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<!DOCTYPE html>

<head>

<title>Taskflow Algorithms » Module Algorithm | Taskflow QuickStart</title>

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<a href="https://taskflow.github.io"><img src="taskflow_logo.png" alt="" />Taskflow</a> | <a href="index.html" class="m-thin">QuickStart</a>

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<h1>

<a href="Algorithms.html">Taskflow Algorithms</a> »

Module Algorithm

</h1>

<h3>Contents</h3>

<ul>

<li><a href="#ModuleAlgorithmInclude">Include the Header</a></li>

<li><a href="#WhatIsAModuleTask">What is a Module Task</a></li>

<li><a href="#CreateAModuleTaskOverACustomGraph">Create a Module Task over a Custom Graph</a></li>

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Taskflow provides template methods that let users create reusable building blocks called modules. Users can connect modules together to build more complex parallel algorithms.<section id="ModuleAlgorithmInclude"><h2><a href="#ModuleAlgorithmInclude">Include the Header</a></h2>You need to include the header file, <code><a href="module_8hpp_source.html" class="m-doc">taskflow/algorithm/module.hpp</a></code>, for creating a module task over a schedulable graph target.<pre class="m-code">#include <taskflow/algorithm/module.hpp></pre></section><section id="WhatIsAModuleTask"><h2><a href="#WhatIsAModuleTask">What is a Module Task</a></h2>Similar to <a href="ComposableTasking.html" class="m-doc">Composable Tasking</a>, but in a more general setting, the template function <a href="namespacetf.html#a68bb6933d40ea4468cc08191a0822f10" class="m-doc">tf::make_module_task</a> allows you to create a task over a Taskflow graph that can be executed by an executor. This provides a flexible mechanism to encapsulate and reuse complex task logic within your Taskflow applications. The following example demonstrates how to create and launch multiple Taskflow graphs in parallel using asynchronous tasking:<pre class="m-code">#include <taskflow/taskflow.hpp>

#include <taskflow/algorithm/module.hpp>

int main() {

tf::Executor executor;

tf::Taskflow A;

tf::Taskflow B;

tf::Taskflow C;

tf::Taskflow D;

A.emplace([](){ printf("Taskflow A\n"); });

B.emplace([](){ printf("Taskflow B\n"); });

C.emplace([](){ printf("Taskflow C\n"); });

D.emplace([](){ printf("Taskflow D\n"); });

// launch the four taskflows using asynchronous tasking

executor.async(tf::make_module_task(A));

executor.wait_for_all();

return 0;

}</pre><div class="m-graph"><svg style="width: 27.800rem; height: 4.400rem;" viewBox="0.00 0.00 278.00 44.00">

<title>Taskflow</title>

</g>

</g>

</g>

</g>

</svg>

</div>Since the four taskflows are launched asynchronously without any dependencies between them, we can observe any order of the output message:<pre class="m-code"># one possible output

Taskflow B

Taskflow C

Taskflow A

Taskflow D

# another possible output

Taskflow D

Taskflow A

Taskflow B

Taskflow C</pre>If you need to enforce dependencies among these four taskflows, you can use dependent-async tasks. The example below launches the four taskflows one by one in sequential:<pre class="m-code">tf::Executor executor;

tf::Taskflow A;

tf::Taskflow B;

tf::Taskflow C;

tf::Taskflow D;

A.emplace([](){ printf("Taskflow A\n"); });

B.emplace([](){ printf("Taskflow B\n"); });

C.emplace([](){ printf("Taskflow C\n"); });

D.emplace([](){ printf("Taskflow D\n"); });

auto TA = executor.silent_dependent_async(tf::make_module_task(A));

auto TB = executor.silent_dependent_async(tf::make_module_task(B), TA);

auto TC = executor.silent_dependent_async(tf::make_module_task(C), TB);

auto [TD, FD] = executor.dependent_async(tf::make_module_task(D), TC);

FD.get();</pre><div class="m-graph"><svg style="width: 33.200rem; height: 4.400rem;" viewBox="0.00 0.00 332.00 44.00">

<title>Taskflow</title>

</g>

</g>

</g>

</g>

</g>

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</div><pre class="m-code"># dependent-async tasks enforce a sequential execution of the four taskflows

Taskflow A

Taskflow B

Taskflow C

Taskflow D</pre>The module task maker, <a href="namespacetf.html#a68bb6933d40ea4468cc08191a0822f10" class="m-doc">tf::make_module_task</a>, operates similarly to <a href="classtf_1_1FlowBuilder.html#ac6f22228d4c2ea2e643c4b0d42c0e92a" class="m-doc">tf::Taskflow::composed_of</a>, but provides a more general interface that can be used beyond Taskflow. Specifically, the following two approaches achieve equivalent functionality:<pre class="m-code">// approach 1: composition using composed_of

// approach 2: composition using make_module_task

tf::Task m1 = taskflow1.emplace(tf::make_module_task(taskflow2));</pre><aside class="m-note m-warning"><h4>Attention</h4>Similar to <a href="classtf_1_1FlowBuilder.html#ac6f22228d4c2ea2e643c4b0d42c0e92a" class="m-doc">tf::Taskflow::composed_of</a>, <a href="namespacetf.html#a68bb6933d40ea4468cc08191a0822f10" class="m-doc">tf::make_module_task</a> does not assume ownership of the provided taskflow but a soft reference. You are responsible for ensuring that the encapsulated taskflow remains valid throughout its execution.</aside></section><section id="CreateAModuleTaskOverACustomGraph"><h2><a href="#CreateAModuleTaskOverACustomGraph">Create a Module Task over a Custom Graph</a></h2>In addition to encapsulate taskflow graphs, you can create a module task to schedule a custom graph target. A schedulable target (of type <code>T</code>) must define the method <code>T::graph()</code> that returns a reference to the <a href="classtf_1_1Graph.html" class="m-doc">tf::Graph</a> object managed by <code>T</code>. The following example defines a custom graph that can be scheduled through making module tasks:<pre class="m-code">struct CustomGraph {

tf::Graph graph;

CustomGraph() {

// use flow builder to inherit all task creation methods in tf::Taskflow

tf::FlowBuilder builder(graph);

tf::Task task = builder.emplace([](){

std::cout << "a task\n"; // static task

});

}

// returns a reference to the graph for taskflow composition

Graph& graph() { return graph; }

};

CustomGraph target;

executor.async(tf::make_module_task(target));</pre><aside class="m-note m-warning"><h4>Attention</h4>Users are responsible for ensuring the given custom graph remains valid throughout its execution. The executor does not assume ownership of the custom graph.</aside></section>

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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>, 2018–2026. Generated by <a href="https://doxygen.org/">Doxygen</a> 1.9.1 and <a href="https://mcss.mosra.cz/">m.css</a>.

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