DominatorTree.webidl (3117B)
1 /* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ 2 /* This Source Code Form is subject to the terms of the Mozilla Public 3 * License, v. 2.0. If a copy of the MPL was not distributed with this file, 4 * You can obtain one at http://mozilla.org/MPL/2.0/. 5 */ 6 7 typedef unsigned long long NodeId; 8 typedef unsigned long long NodeSize; 9 10 /** 11 * In a directed graph with a root node `R`, a node `A` is said to "dominate" a 12 * node `B` iff every path from `R` to `B` contains `A`. A node `A` is said to 13 * be the "immediate dominator" of a node `B` iff it dominates `B`, is not `B` 14 * itself, and does not dominate any other nodes which also dominate `B` in 15 * turn. 16 * 17 * If we take every node from a graph `G` and create a new graph `T` with edges 18 * to each node from its immediate dominator, then `T` is a tree (each node has 19 * only one immediate dominator, or none if it is the root). This tree is called 20 * a "dominator tree". 21 * 22 * This interface represents a dominator tree constructed from a HeapSnapshot's 23 * heap graph. The domination relationship and dominator trees are useful tools 24 * for analyzing heap graphs because they tell you: 25 * 26 * - Exactly what could be reclaimed by the GC if some node `A` became 27 * unreachable: those nodes which are dominated by `A`, 28 * 29 * - The "retained size" of a node in the heap graph, in contrast to its 30 * "shallow size". The "shallow size" is the space taken by a node itself, 31 * not counting anything it references. The "retained size" of a node is its 32 * shallow size plus the size of all the things that would be collected if 33 * the original node wasn't (directly or indirectly) referencing them. In 34 * other words, the retained size is the shallow size of a node plus the 35 * shallow sizes of every other node it dominates. For example, the root 36 * node in a binary tree might have a small shallow size that does not take 37 * up much space itself, but it dominates the rest of the binary tree and 38 * its retained size is therefore significant (assuming no external 39 * references into the tree). 40 */ 41 [ChromeOnly, Exposed=(Window,Worker)] 42 interface DominatorTree { 43 /** 44 * The `NodeId` for the root of the dominator tree. This is a "meta-root" in 45 * that it has an edge to each GC root in the heap snapshot this dominator 46 * tree was created from. 47 */ 48 readonly attribute NodeId root; 49 50 /** 51 * Get the retained size of the node with the given id. If given an invalid 52 * id, null is returned. Throws an error on OOM. 53 */ 54 [Throws] 55 NodeSize? getRetainedSize(NodeId node); 56 57 /** 58 * Get the set of ids of nodes immediately dominated by the node with the 59 * given id. The resulting array is sorted by greatest to least retained 60 * size. If given an invalid id, null is returned. Throws an error on OOM. 61 */ 62 [Throws] 63 sequence<NodeId>? getImmediatelyDominated(NodeId node); 64 65 /** 66 * Get the immediate dominator of the node with the given id. Returns null if 67 * given an invalid id, or the id of the root node. 68 */ 69 NodeId? getImmediateDominator(NodeId node); 70 };