1 files changed, 38 insertions, 0 deletions
diff --git a/toolkit/modules/ResponsivenessMonitor.sys.mjs b/toolkit/modules/ResponsivenessMonitor.sys.mjs
new file mode 100644
index 0000000000..e92563d8ec
--- /dev/null
+++ b/toolkit/modules/ResponsivenessMonitor.sys.mjs
@@ -0,0 +1,38 @@
+/* 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/. */
+
+export function ResponsivenessMonitor(intervalMS = 100) {
+  this._intervalMS = intervalMS;
+  this._prevTimestamp = Date.now();
+  this._accumulatedDelay = 0;
+  this._timer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
+  this._timer.initWithCallback(
+    this,
+    this._intervalMS,
+    Ci.nsITimer.TYPE_REPEATING_SLACK
+  );
+}
+
+ResponsivenessMonitor.prototype = {
+  notify() {
+    let now = Date.now();
+    this._accumulatedDelay += Math.max(
+      0,
+      now - this._prevTimestamp - this._intervalMS
+    );
+    this._prevTimestamp = now;
+  },
+
+  abort() {
+    if (this._timer) {
+      this._timer.cancel();
+      this._timer = null;
+    }
+  },
+
+  finish() {
+    this.abort();
+    return this._accumulatedDelay;
+  },
+};