tor-browser

census-tree-node.js (23559B)

---

/* 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/. */
"use strict";

// CensusTreeNode is an intermediate representation of a census report that
// exists between after a report is generated by taking a census and before the
// report is rendered in the DOM. It must be dead simple to render, with no
// further data processing or massaging needed before rendering DOM nodes. Our
// goal is to do the census report to CensusTreeNode transformation in the
// HeapAnalysesWorker, and ensure that the **only** work that the main thread
// has to do is strictly DOM rendering work.

const {
 Visitor,
 walk,
 basisTotalBytes,
 basisTotalCount,
} = require("resource://devtools/shared/heapsnapshot/CensusUtils.js");

// Monotonically increasing integer for CensusTreeNode `id`s.
let censusTreeNodeIdCounter = 0;

/**
* Return true if the given object is a SavedFrame stack object, false otherwise.
*
* @param {any} obj
* @returns {boolean}
*/
function isSavedFrame(obj) {
 return Object.prototype.toString.call(obj) === "[object SavedFrame]";
}

/**
* A CensusTreeNodeCache maps from SavedFrames to CensusTreeNodes. It is used when
* aggregating multiple SavedFrame allocation stack keys into a tree of many
* CensusTreeNodes. Each stack may share older frames, and we want to preserve
* this sharing when converting to CensusTreeNode, so before creating a new
* CensusTreeNode, we look for an existing one in one of our CensusTreeNodeCaches.
*/
class CensusTreeNodeCache {
 /**
  * Create a unique string for the given SavedFrame (ignoring the frame's parent
  * chain) that can be used as a hash to key this frame within a CensusTreeNodeCache.
  *
  * NB: We manually hash rather than using an ES6 Map because we are purposely
  * ignoring the parent chain and wish to consider frames with everything the
  * same except their parents as the same.
  *
  * @param {SavedFrame} frame
  *        The SavedFrame object we would like to lookup in or insert into a
  *        CensusTreeNodeCache.
  *
  * @returns {string}
  *          The unique string that can be used as a key in a CensusTreeNodeCache.
  */
 static hashFrame(frame) {
   // eslint-disable-next-line max-len
   return `FRAME,${frame.functionDisplayName},${frame.source},${frame.line},${frame.column},${frame.asyncCause}`;
 }

 /**
  * Create a unique string for the given CensusTreeNode **with regards to
  * siblings at the current depth of the tree, not within the whole tree.** It
  * can be used as a hash to key this node within a CensusTreeNodeCache.
  *
  * @param {CensusTreeNode} node
  *        The node we would like to lookup in or insert into a cache.
  *
  * @returns {string}
  *          The unique string that can be used as a key in a CensusTreeNodeCache.
  */
 static hashNode(node) {
   return isSavedFrame(node.name)
     ? this.hashFrame(node.name)
     : `NODE,${node.name}`;
 }

 /**
  * Insert the given CensusTreeNodeCacheValue whose node.name is a SavedFrame
  * object in the given cache.
  *
  * @param {CensusTreeNodeCache} cache
  * @param {CensusTreeNodeCacheValue} value
  */
 static insertFrame(cache, value) {
   cache[this.hashFrame(value.node.name)] = value;
 }

 /**
  * Insert the given value in the cache.
  *
  * @param {CensusTreeNodeCache} cache
  * @param {CensusTreeNodeCacheValue} value
  */
 static insertNode(cache, value) {
   if (isSavedFrame(value.node.name)) {
     this.insertFrame(cache, value);
   } else {
     cache[this.hashNode(value.node)] = value;
   }
 }

 /**
  * Lookup `frame` in `cache` and return its value if it exists.
  *
  * @param {CensusTreeNodeCache} cache
  * @param {SavedFrame} frame
  *
  * @returns {undefined|CensusTreeNodeCacheValue}
  */
 static lookupFrame(cache, frame) {
   return cache[this.hashFrame(frame)];
 }

 /**
  * Lookup `node` in `cache` and return its value if it exists.
  *
  * @param {CensusTreeNodeCache} cache
  * @param {CensusTreeNode} node
  *
  * @returns {undefined|CensusTreeNodeCacheValue}
  */
 static lookupNode(cache, node) {
   return isSavedFrame(node.name)
     ? this.lookupFrame(cache, node.name)
     : cache[this.hashNode(node)];
 }
}

/**
* The value of a single entry stored in a CensusTreeNodeCache. It is a pair of
* the CensusTreeNode for this cache value, and the subsequent
* CensusTreeNodeCache for this node's children.
*/
class CensusTreeNodeCacheValue {
 constructor() {
   // The CensusTreeNode for this cache value.
   this.node = undefined;
   // The CensusTreeNodeCache for this frame's children.
   this.children = undefined;
 }
}

/**
* Add `child` to `parent`'s set of children and store the parent ID
* on the child.
*
* @param {CensusTreeNode} parent
* @param {CensusTreeNode} child
*/
function addChild(parent, child) {
 if (!parent.children) {
   parent.children = [];
 }
 child.parent = parent.id;
 parent.children.push(child);
}

/**
* Get an array of each frame in the provided stack.
*
* @param {SavedFrame} stack
* @returns {Array<SavedFrame>}
*/
function getArrayOfFrames(stack) {
 const frames = [];
 let frame = stack;
 while (frame) {
   frames.push(frame);
   frame = frame.parent;
 }
 frames.reverse();
 return frames;
}

/**
* Given an `edge` to a sub-`report` whose structure is described by
* `breakdown`, create a CensusTreeNode tree.
*
* @param {object} breakdown
*        The breakdown specifying the structure of the given report.
*
* @param {object} report
*        The census report.
*
* @param {null | string | SavedFrame} edge
*        The edge leading to this report from the parent report.
*
* @param {CensusTreeNodeCache} cache
*        The cache of CensusTreeNodes we have already made for the siblings of
*        the node being created. The existing nodes are reused when possible.
*
* @param {object} outParams
*        The return values are attached to this object after this function
*        returns. Because we create a CensusTreeNode for each frame in a
*        SavedFrame stack edge, there may multiple nodes per sub-report.
*
*          - top: The deepest node in the CensusTreeNode subtree created.
*
*          - bottom: The shallowest node in the CensusTreeNode subtree created.
*                    This is null if the shallowest node in the subtree was
*                    found in the `cache` and reused.
*
*        Note that top and bottom are not necessarily different. In the case
*        where there is a 1:1 correspondence between an edge in the report and
*        a CensusTreeNode, top and bottom refer to the same node.
*/
function makeCensusTreeNodeSubTree(breakdown, report, edge, cache, outParams) {
 if (!isSavedFrame(edge)) {
   const node = new CensusTreeNode(edge);
   outParams.top = outParams.bottom = node;
   return;
 }

 const frames = getArrayOfFrames(edge);
 let currentCache = cache;
 let prevNode;
 for (let i = 0, length = frames.length; i < length; i++) {
   const frame = frames[i];

   // Get or create the CensusTreeNodeCacheValue for this frame. If we already
   // have a CensusTreeNodeCacheValue (and hence a CensusTreeNode) for this
   // frame, we don't need to add the node to the previous node's children as
   // we have already done that. If we don't have a CensusTreeNodeCacheValue
   // and CensusTreeNode for this frame, then create one and make sure to hook
   // it up as a child of the previous node.
   let isNewNode = false;
   let val = CensusTreeNodeCache.lookupFrame(currentCache, frame);
   if (!val) {
     isNewNode = true;
     val = new CensusTreeNodeCacheValue();
     val.node = new CensusTreeNode(frame);

     CensusTreeNodeCache.insertFrame(currentCache, val);
     if (prevNode) {
       addChild(prevNode, val.node);
     }
   }

   if (i === 0) {
     outParams.bottom = isNewNode ? val.node : null;
   }
   if (i === length - 1) {
     outParams.top = val.node;
   }

   prevNode = val.node;

   if (i !== length - 1 && !val.children) {
     // This is not the last frame and therefore this node will have
     // children, which we must cache.
     val.children = new CensusTreeNodeCache();
   }

   currentCache = val.children;
 }
}

/**
* A Visitor that walks a census report and creates the corresponding
* CensusTreeNode tree.
*/
class CensusTreeNodeVisitor extends Visitor {
 constructor() {
   super();
   // The root of the resulting CensusTreeNode tree.
   this._root = null;

   // The stack of CensusTreeNodes that we are in the process of building while
   // walking the census report.
   this._nodeStack = [];

   // To avoid unnecessary allocations, we reuse the same out parameter object
   // passed to `makeCensusTreeNodeSubTree` every time we call it.
   this._outParams = {
     top: null,
     bottom: null,
   };

   // The stack of `CensusTreeNodeCache`s that we use to aggregate many
   // SavedFrame stacks into a single CensusTreeNode tree.
   this._cacheStack = [new CensusTreeNodeCache()];

   // The current index in the DFS of the census report tree.
   this._index = -1;
 }

 /**
  * Create the CensusTreeNode subtree for this sub-report and link it to the
  * parent CensusTreeNode.
  *
  * @override
  */
 enter(breakdown, report, edge) {
   this._index++;

   const cache = this._cacheStack[this._cacheStack.length - 1];
   makeCensusTreeNodeSubTree(breakdown, report, edge, cache, this._outParams);
   const { top, bottom } = this._outParams;

   if (!this._root) {
     this._root = bottom;
   } else if (bottom) {
     addChild(this._nodeStack[this._nodeStack.length - 1], bottom);
   }

   this._cacheStack.push(new CensusTreeNodeCache());
   this._nodeStack.push(top);
 }

 /**
  * We have finished adding children to the CensusTreeNode subtree for the
  * current sub-report. Make sure that the children are sorted for every node in
  * the subtree.
  *
  * @override
  */
 exit() {
   // Ensure all children are sorted and have their counts/bytes aggregated. We
   // only need to consider cache children here, because other children
   // correspond to other sub-reports and we already fixed them up in an earlier
   // invocation of `exit`.

   function dfs(node, childrenCache) {
     if (childrenCache) {
       const childValues = values(childrenCache);
       for (let i = 0, length = childValues.length; i < length; i++) {
         dfs(childValues[i].node, childValues[i].children);
       }
     }

     node.totalCount = node.count;
     node.totalBytes = node.bytes;

     if (node.children) {
       // Prune empty leaves.
       node.children = node.children.filter(isNonEmpty);

       node.children.sort(compareByTotal);

       for (let i = 0, length = node.children.length; i < length; i++) {
         node.totalCount += node.children[i].totalCount;
         node.totalBytes += node.children[i].totalBytes;
       }
     }
   }

   const top = this._nodeStack.pop();
   const cache = this._cacheStack.pop();
   dfs(top, cache);
 }

 /**
  * @override
  */
 count(breakdown, report) {
   const node = this._nodeStack[this._nodeStack.length - 1];
   node.reportLeafIndex = this._index;

   if (breakdown.count) {
     node.count = report.count;
   }

   if (breakdown.bytes) {
     node.bytes = report.bytes;
   }
 }

 /**
  * Get the root of the resulting CensusTreeNode tree.
  *
  * @returns {CensusTreeNode}
  */
 root() {
   if (!this._root) {
     throw new Error(
       "Attempt to get the root before walking the census report!"
     );
   }

   if (this._nodeStack.length) {
     throw new Error(
       "Attempt to get the root while walking the census report!"
     );
   }

   return this._root;
 }
}

function values(cache) {
 return Object.keys(cache).map(k => cache[k]);
}

function isNonEmpty(node) {
 return (
   (node.children !== undefined && node.children.length) ||
   node.bytes !== 0 ||
   node.count !== 0
 );
}

/**
* Create a single, uninitialized CensusTreeNode.
*/
class CensusTreeNode {
 /**
  *
  * @param {null | string | SavedFrame} name
  */
 constructor(name) {
   // Display name for this CensusTreeNode. Either null, a string, or a
   // SavedFrame.
   this.name = name;

   // The number of bytes occupied by matching things in the heap snapshot.
   this.bytes = 0;

   // The sum of `this.bytes` and `child.totalBytes` for each child in
   // `this.children`.
   this.totalBytes = 0;

   // The number of things in the heap snapshot that match this node in the
   // census tree.
   this.count = 0;

   // The sum of `this.count` and `child.totalCount` for each child in
   // `this.children`.
   this.totalCount = 0;

   // An array of this node's children, or undefined if it has no children.
   this.children = undefined;

   // The unique ID of this node.
   this.id = ++censusTreeNodeIdCounter;

   // If present, the unique ID of this node's parent. If this node does not have
   // a parent, then undefined.
   this.parent = undefined;

   // The `reportLeafIndex` property allows mapping a CensusTreeNode node back to
   // a leaf in the census report it was generated from. It is always one of the
   // following variants:
   //
   // * A `Number` index pointing a leaf report in a pre-order DFS traversal of
   //   this CensusTreeNode's census report.
   //
   // * A `Set` object containing such indices, when this is part of an inverted
   //   CensusTreeNode tree and multiple leaves in the report map onto this node.
   //
   // * Finally, `undefined` when no leaves in the census report correspond with
   //   this node.
   //
   // The first and third cases are the common cases. The second case is rather
   // uncommon, and to avoid doubling the number of allocations when creating
   // CensusTreeNode trees, and objects that get structured cloned when sending
   // such trees from the HeapAnalysesWorker to the main thread, we only allocate
   // a Set object once a node actually does have multiple leaves it corresponds
   // to.
   this.reportLeafIndex = undefined;
 }
}

/**
* Compare the given nodes by their `totalBytes` properties, and breaking ties
* with the `totalCount`, `bytes`, and `count` properties (in that order).
*
* @param {CensusTreeNode} node1
* @param {CensusTreeNode} node2
*
* @returns {number}
*          A number suitable for using with Array.prototype.sort.
*/
function compareByTotal(node1, node2) {
 return (
   Math.abs(node2.totalBytes) - Math.abs(node1.totalBytes) ||
   Math.abs(node2.totalCount) - Math.abs(node1.totalCount) ||
   Math.abs(node2.bytes) - Math.abs(node1.bytes) ||
   Math.abs(node2.count) - Math.abs(node1.count)
 );
}

/**
* Compare the given nodes by their `bytes` properties, and breaking ties with
* the `count`, `totalBytes`, and `totalCount` properties (in that order).
*
* @param {CensusTreeNode} node1
* @param {CensusTreeNode} node2
*
* @returns {number}
*          A number suitable for using with Array.prototype.sort.
*/
function compareBySelf(node1, node2) {
 return (
   Math.abs(node2.bytes) - Math.abs(node1.bytes) ||
   Math.abs(node2.count) - Math.abs(node1.count) ||
   Math.abs(node2.totalBytes) - Math.abs(node1.totalBytes) ||
   Math.abs(node2.totalCount) - Math.abs(node1.totalCount)
 );
}

/**
* Given a parent cache value from a tree we are building and a child node from
* a tree we are basing the new tree off of, if we already have a corresponding
* node in the parent's children cache, merge this node's counts with
* it. Otherwise, create the corresponding node, add it to the parent's children
* cache, and create the parent->child edge.
*
* @param {CensusTreeNodeCacheValue} parentCachevalue
* @param {CensusTreeNode} node
*
* @returns {CensusTreeNodeCacheValue}
*          The new or extant child node's corresponding cache value.
*/
function insertOrMergeNode(parentCacheValue, node) {
 if (!parentCacheValue.children) {
   parentCacheValue.children = new CensusTreeNodeCache();
 }

 let val = CensusTreeNodeCache.lookupNode(parentCacheValue.children, node);

 if (val) {
   // When inverting, it is possible that multiple leaves in the census report
   // get merged into a single CensusTreeNode node. When this occurs, switch
   // from a single index to a set of indices.
   if (
     val.node.reportLeafIndex !== undefined &&
     val.node.reportLeafIndex !== node.reportLeafIndex
   ) {
     if (typeof val.node.reportLeafIndex === "number") {
       const oldIndex = val.node.reportLeafIndex;
       val.node.reportLeafIndex = new Set();
       val.node.reportLeafIndex.add(oldIndex);
       val.node.reportLeafIndex.add(node.reportLeafIndex);
     } else {
       val.node.reportLeafIndex.add(node.reportLeafIndex);
     }
   }

   val.node.count += node.count;
   val.node.bytes += node.bytes;
 } else {
   val = new CensusTreeNodeCacheValue();

   val.node = new CensusTreeNode(node.name);
   val.node.reportLeafIndex = node.reportLeafIndex;
   val.node.count = node.count;
   val.node.totalCount = node.totalCount;
   val.node.bytes = node.bytes;
   val.node.totalBytes = node.totalBytes;

   addChild(parentCacheValue.node, val.node);
   CensusTreeNodeCache.insertNode(parentCacheValue.children, val);
 }

 return val;
}

/**
* Given an un-inverted CensusTreeNode tree, return the corresponding inverted
* CensusTreeNode tree. The input tree is not modified. The resulting inverted
* tree is sorted by self bytes rather than by total bytes.
*
* @param {CensusTreeNode} tree
*        The un-inverted tree.
*
* @returns {CensusTreeNode}
*          The corresponding inverted tree.
*/
function invert(tree) {
 const inverted = new CensusTreeNodeCacheValue();
 inverted.node = new CensusTreeNode(null);

 // Do a depth-first search of the un-inverted tree. As we reach each leaf,
 // take the path from the old root to the leaf, reverse that path, and add it
 // to the new, inverted tree's root.

 const path = [];
 (function addInvertedPaths(node) {
   path.push(node);

   if (node.children) {
     for (let i = 0, length = node.children.length; i < length; i++) {
       addInvertedPaths(node.children[i]);
     }
   } else {
     // We found a leaf node, add the reverse path to the inverted tree.
     let currentCacheValue = inverted;
     for (let i = path.length - 1; i >= 0; i--) {
       currentCacheValue = insertOrMergeNode(currentCacheValue, path[i]);
     }
   }

   path.pop();
 })(tree);

 // Ensure that the root node always has the totals.
 inverted.node.totalBytes = tree.totalBytes;
 inverted.node.totalCount = tree.totalCount;

 return inverted.node;
}

/**
* Given a CensusTreeNode tree and predicate function, create the tree
* containing only the nodes in any path `(node_0, node_1, ..., node_n-1)` in
* the given tree where `predicate(node_j)` is true for `0 <= j < n`, `node_0`
* is the given tree's root, and `node_n-1` is a leaf in the given tree. The
* given tree is left unmodified.
*
* @param {CensusTreeNode} tree
* @param {Function} predicate
*
* @returns {CensusTreeNode}
*/
function filter(tree, predicate) {
 const filtered = new CensusTreeNodeCacheValue();
 filtered.node = new CensusTreeNode(null);

 // Do a DFS over the given tree. If the predicate returns true for any node,
 // add that node and its whole subtree to the filtered tree.

 const path = [];
 let match = false;

 function addMatchingNodes(node) {
   path.push(node);

   const oldMatch = match;
   if (!match && predicate(node)) {
     match = true;
   }

   if (node.children) {
     for (let i = 0, length = node.children.length; i < length; i++) {
       addMatchingNodes(node.children[i]);
     }
   } else if (match) {
     // We found a matching leaf node, add it to the filtered tree.
     let currentCacheValue = filtered;
     for (let i = 0, length = path.length; i < length; i++) {
       currentCacheValue = insertOrMergeNode(currentCacheValue, path[i]);
     }
   }

   match = oldMatch;
   path.pop();
 }

 if (tree.children) {
   for (let i = 0, length = tree.children.length; i < length; i++) {
     addMatchingNodes(tree.children[i]);
   }
 }

 filtered.node.count = tree.count;
 filtered.node.totalCount = tree.totalCount;
 filtered.node.bytes = tree.bytes;
 filtered.node.totalBytes = tree.totalBytes;

 return filtered.node;
}

/**
* Given a filter string, return a predicate function that takes a node and
* returns true iff the node matches the filter.
*
* @param {string} filterString
* @returns {Function}
*/
function makeFilterPredicate(filterString) {
 return function (node) {
   if (!node.name) {
     return false;
   }

   if (isSavedFrame(node.name)) {
     return (
       node.name.source.includes(filterString) ||
       (node.name.functionDisplayName || "").includes(filterString) ||
       (node.name.asyncCause || "").includes(filterString)
     );
   }

   return String(node.name).includes(filterString);
 };
}

/**
* Takes a report from a census (`dbg.memory.takeCensus()`) and the breakdown
* used to generate the census and returns a structure used to render
* a tree to display the data.
*
* Returns a recursive "CensusTreeNode" object, looking like:
*
* CensusTreeNode = {
*   // `children` if it exists, is sorted by `bytes`, if they are leaf nodes.
*   children: ?[<CensusTreeNode...>],
*   name: <?String>
*   count: <?Number>
*   bytes: <?Number>
*   id: <?Number>
*   parent: <?Number>
* }
*
* @param {object} breakdown
*        The breakdown used to generate the census report.
*
* @param {object} report
*        The census report generated with the specified breakdown.
*
* @param {object} options
*        Configuration options.
*          - invert: Whether to invert the resulting tree or not. Defaults to
*                    false, ie uninverted.
*
* @returns {CensusTreeNode}
*/
exports.censusReportToCensusTreeNode = function (
 breakdown,
 report,
 options = {
   invert: false,
   filter: null,
 }
) {
 // Reset the counter so that turning the same census report into a
 // CensusTreeNode tree repeatedly is idempotent.
 censusTreeNodeIdCounter = 0;

 const visitor = new CensusTreeNodeVisitor();
 walk(breakdown, report, visitor);
 let result = visitor.root();

 if (options.invert) {
   result = invert(result);
 }

 if (typeof options.filter === "string") {
   result = filter(result, makeFilterPredicate(options.filter));
 }

 // If the report is a delta report that was generated by diffing two other
 // reports, make sure to use the basis totals rather than the totals of the
 // difference.
 if (typeof report[basisTotalBytes] === "number") {
   result.totalBytes = report[basisTotalBytes];
   result.totalCount = report[basisTotalCount];
 }

 // Inverting and filtering could have messed up the sort order, so do a
 // depth-first search of the tree and ensure that siblings are sorted.
 const comparator = options.invert ? compareBySelf : compareByTotal;
 (function ensureSorted(node) {
   if (node.children) {
     node.children.sort(comparator);
     for (let i = 0, length = node.children.length; i < length; i++) {
       ensureSorted(node.children[i]);
     }
   }
 })(result);

 return result;
};