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<h1 class="topictitle1">parallel_pipeline Function</h1>
<div>
<div class="section"><h2 class="sectiontitle">Summary</h2> Strongly typed interface for pipelined execution. </div>
<div class="section"><h2 class="sectiontitle">Header</h2>
<pre>#include "tbb/pipeline.h"</pre>
</div>
<div class="section"><h2 class="sectiontitle">Syntax</h2>
<pre>void parallel_pipeline( size_t max_number_of_live_tokens,
const filter_t<void,void>& filter_chain
[, task_group_context& group] );
</pre></div>
<div class="section"><h2 class="sectiontitle">Description</h2>
<p> Function <samp class="codeph">parallel_pipeline</samp> is a strongly typed lambda-friendly
interface for building and running pipelines. The pipeline has characteristics
similar to class <samp class="codeph">pipeline</samp>, except that the stages of the pipeline
are specified via functors instead of class derivation.</p>
<p>To build and run a pipeline from functors <em>g</em><sub>0</sub>, <em>g</em><sub>1</sub>,
<em>g</em><sub>2</sub>, ..., <em>g</em><sub>n</sub>, write:</p>
<pre>parallel_pipeline( max_number_of_live_tokens,
make_filter<void,I1>(mode0,g0) &
make_filter<I1,I2>(mode1,g1) &
make_filter<I2,I3>(mode2,g2) &
...
make_filter<In,void>(moden,gn) );
</pre><p>In
general, functor <em>g</em><sub>i</sub> should define its <samp class="codeph">operator()</samp> to map objects of type
<em>I</em><sub>i</sub> to objects of type <em>I</em><sub>i+1</sub>. Functor <em>g</em><sub>0</sub> is a special case, because it notifies the pipeline when the end of the
input stream is reached. Functor <em>g</em><sub>0</sub> must be defined such that for a flow_control object <em>fc</em>, the
expression <em>g</em><sub>0</sub> (<em>fc</em> ) either returns the next value in the input stream, or if
at the end of the input stream, invokes <em>fc.</em>stop() and returns a dummy
value.</p>
The value <em>max_number_of_live_tokens</em> has the same meaning as it
does for <samp class="codeph">pipeline::run</samp>. <p> If the group argument is specified,
pipeline's tasks are executed in this group. By default the algorithm is executed in
a bound group of its own. </p>
</div>
<div class="section"><h2 class="sectiontitle">Example</h2>
<p> The following example uses <samp class="codeph">parallel_pipeline</samp> compute
the root-mean-square of a sequence defined by [ <em>first</em> , <em>last</em> ). The
example is only for demonstrating syntactic mechanics. It is not as a practical way
to do the calculation because parallel overhead would be vastly higher than useful
work. Operator & requires that the output type of its first
<samp class="codeph">filter_t</samp> argument matches the input type of its second
<samp class="codeph">filter_t</samp> argument.</p>
<pre>float RootMeanSquare( float* first, float* last ) {
float sum=0;
parallel_pipeline( /*max_number_of_live_token=*/16,
make_filter<void,float*>(
filter::serial,
[&](flow_control& fc)-> float*{
if( first<last ) {
return first++;
} else {
fc.stop();
return NULL;
}
}
) &
make_filter<float*,float>(
filter::parallel,
[](float* p){return (*p)*(*p);}
) &
make_filter<float,void>(
filter::serial,
[&](float x) {sum+=x;}
)
);
return sqrt(sum);
}
</pre><p>See the Intel® Threading Building Blocks Tutorial for a non-trivial example
of <samp class="codeph">parallel_pipeline</samp>.</p>
</div>
</div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="../../reference/algorithms.htm">Algorithms</a></div>
</div>
<div class="See Also">
<ul class="ullinks">
<li class="ulchildlink"><a href="../../reference/algorithms/parallel_pipeline_func/filter_t_cls.htm">filter_t Template Class</a><br>
</li>
<li class="ulchildlink"><a href="../../reference/algorithms/parallel_pipeline_func/flow_control_cls.htm">flow_control Class</a><br>
</li>
</ul>
<h2>See Also</h2>
<div class="linklist">
<div><a href="pipeline_cls.htm">pipeline Class
</a></div>
<div><a href="../task_scheduler/task_group_context.htm">task_group_context</a></div></div>
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