core(simulator): start nodes in priority order

lighthouse-core/lib/dependency-graph/network-node.js

@@ -8,6 +8,13 @@
 const Node = require('./node');
 const WebInspector = require('../web-inspector');
 
+const NETWORK_PRIORITY_NUMBERS = {
+  VeryHigh: 0,
+  High: 1,
+  Medium: 2,
+  Low: 3,
+};
+
 class NetworkNode extends Node {
   /**
    * @param {LH.WebInspector.NetworkRequest} networkRecord
@@ -79,6 +86,14 @@ class NetworkNode extends Node {
     node.setIsMainDocument(this._isMainDocument);
     return node;
   }
+
+  /**
+   * @param {LH.WebInspector.NetworkPriority} priority
+   * @return {number}
+   */
+  static priorityToP0Number(priority) {
+    return NETWORK_PRIORITY_NUMBERS[priority] || 10;
+  }
 }
 
 module.exports = NetworkNode;

lighthouse-core/lib/dependency-graph/simulator/simulator.js

@@ -173,6 +173,25 @@ class Simulator {
     });
   }
 
+  /**
+   * @param {Node[]} nodes
+   * @return {Node[]}
+   */
+  _sortNodesByPriority(nodes) {
+    return nodes.slice().sort((nodeA, nodeB) => {
+      // If nodes are different type it doesn't matter
+      if (nodeA.type !== nodeB.type) return 0;
+      // If nodes are CPU nodes, just prioritize the one that actually executed first
+      if (nodeA.type === Node.TYPES.CPU) return nodeA.startTime - nodeB.startTime;
+      // Else the nodes are network nodes, prioritize by priority, then actual startTime
+      const networkA = /** @type {NetworkNode} */ (nodeA);
+      const networkB = /** @type {NetworkNode} */ (nodeB);
+      const priorityA = NetworkNode.priorityToP0Number(networkA.record.priority());
+      const priorityB = NetworkNode.priorityToP0Number(networkB.record.priority());
+      return priorityA === priorityB ? nodeA.startTime - nodeB.startTime : priorityA - priorityB;
+    });
+  }
+
   /**
    * @param {Node} node
    * @param {number} totalElapsedTime
@@ -398,7 +417,7 @@ class Simulator {
     // loop as long as we have nodes in the queue or currently in progress
     while (nodesReadyToStart.size || nodesInProgress.size) {
       // move all possible queued nodes to in progress
-      for (const node of nodesReadyToStart) {
+      for (const node of this._sortNodesByPriority(Array.from(nodesReadyToStart))) {
         this._startNodeIfPossible(node, totalElapsedTime);
       }
 

typings/web-inspector.d.ts

@@ -6,6 +6,8 @@
 
 declare global {
   module LH.WebInspector {
+    export type NetworkPriority = 'VeryHigh' | 'High' | 'Medium' | 'Low';
+
     // TODO(bckenny): standardize on underscored internal API
     // externs for chrome-devtools-frontend/front_end/sdk/NetworkRequest.js
     export interface NetworkRequest {
@@ -45,7 +47,7 @@ declare global {
       _timing: Crdp.Network.ResourceTiming;
       _resourceType: ResourceType;
       _mimeType: string;
-      priority(): 'VeryHigh' | 'High' | 'Medium' | 'Low';
+      priority(): NetworkPriority;
       _responseHeaders?: {name: string, value: string}[];
 
       _fetchedViaServiceWorker?: boolean;