import FIREFOX_52_6_0esr_RELEASE from mozilla-esr52 hg repo

dom/webidl/DominatorTree.webidl

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