1 files changed, 105 insertions, 0 deletions
diff --git a/devtools/server/performance/framerate.js b/devtools/server/performance/framerate.js
new file mode 100644
index 0000000000..330c270c58
--- /dev/null
+++ b/devtools/server/performance/framerate.js
@@ -0,0 +1,105 @@
+/* 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";
+
+/**
+ * A very simple utility for monitoring framerate. Takes a `targetActor`
+ * and monitors framerate over time. The actor wrapper around this
+ * can be found at devtools/server/actors/framerate.js
+ */
+class Framerate {
+  constructor(targetActor) {
+    this.targetActor = targetActor;
+    this._contentWin = targetActor.window;
+    this._onRefreshDriverTick = this._onRefreshDriverTick.bind(this);
+    this._onGlobalCreated = this._onGlobalCreated.bind(this);
+    this.targetActor.on("window-ready", this._onGlobalCreated);
+  }
+
+  destroy(conn) {
+    this.targetActor.off("window-ready", this._onGlobalCreated);
+    this.stopRecording();
+  }
+
+  /**
+   * Starts monitoring framerate, storing the frames per second.
+   */
+  startRecording() {
+    if (this._recording) {
+      return;
+    }
+    this._recording = true;
+    this._ticks = [];
+    this._startTime = this.targetActor.docShell.now();
+    this._rafID = this._contentWin.requestAnimationFrame(
+      this._onRefreshDriverTick
+    );
+  }
+
+  /**
+   * Stops monitoring framerate, returning the recorded values.
+   */
+  stopRecording(beginAt = 0, endAt = Number.MAX_SAFE_INTEGER) {
+    if (!this._recording) {
+      return [];
+    }
+    const ticks = this.getPendingTicks(beginAt, endAt);
+    this.cancelRecording();
+    return ticks;
+  }
+
+  /**
+   * Stops monitoring framerate, without returning the recorded values.
+   */
+  cancelRecording() {
+    this._contentWin.cancelAnimationFrame(this._rafID);
+    this._recording = false;
+    this._ticks = null;
+    this._rafID = -1;
+  }
+
+  /**
+   * Returns whether this instance is currently recording.
+   */
+  isRecording() {
+    return !!this._recording;
+  }
+
+  /**
+   * Gets the refresh driver ticks recorded so far.
+   */
+  getPendingTicks(beginAt = 0, endAt = Number.MAX_SAFE_INTEGER) {
+    if (!this._ticks) {
+      return [];
+    }
+    return this._ticks.filter(e => e >= beginAt && e <= endAt);
+  }
+
+  /**
+   * Function invoked along with the refresh driver.
+   */
+  _onRefreshDriverTick() {
+    if (!this._recording) {
+      return;
+    }
+    this._rafID = this._contentWin.requestAnimationFrame(
+      this._onRefreshDriverTick
+    );
+    this._ticks.push(this.targetActor.docShell.now() - this._startTime);
+  }
+
+  /**
+   * When the content window for the target actor is created.
+   */
+  _onGlobalCreated(win) {
+    if (this._recording) {
+      this._contentWin.cancelAnimationFrame(this._rafID);
+      this._rafID = this._contentWin.requestAnimationFrame(
+        this._onRefreshDriverTick
+      );
+    }
+  }
+}
+
+exports.Framerate = Framerate;