#### Source code

#### Revision control

#### Copy as Markdown

#### Other Tools

```
/* -*- 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,
```

```
*/
```

```
```

```
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,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);
```

```
};
```