1 files changed, 68 insertions, 0 deletions
diff --git a/xpcom/threads/InputEventStatistics.cpp b/xpcom/threads/InputEventStatistics.cpp
new file mode 100644
index 0000000000..66391d17cb
--- /dev/null
+++ b/xpcom/threads/InputEventStatistics.cpp
@@ -0,0 +1,68 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#include "InputEventStatistics.h"
+
+#include "mozilla/Preferences.h"
+#include "nsRefreshDriver.h"
+
+namespace mozilla {
+
+/*static*/ InputEventStatistics& InputEventStatistics::Get() {
+  static UniquePtr<InputEventStatistics> sInstance;
+  if (!sInstance) {
+    sInstance = MakeUnique<InputEventStatistics>(ConstructorCookie());
+    ClearOnShutdown(&sInstance);
+  }
+  return *sInstance;
+}
+
+TimeDuration InputEventStatistics::TimeDurationCircularBuffer::GetMean() {
+  return mTotal / (int64_t)mSize;
+}
+
+InputEventStatistics::InputEventStatistics(ConstructorCookie&&)
+    : mEnable(false) {
+  MOZ_ASSERT(Preferences::IsServiceAvailable());
+  uint32_t inputDuration = Preferences::GetUint(
+      "input_event_queue.default_duration_per_event", sDefaultInputDuration);
+
+  TimeDuration defaultDuration = TimeDuration::FromMilliseconds(inputDuration);
+
+  uint32_t count = Preferences::GetUint(
+      "input_event_queue.count_for_prediction", sInputCountForPrediction);
+
+  mLastInputDurations =
+      MakeUnique<TimeDurationCircularBuffer>(count, defaultDuration);
+
+  uint32_t maxDuration = Preferences::GetUint("input_event_queue.duration.max",
+                                              sMaxReservedTimeForHandlingInput);
+
+  uint32_t minDuration = Preferences::GetUint("input_event_queue.duration.min",
+                                              sMinReservedTimeForHandlingInput);
+
+  mMaxInputDuration = TimeDuration::FromMilliseconds(maxDuration);
+  mMinInputDuration = TimeDuration::FromMilliseconds(minDuration);
+}
+
+TimeStamp InputEventStatistics::GetInputHandlingStartTime(
+    uint32_t aInputCount) {
+  MOZ_ASSERT(mEnable);
+  Maybe<TimeStamp> nextTickHint = nsRefreshDriver::GetNextTickHint();
+
+  if (nextTickHint.isNothing()) {
+    // Return a past time to process input events immediately.
+    return TimeStamp::Now() - TimeDuration::FromMilliseconds(1);
+  }
+  TimeDuration inputCost = mLastInputDurations->GetMean() * aInputCount;
+  inputCost = inputCost > mMaxInputDuration   ? mMaxInputDuration
+              : inputCost < mMinInputDuration ? mMinInputDuration
+                                              : inputCost;
+
+  return nextTickHint.value() - inputCost;
+}
+
+}  // namespace mozilla