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

Source/devtools/front_end/heap_snapshot_worker/HeapSnapshotLoader.js

Index: Source/devtools/front_end/heap_snapshot_worker/HeapSnapshotLoader.js
diff --git a/Source/devtools/front_end/heap_snapshot_worker/HeapSnapshotLoader.js b/Source/devtools/front_end/heap_snapshot_worker/HeapSnapshotLoader.js
index 8285fa8ccf5f2cd96e53bed43dbf46c16d8e2616..82b8f43b681af68cdb89bc96c785d609bae54ff4 100644
--- a/Source/devtools/front_end/heap_snapshot_worker/HeapSnapshotLoader.js
+++ b/Source/devtools/front_end/heap_snapshot_worker/HeapSnapshotLoader.js
@@ -122,6 +122,12 @@ WebInspector.HeapSnapshotLoader.prototype = {
      */
     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) {
@@ -130,18 +136,16 @@ WebInspector.HeapSnapshotLoader.prototype = {
                 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": {
@@ -265,5 +269,16 @@ WebInspector.HeapSnapshotLoader.prototype = {
                 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";
     }
-};
+}