1 files changed, 77 insertions, 0 deletions
diff --git a/xpcom/threads/MainThreadIdlePeriod.cpp b/xpcom/threads/MainThreadIdlePeriod.cpp
new file mode 100644
index 0000000000..805626dd67
--- /dev/null
+++ b/xpcom/threads/MainThreadIdlePeriod.cpp
@@ -0,0 +1,77 @@
+/* -*- 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 "MainThreadIdlePeriod.h"
+
+#include "mozilla/Maybe.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/StaticPrefs_idle_period.h"
+#include "mozilla/dom/Document.h"
+#include "VRManagerChild.h"
+#include "nsRefreshDriver.h"
+#include "nsThreadUtils.h"
+
+// The amount of idle time (milliseconds) reserved for a long idle period.
+static const double kLongIdlePeriodMS = 50.0;
+
+// The minimum amount of time (milliseconds) required for an idle period to be
+// scheduled on the main thread. N.B. layout.idle_period.time_limit adds
+// padding at the end of the idle period, which makes the point in time that we
+// expect to become busy again be:
+//   now + idle_period.min + layout.idle_period.time_limit
+// or during page load
+//   now + idle_period.during_page_load.min + layout.idle_period.time_limit
+
+static const uint32_t kMaxTimerThreadBound = 25;  // Number of timers to check.
+
+namespace mozilla {
+
+NS_IMETHODIMP
+MainThreadIdlePeriod::GetIdlePeriodHint(TimeStamp* aIdleDeadline) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aIdleDeadline);
+
+  TimeStamp now = TimeStamp::Now();
+  TimeStamp currentGuess =
+      now + TimeDuration::FromMilliseconds(kLongIdlePeriodMS);
+
+  currentGuess = nsRefreshDriver::GetIdleDeadlineHint(
+      currentGuess, nsRefreshDriver::IdleCheck::AllVsyncListeners);
+  if (XRE_IsContentProcess()) {
+    currentGuess = gfx::VRManagerChild::GetIdleDeadlineHint(currentGuess);
+  }
+  currentGuess = NS_GetTimerDeadlineHintOnCurrentThread(currentGuess,
+                                                        kMaxTimerThreadBound);
+
+  // If the idle period is too small, then just return a null time
+  // to indicate we are busy. Otherwise return the actual deadline.
+  double highRateMultiplier = nsRefreshDriver::HighRateMultiplier();
+  TimeDuration minIdlePeriod = TimeDuration::FromMilliseconds(
+      std::max(highRateMultiplier * StaticPrefs::idle_period_min(), 1.0));
+  bool busySoon = currentGuess.IsNull() ||
+                  (now >= (currentGuess - minIdlePeriod)) ||
+                  currentGuess < mLastIdleDeadline;
+
+  // During page load use higher minimum idle period.
+  if (!busySoon && XRE_IsContentProcess() &&
+      mozilla::dom::Document::HasRecentlyStartedForegroundLoads()) {
+    TimeDuration minIdlePeriod = TimeDuration::FromMilliseconds(std::max(
+        highRateMultiplier * StaticPrefs::idle_period_during_page_load_min(),
+        1.0));
+    busySoon = (now >= (currentGuess - minIdlePeriod));
+  }
+
+  if (!busySoon) {
+    *aIdleDeadline = mLastIdleDeadline = currentGuess;
+  }
+
+  return NS_OK;
+}
+
+/* static */
+float MainThreadIdlePeriod::GetLongIdlePeriod() { return kLongIdlePeriodMS; }
+
+}  // namespace mozilla