plugins/org.eclipse.mat.ui.help/concepts/dominatortree.dita

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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA 1.1 Concept//EN" "concept.dtd">
<concept id="concept_dominatortree" xml:lang="en-us">
	<title>Dominator Tree</title>
	<prolog>
		<copyright>
			<copyryear year=""></copyryear>
			<copyrholder>
				Copyright (c) 2008, 2023 SAP AG, IBM Corporation and others.
			    All rights reserved. This program and the accompanying materials
			    are made available under the terms of the Eclipse Public License 2.0
			    which accompanies this distribution, and is available at
			    https://www.eclipse.org/legal/epl-2.0/
			</copyrholder>
		</copyright>
	</prolog>
	
	<conbody>
		<p>Memory Analyzer provides a dominator tree of the object graph. 
		    The transformation of the object reference graph into a
			dominator tree allows you to easily identify the biggest chunks of
			retained memory and the keep-alive dependencies among objects. 
			Below is an informal definition of the terms.</p>
		<p>
			An object x
			<b>dominates</b>
			an object y if every path in the object graph from the start (or the
			root) node to y must go through x.
		</p>
		<p>
			The
			<b>immediate dominator</b>
			x of some object y is the dominator closest to the object y.
		</p>
		<p>
			A
			<b>dominator tree</b>
			is built out of the object graph. In the dominator tree each object
			is the immediate dominator of its children, so dependencies between
			the objects are easily identified.
		</p>
		<p>The dominator tree has the following important properties:</p>
		<ul>
			<li>
				The objects belonging to the sub-tree of
				<keyword>x</keyword>
				(i.e. the objects dominated by
				<keyword>x</keyword>
				) represent the <xref href="shallowretainedheap.dita">retained set</xref> of
				<keyword>x</keyword>
				.
			</li>
			<li>
				If
				<keyword>x</keyword>
				is the immediate dominator of
				<keyword>y</keyword>
				, then the immediate dominator of
				<keyword>x</keyword>
				also dominates
				<keyword>y</keyword>
				, and so on.
			</li>
			<li>The edges in the dominator tree do not directly correspond to
				object references from the object graph.</li>
		</ul>
		<image href="../mimes/m2268b281.png">
			<alt>Object graph transformed to dominator tree</alt>
		</image>

	</conbody>
	<related-links>
		<link href="shallowretainedheap.dita" type="concept">
			<linktext>Shallow vs. Retained Size</linktext>
		</link>
	</related-links>
</concept>