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/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this file,
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* You can obtain one at http://mozilla.org/MPL/2.0/.
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*/
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typedef unsigned long long NodeId;
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typedef unsigned long long NodeSize;
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/**
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* In a directed graph with a root node `R`, a node `A` is said to "dominate" a
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* node `B` iff every path from `R` to `B` contains `A`. A node `A` is said to
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* be the "immediate dominator" of a node `B` iff it dominates `B`, is not `B`
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* itself, and does not dominate any other nodes which also dominate `B` in
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* turn.
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*
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* If we take every node from a graph `G` and create a new graph `T` with edges
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* to each node from its immediate dominator, then `T` is a tree (each node has
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* only one immediate dominator, or none if it is the root). This tree is called
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* a "dominator tree".
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*
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* This interface represents a dominator tree constructed from a HeapSnapshot's
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* heap graph. The domination relationship and dominator trees are useful tools
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* for analyzing heap graphs because they tell you:
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*
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* - Exactly what could be reclaimed by the GC if some node `A` became
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* unreachable: those nodes which are dominated by `A`,
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*
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* - The "retained size" of a node in the heap graph, in contrast to its
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* "shallow size". The "shallow size" is the space taken by a node itself,
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* not counting anything it references. The "retained size" of a node is its
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* shallow size plus the size of all the things that would be collected if
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* the original node wasn't (directly or indirectly) referencing them. In
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* other words, the retained size is the shallow size of a node plus the
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* shallow sizes of every other node it dominates. For example, the root
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* node in a binary tree might have a small shallow size that does not take
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* up much space itself, but it dominates the rest of the binary tree and
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* its retained size is therefore significant (assuming no external
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* references into the tree).
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*/
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[ChromeOnly, Exposed=(Window,Worker)]
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interface DominatorTree {
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/**
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* The `NodeId` for the root of the dominator tree. This is a "meta-root" in
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* that it has an edge to each GC root in the heap snapshot this dominator
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* tree was created from.
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*/
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readonly attribute NodeId root;
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/**
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* Get the retained size of the node with the given id. If given an invalid
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* id, null is returned. Throws an error on OOM.
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*/
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[Throws]
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NodeSize? getRetainedSize(NodeId node);
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/**
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* Get the set of ids of nodes immediately dominated by the node with the
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* given id. The resulting array is sorted by greatest to least retained
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* size. If given an invalid id, null is returned. Throws an error on OOM.
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*/
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[Throws]
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sequence<NodeId>? getImmediatelyDominated(NodeId node);
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/**
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* Get the immediate dominator of the node with the given id. Returns null if
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* given an invalid id, or the id of the root node.
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*/
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NodeId? getImmediateDominator(NodeId node);
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};
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