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<title>Taskflow Algorithms &raquo; Task-parallel Scalable Pipeline | Taskflow QuickStart</title>
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<h1>
<span class="m-breadcrumb"><a href="Algorithms.html">Taskflow Algorithms</a> &raquo;</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">&lt;taskflow/algorithm/pipeline.hpp&gt;</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="nf">taskflow</span><span class="p">(</span><span class="s">&quot;pipeline&quot;</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">&lt;</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="n">num_lines</span><span class="o">&gt;</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">&amp;</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">&amp;</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="o">:</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">&quot;stage 1: input token = %zu</span><span class="se">\n</span><span class="s">&quot;</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">&quot;stage %zu: input buffer[%zu] = %d</span><span class="se">\n</span><span class="s">&quot;</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">&lt;</span><span class="w"> </span><span class="n">tf</span><span class="o">::</span><span class="n">Pipe</span><span class="o">&lt;</span><span class="n">std</span><span class="o">::</span><span class="n">function</span><span class="o">&lt;</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">&amp;</span><span class="p">)</span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="o">&gt;</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">&lt;</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">&lt;&lt;</span><span class="w"> </span><span class="s">&quot;ready</span><span class="se">\n</span><span class="s">&quot;</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">&quot;starting pipeline&quot;</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">&quot;pipeline&quot;</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">&lt;&lt;</span><span class="w"> </span><span class="s">&quot;stopped</span><span class="se">\n</span><span class="s">&quot;</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">&quot;pipeline stopped&quot;</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">&lt;</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&lt;std::function&lt;void(tf::Pipeflow&amp;)&gt;&gt;</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: 24.200rem; height: 29.200rem;" viewBox="0.00 0.00 242.00 292.00">
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<ellipse cx="117" cy="-34" rx="27.84" ry="18"/>
<text text-anchor="middle" x="117" y="-31.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;1</text>
</g>
<g class="m-edge">
<title>p30&#45;&gt;p31</title>
<path d="M71.95,-34C74.28,-34 76.62,-34 78.95,-34"/>
<polygon points="79.19,-37.5 89.19,-34 79.19,-30.5 79.19,-37.5"/>
</g>
<g class="m-edge">
<title>p01&#45;&gt;p11</title>
<path d="M117,-231.7C117,-223.98 117,-214.71 117,-206.11"/>
<polygon points="120.5,-206.1 117,-196.1 113.5,-206.1 120.5,-206.1"/>
</g>
<g class="m-node m-flat">
<title>p02</title>
<ellipse cx="190" cy="-250" rx="27.84" ry="18"/>
<text text-anchor="middle" x="190" y="-247.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;2</text>
</g>
<g class="m-edge">
<title>p01&#45;&gt;p02</title>
<path d="M144.95,-250C147.28,-250 149.62,-250 151.95,-250"/>
<polygon points="152.19,-253.5 162.19,-250 152.19,-246.5 152.19,-253.5"/>
</g>
<g class="m-edge">
<title>p11&#45;&gt;p21</title>
<path d="M117,-159.7C117,-151.98 117,-142.71 117,-134.11"/>
<polygon points="120.5,-134.1 117,-124.1 113.5,-134.1 120.5,-134.1"/>
</g>
<g class="m-node m-flat">
<title>p12</title>
<ellipse cx="190" cy="-178" rx="27.84" ry="18"/>
<text text-anchor="middle" x="190" y="-175.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;2</text>
</g>
<g class="m-edge">
<title>p11&#45;&gt;p12</title>
<path d="M144.95,-178C147.28,-178 149.62,-178 151.95,-178"/>
<polygon points="152.19,-181.5 162.19,-178 152.19,-174.5 152.19,-181.5"/>
</g>
<g class="m-edge">
<title>p21&#45;&gt;p31</title>
<path d="M117,-87.7C117,-79.98 117,-70.71 117,-62.11"/>
<polygon points="120.5,-62.1 117,-52.1 113.5,-62.1 120.5,-62.1"/>
</g>
<g class="m-node m-flat">
<title>p22</title>
<ellipse cx="190" cy="-106" rx="27.84" ry="18"/>
<text text-anchor="middle" x="190" y="-103.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;2</text>
</g>
<g class="m-edge">
<title>p21&#45;&gt;p22</title>
<path d="M144.95,-106C147.28,-106 149.62,-106 151.95,-106"/>
<polygon points="152.19,-109.5 162.19,-106 152.19,-102.5 152.19,-109.5"/>
</g>
<g class="m-node m-flat">
<title>p32</title>
<ellipse cx="190" cy="-34" rx="27.84" ry="18"/>
<text text-anchor="middle" x="190" y="-31.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;2</text>
</g>
<g class="m-edge">
<title>p31&#45;&gt;p32</title>
<path d="M144.95,-34C147.28,-34 149.62,-34 151.95,-34"/>
<polygon points="152.19,-37.5 162.19,-34 152.19,-30.5 152.19,-37.5"/>
</g>
<g class="m-edge">
<title>p02&#45;&gt;p12</title>
<path d="M190,-231.7C190,-223.98 190,-214.71 190,-206.11"/>
<polygon points="193.5,-206.1 190,-196.1 186.5,-206.1 193.5,-206.1"/>
</g>
<g class="m-edge">
<title>p12&#45;&gt;p22</title>
<path d="M190,-159.7C190,-151.98 190,-142.71 190,-134.11"/>
<polygon points="193.5,-134.1 190,-124.1 186.5,-134.1 193.5,-134.1"/>
</g>
<g class="m-edge">
<title>p22&#45;&gt;p32</title>
<path d="M190,-87.7C190,-79.98 190,-70.71 190,-62.11"/>
<polygon points="193.5,-62.1 190,-52.1 186.5,-62.1 193.5,-62.1"/>
</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: 38.800rem; height: 29.200rem;" viewBox="0.00 0.00 388.00 292.00">
<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,-276 372,-276 372,-224 8,-224"/>
</g>
<g class="m-cluster">
<title>cluster1</title>
<polygon stroke-dasharray="5,2" points="8,-152 8,-204 372,-204 372,-152 8,-152"/>
</g>
<g class="m-cluster">
<title>cluster2</title>
<polygon stroke-dasharray="5,2" points="8,-80 8,-132 372,-132 372,-80 8,-80"/>
</g>
<g class="m-cluster">
<title>cluster3</title>
<polygon stroke-dasharray="5,2" points="8,-8 8,-60 372,-60 372,-8 8,-8"/>
</g>
<g class="m-node m-flat">
<title>p00</title>
<ellipse cx="44" cy="-250" rx="27.84" ry="18"/>
<text text-anchor="middle" x="44" y="-247.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;0</text>
</g>
<g class="m-node m-flat">
<title>p10</title>
<ellipse cx="44" cy="-178" rx="27.84" ry="18"/>
<text text-anchor="middle" x="44" y="-175.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;0</text>
</g>
<g class="m-edge">
<title>p00&#45;&gt;p10</title>
<path d="M44,-231.7C44,-223.98 44,-214.71 44,-206.11"/>
<polygon points="47.5,-206.1 44,-196.1 40.5,-206.1 47.5,-206.1"/>
</g>
<g class="m-node m-flat">
<title>p01</title>
<ellipse cx="117" cy="-250" rx="27.84" ry="18"/>
<text text-anchor="middle" x="117" y="-247.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;1</text>
</g>
<g class="m-edge">
<title>p00&#45;&gt;p01</title>
<path d="M71.95,-250C74.28,-250 76.62,-250 78.95,-250"/>
<polygon points="79.19,-253.5 89.19,-250 79.19,-246.5 79.19,-253.5"/>
</g>
<g class="m-node m-flat">
<title>p20</title>
<ellipse cx="44" cy="-106" rx="27.84" ry="18"/>
<text text-anchor="middle" x="44" y="-103.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;0</text>
</g>
<g class="m-edge">
<title>p10&#45;&gt;p20</title>
<path d="M44,-159.7C44,-151.98 44,-142.71 44,-134.11"/>
<polygon points="47.5,-134.1 44,-124.1 40.5,-134.1 47.5,-134.1"/>
</g>
<g class="m-node m-flat">
<title>p11</title>
<ellipse cx="117" cy="-178" rx="27.84" ry="18"/>
<text text-anchor="middle" x="117" y="-175.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;1</text>
</g>
<g class="m-edge">
<title>p10&#45;&gt;p11</title>
<path d="M71.95,-178C74.28,-178 76.62,-178 78.95,-178"/>
<polygon points="79.19,-181.5 89.19,-178 79.19,-174.5 79.19,-181.5"/>
</g>
<g class="m-node m-flat">
<title>p30</title>
<ellipse cx="44" cy="-34" rx="27.84" ry="18"/>
<text text-anchor="middle" x="44" y="-31.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;0</text>
</g>
<g class="m-edge">
<title>p20&#45;&gt;p30</title>
<path d="M44,-87.7C44,-79.98 44,-70.71 44,-62.11"/>
<polygon points="47.5,-62.1 44,-52.1 40.5,-62.1 47.5,-62.1"/>
</g>
<g class="m-node m-flat">
<title>p21</title>
<ellipse cx="117" cy="-106" rx="27.84" ry="18"/>
<text text-anchor="middle" x="117" y="-103.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;1</text>
</g>
<g class="m-edge">
<title>p20&#45;&gt;p21</title>
<path d="M71.95,-106C74.28,-106 76.62,-106 78.95,-106"/>
<polygon points="79.19,-109.5 89.19,-106 79.19,-102.5 79.19,-109.5"/>
</g>
<g class="m-node m-flat">
<title>p31</title>
<ellipse cx="117" cy="-34" rx="27.84" ry="18"/>
<text text-anchor="middle" x="117" y="-31.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;1</text>
</g>
<g class="m-edge">
<title>p30&#45;&gt;p31</title>
<path d="M71.95,-34C74.28,-34 76.62,-34 78.95,-34"/>
<polygon points="79.19,-37.5 89.19,-34 79.19,-30.5 79.19,-37.5"/>
</g>
<g class="m-edge">
<title>p01&#45;&gt;p11</title>
<path d="M117,-231.7C117,-223.98 117,-214.71 117,-206.11"/>
<polygon points="120.5,-206.1 117,-196.1 113.5,-206.1 120.5,-206.1"/>
</g>
<g class="m-node m-flat">
<title>p02</title>
<ellipse cx="190" cy="-250" rx="27.84" ry="18"/>
<text text-anchor="middle" x="190" y="-247.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;2</text>
</g>
<g class="m-edge">
<title>p01&#45;&gt;p02</title>
<path d="M144.95,-250C147.28,-250 149.62,-250 151.95,-250"/>
<polygon points="152.19,-253.5 162.19,-250 152.19,-246.5 152.19,-253.5"/>
</g>
<g class="m-edge">
<title>p11&#45;&gt;p21</title>
<path d="M117,-159.7C117,-151.98 117,-142.71 117,-134.11"/>
<polygon points="120.5,-134.1 117,-124.1 113.5,-134.1 120.5,-134.1"/>
</g>
<g class="m-node m-flat">
<title>p12</title>
<ellipse cx="190" cy="-178" rx="27.84" ry="18"/>
<text text-anchor="middle" x="190" y="-175.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;2</text>
</g>
<g class="m-edge">
<title>p11&#45;&gt;p12</title>
<path d="M144.95,-178C147.28,-178 149.62,-178 151.95,-178"/>
<polygon points="152.19,-181.5 162.19,-178 152.19,-174.5 152.19,-181.5"/>
</g>
<g class="m-edge">
<title>p21&#45;&gt;p31</title>
<path d="M117,-87.7C117,-79.98 117,-70.71 117,-62.11"/>
<polygon points="120.5,-62.1 117,-52.1 113.5,-62.1 120.5,-62.1"/>
</g>
<g class="m-node m-flat">
<title>p22</title>
<ellipse cx="190" cy="-106" rx="27.84" ry="18"/>
<text text-anchor="middle" x="190" y="-103.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;2</text>
</g>
<g class="m-edge">
<title>p21&#45;&gt;p22</title>
<path d="M144.95,-106C147.28,-106 149.62,-106 151.95,-106"/>
<polygon points="152.19,-109.5 162.19,-106 152.19,-102.5 152.19,-109.5"/>
</g>
<g class="m-node m-flat">
<title>p32</title>
<ellipse cx="190" cy="-34" rx="27.84" ry="18"/>
<text text-anchor="middle" x="190" y="-31.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;2</text>
</g>
<g class="m-edge">
<title>p31&#45;&gt;p32</title>
<path d="M144.95,-34C147.28,-34 149.62,-34 151.95,-34"/>
<polygon points="152.19,-37.5 162.19,-34 152.19,-30.5 152.19,-37.5"/>
</g>
<g class="m-edge">
<title>p02&#45;&gt;p12</title>
<path d="M190,-231.7C190,-223.98 190,-214.71 190,-206.11"/>
<polygon points="193.5,-206.1 190,-196.1 186.5,-206.1 193.5,-206.1"/>
</g>
<g class="m-node m-flat">
<title>p03</title>
<ellipse cx="263" cy="-250" rx="27.84" ry="18"/>
<text text-anchor="middle" x="263" y="-247.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;3</text>
</g>
<g class="m-edge">
<title>p02&#45;&gt;p03</title>
<path d="M217.95,-250C220.28,-250 222.62,-250 224.95,-250"/>
<polygon points="225.19,-253.5 235.19,-250 225.19,-246.5 225.19,-253.5"/>
</g>
<g class="m-edge">
<title>p12&#45;&gt;p22</title>
<path d="M190,-159.7C190,-151.98 190,-142.71 190,-134.11"/>
<polygon points="193.5,-134.1 190,-124.1 186.5,-134.1 193.5,-134.1"/>
</g>
<g class="m-node m-flat">
<title>p13</title>
<ellipse cx="263" cy="-178" rx="27.84" ry="18"/>
<text text-anchor="middle" x="263" y="-175.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;3</text>
</g>
<g class="m-edge">
<title>p12&#45;&gt;p13</title>
<path d="M217.95,-178C220.28,-178 222.62,-178 224.95,-178"/>
<polygon points="225.19,-181.5 235.19,-178 225.19,-174.5 225.19,-181.5"/>
</g>
<g class="m-edge">
<title>p22&#45;&gt;p32</title>
<path d="M190,-87.7C190,-79.98 190,-70.71 190,-62.11"/>
<polygon points="193.5,-62.1 190,-52.1 186.5,-62.1 193.5,-62.1"/>
</g>
<g class="m-node m-flat">
<title>p23</title>
<ellipse cx="263" cy="-106" rx="27.84" ry="18"/>
<text text-anchor="middle" x="263" y="-103.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;3</text>
</g>
<g class="m-edge">
<title>p22&#45;&gt;p23</title>
<path d="M217.95,-106C220.28,-106 222.62,-106 224.95,-106"/>
<polygon points="225.19,-109.5 235.19,-106 225.19,-102.5 225.19,-109.5"/>
</g>
<g class="m-node m-flat">
<title>p33</title>
<ellipse cx="263" cy="-34" rx="27.84" ry="18"/>
<text text-anchor="middle" x="263" y="-31.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;3</text>
</g>
<g class="m-edge">
<title>p32&#45;&gt;p33</title>
<path d="M217.95,-34C220.28,-34 222.62,-34 224.95,-34"/>
<polygon points="225.19,-37.5 235.19,-34 225.19,-30.5 225.19,-37.5"/>
</g>
<g class="m-edge">
<title>p03&#45;&gt;p13</title>
<path d="M263,-231.7C263,-223.98 263,-214.71 263,-206.11"/>
<polygon points="266.5,-206.1 263,-196.1 259.5,-206.1 266.5,-206.1"/>
</g>
<g class="m-node m-flat">
<title>p04</title>
<ellipse cx="336" cy="-250" rx="27.84" ry="18"/>
<text text-anchor="middle" x="336" y="-247.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;4</text>
</g>
<g class="m-edge">
<title>p03&#45;&gt;p04</title>
<path d="M290.95,-250C293.28,-250 295.62,-250 297.95,-250"/>
<polygon points="298.19,-253.5 308.19,-250 298.19,-246.5 298.19,-253.5"/>
</g>
<g class="m-edge">
<title>p13&#45;&gt;p23</title>
<path d="M263,-159.7C263,-151.98 263,-142.71 263,-134.11"/>
<polygon points="266.5,-134.1 263,-124.1 259.5,-134.1 266.5,-134.1"/>
</g>
<g class="m-node m-flat">
<title>p14</title>
<ellipse cx="336" cy="-178" rx="27.84" ry="18"/>
<text text-anchor="middle" x="336" y="-175.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;4</text>
</g>
<g class="m-edge">
<title>p13&#45;&gt;p14</title>
<path d="M290.95,-178C293.28,-178 295.62,-178 297.95,-178"/>
<polygon points="298.19,-181.5 308.19,-178 298.19,-174.5 298.19,-181.5"/>
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<g class="m-edge">
<title>p23&#45;&gt;p33</title>
<path d="M263,-87.7C263,-79.98 263,-70.71 263,-62.11"/>
<polygon points="266.5,-62.1 263,-52.1 259.5,-62.1 266.5,-62.1"/>
</g>
<g class="m-node m-flat">
<title>p24</title>
<ellipse cx="336" cy="-106" rx="27.84" ry="18"/>
<text text-anchor="middle" x="336" y="-103.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;4</text>
</g>
<g class="m-edge">
<title>p23&#45;&gt;p24</title>
<path d="M290.95,-106C293.28,-106 295.62,-106 297.95,-106"/>
<polygon points="298.19,-109.5 308.19,-106 298.19,-102.5 298.19,-109.5"/>
</g>
<g class="m-node m-flat">
<title>p34</title>
<ellipse cx="336" cy="-34" rx="27.84" ry="18"/>
<text text-anchor="middle" x="336" y="-31.5" font-family="Helvetica,sans-Serif" font-size="10.00">pipe&#45;4</text>
</g>
<g class="m-edge">
<title>p33&#45;&gt;p34</title>
<path d="M290.95,-34C293.28,-34 295.62,-34 297.95,-34"/>
<polygon points="298.19,-37.5 308.19,-34 298.19,-30.5 298.19,-37.5"/>
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<g class="m-edge">
<title>p04&#45;&gt;p14</title>
<path d="M336,-231.7C336,-223.98 336,-214.71 336,-206.11"/>
<polygon points="339.5,-206.1 336,-196.1 332.5,-206.1 339.5,-206.1"/>
</g>
<g class="m-edge">
<title>p14&#45;&gt;p24</title>
<path d="M336,-159.7C336,-151.98 336,-142.71 336,-134.11"/>
<polygon points="339.5,-134.1 336,-124.1 332.5,-134.1 339.5,-134.1"/>
</g>
<g class="m-edge">
<title>p24&#45;&gt;p34</title>
<path d="M336,-87.7C336,-79.98 336,-70.71 336,-62.11"/>
<polygon points="339.5,-62.1 336,-52.1 332.5,-62.1 339.5,-62.1"/>
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</svg>
</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">&lt;</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipe</span><span class="o">&lt;</span><span class="n">std</span><span class="o">::</span><span class="n">function</span><span class="o">&lt;</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">&amp;</span><span class="p">)</span><span class="o">&gt;&gt;&gt;</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">&lt;</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">&gt;</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">&amp;</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">&lt;</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">&amp;</span><span class="p">](</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipeflow</span><span class="o">&amp;</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">&amp;&amp;</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">&quot;init&quot;</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">&quot;pipeline&quot;</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: 84.800rem; height: 17.800rem;" viewBox="0.00 0.00 848.00 178.00">
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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">&lt;</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipe</span><span class="o">&lt;</span><span class="n">std</span><span class="o">::</span><span class="n">function</span><span class="o">&lt;</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">&amp;</span><span class="p">)</span><span class="o">&gt;&gt;&gt;</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">&lt;</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">&gt;</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">&lt;</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipe</span><span class="o">&lt;</span><span class="n">std</span><span class="o">::</span><span class="n">function</span><span class="o">&lt;</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">&amp;</span><span class="p">)</span><span class="o">&gt;&gt;&gt;</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">&lt;</span><span class="n">tf</span><span class="o">::</span><span class="n">Pipe</span><span class="o">&lt;</span><span class="n">std</span><span class="o">::</span><span class="n">function</span><span class="o">&lt;</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">&amp;</span><span class="p">)</span><span class="o">&gt;&gt;&gt;</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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