DevTools: n^2 -> n while loading heap snapshots and timeline files.

Source/devtools/front_end/heap_snapshot_worker/HeapSnapshotLoader.js

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 104 matching lines @@
             throw new Error("Incomplete JSON");
         this._json = this._json.slice(0, closingBracketIndex + 1);
         this._snapshot.strings = JSON.parse(this._json);
     },
 
     /**
      * @param {string} chunk
      */
     write: function(chunk)
     {
+        if (this._state === "parse-snapshot-info") {

[alph, 2015/03/01 11:30:13]

looks like a hack to the state machine.
why not just put it into the corresponding case block?
you can set this._json to null to specify that it shouldn't be accumulated.
wdyt?

[pfeldman, 2015/03/01 12:18:53]

Done.

+            // Tokenizer takes over input.
+            this._jsonTokenizer.write(chunk);
+            return;
+        }
+
         this._json += chunk;
         while (true) {
             switch (this._state) {
             case "find-snapshot-info": {
                 var snapshotToken = "\"snapshot\"";
                 var snapshotTokenIndex = this._json.indexOf(snapshotToken);
                 if (snapshotTokenIndex === -1)
                     throw new Error("Snapshot token not found");
+
                 this._json = this._json.slice(snapshotTokenIndex + snapshotToken.length + 1);
                 this._state = "parse-snapshot-info";
                 this._progress.updateStatus("Loading snapshot info\u2026");
+                this._jsonTokenizer = new WebInspector.TextUtils.BalancedJSONTokenizer(this._writeBalancedJSON.bind(this));
+                this._jsonTokenizer.write(this._json);
                 break;
             }
             case "parse-snapshot-info": {
-                var closingBracketIndex = WebInspector.TextUtils.findBalancedCurlyBrackets(this._json);
-                if (closingBracketIndex === -1)
-                    return;
-                this._snapshot.snapshot = /** @type {!HeapSnapshotHeader} */ (JSON.parse(this._json.slice(0, closingBracketIndex)));
-                this._json = this._json.slice(closingBracketIndex);
-                this._state = "find-nodes";
+                console.assert(false, "This should nevet happen.")

[alph, 2015/03/01 11:30:14]

typo

[pfeldman, 2015/03/01 12:18:53]

Done.

                 break;
             }
             case "find-nodes": {
                 var nodesToken = "\"nodes\"";
                 var nodesTokenIndex = this._json.indexOf(nodesToken);
                 if (nodesTokenIndex === -1)
                     return;
                 var bracketIndex = this._json.indexOf("[", nodesTokenIndex);
                 if (bracketIndex === -1)
                     return;
@@ skipping 103 matching lines @@
                 if (bracketIndex === -1)
                     return;
                 this._json = this._json.slice(bracketIndex);
                 this._state = "accumulate-strings";
                 break;
             }
             case "accumulate-strings":
                 return;
             }
         }
+    },
+
+    /**
+     * @param {string} data
+     */
+    _writeBalancedJSON: function(data)
+    {
+        this._snapshot.snapshot = /** @type {!HeapSnapshotHeader} */ (JSON.parse(data));
+        this._json = this._jsonTokenizer.remainder();
+        this._jsonTokenizer = null;
+        this._state = "find-nodes";
     }
-};
+}