lock immediately</td>
</tr>
<tr>
<td>read-locked</td>
<td>read-lock</td>
<td>Grant the additional read-lock immediately.</td>
</tr>
<tr>
<td>write-locked</td>
<td>read-lock</td>
<td>Wait to acquire the lock until the thread
									holding the write-lock releases its lock (or until
									the specified time, if any). A
									read-lock will be granted to all pending readers 
									before any other thread can acquire a write-lock.
									<p>TODO: try-lock, timed-lock.</p>
</td>
</tr>
<tr>
<td>unlocked</td>
<td>write-lock</td>
<td>Grant the write-lock immediately, if and
									only if there are no pending read-lock requests.
									<p>TODO: try-lock, timed-lock.</p>
</td>
</tr>
<tr>
<td>read-locked</td>
<td>write-lock</td>
<td> Wait to acquire the lock until all
									threads holding read-locks release their locks 
									<span class="bold"><strong>AND</strong></span> no requests
									for read-locks exist. If other write-lock
									requests exist, the lock is granted in accordance
									with the intra-class scheduling policy.
									<p>TODO: try-lock, timed-lock.</p>
</td>
</tr>
<tr>
<td>write-locked</td>
<td>write-lock</td>
<td>Wait to acquire the lock until the thread
									holding the write-lock releases its lock
									<span class="bold"><strong>AND</strong></span> no requests
									for read-locks exist. If other write-lock
									requests exist, the lock is granted in accordance
									with the intra-class scheduling policy.
									<p>TODO: try-lock, timed-lock.</p>
</td>
</tr>
<tr>
<td>read-locked</td>
<td>promote</td>
<td><p>TODO</p></td>
</tr>
<tr>
<td>write-locked</td>
<td>demote</td>
<td><p>TODO</p></td>
</tr>
</tbody>
</table></div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.read-write-scheduling-policies.writer-priority"></a>WriterPriority</h6></div></div></div>
<p>With WriterPriority scheduling, any pending request
					for a write-lock will have priority over a pending request
					for a read-lock, irrespective of the current lock state 
					of the read/write mutex, and irrespective of the relative
					order that the pending requests arrive.</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Current mutex state</th>
<th>Request Type</th>
<th>Action</th>
</tr></thead>
<tbody>
<tr>
<td>unlocked</td>
<td>read-lock</td>
<td>Grant the read-lock immediately.</td>
</tr>
<tr>
<td>read-locked</td>
<td>read-lock</td>
<td>Grant the additional read-lock immediately, 
									<span class="bold"><strong>IF</strong></span> no outstanding
									requests for a write-lock exist; otherwise TODO.
									<p>TODO: try-lock, timed-lock.</p>
</td>
</tr>
<tr>
<td>write-locked</td>
<td>read-lock</td>
<td> Wait to acquire the lock until the
									thread holding the write-lock 
									releases its lock. The read lock will be granted
									once no other outstanding write-lock requests
									exist.
									<p>TODO: try-lock, timed-lock.</p>
</td>
</tr>
<tr>
<td>unlocked</td>
<td>write-lock</td>
<td>Grant the write-lock immediately.</td>
</tr>
<tr>
<td>read-locked</td>
<td>write-lock</td>
<td>Wait to acquire the lock until all
									threads holding read-locks release their locks.
									If other write-lock requests exist, the lock
									is granted in accordance with the intra-class
									scheduling policy. This request will be granted
									before any new read-lock requests are granted.
									<p>TODO: try-lock, timed-lock.</p>
</td>
</tr>
<tr>
<td>write-locked</td>
<td>write-lock</td>
<td>Wait to acquire the lock until the thread
									holding the write-lock releases its lock. If
									other write-lock requests exist, the lock is
									granted in accordance with the intra-class
									scheduling policy. This request will be granted
									before any new read-lock requests are granted.
									<p>TODO: try-lock, timed-lock.</p>
</td>
</tr>
<tr>
<td>read-locked</td>
<td>promote</td>
<td><p>TODO</p></td>
</tr>
<tr>
<td>write-locked</td>
<td>demote</td>
<td><p>TODO</p></td>
</tr>
</tbody>
</table></div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.read-write-scheduling-policies.alternating-many-reads"></a>AlternatingPriority/ManyReads</h6></div></div></div>
<p>With AlternatingPriority/ManyReads scheduling, reader
					or writer starvation is avoided by alternatively granting read
					or write access when pending requests exist for both types of
					locks. Outstanding read-lock requests are treated as a group
					when it is the "readers' turn"</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Current mutex state</th>
<th>Request Type</th>
<th>Action</th>
</tr></thead>
<tbody>
<tr>
<td>unlocked</td>
<td>read-lock</td>
<td>Grant the read-lock immediately.</td>
</tr>
<tr>
<td>read-locked</td>
<td>read-lock</td>
<td>Grant the additional read-lock immediately,
									<span class="bold"><strong>IF</strong></span> no outstanding 
									requests for a write-lock exist. If outstanding
									write-lock requests exist, this lock will not
									be granted until at least one of the 
									write-locks is granted and released. If other
									read-lock requests exist, all read-locks will be
									granted as a group.
									<p>TODO: try-lock, timed-lock.</p>
</td>
</tr>
<tr>
<td>write-locked</td>
<td>read-lock</td>
<td> Wait to acquire the lock until the thread
									holding the write-lock releases its lock. If other
									outstanding write-lock requests exist, they will
									have to wait until all current read-lock requests
									are serviced.
									<p>TODO: try-lock, timed-lock.</p>
</td>
</tr>
<tr>
<td>unlocked</td>
<td>write-lock</td>
<td>Grant the write-lock immediately.</td>
</tr>
<tr>
<td>read-locked</td>
<td>write-lock</td>
<td>
<p>Wait to acquire the lock until all threads
									holding read-locks release their locks.</p>
<p>If other write-lock requests exist, this
									lock will be granted to one of them in accordance
									with the intra-class scheduling policy.</p>
<p>TODO: try-lock, timed-lock.</p>
</td>
</tr>
<tr>
<td>write-locked</td>
<td>write-lock</td>
<td>Wait to acquire the lock until the thread
									holding the write-lock releases its lock.  If
									other outstanding read-lock requests exist, this
									lock will not be granted until all of the
									currently waiting read-locks are granted and
									released. If other write-lock requests exist,
									this lock will be granted in accordance with the
									intra-class scheduling policy.
									<p>TODO: try-lock, timed-lock.</p>
</td>
</tr>
<tr>
<td>read-locked</td>
<td>promote</td>
<td><p>TODO</p></td>
</tr>
<tr>
<td>write-locked</td>
<td>demote</td>
<td><p>TODO</p></td>
</tr>
</tbody>
</table></div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.read-write-scheduling-policies.alternating-single-read"></a>AlternatingPriority/SingleRead</h6></div></div></div>
<p>With AlternatingPriority/SingleRead scheduling, reader
					or writer starvation is avoided by alternatively granting read
					or write access when pending requests exist for both types of
					locks. Outstanding read-lock requests are services one at a
					time when it is the "readers' turn"</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Current mutex state</th>
<th>Request Type</th>
<th>Action</th>
</tr></thead>
<tbody>
<tr>
<td>unlocked</td>
<td>read-lock</td>
<td>Grant the read-lock immediately.</td>
</tr>
<tr>
<td>read-locked</td>
<td>read-lock</td>
<td>Grant the additional read-lock immediately,
									<span class="bold"><strong>IF</strong></span> no outstanding 
									requests for a write-lock exist. If outstanding
									write-lock requests exist, this lock will not
									be granted until at least one of the write-locks
									is granted and released.
									<p>TODO: try-lock, timed-lock.</p>
</td>
</tr>
<tr>
<td>write-locked</td>
<td>read-lock</td>
<td>
<p>Wait to acquire the lock until the thread
									holding the write-lock releases its lock.</p>
<p>If other outstanding write-lock requests
									exist, exactly one read-lock request will be
									granted before the next write-lock is granted.
									</p>
<p>TODO: try-lock, timed-lock.</p>
</td>
</tr>
<tr>
<td>unlocked</td>
<td>write-lock</td>
<td>Grant the write-lock immediately.</td>
</tr>
<tr>
<td>read-locked</td>
<td>write-lock</td>
<td>
<p>Wait to acquire the lock until all
									threads holding read-locks release their 
									locks.</p>
<p>If other write-lock requests exist,
									this lock will be granted to one of them
									in accordance with the intra-class
									scheduling policy.</p>
</td>
</tr>
<tr>
<td>write-locked</td>
<td>write-lock</td>
<td>Wait to acquire the lock until the
									thread holding the write-lock releases its
									lock.  If other outstanding read-lock requests
									exist, this lock can not be granted until
									exactly one read-lock request is granted and
									released. If other write-lock requests exist,
									this lock will be granted in accordance with
									the intra-class scheduling policy.
									<p>TODO: try-lock, timed-lock.</p>
</td>
</tr>
<tr>
<td>read-locked</td>
<td>promote</td>
<td><p>TODO</p></td>
</tr>
<tr>
<td>write-locked</td>
<td>demote</td>
<td><p>TODO</p></td>
</tr>
</tbody>
</table></div>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.read-write-scheduling-policies.intra-class"></a>Intra-Class Scheduling Policies</h6></div></div></div>
<p>Please refer to 
				<a href="concepts.html#threads.concepts.sheduling-policies" title="Scheduling Policies">the section called &#8220;Scheduling Policies&#8221;</a>
				for a discussion of mutex scheduling policies, which are identical to 
				read/write mutex intra-class scheduling policies.</p>
<p>For threads waiting to obtain write-locks, the read/write mutex
				supports only the 
				<a href="concepts.html#threads.concepts.unspecified-scheduling-policy" title="Unspecified Policy">Unspecified</a>
				intra-class scheduling policy. That is, given a set of threads
				waiting for write-locks, the order, relative to one another, in
				which they receive the write-lock is unspecified.</p>
<p>For threads waiting to obtain read-locks, the read/write mutex
				supports only the 
				<a href="concepts.html#threads.concepts.unspecified-scheduling-policy" title="Unspecified Policy">Unspecified</a>
				intra-class scheduling policy. That is, given a set of threads
				waiting for read-locks, the order, relative to one another, in
				which they receive the read-lock is unspecified.</p>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h5 class="title">
<a name="threads.concepts.read-write-mutex-concepts"></a>Mutex Concepts</h5></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="concepts.html#threads.concepts.ReadWriteMutex">ReadWriteMutex Concept</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.TryReadWriteMutex">TryReadWriteMutex Concept</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.TimedReadWriteMutex">TimedReadWriteMutex Concept</a></span></dt>
</dl></div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.ReadWriteMutex"></a>ReadWriteMutex Concept</h6></div></div></div>
<p>A ReadWriteMutex object has three states: read-locked,
				write-locked, and unlocked. ReadWriteMutex object state can
				only be determined by a lock object meeting the appropriate lock concept
				requirements and constructed for the ReadWriteMutex object.</p>
<p>A ReadWriteMutex is 
				<a href="../../../libs/utility/utility.htm#Class%20noncopyable" target="_top">NonCopyable</a>.
				</p>
<p>For a ReadWriteMutex type <code class="computeroutput">M</code>, 
				and an object <code class="computeroutput">m</code> of that type, 
				the following expressions must be well-formed 
				and have the indicated effects.</p>
<div class="table">
<a name="id1361243"></a><p class="title"><b>Table 12.12. ReadWriteMutex Expressions</b></p>
<table class="table" summary="ReadWriteMutex Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody>
<tr>
<td><code class="computeroutput">M m;</code></td>
<td>Constructs a read/write mutex object <code class="computeroutput">m</code>.
								Post-condition: <code class="computeroutput">m</code> is unlocked.</td>
</tr>
<tr>
<td><code class="computeroutput">(&amp;m)-&gt;~M();</code></td>
<td>Precondition: <code class="computeroutput">m</code> is unlocked. 
								Destroys a read/write mutex object <code class="computeroutput">m</code>.
								</td>
</tr>
<tr>
<td><code class="computeroutput">M::scoped_read_write_lock</code></td>
<td>A type meeting the 
								<a href="concepts.html#threads.concepts.ScopedReadWriteLock" title="ScopedReadWriteLock Concept">ScopedReadWriteLock</a>
								requirements. </td>
</tr>
<tr>
<td><code class="computeroutput">M::scoped_read_lock</code></td>
<td>A type meeting the 
								<a href="concepts.html#threads.concepts.ScopedLock" title="ScopedLock Concept">ScopedLock</a>
								requirements. </td>
</tr>
<tr>
<td><code class="computeroutput">M::scoped_write_lock</code></td>
<td>A type meeting the 
								<a href="concepts.html#threads.concepts.ScopedLock" title="ScopedLock Concept">ScopedLock</a>
								requirements. </td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.TryReadWriteMutex"></a>TryReadWriteMutex Concept</h6></div></div></div>
<p>A TryReadWriteMutex is a refinement of
				<a href="concepts.html#threads.concepts.ReadWriteMutex" title="ReadWriteMutex Concept">ReadWriteMutex</a>.
				For a TryReadWriteMutex type <code class="computeroutput">M</code> 
				and an object <code class="computeroutput">m</code> of that type,
				the following expressions must be well-formed 
				and have the indicated effects.</p>
<div class="table">
<a name="id1361388"></a><p class="title"><b>Table 12.13. TryReadWriteMutex Expressions</b></p>
<table class="table" summary="TryReadWriteMutex Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody>
<tr>
<td><code class="computeroutput">M::scoped_try_read_write_lock</code></td>
<td>A type meeting the 
								<a href="concepts.html#threads.concepts.ScopedTryReadWriteLock" title="ScopedTryReadWriteLock Expressions">ScopedTryReadWriteLock</a>
								requirements.</td>
</tr>
<tr>
<td><code class="computeroutput">M::scoped_try_read_lock</code></td>
<td>A type meeting the 
								<a href="concepts.html#threads.concepts.ScopedTryLock" title="ScopedTryLock Concept">ScopedTryLock</a>
								requirements.</td>
</tr>
<tr>
<td><code class="computeroutput">M::scoped_try_write_lock</code></td>
<td>A type meeting the 
								<a href="concepts.html#threads.concepts.ScopedTryLock" title="ScopedTryLock Concept">ScopedTryLock</a>
								requirements.</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.TimedReadWriteMutex"></a>TimedReadWriteMutex Concept</h6></div></div></div>
<p>A TimedReadWriteMutex is a refinement of
				<a href="concepts.html#threads.concepts.TryReadWriteMutex" title="TryReadWriteMutex Concept">TryReadWriteMutex</a>.
				For a TimedReadWriteMutex type <code class="computeroutput">M</code> 
				and an object <code class="computeroutput">m</code> of that type
				the following expressions must be well-formed 
				and have the indicated effects.</p>
<div class="table">
<a name="id1361491"></a><p class="title"><b>Table 12.14. TimedReadWriteMutex Expressions</b></p>
<table class="table" summary="TimedReadWriteMutex Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody>
<tr>
<td><code class="computeroutput">M::scoped_timed_read_write_lock</code></td>
<td>A type meeting the 
								<a href="concepts.html#threads.concepts.ScopedTimedReadWriteLock" title="ScopedTimedReadWriteLock Concept">ScopedTimedReadWriteLock</a> 
								requirements.</td>
</tr>
<tr>
<td><code class="computeroutput">M::scoped_timed_read_lock</code></td>
<td>A type meeting the 
								<a href="concepts.html#threads.concepts.ScopedTimedLock" title="ScopedTimedLock Concept">ScopedTimedLock</a> 
								requirements.</td>
</tr>
<tr>
<td><code class="computeroutput">M::scoped_timed_write_lock</code></td>
<td>A type meeting the 
								<a href="concepts.html#threads.concepts.ScopedTimedLock" title="ScopedTimedLock Concept">ScopedTimedLock</a> 
								requirements.</td>
</tr>
</tbody>
</table>
</div>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h5 class="title">
<a name="threads.concepts.read-write-mutex-models"></a>Mutex Models</h5></div></div></div>
<p> currently supplies three models of
			<a href="concepts.html#threads.concepts.ReadWriteMutex" title="ReadWriteMutex Concept">ReadWriteMutex</a>
			and its refinements.</p>
<div class="table">
<a name="id1361580"></a><p class="title"><b>Table 12.15. Mutex Models</b></p>
<table class="table" summary="Mutex Models">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Concept</th>
<th>Refines</th>
<th>Models</th>
</tr></thead>
<tbody>
<tr>
<td><a href="concepts.html#threads.concepts.ReadWriteMutex" title="ReadWriteMutex Concept">ReadWriteMutex</a></td>
<td> </td>
<td><code class="computeroutput"><a href="../read_write_mutex.html" title="Class read_write_mutex">boost::read_write_mutex</a></code></td>
</tr>
<tr>
<td><a href="concepts.html#threads.concepts.TryReadWriteMutex" title="TryReadWriteMutex Concept">TryReadWriteMutex</a></td>
<td><a href="concepts.html#threads.concepts.ReadWriteMutex" title="ReadWriteMutex Concept">ReadWriteMutex</a></td>
<td><code class="computeroutput"><a href="../try_read_write_mutex.html" title="Class try_read_write_mutex">boost::try_read_write_mutex</a></code></td>
</tr>
<tr>
<td><a href="concepts.html#threads.concepts.TimedReadWriteMutex" title="TimedReadWriteMutex Concept">TimedReadWriteMutex</a></td>
<td><a href="concepts.html#threads.concepts.TryReadWriteMutex" title="TryReadWriteMutex Concept">TryReadWriteMutex</a></td>
<td><code class="computeroutput"><a href="../timed_read_write_mutex.html" title="Class timed_read_write_mutex">boost::timed_read_write_mutex</a></code></td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h5 class="title">
<a name="threads.concepts.read-write-lock-concepts"></a>Lock Concepts</h5></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="concepts.html#threads.concepts.ReadWriteLock">ReadWriteLock Concept</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.ScopedReadWriteLock">ScopedReadWriteLock Concept</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.TryReadWriteLock">TryReadWriteLock Expressions</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.ScopedTryReadWriteLock">ScopedTryReadWriteLock Expressions</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.TimedReadWriteLock">TimedReadWriteLock Concept</a></span></dt>
<dt><span class="section"><a href="concepts.html#threads.concepts.ScopedTimedReadWriteLock">ScopedTimedReadWriteLock Concept</a></span></dt>
</dl></div>
<p>A read/write lock object provides a safe means for locking
			and unlocking a read/write mutex object (an object whose type is
			a model of 
			<a href="concepts.html#threads.concepts.ReadWriteMutex" title="ReadWriteMutex Concept">ReadWriteMutex</a> 
			or one of its refinements). In other words they are an
			implementation of the <span class="emphasis"><em>Scoped Locking</em></span> pattern. The 
			<a href="concepts.html#threads.concepts.ScopedReadWriteLock" title="ScopedReadWriteLock Concept">ScopedReadWriteLock</a>, 
			<a href="concepts.html#threads.concepts.ScopedTryReadWriteLock" title="ScopedTryReadWriteLock Expressions">ScopedTryReadWriteLock</a>, and 
			<a href="concepts.html#threads.concepts.ScopedTimedReadWriteLock" title="ScopedTimedReadWriteLock Concept">ScopedTimedReadWriteLock</a>
			concepts formalize the requirements.</p>
<p>Read/write lock objects are constructed with a reference to a
			read/write mutex object and typically acquire ownership of the 
			read/write mutex object by setting its state to locked. They also
			ensure ownership is relinquished in the destructor. Lock objects
			also expose functions to query the lock status and to manually lock
			and unlock the read/write mutex object.</p>
<p>Read/write lock objects are meant to be short lived, expected
			to be used at block scope only. The read/write lock objects are not 
			<a href="../threads.html#threads.glossary.thread-safe">thread-safe</a>.
			Read/write lock objects must maintain state to indicate whether or
			not they've been locked and this state is not protected by any
			synchronization concepts. For this reason a read/write lock object
			should never be shared between multiple threads.</p>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.ReadWriteLock"></a>ReadWriteLock Concept</h6></div></div></div>
<p>For a read/write lock type <code class="computeroutput">L</code>
				and an object <code class="computeroutput">lk</code> 
				and const object <code class="computeroutput">clk</code> of that type,
				the following expressions must be well-formed
				and have the indicated effects.</p>
<div class="table">
<a name="id1361782"></a><p class="title"><b>Table 12.16. ReadWriteLock Expressions</b></p>
<table class="table" summary="ReadWriteLock Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody>
<tr>
<td><code class="computeroutput">(&amp;lk)-&gt;~L();</code></td>
<td><code class="computeroutput">if (locked()) unlock();</code></td>
</tr>
<tr>
<td><code class="computeroutput">(&amp;clk)-&gt;operator const void*()</code></td>
<td>Returns type void*, non-zero if the associated read/write
								mutex object has been either read-locked or write-locked by 
								<code class="computeroutput">clk</code>, otherwise 0.</td>
</tr>
<tr>
<td><code class="computeroutput">clk.locked()</code></td>
<td>Returns a <code class="computeroutput">bool</code>, <code class="computeroutput">(&amp;clk)-&gt;operator
								const void*() != 0</code>
</td>
</tr>
<tr>
<td><code class="computeroutput">clk.state()</code></td>
<td>Returns an enumeration constant of type <code class="computeroutput">read_write_lock_state</code>:
								<code class="computeroutput">read_write_lock_state::read_locked</code> if the associated read/write mutex object has been
								read-locked by <code class="computeroutput">clk</code>, <code class="computeroutput">read_write_lock_state::write_locked</code> if it
								has been write-locked by <code class="computeroutput">clk</code>, and <code class="computeroutput">read_write_lock_state::unlocked</code>
								if has not been locked by <code class="computeroutput">clk</code>.</td>
</tr>
<tr>
<td><code class="computeroutput">clk.read_locked()</code></td>
<td>Returns a <code class="computeroutput">bool</code>, <code class="computeroutput">(&amp;clk)-&gt;state() == read_write_lock_state::read_locked</code>.</td>
</tr>
<tr>
<td><code class="computeroutput">clk.write_locked()</code></td>
<td>Returns a <code class="computeroutput">bool</code>, <code class="computeroutput">(&amp;clk)-&gt;state() == read_write_lock_state::write_locked</code>.</td>
</tr>
<tr>
<td><code class="computeroutput">lk.read_lock()</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code> 
									if <code class="computeroutput">locked()</code>.</p>
<p>If the associated read/write mutex
									object is already read-locked by some other
									thread, the effect depends on the
									<a href="concepts.html#threads.concepts.read-write-scheduling-policies.inter-class" title="Inter-Class Scheduling Policies">inter-class scheduling policy</a>
									of the associated read/write mutex:
									either immediately obtains an additional
									read-lock on the associated read/write
									mutex, or places the current thread in the
									<a href="../threads.html#threads.glossary.thread-state">Blocked</a>
									state until the associated read/write mutex
									is unlocked, after which the current thread
									is placed in the 
									<a href="../threads.html#threads.glossary.thread-state">Ready</a>
									state, eventually to be returned to the 
									<a href="../threads.html#threads.glossary.thread-state">Running</a>
									state.</p>
<p>If the associated read/write mutex
									object is already write-locked by some other
									thread, places the current thread in the
									<a href="../threads.html#threads.glossary.thread-state">Blocked</a>
									state until the associated read/write mutex
									is unlocked, after which the current thread
									is placed in the 
									<a href="../threads.html#threads.glossary.thread-state">Ready</a>
									state, eventually to be returned to the
									<a href="../threads.html#threads.glossary.thread-state">Running</a>
									state.</p>
<p>If the associated read/write mutex
									object is already locked by the same thread
									the behavior is dependent on the
									<a href="concepts.html#threads.concepts.read-write-locking-strategies" title="Locking Strategies">locking strategy</a>
									of the associated read/write mutex object.
									</p>
<p>Postcondition: <code class="computeroutput">state() == read_write_lock_state::read_locked</code></p>
</td>
</tr>
<tr>
<td><code class="computeroutput">lk.write_lock()</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code> 
									if <code class="computeroutput">locked()</code>.</p>
<p>If the associated read/write mutex
									object is already locked by some other
									thread, places the current thread in the
									<a href="../threads.html#threads.glossary.thread-state">Blocked</a>
									state until the associated read/write mutex
									is unlocked, after which the current thread
									is placed in the 
									<a href="../threads.html#threads.glossary.thread-state">Ready</a>
									state, eventually to be returned to the
									<a href="../threads.html#threads.glossary.thread-state">Running</a>
									state.</p>
<p>If the associated read/write mutex
									object is already locked by the same thread
									the behavior is dependent on the
									<a href="concepts.html#threads.concepts.read-write-locking-strategies" title="Locking Strategies">locking strategy</a>
									of the associated read/write mutex object.
									</p>
<p>Postcondition: <code class="computeroutput">state() == read_write_lock_state::write_locked</code></p>
</td>
</tr>
<tr>
<td><code class="computeroutput">lk.demote()</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
									if <code class="computeroutput">state() != read_write_lock_state::write_locked</code>.</p>
<p>Converts the lock held on the associated read/write mutex
									object from a write-lock to a read-lock without releasing
									the lock.</p>
<p>Postcondition: <code class="computeroutput">state() == read_write_lock_state::read_locked</code></p>
</td>
</tr>
<tr>
<td><code class="computeroutput">lk.promote()</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
									if <code class="computeroutput">state() != read_write_lock_state::read_locked</code>
									or if the lock cannot be promoted because another lock
									on the same mutex is already waiting to be promoted.</p>
<p>Makes a blocking attempt to convert the lock held on the associated
									read/write mutex object from a read-lock to a write-lock without releasing
									the lock.</p>
</td>
</tr>
<tr>
<td><code class="computeroutput">lk.unlock()</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
									if <code class="computeroutput">!locked()</code>.</p>
<p>Unlocks the associated read/write mutex.</p>
<p>Postcondition: <code class="computeroutput">!locked()</code></p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.ScopedReadWriteLock"></a>ScopedReadWriteLock Concept</h6></div></div></div>
<p>A ScopedReadWriteLock is a refinement of 
				<a href="concepts.html#threads.concepts.ReadWriteLock" title="ReadWriteLock Concept">ReadWriteLock</a>. 
				For a ScopedReadWriteLock type <code class="computeroutput">L</code> 
				and an object <code class="computeroutput">lk</code> of that type,
				and an object <code class="computeroutput">m</code> of a type meeting the 
				<a href="concepts.html#threads.concepts.ReadWriteMutex" title="ReadWriteMutex Concept">ReadWriteMutex</a> requirements,
				and an object <code class="computeroutput">s</code> of type <code class="computeroutput">read_write_lock_state</code>,
				the following expressions must be well-formed 
				and have the indicated effects.</p>
<div class="table">
<a name="id1362317"></a><p class="title"><b>Table 12.17. ScopedReadWriteLock Expressions</b></p>
<table class="table" summary="ScopedReadWriteLock Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody><tr>
<td><code class="computeroutput">L lk(m,s);</code></td>
<td>Constructs an object <code class="computeroutput">lk</code> and associates read/write mutex
								object <code class="computeroutput">m</code> with it, then: if <code class="computeroutput">s == read_write_lock_state::read_locked</code>, calls
								<code class="computeroutput">read_lock()</code>; if <code class="computeroutput">s==read_write_lock_state::write_locked</code>,
								calls <code class="computeroutput">write_lock()</code>.</td>
</tr></tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.TryReadWriteLock"></a>TryReadWriteLock Expressions</h6></div></div></div>
<p>A TryReadWriteLock is a refinement of 
				<a href="concepts.html#threads.concepts.ReadWriteLock" title="ReadWriteLock Concept">ReadWriteLock</a>.
				For a TryReadWriteLock type <code class="computeroutput">L</code>
				and an object <code class="computeroutput">lk</code> of that type,
				the following expressions must be well-formed
				and have the indicated effects.</p>
<div class="table">
<a name="id1362411"></a><p class="title"><b>Table 12.18. TryReadWriteLock Expressions</b></p>
<table class="table" summary="TryReadWriteLock Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody>
<tr>
<td><code class="computeroutput">lk.try_read_lock()</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
									if locked().</p>
<p>Makes a non-blocking attempt to read-lock the associated read/write
									mutex object, returning <code class="computeroutput">true</code> if the attempt is successful,
									otherwise <code class="computeroutput">false</code>. If the associated read/write mutex object is
									already locked by the same thread the behavior is dependent on the
									<a href="concepts.html#threads.concepts.locking-strategies" title="Locking Strategies">locking
									strategy</a> of the associated read/write mutex object.</p>
</td>
</tr>
<tr>
<td><code class="computeroutput">lk.try_write_lock()</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
									if locked().</p>
<p>Makes a non-blocking attempt to write-lock the associated read/write
									mutex object, returning <code class="computeroutput">true</code> if the attempt is successful,
									otherwise <code class="computeroutput">false</code>. If the associated read/write mutex object is
									already locked by the same thread the behavior is dependent on the
									<a href="concepts.html#threads.concepts.locking-strategies" title="Locking Strategies">locking
									strategy</a> of the associated read/write mutex object.</p>
</td>
</tr>
<tr>
<td><code class="computeroutput">lk.try_demote()</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
									if <code class="computeroutput">state() != read_write_lock_state::write_locked</code>.</p>
<p>Makes a non-blocking attempt to convert the lock held on the associated
									read/write mutex object from a write-lock to a read-lock without releasing
									the lock, returning <code class="computeroutput">true</code> if the attempt is successful,
									otherwise <code class="computeroutput">false</code>.</p>
</td>
</tr>
<tr>
<td><code class="computeroutput">lk.try_promote()</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
									if <code class="computeroutput">state() != read_write_lock_state::read_locked</code>.</p>
<p>Makes a non-blocking attempt to convert the lock held on the associated
									read/write mutex object from a read-lock to a write-lock without releasing
									the lock, returning <code class="computeroutput">true</code> if the attempt is successful,
									otherwise <code class="computeroutput">false</code>.</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.ScopedTryReadWriteLock"></a>ScopedTryReadWriteLock Expressions</h6></div></div></div>
<p>A ScopedTryReadWriteLock is a refinement of 
				<a href="concepts.html#threads.concepts.TryReadWriteLock" title="TryReadWriteLock Expressions">TryReadWriteLock</a>.
				For a ScopedTryReadWriteLock type <code class="computeroutput">L</code>
				and an object <code class="computeroutput">lk</code> of that type,
				and an object <code class="computeroutput">m</code> of a type meeting the
				<a href="concepts.html#threads.concepts.TryMutex" title="TryMutex Concept">TryReadWriteMutex</a> requirements,
				and an object <code class="computeroutput">s</code> of type <code class="computeroutput">read_write_lock_state</code>,
				and an object <code class="computeroutput">b</code> of type <code class="computeroutput">blocking_mode</code>, 
				the following expressions must be well-formed
				and have the indicated effects.</p>
<div class="table">
<a name="id1362685"></a><p class="title"><b>Table 12.19. ScopedTryReadWriteLock Expressions</b></p>
<table class="table" summary="ScopedTryReadWriteLock Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody><tr>
<td><code class="computeroutput">L lk(m,s,b);</code></td>
<td>Constructs an object <code class="computeroutput">lk</code> and associates read/write mutex
								object <code class="computeroutput">m</code> with it, then: if <code class="computeroutput">s == read_write_lock_state::read_locked</code>, calls
								<code class="computeroutput">read_lock()</code> if <code class="computeroutput">b</code>, otherwise <code class="computeroutput">try_read_lock()</code>;
								if <code class="computeroutput">s==read_write_lock_state::write_locked</code>, calls <code class="computeroutput">write_lock()</code> if <code class="computeroutput">b</code>,
								otherwise <code class="computeroutput">try_write_lock</code>.</td>
</tr></tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.TimedReadWriteLock"></a>TimedReadWriteLock Concept</h6></div></div></div>
<p>A TimedReadWriteLock is a refinement of 
				<a href="concepts.html#threads.concepts.TryReadWriteLock" title="TryReadWriteLock Expressions">TryReadWriteLock</a>. 
				For a TimedReadWriteLock type <code class="computeroutput">L</code>
				and an object <code class="computeroutput">lk</code> of that type,
				and an object <code class="computeroutput">t</code> of type <code class="computeroutput"><a href="../xtime.html" title="Struct xtime">boost::xtime</a></code>, 
				the following expressions must be well-formed
				and have the indicated effects.</p>
<div class="table">
<a name="id1362819"></a><p class="title"><b>Table 12.20. TimedReadWriteLock Expressions</b></p>
<table class="table" summary="TimedReadWriteLock Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody>
<tr>
<td><code class="computeroutput">lk.timed_read_lock(t)</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
									if locked().</p>
<p>Makes a blocking attempt to read-lock the associated read/write mutex object,
									and returns <code class="computeroutput">true</code> if successful within the specified time <code class="computeroutput">t</code>,
									otherwise <code class="computeroutput">false</code>. If the associated read/write mutex object is already
									locked by the same thread the behavior is dependent on the <a href="concepts.html#threads.concepts.locking-strategies" title="Locking Strategies">locking
									strategy</a> of the associated read/write mutex object.</p>
</td>
</tr>
<tr>
<td><code class="computeroutput">lk.timed_write_lock(t)</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
									if locked().</p>
<p>Makes a blocking attempt to write-lock the associated read/write mutex object, 
									and returns <code class="computeroutput">true</code> if successful within the specified time <code class="computeroutput">t</code>,
									otherwise <code class="computeroutput">false</code>. If the associated read/write mutex object is already
									locked by the same thread the behavior is dependent on the <a href="concepts.html#threads.concepts.locking-strategies" title="Locking Strategies">locking
									strategy</a> of the associated read/write mutex object.</p>
</td>
</tr>
<tr>
<td><code class="computeroutput">lk.timed_demote(t)</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
									if <code class="computeroutput">state() != read_write_lock_state::write_locked</code>.</p>
<p>Makes a blocking attempt to convert the lock held on the associated
									read/write mutex object from a write-lock to a read-lock without releasing
									the lock, returning <code class="computeroutput">true</code> if the attempt is successful
									in the specified time <code class="computeroutput">t</code>, otherwise <code class="computeroutput">false</code>.</p>
</td>
</tr>
<tr>
<td><code class="computeroutput">lk.timed_promote(t)</code></td>
<td>
<p>Throws <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>
									if <code class="computeroutput">state() != read_write_lock_state::read_locked</code>.</p>
<p>Makes a blocking attempt to convert the lock held on the associated
									read/write mutex object from a read-lock to a write-lock without releasing
									the lock, returning <code class="computeroutput">true</code> if the attempt is successful
									in the specified time <code class="computeroutput">t</code>, otherwise <code class="computeroutput">false</code>.</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h6 class="title">
<a name="threads.concepts.ScopedTimedReadWriteLock"></a>ScopedTimedReadWriteLock Concept</h6></div></div></div>
<p>A ScopedTimedReadWriteLock is a refinement of 
				<a href="concepts.html#threads.concepts.TimedReadWriteLock" title="TimedReadWriteLock Concept">TimedReadWriteLock</a>. 
				For a ScopedTimedReadWriteLock type <code class="computeroutput">L</code>
				and an object <code class="computeroutput">lk</code> of that type,
				and an object <code class="computeroutput">m</code> of a type meeting the 
				<a href="concepts.html#threads.concepts.TimedReadWriteMutex" title="TimedReadWriteMutex Concept">TimedReadWriteMutex</a> requirements,
				and an object <code class="computeroutput">s</code> of type <code class="computeroutput">read_write_lock_state</code>,
				and an object <code class="computeroutput">t</code> of type <code class="computeroutput"><a href="../xtime.html" title="Struct xtime">boost::xtime</a></code>, 
				and an object <code class="computeroutput">b</code> of type <code class="computeroutput">blocking_mode</code>, 
				the following expressions must be well-formed and have the
				indicated effects.</p>
<div class="table">
<a name="id1363131"></a><p class="title"><b>Table 12.21. ScopedTimedReadWriteLock Expressions</b></p>
<table class="table" summary="ScopedTimedReadWriteLock Expressions">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>Expression</th>
<th>Effects</th>
</tr></thead>
<tbody>
<tr>
<td><code class="computeroutput">L lk(m,s,b);</code></td>
<td>Constructs an object <code class="computeroutput">lk</code> and associates read/write mutex
								object <code class="computeroutput">m</code> with it, then: if <code class="computeroutput">s == read_write_lock_state::read_locked</code>, calls
								<code class="computeroutput">read_lock()</code> if <code class="computeroutput">b</code>, otherwise <code class="computeroutput">try_read_lock()</code>;
								if <code class="computeroutput">s==read_write_lock_state::write_locked</code>, calls <code class="computeroutput">write_lock()</code> if <code class="computeroutput">b</code>,
								otherwise <code class="computeroutput">try_write_lock</code>.</td>
</tr>
<tr>
<td><code class="computeroutput">L lk(m,s,t);</code></td>
<td>Constructs an object <code class="computeroutput">lk</code> and associates read/write mutex
								object <code class="computeroutput">m</code> with it, then: if <code class="computeroutput">s == read_write_lock_state::read_locked</code>, calls
								<code class="computeroutput">timed_read_lock(t)</code>; if <code class="computeroutput">s==read_write_lock_state::write_locked</code>,
								calls <code class="computeroutput">timed_write_lock(t)</code>.</td>
</tr>
</tbody>
</table>
</div>
</div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h5 class="title">
<a name="threads.concepts.read-write-lock-models"></a>Lock Models</h5></div></div></div>
<p> currently supplies six models of
			<a href="concepts.html#threads.concepts.ReadWriteLock" title="ReadWriteLock Concept">ReadWriteLock</a>
			and its refinements.</p>
<div class="table">
<a name="id1555521"></a><p class="title"><b>Table 12.22. Lock Models</b></p>
<table class="table" summary="Lock Models">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Concept</th>
<th>Refines</th>
<th>Models</th>
</tr></thead>
<tbody>
<tr>
<td><a href="concepts.html#threads.concepts.ReadWriteLock" title="ReadWriteLock Concept">ReadWriteLock</a></td>
<td> </td>
<td> </td>
</tr>
<tr>
<td><a href="concepts.html#threads.concepts.ScopedReadWriteLock" title="ScopedReadWriteLock Concept">ScopedReadWriteLock</a></td>
<td><a href="concepts.html#threads.concepts.ReadWriteLock" title="ReadWriteLock Concept">ReadWriteLock</a></td>
<td>
<p><code class="computeroutput">boost::read_write_mutex::scoped_read_write_lock</code></p>
<p><code class="computeroutput">boost::try_read_write_mutex::scoped_read_write_lock</code></p>
<p><code class="computeroutput">boost::timed_read_write_mutex::scoped_read_write_lock</code></p>
</td>
</tr>
<tr>
<td><a href="concepts.html#threads.concepts.TryReadWriteLock" title="TryReadWriteLock Expressions">TryReadWriteLock</a></td>
<td><a href="concepts.html#threads.concepts.ReadWriteLock" title="ReadWriteLock Concept">ReadWriteLock</a></td>
<td> </td>
</tr>
<tr>
<td><a href="concepts.html#threads.concepts.ScopedTryReadWriteLock" title="ScopedTryReadWriteLock Expressions">ScopedTryReadWriteLock</a></td>
<td><a href="concepts.html#threads.concepts.TryReadWriteLock" title="TryReadWriteLock Expressions">TryReadWriteLock</a></td>
<td>
<p><code class="computeroutput">boost::try_read_write_mutex::scoped_try_read_write_lock</code></p>
<p><code class="computeroutput">boost::timed_read_write_mutex::scoped_try_read_write_lock</code></p>
</td>
</tr>
<tr>
<td><a href="concepts.html#threads.concepts.TimedReadWriteLock" title="TimedReadWriteLock Concept">TimedReadWriteLock</a></td>
<td><a href="concepts.html#threads.concepts.TryReadWriteLock" title="TryReadWriteLock Expressions">TryReadWriteLock</a></td>
<td> </td>
</tr>
<tr>
<td><a href="concepts.html#threads.concepts.ScopedTimedReadWriteLock" title="ScopedTimedReadWriteLock Concept">ScopedTimedReadWriteLock</a></td>
<td><a href="concepts.html#threads.concepts.TimedReadWriteLock" title="TimedReadWriteLock Concept">TimedReadWriteLock</a></td>
<td><p><code class="computeroutput">boost::timed_read_write_mutex::scoped_timed_read_write_lock</code></p></td>
</tr>
</tbody>
</table>
</div>
</div>
</div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"><small><p>Last revised: November 28, 2004 at 04:29:36 GMT</p></small></td>
<td align="right"><small>Copyright © 2001-2003 William E. Kempf</small></td>
</tr></table>
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