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<h1 class="topictitle1">combinable Template Class</h1>
<div>
<div class="section"><h2 class="sectiontitle">Summary</h2>
<p>Template class for holding thread-local values
during a parallel computation that will be merged into a final value.
</p>
</div>
<div class="section"><h2 class="sectiontitle">Syntax</h2>
<pre>template<typename T> class combinable;</pre>
</div>
<div class="section"><h2 class="sectiontitle">Header</h2>
<pre>#include "tbb/combinable.h"</pre>
</div>
<div class="section"><h2 class="sectiontitle">Description</h2>
<p>A
<samp class="codeph">combinable<T></samp> provides each thread with its own
local instance of type
<samp class="codeph">T</samp>.
</p>
</div>
<div class="section"><h2 class="sectiontitle">Members</h2>
<pre>namespace tbb {
template <typename T>
class combinable {
public:
combinable();
template <typename FInit>
combinable(FInit finit);}
combinable(const combinable& other);
~combinable();
combinable& operator=( const combinable& other);
void clear();
T& local();
T& local(bool & exists);
template<typename FCombine> T combine(FCombine fcombine);
template<typename Func> void combine_each(Func f);
};
}</pre>
<div class="tablenoborder"><table cellpadding="4" summary="" frame="border" border="1" cellspacing="0" rules="all"><span class="tabledesc">The following table provides additional information on the
members of this template class.
</span><thead align="left">
<tr>
<th class="cellrowborder" valign="top" width="33.89830508474576%" id="d118194e79">Member
</th>
<th class="cellrowborder" valign="top" width="66.10169491525423%" id="d118194e82">Description
</th>
</tr>
</thead>
<tbody>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d118194e79 "><span class="keyword">combinable()</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d118194e82 ">
<p>Constructs
<samp class="codeph">combinable</samp> such that any thread-local
instances of
<samp class="codeph">T</samp> will be created using default
construction.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d118194e79 "><span class="keyword">template<typename FInit>
combinable(FInit finit)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d118194e82 ">
<p>Constructs
<samp class="codeph">combinable</samp> such that any thread-local
element will be created by copying the result of
<em>finit()</em>.
</p>
<div class="Note"><h3 class="NoteTipHead">
Caution</h3>
<p>The expression finit() must be safe to evaluate
concurrently by multiple threads. It is evaluated each time a thread-local
element is created.
</p>
</div>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d118194e79 "><span class="keyword">combinable( const combinable&
other );</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d118194e82 ">
<p>Construct a copy of
<em>other</em>, so that it has copies of each element in
<em>other</em> with the same thread mapping.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d118194e79 "><span class="keyword">~combinable()</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d118194e82 ">
<p>Destroy all thread-local elements in
<samp class="codeph">*this</samp>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d118194e79 "><span class="keyword">combinable& operator=( const
combinable& other )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d118194e82 ">
<p>Set<samp class="codeph"> *this</samp> to be a copy of
<em>other</em>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d118194e79 "><span class="keyword">void clear()</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d118194e82 ">
<p>Remove all elements from
<samp class="codeph">*this</samp>.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d118194e79 "><span class="keyword">T& local()</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d118194e82 ">
<p>If thread-local element does not exist, create it.
</p>
<p><strong>Returns</strong>: Reference to thread-local element.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d118194e79 "><span class="keyword">T& local( bool& exists
)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d118194e82 ">
<p>Similar to
<samp class="codeph">local()</samp>, except that
<em>exists</em> is set to true if an element was already
present for the current thread; false otherwise.
</p>
<p><strong>Returns</strong>: Reference to thread-local element.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d118194e79 "><span class="keyword">template<typename FCombine>T
combine(FCombine fcombine)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d118194e82 ">
<p><strong>Requires</strong>: Parameter
<samp class="codeph"><em>fcombine</em></samp> should be an associative
binary functor with the signature
<samp class="codeph">T(T,T)</samp> or<samp class="codeph"> T(const T&,const
T&)</samp>.
</p>
<p><strong>Effects</strong>: Computes a reduction over
all elements using binary functor
<em>fcombine</em>. If there are no elements, creates the result
using the same rules as for creating a thread-local element.
</p>
<p><strong>Returns</strong>: Result of the reduction.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d118194e79 "><span class="keyword">template<typename Func> void
combine_each(Func f)</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d118194e82 ">
<p><strong>Requires</strong>: Parameter
<samp class="codeph"><em>f
</em></samp>should be a unary functor with the signature
<samp class="codeph">void(T)</samp> or
<samp class="codeph">void(const T&)</samp>.
</p>
<p><strong>Effects</strong>: Evaluates
<samp class="codeph"><em>f(x)</em></samp> for each instance
<samp class="codeph"><em>x</em></samp> of
<samp class="codeph">T</samp> in
<samp class="codeph">*this</samp>.
</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
</div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="../../reference/thread_local_storage.htm">Thread Local Storage</a></div>
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