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<h1>
<span class="m-breadcrumb"><a href="Algorithms.html">Taskflow Algorithms</a> »</span>
Task-parallel Scalable Pipeline
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<h3>Contents</h3>
<ul>
<li><a href="#IncludeTheScalablePipelineHeader">Include the Header</a></li>
<li><a href="#CreateAScalablePipelineModuleTask">Create a Scalable Pipeline Module Task</a></li>
<li><a href="#ResetAPlaceholderScalablePipeline">Reset a Placeholder Scalable Pipeline</a></li>
<li><a href="#ScalablePipelineUseOtherIteratorTypes">Use Other Iterator Types</a></li>
<li><a href="#ParallelScalablePipelineLearnMore">Learn More about Taskflow Pipeline</a></li>
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<p>Unlike <a href="classtf_1_1Pipeline.html" class="m-doc">tf::<wbr />Pipeline</a> (see <a href="TaskParallelPipeline.html" class="m-doc">Task-parallel Pipeline</a>) that instantiates all pipes at the construction time, Taskflow provides a scalable alternative called <a href="classtf_1_1ScalablePipeline.html" class="m-doc">tf::<wbr />ScalablePipeline</a> to allow variable assignments of pipes using range iterators. A scalable pipeline is thus more flexible for applications to create a pipeline scheduling framework whose pipeline structure depends on runtime variables.</p><section id="IncludeTheScalablePipelineHeader"><h2><a href="#IncludeTheScalablePipelineHeader">Include the Header</a></h2><p>You need to include the header file, <code>taskflow/algorithm/pipeline.hpp</code>, for creating a scalable pipeline scheduling framework.</p><pre class="m-code"><span class="cp">#include</span><span class="w"> </span><span class="cpf"><taskflow/algorithm/pipeline.hpp></span></pre></section><section id="CreateAScalablePipelineModuleTask"><h2><a href="#CreateAScalablePipelineModuleTask">Create a Scalable Pipeline Module Task</a></h2><p>Similar to <a href="classtf_1_1Pipeline.html" class="m-doc">tf::<wbr />Pipeline</a>, <a href="classtf_1_1ScalablePipeline.html" class="m-doc">tf::<wbr />ScalablePipeline</a> is a composable graph object to implement a <em>pipeline scheduling framework</em> in a taskflow. The key difference between <a href="classtf_1_1Pipeline.html" class="m-doc">tf::<wbr />Pipeline</a> and <a href="classtf_1_1ScalablePipeline.html" class="m-doc">tf::<wbr />ScalablePipeline</a> is that a scalable pipeline can accept <em>variable</em> assignments of pipes rather than instantiating all pipes at construction or programming time. Users define a linear range of pipes, each of the same callable type, and apply that range to construct a scalable pipeline. Between successive runs, users can reset the pipeline to a different range of pipes. The following code creates a scalable pipeline that uses four parallel lines to schedule tokens through three serial pipes in the given vector, then resetting that pipeline to a new range of five serial pipes:</p><pre class="m-code"><span class="n">tf</span><span class="o">::</span><span class="n">Taskflow</span><span class="w"> </span><span class="n">taskflow</span><span class="p">(</span><span class="s">"pipeline"</span><span class="p">);</span>
<span class="n">tf</span><span class="o">::</span><span class="n">Executor</span><span class="w"> </span><span class="n">executor</span><span class="p">;</span>
<span class="k">const</span><span class="w"> </span><span class="kt">size_t</span><span class="w"> </span><span class="n">num_lines</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span>
<span class="c1">// create data storage</span>
<span class="n">std</span><span class="o">::</span><span class="n">array</span><span class="o"><</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="n">num_lines</span><span class="o">></span><span class="w"> </span><span class="n">buffer</span><span class="p">;</span>
<span class="c1">// define the pipe callable</span>
<span class="k">auto</span><span class="w"> </span><span class="n">pipe_callable</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[</span><span class="o">&</span><span class="n">buffer</span><span class="p">]</span><span class="w"> </span><span class="p">(</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipeflow</span><span class="o">&</span><span class="w"> </span><span class="n">pf</span><span class="p">)</span><span class="w"> </span><span class="k">mutable</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">switch</span><span class="p">(</span><span class="n">pf</span><span class="p">.</span><span class="n">pipe</span><span class="p">())</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="c1">// first stage generates only 5 scheduling tokens and saves the </span>
<span class="w"> </span><span class="c1">// token number into the buffer.</span>
<span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="mi">0</span><span class="p">:</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">if</span><span class="p">(</span><span class="n">pf</span><span class="p">.</span><span class="n">token</span><span class="p">()</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">5</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">pf</span><span class="p">.</span><span class="n">stop</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">printf</span><span class="p">(</span><span class="s">"stage 1: input token = %zu</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="n">pf</span><span class="p">.</span><span class="n">token</span><span class="p">());</span>
<span class="w"> </span><span class="n">buffer</span><span class="p">[</span><span class="n">pf</span><span class="p">.</span><span class="n">line</span><span class="p">()]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">pf</span><span class="p">.</span><span class="n">token</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="k">return</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="k">break</span><span class="p">;</span>
<span class="w"> </span>
<span class="w"> </span><span class="c1">// other stages propagate the previous result to this pipe and</span>
<span class="w"> </span><span class="c1">// increment it by one</span>
<span class="w"> </span><span class="k">default</span><span class="o">:</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">printf</span><span class="p">(</span>
<span class="w"> </span><span class="s">"stage %zu: input buffer[%zu] = %d</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="n">pf</span><span class="p">.</span><span class="n">pipe</span><span class="p">(),</span><span class="w"> </span><span class="n">pf</span><span class="p">.</span><span class="n">line</span><span class="p">(),</span><span class="w"> </span><span class="n">buffer</span><span class="p">[</span><span class="n">pf</span><span class="p">.</span><span class="n">line</span><span class="p">()]</span>
<span class="w"> </span><span class="p">);</span>
<span class="w"> </span><span class="n">buffer</span><span class="p">[</span><span class="n">pf</span><span class="p">.</span><span class="n">line</span><span class="p">()]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buffer</span><span class="p">[</span><span class="n">pf</span><span class="p">.</span><span class="n">line</span><span class="p">()]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span><span class="w"> </span>
<span class="w"> </span><span class="k">break</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="p">};</span>
<span class="c1">// create a vector of three pipes</span>
<span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="w"> </span><span class="n">tf</span><span class="o">::</span><span class="n">Pipe</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">function</span><span class="o"><</span><span class="kt">void</span><span class="p">(</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipeflow</span><span class="o">&</span><span class="p">)</span><span class="o">>></span><span class="w"> </span><span class="o">></span><span class="w"> </span><span class="n">pipes</span><span class="p">;</span>
<span class="k">for</span><span class="p">(</span><span class="kt">size_t</span><span class="w"> </span><span class="n">i</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o"><</span><span class="mi">3</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">pipes</span><span class="p">.</span><span class="n">emplace_back</span><span class="p">(</span><span class="n">tf</span><span class="o">::</span><span class="n">PipeType</span><span class="o">::</span><span class="n">SERIAL</span><span class="p">,</span><span class="w"> </span><span class="n">pipe_callable</span><span class="p">);</span>
<span class="p">}</span>
<span class="c1">// create a pipeline of four parallel lines based on the given vector of pipes</span>
<span class="n">tf</span><span class="o">::</span><span class="n">ScalablePipeline</span><span class="w"> </span><span class="n">pl</span><span class="p">(</span><span class="n">num_lines</span><span class="p">,</span><span class="w"> </span><span class="n">pipes</span><span class="p">.</span><span class="n">begin</span><span class="p">(),</span><span class="w"> </span><span class="n">pipes</span><span class="p">.</span><span class="n">end</span><span class="p">());</span>
<span class="c1">// build the pipeline graph using composition</span>
<span class="n">tf</span><span class="o">::</span><span class="n">Task</span><span class="w"> </span><span class="n">init</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">taskflow</span><span class="p">.</span><span class="n">emplace</span><span class="p">([](){</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"ready</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span><span class="w"> </span><span class="p">})</span>
<span class="w"> </span><span class="p">.</span><span class="n">name</span><span class="p">(</span><span class="s">"starting pipeline"</span><span class="p">);</span>
<span class="n">tf</span><span class="o">::</span><span class="n">Task</span><span class="w"> </span><span class="n">task</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">taskflow</span><span class="p">.</span><span class="n">composed_of</span><span class="p">(</span><span class="n">pl</span><span class="p">)</span>
<span class="w"> </span><span class="p">.</span><span class="n">name</span><span class="p">(</span><span class="s">"pipeline"</span><span class="p">);</span>
<span class="n">tf</span><span class="o">::</span><span class="n">Task</span><span class="w"> </span><span class="n">stop</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">taskflow</span><span class="p">.</span><span class="n">emplace</span><span class="p">([](){</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"stopped</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span><span class="w"> </span><span class="p">})</span>
<span class="w"> </span><span class="p">.</span><span class="n">name</span><span class="p">(</span><span class="s">"pipeline stopped"</span><span class="p">);</span>
<span class="c1">// create task dependency</span>
<span class="n">init</span><span class="p">.</span><span class="n">precede</span><span class="p">(</span><span class="n">task</span><span class="p">);</span>
<span class="n">task</span><span class="p">.</span><span class="n">precede</span><span class="p">(</span><span class="n">stop</span><span class="p">);</span>
<span class="c1">// dump the pipeline graph structure (with composition)</span>
<span class="n">taskflow</span><span class="p">.</span><span class="n">dump</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="p">);</span>
<span class="c1">// run the pipeline</span>
<span class="n">executor</span><span class="p">.</span><span class="n">run</span><span class="p">(</span><span class="n">taskflow</span><span class="p">).</span><span class="n">wait</span><span class="p">();</span>
<span class="c1">// reset the pipeline to a new range of five pipes and starts from</span>
<span class="c1">// the initial state (i.e., token counts from zero)</span>
<span class="k">for</span><span class="p">(</span><span class="kt">size_t</span><span class="w"> </span><span class="n">i</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o"><</span><span class="mi">2</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">pipes</span><span class="p">.</span><span class="n">emplace_back</span><span class="p">(</span><span class="n">tf</span><span class="o">::</span><span class="n">PipeType</span><span class="o">::</span><span class="n">SERIAL</span><span class="p">,</span><span class="w"> </span><span class="n">pipe_callable</span><span class="p">);</span>
<span class="p">}</span>
<span class="n">pl</span><span class="p">.</span><span class="n">reset</span><span class="p">(</span><span class="n">pipes</span><span class="p">.</span><span class="n">begin</span><span class="p">(),</span><span class="w"> </span><span class="n">pipes</span><span class="p">.</span><span class="n">end</span><span class="p">());</span>
<span class="n">executor</span><span class="p">.</span><span class="n">run</span><span class="p">(</span><span class="n">taskflow</span><span class="p">).</span><span class="n">wait</span><span class="p">();</span></pre><p>The program defines a uniform pipe type of <code>tf::Pipe<std::function<void(tf::Pipeflow&)>></code> and keep all pipes in a vector that is amenable to change. Then, it constructs a scalable pipeline using two range iterators, <code>[first, last)</code>, that point to the beginning and the end of the pipe vector, resulting in a pipeline of three serial stages:</p><div class="m-graph"><svg style="width: 23.800rem; height: 29.200rem;" viewBox="0.00 0.00 238.00 292.00">
<g transform="scale(1 1) rotate(0) translate(4 288)">
<title>Taskflow</title>
<g class="m-cluster">
<title>cluster0</title>
<polygon stroke-dasharray="5,2" points="8,-224 8,-276 222,-276 222,-224 8,-224"/>
</g>
<g class="m-cluster">
<title>cluster1</title>
<polygon stroke-dasharray="5,2" points="8,-152 8,-204 222,-204 222,-152 8,-152"/>
</g>
<g class="m-cluster">
<title>cluster2</title>
<polygon stroke-dasharray="5,2" points="8,-80 8,-132 222,-132 222,-80 8,-80"/>
</g>
<g class="m-cluster">
<title>cluster3</title>
<polygon stroke-dasharray="5,2" points="8,-8 8,-60 222,-60 222,-8 8,-8"/>
</g>
<g class="m-node m-flat">
<title>p00</title>
<ellipse cx="43" cy="-250" rx="27" ry="18"/>
<text text-anchor="middle" x="43" y="-246.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-0</text>
</g>
<g class="m-node m-flat">
<title>p10</title>
<ellipse cx="43" cy="-178" rx="27" ry="18"/>
<text text-anchor="middle" x="43" y="-174.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-0</text>
</g>
<g class="m-edge">
<title>p00->p10</title>
<path d="M43,-231.7C43,-224.41 43,-215.73 43,-207.54"/>
<polygon points="46.5,-207.62 43,-197.62 39.5,-207.62 46.5,-207.62"/>
</g>
<g class="m-node m-flat">
<title>p01</title>
<ellipse cx="115" cy="-250" rx="27" ry="18"/>
<text text-anchor="middle" x="115" y="-246.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-1</text>
</g>
<g class="m-edge">
<title>p00->p01</title>
<path d="M70.28,-250C72.28,-250 74.28,-250 76.29,-250"/>
<polygon points="76.24,-253.5 86.24,-250 76.24,-246.5 76.24,-253.5"/>
</g>
<g class="m-node m-flat">
<title>p20</title>
<ellipse cx="43" cy="-106" rx="27" ry="18"/>
<text text-anchor="middle" x="43" y="-102.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-0</text>
</g>
<g class="m-edge">
<title>p10->p20</title>
<path d="M43,-159.7C43,-152.41 43,-143.73 43,-135.54"/>
<polygon points="46.5,-135.62 43,-125.62 39.5,-135.62 46.5,-135.62"/>
</g>
<g class="m-node m-flat">
<title>p11</title>
<ellipse cx="115" cy="-178" rx="27" ry="18"/>
<text text-anchor="middle" x="115" y="-174.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-1</text>
</g>
<g class="m-edge">
<title>p10->p11</title>
<path d="M70.28,-178C72.28,-178 74.28,-178 76.29,-178"/>
<polygon points="76.24,-181.5 86.24,-178 76.24,-174.5 76.24,-181.5"/>
</g>
<g class="m-node m-flat">
<title>p30</title>
<ellipse cx="43" cy="-34" rx="27" ry="18"/>
<text text-anchor="middle" x="43" y="-30.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-0</text>
</g>
<g class="m-edge">
<title>p20->p30</title>
<path d="M43,-87.7C43,-80.41 43,-71.73 43,-63.54"/>
<polygon points="46.5,-63.62 43,-53.62 39.5,-63.62 46.5,-63.62"/>
</g>
<g class="m-node m-flat">
<title>p21</title>
<ellipse cx="115" cy="-106" rx="27" ry="18"/>
<text text-anchor="middle" x="115" y="-102.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-1</text>
</g>
<g class="m-edge">
<title>p20->p21</title>
<path d="M70.28,-106C72.28,-106 74.28,-106 76.29,-106"/>
<polygon points="76.24,-109.5 86.24,-106 76.24,-102.5 76.24,-109.5"/>
</g>
<g class="m-node m-flat">
<title>p31</title>
<ellipse cx="115" cy="-34" rx="27" ry="18"/>
<text text-anchor="middle" x="115" y="-30.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-1</text>
</g>
<g class="m-edge">
<title>p30->p31</title>
<path d="M70.28,-34C72.28,-34 74.28,-34 76.29,-34"/>
<polygon points="76.24,-37.5 86.24,-34 76.24,-30.5 76.24,-37.5"/>
</g>
<g class="m-edge">
<title>p01->p11</title>
<path d="M115,-231.7C115,-224.41 115,-215.73 115,-207.54"/>
<polygon points="118.5,-207.62 115,-197.62 111.5,-207.62 118.5,-207.62"/>
</g>
<g class="m-node m-flat">
<title>p02</title>
<ellipse cx="187" cy="-250" rx="27" ry="18"/>
<text text-anchor="middle" x="187" y="-246.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-2</text>
</g>
<g class="m-edge">
<title>p01->p02</title>
<path d="M142.28,-250C144.28,-250 146.28,-250 148.29,-250"/>
<polygon points="148.24,-253.5 158.24,-250 148.24,-246.5 148.24,-253.5"/>
</g>
<g class="m-edge">
<title>p11->p21</title>
<path d="M115,-159.7C115,-152.41 115,-143.73 115,-135.54"/>
<polygon points="118.5,-135.62 115,-125.62 111.5,-135.62 118.5,-135.62"/>
</g>
<g class="m-node m-flat">
<title>p12</title>
<ellipse cx="187" cy="-178" rx="27" ry="18"/>
<text text-anchor="middle" x="187" y="-174.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-2</text>
</g>
<g class="m-edge">
<title>p11->p12</title>
<path d="M142.28,-178C144.28,-178 146.28,-178 148.29,-178"/>
<polygon points="148.24,-181.5 158.24,-178 148.24,-174.5 148.24,-181.5"/>
</g>
<g class="m-edge">
<title>p21->p31</title>
<path d="M115,-87.7C115,-80.41 115,-71.73 115,-63.54"/>
<polygon points="118.5,-63.62 115,-53.62 111.5,-63.62 118.5,-63.62"/>
</g>
<g class="m-node m-flat">
<title>p22</title>
<ellipse cx="187" cy="-106" rx="27" ry="18"/>
<text text-anchor="middle" x="187" y="-102.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-2</text>
</g>
<g class="m-edge">
<title>p21->p22</title>
<path d="M142.28,-106C144.28,-106 146.28,-106 148.29,-106"/>
<polygon points="148.24,-109.5 158.24,-106 148.24,-102.5 148.24,-109.5"/>
</g>
<g class="m-node m-flat">
<title>p32</title>
<ellipse cx="187" cy="-34" rx="27" ry="18"/>
<text text-anchor="middle" x="187" y="-30.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-2</text>
</g>
<g class="m-edge">
<title>p31->p32</title>
<path d="M142.28,-34C144.28,-34 146.28,-34 148.29,-34"/>
<polygon points="148.24,-37.5 158.24,-34 148.24,-30.5 148.24,-37.5"/>
</g>
<g class="m-edge">
<title>p02->p12</title>
<path d="M187,-231.7C187,-224.41 187,-215.73 187,-207.54"/>
<polygon points="190.5,-207.62 187,-197.62 183.5,-207.62 190.5,-207.62"/>
</g>
<g class="m-edge">
<title>p12->p22</title>
<path d="M187,-159.7C187,-152.41 187,-143.73 187,-135.54"/>
<polygon points="190.5,-135.62 187,-125.62 183.5,-135.62 190.5,-135.62"/>
</g>
<g class="m-edge">
<title>p22->p32</title>
<path d="M187,-87.7C187,-80.41 187,-71.73 187,-63.54"/>
<polygon points="190.5,-63.62 187,-53.62 183.5,-63.62 190.5,-63.62"/>
</g>
</g>
</svg>
</div><p>Then, the program appends another two pipes into the vector and resets the pipeline to the new range of two additional pipes, resulting in a pipeline of five serial stages:</p><div class="m-graph"><svg style="width: 38.200rem; height: 29.200rem;" viewBox="0.00 0.00 382.00 292.00">
<g transform="scale(1 1) rotate(0) translate(4 288)">
<title>Taskflow</title>
<g class="m-cluster">
<title>cluster0</title>
<polygon stroke-dasharray="5,2" points="8,-224 8,-276 366,-276 366,-224 8,-224"/>
</g>
<g class="m-cluster">
<title>cluster1</title>
<polygon stroke-dasharray="5,2" points="8,-152 8,-204 366,-204 366,-152 8,-152"/>
</g>
<g class="m-cluster">
<title>cluster2</title>
<polygon stroke-dasharray="5,2" points="8,-80 8,-132 366,-132 366,-80 8,-80"/>
</g>
<g class="m-cluster">
<title>cluster3</title>
<polygon stroke-dasharray="5,2" points="8,-8 8,-60 366,-60 366,-8 8,-8"/>
</g>
<g class="m-node m-flat">
<title>p00</title>
<ellipse cx="43" cy="-250" rx="27" ry="18"/>
<text text-anchor="middle" x="43" y="-246.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-0</text>
</g>
<g class="m-node m-flat">
<title>p10</title>
<ellipse cx="43" cy="-178" rx="27" ry="18"/>
<text text-anchor="middle" x="43" y="-174.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-0</text>
</g>
<g class="m-edge">
<title>p00->p10</title>
<path d="M43,-231.7C43,-224.41 43,-215.73 43,-207.54"/>
<polygon points="46.5,-207.62 43,-197.62 39.5,-207.62 46.5,-207.62"/>
</g>
<g class="m-node m-flat">
<title>p01</title>
<ellipse cx="115" cy="-250" rx="27" ry="18"/>
<text text-anchor="middle" x="115" y="-246.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-1</text>
</g>
<g class="m-edge">
<title>p00->p01</title>
<path d="M70.28,-250C72.28,-250 74.28,-250 76.29,-250"/>
<polygon points="76.24,-253.5 86.24,-250 76.24,-246.5 76.24,-253.5"/>
</g>
<g class="m-node m-flat">
<title>p20</title>
<ellipse cx="43" cy="-106" rx="27" ry="18"/>
<text text-anchor="middle" x="43" y="-102.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-0</text>
</g>
<g class="m-edge">
<title>p10->p20</title>
<path d="M43,-159.7C43,-152.41 43,-143.73 43,-135.54"/>
<polygon points="46.5,-135.62 43,-125.62 39.5,-135.62 46.5,-135.62"/>
</g>
<g class="m-node m-flat">
<title>p11</title>
<ellipse cx="115" cy="-178" rx="27" ry="18"/>
<text text-anchor="middle" x="115" y="-174.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-1</text>
</g>
<g class="m-edge">
<title>p10->p11</title>
<path d="M70.28,-178C72.28,-178 74.28,-178 76.29,-178"/>
<polygon points="76.24,-181.5 86.24,-178 76.24,-174.5 76.24,-181.5"/>
</g>
<g class="m-node m-flat">
<title>p30</title>
<ellipse cx="43" cy="-34" rx="27" ry="18"/>
<text text-anchor="middle" x="43" y="-30.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-0</text>
</g>
<g class="m-edge">
<title>p20->p30</title>
<path d="M43,-87.7C43,-80.41 43,-71.73 43,-63.54"/>
<polygon points="46.5,-63.62 43,-53.62 39.5,-63.62 46.5,-63.62"/>
</g>
<g class="m-node m-flat">
<title>p21</title>
<ellipse cx="115" cy="-106" rx="27" ry="18"/>
<text text-anchor="middle" x="115" y="-102.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-1</text>
</g>
<g class="m-edge">
<title>p20->p21</title>
<path d="M70.28,-106C72.28,-106 74.28,-106 76.29,-106"/>
<polygon points="76.24,-109.5 86.24,-106 76.24,-102.5 76.24,-109.5"/>
</g>
<g class="m-node m-flat">
<title>p31</title>
<ellipse cx="115" cy="-34" rx="27" ry="18"/>
<text text-anchor="middle" x="115" y="-30.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-1</text>
</g>
<g class="m-edge">
<title>p30->p31</title>
<path d="M70.28,-34C72.28,-34 74.28,-34 76.29,-34"/>
<polygon points="76.24,-37.5 86.24,-34 76.24,-30.5 76.24,-37.5"/>
</g>
<g class="m-edge">
<title>p01->p11</title>
<path d="M115,-231.7C115,-224.41 115,-215.73 115,-207.54"/>
<polygon points="118.5,-207.62 115,-197.62 111.5,-207.62 118.5,-207.62"/>
</g>
<g class="m-node m-flat">
<title>p02</title>
<ellipse cx="187" cy="-250" rx="27" ry="18"/>
<text text-anchor="middle" x="187" y="-246.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-2</text>
</g>
<g class="m-edge">
<title>p01->p02</title>
<path d="M142.28,-250C144.28,-250 146.28,-250 148.29,-250"/>
<polygon points="148.24,-253.5 158.24,-250 148.24,-246.5 148.24,-253.5"/>
</g>
<g class="m-edge">
<title>p11->p21</title>
<path d="M115,-159.7C115,-152.41 115,-143.73 115,-135.54"/>
<polygon points="118.5,-135.62 115,-125.62 111.5,-135.62 118.5,-135.62"/>
</g>
<g class="m-node m-flat">
<title>p12</title>
<ellipse cx="187" cy="-178" rx="27" ry="18"/>
<text text-anchor="middle" x="187" y="-174.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-2</text>
</g>
<g class="m-edge">
<title>p11->p12</title>
<path d="M142.28,-178C144.28,-178 146.28,-178 148.29,-178"/>
<polygon points="148.24,-181.5 158.24,-178 148.24,-174.5 148.24,-181.5"/>
</g>
<g class="m-edge">
<title>p21->p31</title>
<path d="M115,-87.7C115,-80.41 115,-71.73 115,-63.54"/>
<polygon points="118.5,-63.62 115,-53.62 111.5,-63.62 118.5,-63.62"/>
</g>
<g class="m-node m-flat">
<title>p22</title>
<ellipse cx="187" cy="-106" rx="27" ry="18"/>
<text text-anchor="middle" x="187" y="-102.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-2</text>
</g>
<g class="m-edge">
<title>p21->p22</title>
<path d="M142.28,-106C144.28,-106 146.28,-106 148.29,-106"/>
<polygon points="148.24,-109.5 158.24,-106 148.24,-102.5 148.24,-109.5"/>
</g>
<g class="m-node m-flat">
<title>p32</title>
<ellipse cx="187" cy="-34" rx="27" ry="18"/>
<text text-anchor="middle" x="187" y="-30.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-2</text>
</g>
<g class="m-edge">
<title>p31->p32</title>
<path d="M142.28,-34C144.28,-34 146.28,-34 148.29,-34"/>
<polygon points="148.24,-37.5 158.24,-34 148.24,-30.5 148.24,-37.5"/>
</g>
<g class="m-edge">
<title>p02->p12</title>
<path d="M187,-231.7C187,-224.41 187,-215.73 187,-207.54"/>
<polygon points="190.5,-207.62 187,-197.62 183.5,-207.62 190.5,-207.62"/>
</g>
<g class="m-node m-flat">
<title>p03</title>
<ellipse cx="259" cy="-250" rx="27" ry="18"/>
<text text-anchor="middle" x="259" y="-246.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-3</text>
</g>
<g class="m-edge">
<title>p02->p03</title>
<path d="M214.28,-250C216.28,-250 218.28,-250 220.29,-250"/>
<polygon points="220.24,-253.5 230.24,-250 220.24,-246.5 220.24,-253.5"/>
</g>
<g class="m-edge">
<title>p12->p22</title>
<path d="M187,-159.7C187,-152.41 187,-143.73 187,-135.54"/>
<polygon points="190.5,-135.62 187,-125.62 183.5,-135.62 190.5,-135.62"/>
</g>
<g class="m-node m-flat">
<title>p13</title>
<ellipse cx="259" cy="-178" rx="27" ry="18"/>
<text text-anchor="middle" x="259" y="-174.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-3</text>
</g>
<g class="m-edge">
<title>p12->p13</title>
<path d="M214.28,-178C216.28,-178 218.28,-178 220.29,-178"/>
<polygon points="220.24,-181.5 230.24,-178 220.24,-174.5 220.24,-181.5"/>
</g>
<g class="m-edge">
<title>p22->p32</title>
<path d="M187,-87.7C187,-80.41 187,-71.73 187,-63.54"/>
<polygon points="190.5,-63.62 187,-53.62 183.5,-63.62 190.5,-63.62"/>
</g>
<g class="m-node m-flat">
<title>p23</title>
<ellipse cx="259" cy="-106" rx="27" ry="18"/>
<text text-anchor="middle" x="259" y="-102.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-3</text>
</g>
<g class="m-edge">
<title>p22->p23</title>
<path d="M214.28,-106C216.28,-106 218.28,-106 220.29,-106"/>
<polygon points="220.24,-109.5 230.24,-106 220.24,-102.5 220.24,-109.5"/>
</g>
<g class="m-node m-flat">
<title>p33</title>
<ellipse cx="259" cy="-34" rx="27" ry="18"/>
<text text-anchor="middle" x="259" y="-30.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-3</text>
</g>
<g class="m-edge">
<title>p32->p33</title>
<path d="M214.28,-34C216.28,-34 218.28,-34 220.29,-34"/>
<polygon points="220.24,-37.5 230.24,-34 220.24,-30.5 220.24,-37.5"/>
</g>
<g class="m-edge">
<title>p03->p13</title>
<path d="M259,-231.7C259,-224.41 259,-215.73 259,-207.54"/>
<polygon points="262.5,-207.62 259,-197.62 255.5,-207.62 262.5,-207.62"/>
</g>
<g class="m-node m-flat">
<title>p04</title>
<ellipse cx="331" cy="-250" rx="27" ry="18"/>
<text text-anchor="middle" x="331" y="-246.12" font-family="Helvetica,sans-Serif" font-size="10.00">pipe-4</text>
</g>
<g class="m-edge">
<title>p03->p04</title>
<path d="M286.28,-250C288.28,-250 290.28,-250 292.29,-250"/>
<polygon points="292.24,-253.5 302.24,-250 292.24,-246.5 292.24,-253.5"/>
</g>
<g class="m-edge">
<title>p13->p23</title>
<path d="M259,-159.7C259,-152.41 259,-143.73 259,-135.54"/>
<polygon points="262.5,-135.62 259,-125.62 255.5,-135.62 262.5,-135.62"/>
</g>
<g class="m-node m-flat">
<title>p14</title>
<ellipse cx="331" cy="-178" rx="27" ry="18"/>
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</div><p>When resetting a scalable pipeline to a new range, it will start from the initial state as if it has just been constructed, i.e., the token number counts from zero.</p><aside class="m-note m-warning"><h4>Attention</h4><p>Unlike <a href="classtf_1_1Pipeline.html" class="m-doc">tf::<wbr />Pipeline</a> that keeps the given pipes in a <a href="http://en.cppreference.com/w/cpp/utility/tuple.html" class="m-doc-external">std::<wbr />tuple</a> object, <a href="classtf_1_1ScalablePipeline.html" class="m-doc">tf::<wbr />ScalablePipeline</a> does not own the given pipe but maintains a vector of iterators to each pipe in the given range. It is your responsibility to keep those pipe objects alive during the execution of the pipeline task.</p></aside></section><section id="ResetAPlaceholderScalablePipeline"><h2><a href="#ResetAPlaceholderScalablePipeline">Reset a Placeholder Scalable Pipeline</a></h2><p>It is possible to create a scalable pipeline as a placeholder using the constructor <a href="classtf_1_1ScalablePipeline.html" class="m-doc">tf::<wbr />ScalablePipeline(size_t num_lines)</a> and reset it to another range later in the application. The following code creates a task to emplace a range of pipes and reset the pipeline to that range, before running the pipeline task:</p><pre class="m-code"><span class="n">tf</span><span class="o">::</span><span class="n">Executor</span><span class="w"> </span><span class="n">executor</span><span class="p">;</span>
<span class="n">tf</span><span class="o">::</span><span class="n">Taskflow</span><span class="w"> </span><span class="n">taskflow</span><span class="p">;</span>
<span class="kt">size_t</span><span class="w"> </span><span class="n">num_pipes</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">10</span><span class="p">;</span>
<span class="kt">size_t</span><span class="w"> </span><span class="n">num_lines</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">10</span><span class="p">;</span>
<span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipe</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">function</span><span class="o"><</span><span class="kt">void</span><span class="p">(</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipeflow</span><span class="o">&</span><span class="p">)</span><span class="o">>>></span><span class="w"> </span><span class="n">pipes</span><span class="p">;</span>
<span class="n">tf</span><span class="o">::</span><span class="n">ScalablePipeline</span><span class="o"><</span><span class="k">typename</span><span class="w"> </span><span class="nc">decltype</span><span class="p">(</span><span class="n">pipes</span><span class="p">)</span><span class="o">::</span><span class="n">iterator</span><span class="o">></span><span class="w"> </span><span class="n">spl</span><span class="p">(</span><span class="n">num_lines</span><span class="p">);</span><span class="w"> </span>
<span class="n">tf</span><span class="o">::</span><span class="n">Task</span><span class="w"> </span><span class="n">init</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">taskflow</span><span class="p">.</span><span class="n">emplace</span><span class="p">([</span><span class="o">&</span><span class="p">](){</span>
<span class="w"> </span><span class="k">for</span><span class="p">(</span><span class="kt">size_t</span><span class="w"> </span><span class="n">i</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o"><</span><span class="n">num_pipes</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">pipes</span><span class="p">.</span><span class="n">emplace_back</span><span class="p">(</span><span class="n">tf</span><span class="o">::</span><span class="n">PipeType</span><span class="o">::</span><span class="n">SERIAL</span><span class="p">,</span><span class="w"> </span><span class="p">[</span><span class="o">&</span><span class="p">](</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipeflow</span><span class="o">&</span><span class="w"> </span><span class="n">pf</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"> </span>
<span class="w"> </span><span class="k">if</span><span class="p">(</span><span class="n">pf</span><span class="p">.</span><span class="n">pipe</span><span class="p">()</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="n">pf</span><span class="p">.</span><span class="n">token</span><span class="p">()</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1024</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">pf</span><span class="p">.</span><span class="n">stop</span><span class="p">();</span>
<span class="w"> </span><span class="k">return</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="p">});</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="n">spl</span><span class="p">.</span><span class="n">reset</span><span class="p">(</span><span class="n">pipes</span><span class="p">.</span><span class="n">begin</span><span class="p">(),</span><span class="w"> </span><span class="n">pipes</span><span class="p">.</span><span class="n">end</span><span class="p">());</span>
<span class="p">}).</span><span class="n">name</span><span class="p">(</span><span class="s">"init"</span><span class="p">);</span>
<span class="n">tf</span><span class="o">::</span><span class="n">Task</span><span class="w"> </span><span class="n">pipeline</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">taskflow</span><span class="p">.</span><span class="n">composed_of</span><span class="p">(</span><span class="n">spl</span><span class="p">).</span><span class="n">name</span><span class="p">(</span><span class="s">"pipeline"</span><span class="p">);</span>
<span class="n">pipeline</span><span class="p">.</span><span class="n">succeed</span><span class="p">(</span><span class="n">init</span><span class="p">);</span>
<span class="n">executor</span><span class="p">.</span><span class="n">run</span><span class="p">(</span><span class="n">taskflow</span><span class="p">).</span><span class="n">wait</span><span class="p">();</span><span class="w"> </span></pre><p>The task graph of this program is shown below:</p><div class="m-graph"><svg style="width: 83.800rem; height: 17.900rem;" viewBox="0.00 0.00 838.00 178.50">
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</div><aside class="m-note m-warning"><h4>Attention</h4><p>It is your responsibility to ensure a scalable pipeline has a valid structure before running it. A valid pipeline must have at least one parallel line and one pipe, where the first pipe is a serial type.</p></aside><p>Similarly, you can create an empty scalable pipeline using the default constructor <a href="classtf_1_1ScalablePipeline.html" class="m-doc">tf::<wbr />ScalablePipeline()</a> and reset it later in your program.</p><pre class="m-code"><span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipe</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">function</span><span class="o"><</span><span class="kt">void</span><span class="p">(</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipeflow</span><span class="o">&</span><span class="p">)</span><span class="o">>>></span><span class="w"> </span><span class="n">pipes</span><span class="p">;</span>
<span class="n">tf</span><span class="o">::</span><span class="n">ScalablePipeline</span><span class="o"><</span><span class="k">typename</span><span class="w"> </span><span class="nc">decltype</span><span class="p">(</span><span class="n">pipes</span><span class="p">)</span><span class="o">::</span><span class="n">iterator</span><span class="o">></span><span class="w"> </span><span class="n">spl</span><span class="p">;</span><span class="w"> </span>
<span class="c1">// create pipes ...</span>
<span class="n">spl</span><span class="p">.</span><span class="n">reset</span><span class="p">(</span><span class="n">num_lines</span><span class="p">,</span><span class="w"> </span><span class="n">pipes</span><span class="p">.</span><span class="n">begin</span><span class="p">(),</span><span class="w"> </span><span class="n">pipes</span><span class="p">.</span><span class="n">end</span><span class="p">());</span></pre></section><section id="ScalablePipelineUseOtherIteratorTypes"><h2><a href="#ScalablePipelineUseOtherIteratorTypes">Use Other Iterator Types</a></h2><p>When assigning a range to a scalable pipeline, the pipeline fetches all pipe iterators in that range to an internal vector. This organization allows invoking a pipe callable to be a random accessible operation, regardless of the pipe container type. Taskflow does not have much restriction on the iterator type, as long as these pipes can be iterated in a sequential order using the postfix increment operator, <code>++</code>.</p><pre class="m-code"><span class="c1">// use vector to store pipes</span>
<span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipe</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">function</span><span class="o"><</span><span class="kt">void</span><span class="p">(</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipeflow</span><span class="o">&</span><span class="p">)</span><span class="o">>>></span><span class="w"> </span><span class="n">vector</span><span class="p">;</span>
<span class="n">tf</span><span class="o">::</span><span class="n">ScalablePipeline</span><span class="w"> </span><span class="nf">spl1</span><span class="p">(</span><span class="n">num_lines</span><span class="p">,</span><span class="w"> </span><span class="n">vector</span><span class="p">.</span><span class="n">begin</span><span class="p">(),</span><span class="w"> </span><span class="n">vector</span><span class="p">.</span><span class="n">end</span><span class="p">());</span>
<span class="c1">// use list to store pipes</span>
<span class="n">std</span><span class="o">::</span><span class="n">list</span><span class="o"><</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipe</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">function</span><span class="o"><</span><span class="kt">void</span><span class="p">(</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipeflow</span><span class="o">&</span><span class="p">)</span><span class="o">>>></span><span class="w"> </span><span class="n">list</span><span class="p">;</span>
<span class="n">tf</span><span class="o">::</span><span class="n">ScalablePipeline</span><span class="w"> </span><span class="nf">spl2</span><span class="p">(</span><span class="n">num_lines</span><span class="p">,</span><span class="w"> </span><span class="n">list</span><span class="p">.</span><span class="n">begin</span><span class="p">(),</span><span class="w"> </span><span class="n">list</span><span class="p">.</span><span class="n">end</span><span class="p">());</span></pre></section><section id="ParallelScalablePipelineLearnMore"><h2><a href="#ParallelScalablePipelineLearnMore">Learn More about Taskflow Pipeline</a></h2><p>Visit the following pages to learn more about pipeline:</p><ul><li><a href="TaskParallelPipeline.html" class="m-doc">Task-parallel Pipeline</a></li><li><a href="DataParallelPipeline.html" class="m-doc">Data-parallel Pipeline</a></li><li><a href="TextProcessingPipeline.html" class="m-doc">Text Processing Pipeline</a></li><li><a href="GraphProcessingPipeline.html" class="m-doc">Graph Processing Pipeline</a></li><li><a href="TaskflowProcessingPipeline.html" class="m-doc">Taskflow Processing Pipeline</a></li></ul></section>
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