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<h1>
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<div class="m-doc-include m-code m-inverted m-right-m m-text-right"><span class="cp">#include</span> <a class="cpf" href="partitioner_8hpp.html"><taskflow/algorithm/partitioner.hpp></a></div>
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<div class="m-doc-template">template<typename C = <a href="structtf_1_1DefaultClosureWrapper.html" class="m-doc">DefaultClosureWrapper</a>></div>
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<span class="m-breadcrumb"><a href="namespacetf.html">tf</a>::<wbr/></span>PartitionerBase <span class="m-thin">class</span>
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</h1>
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<p>class to derive a partitioner for scheduling parallel algorithms</p>
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<table class="m-table m-fullwidth m-flat">
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<tr><th colspan="2">Template parameters</th></tr>
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<td style="width: 1%">C</td>
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<td>closure wrapper type</td>
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<h3>Contents</h3>
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Reference
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<li><a href="#pub-types">Public types</a></li>
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<li><a href="#typeless-methods">Constructors, destructors, conversion operators</a></li>
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<li><a href="#pub-methods">Public functions</a></li>
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<p>The class provides base methods to derive a partitioner that can be used to schedule parallel iterations (e.g., <a href="classtf_1_1FlowBuilder.html#aae3edfa278baa75b08414e083c14c836" class="m-doc">tf::<wbr />Taskflow::<wbr />for_each</a>).</p><p>An partitioner defines the scheduling method for running parallel algorithms, such <a href="classtf_1_1FlowBuilder.html#aae3edfa278baa75b08414e083c14c836" class="m-doc">tf::<wbr />Taskflow::<wbr />for_each</a>, <a href="classtf_1_1FlowBuilder.html#afb24798ebf46e253a40b01bffb1da6a7" class="m-doc">tf::<wbr />Taskflow::<wbr />reduce</a>, and so on. By default, we provide the following partitioners:</p><ul><li><a href="classtf_1_1GuidedPartitioner.html" class="m-doc">tf::<wbr />GuidedPartitioner</a> to enable guided scheduling algorithm of adaptive chunk size</li><li><a href="classtf_1_1DynamicPartitioner.html" class="m-doc">tf::<wbr />DynamicPartitioner</a> to enable dynamic scheduling algorithm of equal chunk size</li><li><a href="classtf_1_1StaticPartitioner.html" class="m-doc">tf::<wbr />StaticPartitioner</a> to enable static scheduling algorithm of static chunk size</li><li><a href="classtf_1_1RandomPartitioner.html" class="m-doc">tf::<wbr />RandomPartitioner</a> to enable random scheduling algorithm of random chunk size</li></ul><p>Depending on applications, partitioning algorithms can impact the performance a lot. For example, if a parallel-iteration workload contains a regular work unit per iteration, <a href="classtf_1_1StaticPartitioner.html" class="m-doc">tf::<wbr />StaticPartitioner</a> can deliver the best performance. On the other hand, if the work unit per iteration is irregular and unbalanced, <a href="classtf_1_1GuidedPartitioner.html" class="m-doc">tf::<wbr />GuidedPartitioner</a> or <a href="classtf_1_1DynamicPartitioner.html" class="m-doc">tf::<wbr />DynamicPartitioner</a> can outperform <a href="classtf_1_1StaticPartitioner.html" class="m-doc">tf::<wbr />StaticPartitioner</a>. In most situations, <a href="classtf_1_1GuidedPartitioner.html" class="m-doc">tf::<wbr />GuidedPartitioner</a> can deliver decent performance and is thus used as our default partitioner.</p><aside class="m-note m-info"><h4>Note</h4><p>Giving the partition size of 0 lets the Taskflow runtime automatically determines the partition size for the given partitioner.</p></aside><p>In addition to partition size, the application can specify a closure wrapper for a partitioner. A closure wrapper allows the application to wrapper a partitioned task (i.e., closure) with a custom function object that performs additional tasks. For example:</p><pre class="m-code"><span class="n">std</span><span class="o">::</span><span class="n">atomic</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="w"> </span><span class="n">count</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
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<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>
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<span class="n">taskflow</span><span class="p">.</span><span class="n">for_each_index</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">100</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span>
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<span class="w"> </span><span class="p">[](){</span><span class="w"> </span>
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<span class="w"> </span><span class="n">printf</span><span class="p">(</span><span class="s">"%d</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="n">i</span><span class="p">);</span><span class="w"> </span>
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<span class="w"> </span><span class="p">},</span>
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<span class="w"> </span><span class="n">tf</span><span class="o">::</span><span class="n">StaticPartitioner</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">[](</span><span class="k">auto</span><span class="o">&&</span><span class="w"> </span><span class="n">closure</span><span class="p">){</span>
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<span class="w"> </span><span class="c1">// do something before invoking the partitioned task</span>
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<span class="w"> </span><span class="c1">// ...</span>
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<span class="w"> </span>
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<span class="w"> </span><span class="c1">// invoke the partitioned task</span>
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<span class="w"> </span><span class="n">closure</span><span class="p">();</span>
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<span class="w"> </span><span class="c1">// do something else after invoking the partitioned task</span>
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<span class="w"> </span><span class="c1">// ...</span>
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<span class="w"> </span><span class="p">}</span>
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<span class="p">);</span>
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<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><aside class="m-note m-info"><h4>Note</h4><p>The default closure wrapper (<a href="structtf_1_1DefaultClosureWrapper.html" class="m-doc">tf::<wbr />DefaultClosureWrapper</a>) does nothing but invoke the partitioned task (closure).</p></aside>
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<section id="pub-types">
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<h2><a href="#pub-types">Public types</a></h2>
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<dl class="m-doc">
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<dt id="a2b6152f24c2a3d6e750349d02ecb4595">
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using <a href="#a2b6152f24c2a3d6e750349d02ecb4595" class="m-doc-self">closure_wrapper_type</a> = C
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</dt>
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<dd>the closure type</dd>
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</dl>
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</section>
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<section id="typeless-methods">
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<h2><a href="#typeless-methods">Constructors, destructors, conversion operators</a></h2>
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<dl class="m-doc">
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<dt id="ad0037e70726a054527a923821ec2d95a">
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<span class="m-doc-wrap-bumper"><a href="#ad0037e70726a054527a923821ec2d95a" class="m-doc-self">PartitionerBase</a>(</span><span class="m-doc-wrap">) <span class="m-label m-flat m-info">defaulted</span></span>
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</dt>
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<dd>default constructor</dd>
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<dt id="a099464a339e09d9f6e4a59bec425c53a">
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<span class="m-doc-wrap-bumper"><a href="#a099464a339e09d9f6e4a59bec425c53a" class="m-doc-self">PartitionerBase</a>(</span><span class="m-doc-wrap">size_t chunk_size) <span class="m-label m-flat m-info">explicit</span> </span>
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</dt>
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<dd>construct a partitioner with the given chunk size</dd>
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<dt id="a9cf9f5400992c6d9bd4131b5af2b9e8e">
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<span class="m-doc-wrap-bumper"><a href="#a9cf9f5400992c6d9bd4131b5af2b9e8e" class="m-doc-self">PartitionerBase</a>(</span><span class="m-doc-wrap">size_t chunk_size,
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C&& closure_wrapper)</span>
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</dt>
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<dd>construct a partitioner with the given chunk size and closure wrapper</dd>
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</dl>
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</section>
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<section id="pub-methods">
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<h2><a href="#pub-methods">Public functions</a></h2>
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<dl class="m-doc">
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<dt id="afa34299dea355738efa5684024d08215">
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<span class="m-doc-wrap-bumper">auto <a href="#afa34299dea355738efa5684024d08215" class="m-doc-self">chunk_size</a>(</span><span class="m-doc-wrap">) const -> size_t</span>
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</dt>
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<dd>query the chunk size of this partitioner</dd>
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<dt id="a481097aeb7ec62dcc23584eaa48cbce4">
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<span class="m-doc-wrap-bumper">void <a href="#a481097aeb7ec62dcc23584eaa48cbce4" class="m-doc-self">chunk_size</a>(</span><span class="m-doc-wrap">size_t cz)</span>
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</dt>
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<dd>update the chunk size of this partitioner</dd>
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<dt id="a929714296243b2c63e4f2baa2025d380">
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<span class="m-doc-wrap-bumper">auto <a href="#a929714296243b2c63e4f2baa2025d380" class="m-doc-self">closure_wrapper</a>(</span><span class="m-doc-wrap">) const -> const C&</span>
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</dt>
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<dd>acquire an immutable access to the closure wrapper object</dd>
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<dt id="a99e23ce7c0faf3a932ab2b7ac51e58f4">
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<div class="m-doc-template">template<typename F></div>
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<span class="m-doc-wrap-bumper">void <a href="#a99e23ce7c0faf3a932ab2b7ac51e58f4" class="m-doc-self">closure_wrapper</a>(</span><span class="m-doc-wrap">F&& fn)</span>
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</dt>
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<dd>modify the closure wrapper object</dd>
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</dl>
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</section>
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<section id="pro-attribs">
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<h2><a href="#pro-attribs">Protected variables</a></h2>
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<dl class="m-doc">
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<dt id="a9ff56f7150ee4ff42b5006942f9c4b52">
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size_t <a href="#a9ff56f7150ee4ff42b5006942f9c4b52" class="m-doc-self">_chunk_size</a>
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</dt>
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<dd>chunk size</dd>
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<dt id="a9c5a8d350a913bea4c63d350e2bc9d1b">
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C <a href="#a9c5a8d350a913bea4c63d350e2bc9d1b" class="m-doc-self">_closure_wrapper</a>
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</dt>
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<dd>closure wrapper</dd>
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</dl>
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</section>
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<p>Taskflow handbook is part of the <a href="https://taskflow.github.io">Taskflow project</a>, copyright © <a href="https://tsung-wei-huang.github.io/">Dr. Tsung-Wei Huang</a>, 2018–2024.<br />Generated by <a href="https://doxygen.org/">Doxygen</a> 1.9.1 and <a href="https://mcss.mosra.cz/">m.css</a>.</p>
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