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<p>Simulator mode is specifically designed for topology developers to easily debug or optimize their
topologies.</p>
<p>Simulator mode simulates a heron cluster in a single JVM process, which is useful for developing and
testing topologies. Running topologies under simulator mode is similar to running topologies on a
cluster.</p>
<h1><a class="anchor" aria-hidden="true" id="develop-a-topology-using-simulator-mode"></a><a href="#develop-a-topology-using-simulator-mode" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Develop a topology using simulator mode</h1>
<p>To run in simulator mode, use the <code>SimulatorMode</code> class, which is
in <code>storm-compatibility-unshaded_deploy.jar</code>  (under <code>bazel-bin/storm-compatibility/v0.10.2/src/java</code>).</p>
<p>For example:</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">import</span> org.apache.heron.simulator.Simulator;
Simulator simulator = <span class="hljs-keyword">new</span> Simulator();
</code></pre>
<p>You can then submit topologies using the <code>submitTopology</code> method on the <code>Simulator</code> object. Just
like the corresponding method on <code>StormSubmitter</code>, <code>submitTopology</code> takes a name, a topology
configuration, and a topology object.</p>
<p>For example:</p>
<pre><code class="hljs css language-java">simulator.submitTopology(<span class="hljs-string">"test"</span>, conf, builder.createTopology());
</code></pre>
<p>Other lifecycle methods to use with simulator mode are:</p>
<pre><code class="hljs css language-java">simulator.killTopology(<span class="hljs-string">"test"</span>);
simulator.activate(<span class="hljs-string">"test"</span>);
simulator.deactivate(<span class="hljs-string">"test"</span>);
simulator.shutdown();
</code></pre>
<p>To kill a topology, one could also terminate the process.</p>
<p>The simulator mode will run in separate threads other than the main thread. All the above methods are
thread-safe. This means that one could invoke these methods in other threads and monitor the
corresponding behaviors interactively.</p>
<h1><a class="anchor" aria-hidden="true" id="debug-topology-using-intellij"></a><a href="#debug-topology-using-intellij" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Debug topology using IntelliJ</h1>
<p>Bolts and Spouts run as separate threads in simulator. To add breakpoints inside a bolt/spout, the
Suspend Policy of the breakpoint needs to be set to Thread. To change the Suspend Policy, right
click on the breakpoint as shown in the following image:</p>
<p><img src="/docs/assets/intellij-set-breakpoint.jpg" alt="Set Breakpoint"></p>
<p>If it's not convenient to check the output and logs in the IntelliJ console, save them to a local file
by choosing <code>Run -&gt; Edit Configurations....</code> as shown in the following image:</p>
<p><img src="/docs/assets/intellij-save-console.jpg" alt="Save Console"></p>
</span></div></article></div><div class="docs-prevnext"><a class="docs-prev button" href="/docs/0.20.0-incubating/guides-packing-algorithms"><span class="arrow-prev">← </span><span>Packing Algorithms</span></a><a class="docs-next button" href="/docs/0.20.0-incubating/guides-troubeshooting-guide"><span>Topology Troubleshooting Guide</span><span class="arrow-next"> →</span></a></div></div></div><nav class="onPageNav"></nav></div><footer class="nav-footer" id="footer"><div class="apache-disclaimer">Apache Heron is an effort undergoing incubation at <a target="_blank" href="https://apache.org/">The Apache Software Foundation (ASF)</a> sponsored by the Apache Incubator PMC. Incubation is required of all newly accepted projects until a further review indicates that the infrastructure, communications, and decision making process have stabilized in a manner consistent with other successful ASF projects. While incubation status is not necessarily a reflection of the completeness or stability of the code, it does indicate that the project has yet to be fully endorsed by the ASF.<br/><br/>Apache®, the names of Apache projects, and the feather logo are either <a rel="external" href="https://www.apache.org/foundation/marks/list/">registered trademarks or trademarks</a> of the Apache Software Foundation in the United States and/or other countries.<br/><br/><div class="copyright-box">Copyright © 2023 the Apache Software Foundation, Apache Heron, Heron, 
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