Adding upstream version 86.0.1.upstream/86.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1331 insertions, 0 deletions

diff --git a/dom/base/TimeoutManager.cpp b/dom/base/TimeoutManager.cpp
new file mode 100644
index 0000000000..67e57f589e
--- /dev/null
+++ b/dom/base/TimeoutManager.cpp
@@ -0,0 +1,1331 @@
+/* -*- 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 "TimeoutManager.h"
+#include "nsGlobalWindow.h"
+#include "mozilla/Logging.h"
+#include "mozilla/PerformanceCounter.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/StaticPrefs_dom.h"
+#include "mozilla/StaticPrefs_privacy.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/ThrottledEventQueue.h"
+#include "mozilla/TimeStamp.h"
+#include "nsINamed.h"
+#include "mozilla/dom/DocGroup.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/PopupBlocker.h"
+#include "mozilla/dom/ContentChild.h"
+#include "mozilla/dom/TimeoutHandler.h"
+#include "TimeoutExecutor.h"
+#include "TimeoutBudgetManager.h"
+#include "mozilla/net/WebSocketEventService.h"
+#include "mozilla/MediaManager.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+LazyLogModule gTimeoutLog("Timeout");
+
+static int32_t gRunningTimeoutDepth = 0;
+
+// static
+const uint32_t TimeoutManager::InvalidFiringId = 0;
+
+namespace {
+double GetRegenerationFactor(bool aIsBackground) {
+  // Lookup function for "dom.timeout.{background,
+  // foreground}_budget_regeneration_rate".
+
+  // Returns the rate of regeneration of the execution budget as a
+  // fraction. If the value is 1.0, the amount of time regenerated is
+  // equal to time passed. At this rate we regenerate 1ms/ms. If it is
+  // 0.01 the amount regenerated is 1% of time passed. At this rate we
+  // regenerate 1ms/100ms, etc.
+  double denominator = std::max(
+      aIsBackground
+          ? StaticPrefs::dom_timeout_background_budget_regeneration_rate()
+          : StaticPrefs::dom_timeout_foreground_budget_regeneration_rate(),
+      1);
+  return 1.0 / denominator;
+}
+
+TimeDuration GetMaxBudget(bool aIsBackground) {
+  // Lookup function for "dom.timeout.{background,
+  // foreground}_throttling_max_budget".
+
+  // Returns how high a budget can be regenerated before being
+  // clamped. If this value is less or equal to zero,
+  // TimeDuration::Forever() is implied.
+  int32_t maxBudget =
+      aIsBackground
+          ? StaticPrefs::dom_timeout_background_throttling_max_budget()
+          : StaticPrefs::dom_timeout_foreground_throttling_max_budget();
+  return maxBudget > 0 ? TimeDuration::FromMilliseconds(maxBudget)
+                       : TimeDuration::Forever();
+}
+
+TimeDuration GetMinBudget(bool aIsBackground) {
+  // The minimum budget is computed by looking up the maximum allowed
+  // delay and computing how long time it would take to regenerate
+  // that budget using the regeneration factor. This number is
+  // expected to be negative.
+  return TimeDuration::FromMilliseconds(
+      -StaticPrefs::dom_timeout_budget_throttling_max_delay() /
+      std::max(
+          aIsBackground
+              ? StaticPrefs::dom_timeout_background_budget_regeneration_rate()
+              : StaticPrefs::dom_timeout_foreground_budget_regeneration_rate(),
+          1));
+}
+}  // namespace
+
+//
+
+bool TimeoutManager::IsBackground() const {
+  return !IsActive() && mWindow.IsBackgroundInternal();
+}
+
+bool TimeoutManager::IsActive() const {
+  // A window is considered active if:
+  // * It is a chrome window
+  // * It is playing audio
+  //
+  // Note that a window can be considered active if it is either in the
+  // foreground or in the background.
+
+  if (mWindow.IsChromeWindow()) {
+    return true;
+  }
+
+  // Check if we're playing audio
+  if (mWindow.IsPlayingAudio()) {
+    return true;
+  }
+
+  return false;
+}
+
+void TimeoutManager::SetLoading(bool value) {
+  // When moving from loading to non-loading, we may need to
+  // reschedule any existing timeouts from the idle timeout queue
+  // to the normal queue.
+  MOZ_LOG(gTimeoutLog, LogLevel::Debug, ("%p: SetLoading(%d)", this, value));
+  if (mIsLoading && !value) {
+    MoveIdleToActive();
+  }
+  // We don't immediately move existing timeouts to the idle queue if we
+  // move to loading.  When they would have fired, we'll see we're loading
+  // and move them then.
+  mIsLoading = value;
+}
+
+void TimeoutManager::MoveIdleToActive() {
+  uint32_t num = 0;
+  TimeStamp when;
+#if MOZ_GECKO_PROFILER
+  TimeStamp now;
+#endif
+  // Ensure we maintain the ordering of timeouts, so timeouts
+  // never fire before a timeout set for an earlier time, or
+  // before a timeout for the same time already submitted.
+  // See https://html.spec.whatwg.org/#dom-settimeout #16 and #17
+  while (RefPtr<Timeout> timeout = mIdleTimeouts.GetLast()) {
+    if (num == 0) {
+      when = timeout->When();
+    }
+    timeout->remove();
+    mTimeouts.InsertFront(timeout);
+#if MOZ_GECKO_PROFILER
+    if (profiler_can_accept_markers()) {
+      if (num == 0) {
+        now = TimeStamp::Now();
+      }
+      TimeDuration elapsed = now - timeout->SubmitTime();
+      TimeDuration target = timeout->When() - timeout->SubmitTime();
+      TimeDuration delta = now - timeout->When();
+      nsPrintfCString marker(
+          "Releasing deferred setTimeout() for %dms (original target time was "
+          "%dms (%dms delta))",
+          int(elapsed.ToMilliseconds()), int(target.ToMilliseconds()),
+          int(delta.ToMilliseconds()));
+      // don't have end before start...
+      PROFILER_MARKER_TEXT(
+          "setTimeout deferred release", DOM,
+          MarkerOptions(
+              MarkerTiming::Interval(
+                  delta.ToMilliseconds() >= 0 ? timeout->When() : now, now),
+              MarkerInnerWindowId(mWindow.WindowID())),
+          marker);
+    }
+#endif
+    num++;
+  }
+  if (num > 0) {
+    MOZ_ALWAYS_SUCCEEDS(MaybeSchedule(when));
+    mIdleExecutor->Cancel();
+  }
+  MOZ_LOG(gTimeoutLog, LogLevel::Debug,
+          ("%p: Moved %d timeouts from Idle to active", this, num));
+}
+
+uint32_t TimeoutManager::CreateFiringId() {
+  uint32_t id = mNextFiringId;
+  mNextFiringId += 1;
+  if (mNextFiringId == InvalidFiringId) {
+    mNextFiringId += 1;
+  }
+
+  mFiringIdStack.AppendElement(id);
+
+  return id;
+}
+
+void TimeoutManager::DestroyFiringId(uint32_t aFiringId) {
+  MOZ_DIAGNOSTIC_ASSERT(!mFiringIdStack.IsEmpty());
+  MOZ_DIAGNOSTIC_ASSERT(mFiringIdStack.LastElement() == aFiringId);
+  mFiringIdStack.RemoveLastElement();
+}
+
+bool TimeoutManager::IsValidFiringId(uint32_t aFiringId) const {
+  return !IsInvalidFiringId(aFiringId);
+}
+
+TimeDuration TimeoutManager::MinSchedulingDelay() const {
+  if (IsActive()) {
+    return TimeDuration();
+  }
+
+  bool isBackground = mWindow.IsBackgroundInternal();
+
+  // If a window isn't active as defined by TimeoutManager::IsActive()
+  // and we're throttling timeouts using an execution budget, we
+  // should adjust the minimum scheduling delay if we have used up all
+  // of our execution budget. Note that a window can be active or
+  // inactive regardless of wether it is in the foreground or in the
+  // background. Throttling using a budget depends largely on the
+  // regeneration factor, which can be specified separately for
+  // foreground and background windows.
+  //
+  // The value that we compute is the time in the future when we again
+  // have a positive execution budget. We do this by taking the
+  // execution budget into account, which if it positive implies that
+  // we have time left to execute, and if it is negative implies that
+  // we should throttle it until the budget again is positive. The
+  // factor used is the rate of budget regeneration.
+  //
+  // We clamp the delay to be less than or equal to
+  // "dom.timeout.budget_throttling_max_delay" to not entirely starve
+  // the timeouts.
+  //
+  // Consider these examples assuming we should throttle using
+  // budgets:
+  //
+  // mExecutionBudget is 20ms
+  // factor is 1, which is 1 ms/ms
+  // delay is 0ms
+  // then we will compute the minimum delay:
+  // max(0, - 20 * 1) = 0
+  //
+  // mExecutionBudget is -50ms
+  // factor is 0.1, which is 1 ms/10ms
+  // delay is 1000ms
+  // then we will compute the minimum delay:
+  // max(1000, - (- 50) * 1/0.1) = max(1000, 500) = 1000
+  //
+  // mExecutionBudget is -15ms
+  // factor is 0.01, which is 1 ms/100ms
+  // delay is 1000ms
+  // then we will compute the minimum delay:
+  // max(1000, - (- 15) * 1/0.01) = max(1000, 1500) = 1500
+  TimeDuration unthrottled =
+      isBackground ? TimeDuration::FromMilliseconds(
+                         StaticPrefs::dom_min_background_timeout_value())
+                   : TimeDuration();
+  bool budgetThrottlingEnabled = BudgetThrottlingEnabled(isBackground);
+  if (budgetThrottlingEnabled && mExecutionBudget < TimeDuration()) {
+    // Only throttle if execution budget is less than 0
+    double factor = 1.0 / GetRegenerationFactor(mWindow.IsBackgroundInternal());
+    return TimeDuration::Max(unthrottled, -mExecutionBudget.MultDouble(factor));
+  }
+  if (!budgetThrottlingEnabled && isBackground) {
+    return TimeDuration::FromMilliseconds(
+        StaticPrefs::
+            dom_min_background_timeout_value_without_budget_throttling());
+  }
+
+  return unthrottled;
+}
+
+nsresult TimeoutManager::MaybeSchedule(const TimeStamp& aWhen,
+                                       const TimeStamp& aNow) {
+  MOZ_DIAGNOSTIC_ASSERT(mExecutor);
+
+  // Before we can schedule the executor we need to make sure that we
+  // have an updated execution budget.
+  UpdateBudget(aNow);
+  return mExecutor->MaybeSchedule(aWhen, MinSchedulingDelay());
+}
+
+bool TimeoutManager::IsInvalidFiringId(uint32_t aFiringId) const {
+  // Check the most common ways to invalidate a firing id first.
+  // These should be quite fast.
+  if (aFiringId == InvalidFiringId || mFiringIdStack.IsEmpty()) {
+    return true;
+  }
+
+  if (mFiringIdStack.Length() == 1) {
+    return mFiringIdStack[0] != aFiringId;
+  }
+
+  // Next do a range check on the first and last items in the stack
+  // of active firing ids.  This is a bit slower.
+  uint32_t low = mFiringIdStack[0];
+  uint32_t high = mFiringIdStack.LastElement();
+  MOZ_DIAGNOSTIC_ASSERT(low != high);
+  if (low > high) {
+    // If the first element is bigger than the last element in the
+    // stack, that means mNextFiringId wrapped around to zero at
+    // some point.
+    std::swap(low, high);
+  }
+  MOZ_DIAGNOSTIC_ASSERT(low < high);
+
+  if (aFiringId < low || aFiringId > high) {
+    return true;
+  }
+
+  // Finally, fall back to verifying the firing id is not anywhere
+  // in the stack.  This could be slow for a large stack, but that
+  // should be rare.  It can only happen with deeply nested event
+  // loop spinning.  For example, a page that does a lot of timers
+  // and a lot of sync XHRs within those timers could be slow here.
+  return !mFiringIdStack.Contains(aFiringId);
+}
+
+// The number of nested timeouts before we start clamping. HTML says 5.
+#define DOM_CLAMP_TIMEOUT_NESTING_LEVEL 5u
+
+TimeDuration TimeoutManager::CalculateDelay(Timeout* aTimeout) const {
+  MOZ_DIAGNOSTIC_ASSERT(aTimeout);
+  TimeDuration result = aTimeout->mInterval;
+
+  if (aTimeout->mNestingLevel >= DOM_CLAMP_TIMEOUT_NESTING_LEVEL) {
+    uint32_t minTimeoutValue = StaticPrefs::dom_min_timeout_value();
+    result = TimeDuration::Max(result,
+                               TimeDuration::FromMilliseconds(minTimeoutValue));
+  }
+
+  return result;
+}
+
+PerformanceCounter* TimeoutManager::GetPerformanceCounter() {
+  Document* doc = mWindow.GetDocument();
+  if (doc) {
+    dom::DocGroup* docGroup = doc->GetDocGroup();
+    if (docGroup) {
+      return docGroup->GetPerformanceCounter();
+    }
+  }
+  return nullptr;
+}
+
+void TimeoutManager::RecordExecution(Timeout* aRunningTimeout,
+                                     Timeout* aTimeout) {
+  TimeoutBudgetManager& budgetManager = TimeoutBudgetManager::Get();
+  TimeStamp now = TimeStamp::Now();
+
+  if (aRunningTimeout) {
+    // If we're running a timeout callback, record any execution until
+    // now.
+    TimeDuration duration = budgetManager.RecordExecution(now, aRunningTimeout);
+
+    UpdateBudget(now, duration);
+
+    // This is an ad-hoc way to use the counters for the timers
+    // that should be removed at somepoint. See Bug 1482834
+    PerformanceCounter* counter = GetPerformanceCounter();
+    if (counter) {
+      counter->IncrementExecutionDuration(duration.ToMicroseconds());
+    }
+  }
+
+  if (aTimeout) {
+    // If we're starting a new timeout callback, start recording.
+    budgetManager.StartRecording(now);
+    PerformanceCounter* counter = GetPerformanceCounter();
+    if (counter) {
+      counter->IncrementDispatchCounter(DispatchCategory(TaskCategory::Timer));
+    }
+  } else {
+    // Else stop by clearing the start timestamp.
+    budgetManager.StopRecording();
+  }
+}
+
+void TimeoutManager::UpdateBudget(const TimeStamp& aNow,
+                                  const TimeDuration& aDuration) {
+  if (mWindow.IsChromeWindow()) {
+    return;
+  }
+
+  // The budget is adjusted by increasing it with the time since the
+  // last budget update factored with the regeneration rate. If a
+  // runnable has executed, subtract that duration from the
+  // budget. The budget updated without consideration of wether the
+  // window is active or not. If throttling is enabled and the window
+  // is active and then becomes inactive, an overdrawn budget will
+  // still be counted against the minimum delay.
+  bool isBackground = mWindow.IsBackgroundInternal();
+  if (BudgetThrottlingEnabled(isBackground)) {
+    double factor = GetRegenerationFactor(isBackground);
+    TimeDuration regenerated = (aNow - mLastBudgetUpdate).MultDouble(factor);
+    // Clamp the budget to the range of minimum and maximum allowed budget.
+    mExecutionBudget = TimeDuration::Max(
+        GetMinBudget(isBackground),
+        TimeDuration::Min(GetMaxBudget(isBackground),
+                          mExecutionBudget - aDuration + regenerated));
+  } else {
+    // If budget throttling isn't enabled, reset the execution budget
+    // to the max budget specified in preferences. Always doing this
+    // will catch the case of BudgetThrottlingEnabled going from
+    // returning true to returning false. This prevent us from looping
+    // in RunTimeout, due to totalTimeLimit being set to zero and no
+    // timeouts being executed, even though budget throttling isn't
+    // active at the moment.
+    mExecutionBudget = GetMaxBudget(isBackground);
+  }
+
+  mLastBudgetUpdate = aNow;
+}
+
+// The longest interval (as PRIntervalTime) we permit, or that our
+// timer code can handle, really. See DELAY_INTERVAL_LIMIT in
+// nsTimerImpl.h for details.
+#define DOM_MAX_TIMEOUT_VALUE DELAY_INTERVAL_LIMIT
+
+uint32_t TimeoutManager::sNestingLevel = 0;
+
+TimeoutManager::TimeoutManager(nsGlobalWindowInner& aWindow,
+                               uint32_t aMaxIdleDeferMS)
+    : mWindow(aWindow),
+      mExecutor(new TimeoutExecutor(this, false, 0)),
+      mIdleExecutor(new TimeoutExecutor(this, true, aMaxIdleDeferMS)),
+      mTimeouts(*this),
+      mTimeoutIdCounter(1),
+      mNextFiringId(InvalidFiringId + 1),
+#ifdef DEBUG
+      mFiringIndex(0),
+      mLastFiringIndex(-1),
+#endif
+      mRunningTimeout(nullptr),
+      mIdleTimeouts(*this),
+      mIdleCallbackTimeoutCounter(1),
+      mLastBudgetUpdate(TimeStamp::Now()),
+      mExecutionBudget(GetMaxBudget(mWindow.IsBackgroundInternal())),
+      mThrottleTimeouts(false),
+      mThrottleTrackingTimeouts(false),
+      mBudgetThrottleTimeouts(false),
+      mIsLoading(false) {
+  MOZ_LOG(gTimeoutLog, LogLevel::Debug,
+          ("TimeoutManager %p created, tracking bucketing %s\n", this,
+           StaticPrefs::privacy_trackingprotection_annotate_channels()
+               ? "enabled"
+               : "disabled"));
+}
+
+TimeoutManager::~TimeoutManager() {
+  MOZ_DIAGNOSTIC_ASSERT(mWindow.IsDying());
+  MOZ_DIAGNOSTIC_ASSERT(!mThrottleTimeoutsTimer);
+
+  mExecutor->Shutdown();
+  mIdleExecutor->Shutdown();
+
+  MOZ_LOG(gTimeoutLog, LogLevel::Debug,
+          ("TimeoutManager %p destroyed\n", this));
+}
+
+uint32_t TimeoutManager::GetTimeoutId(Timeout::Reason aReason) {
+  switch (aReason) {
+    case Timeout::Reason::eIdleCallbackTimeout:
+      return ++mIdleCallbackTimeoutCounter;
+    case Timeout::Reason::eTimeoutOrInterval:
+    default:
+      return ++mTimeoutIdCounter;
+  }
+}
+
+bool TimeoutManager::IsRunningTimeout() const { return mRunningTimeout; }
+
+nsresult TimeoutManager::SetTimeout(TimeoutHandler* aHandler, int32_t interval,
+                                    bool aIsInterval, Timeout::Reason aReason,
+                                    int32_t* aReturn) {
+  // If we don't have a document (we could have been unloaded since
+  // the call to setTimeout was made), do nothing.
+  nsCOMPtr<Document> doc = mWindow.GetExtantDoc();
+  if (!doc) {
+    return NS_OK;
+  }
+
+  // Disallow negative intervals.
+  interval = std::max(0, interval);
+
+  // Make sure we don't proceed with an interval larger than our timer
+  // code can handle. (Note: we already forced |interval| to be non-negative,
+  // so the uint32_t cast (to avoid compiler warnings) is ok.)
+  uint32_t maxTimeoutMs = PR_IntervalToMilliseconds(DOM_MAX_TIMEOUT_VALUE);
+  if (static_cast<uint32_t>(interval) > maxTimeoutMs) {
+    interval = maxTimeoutMs;
+  }
+
+  RefPtr<Timeout> timeout = new Timeout();
+#ifdef DEBUG
+  timeout->mFiringIndex = -1;
+#endif
+  timeout->mWindow = &mWindow;
+  timeout->mIsInterval = aIsInterval;
+  timeout->mInterval = TimeDuration::FromMilliseconds(interval);
+  timeout->mScriptHandler = aHandler;
+  timeout->mReason = aReason;
+
+  // No popups from timeouts by default
+  timeout->mPopupState = PopupBlocker::openAbused;
+
+  timeout->mNestingLevel = sNestingLevel < DOM_CLAMP_TIMEOUT_NESTING_LEVEL
+                               ? sNestingLevel + 1
+                               : sNestingLevel;
+
+  // Now clamp the actual interval we will use for the timer based on
+  TimeDuration realInterval = CalculateDelay(timeout);
+  TimeStamp now = TimeStamp::Now();
+  timeout->SetWhenOrTimeRemaining(now, realInterval);
+
+  // If we're not suspended, then set the timer.
+  if (!mWindow.IsSuspended()) {
+    nsresult rv = MaybeSchedule(timeout->When(), now);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+  }
+
+  if (gRunningTimeoutDepth == 0 &&
+      PopupBlocker::GetPopupControlState() < PopupBlocker::openBlocked) {
+    // This timeout is *not* set from another timeout and it's set
+    // while popups are enabled. Propagate the state to the timeout if
+    // its delay (interval) is equal to or less than what
+    // "dom.disable_open_click_delay" is set to (in ms).
+
+    // This is checking |interval|, not realInterval, on purpose,
+    // because our lower bound for |realInterval| could be pretty high
+    // in some cases.
+    if (interval <= StaticPrefs::dom_disable_open_click_delay()) {
+      timeout->mPopupState = PopupBlocker::GetPopupControlState();
+    }
+  }
+
+  Timeouts::SortBy sort(mWindow.IsFrozen() ? Timeouts::SortBy::TimeRemaining
+                                           : Timeouts::SortBy::TimeWhen);
+
+  timeout->mTimeoutId = GetTimeoutId(aReason);
+  mTimeouts.Insert(timeout, sort);
+
+  *aReturn = timeout->mTimeoutId;
+
+  MOZ_LOG(
+      gTimeoutLog, LogLevel::Debug,
+      ("Set%s(TimeoutManager=%p, timeout=%p, delay=%i, "
+       "minimum=%f, throttling=%s, state=%s(%s), realInterval=%f) "
+       "returned timeout ID %u, budget=%d\n",
+       aIsInterval ? "Interval" : "Timeout", this, timeout.get(), interval,
+       (CalculateDelay(timeout) - timeout->mInterval).ToMilliseconds(),
+       mThrottleTimeouts ? "yes" : (mThrottleTimeoutsTimer ? "pending" : "no"),
+       IsActive() ? "active" : "inactive",
+       mWindow.IsBackgroundInternal() ? "background" : "foreground",
+       realInterval.ToMilliseconds(), timeout->mTimeoutId,
+       int(mExecutionBudget.ToMilliseconds())));
+
+  return NS_OK;
+}
+
+// Make sure we clear it no matter which list it's in
+void TimeoutManager::ClearTimeout(int32_t aTimerId, Timeout::Reason aReason) {
+  if (ClearTimeoutInternal(aTimerId, aReason, false) ||
+      mIdleTimeouts.IsEmpty()) {
+    return;  // no need to check the other list if we cleared the timeout
+  }
+  ClearTimeoutInternal(aTimerId, aReason, true);
+}
+
+bool TimeoutManager::ClearTimeoutInternal(int32_t aTimerId,
+                                          Timeout::Reason aReason,
+                                          bool aIsIdle) {
+  uint32_t timerId = (uint32_t)aTimerId;
+  Timeouts& timeouts = aIsIdle ? mIdleTimeouts : mTimeouts;
+  RefPtr<TimeoutExecutor>& executor = aIsIdle ? mIdleExecutor : mExecutor;
+  bool deferredDeletion = false;
+
+  Timeout* timeout = timeouts.GetTimeout(timerId, aReason);
+  if (!timeout) {
+    return false;
+  }
+  bool firstTimeout = timeout == timeouts.GetFirst();
+
+  MOZ_LOG(gTimeoutLog, LogLevel::Debug,
+          ("%s(TimeoutManager=%p, timeout=%p, ID=%u)\n",
+           timeout->mReason == Timeout::Reason::eIdleCallbackTimeout
+               ? "CancelIdleCallback"
+           : timeout->mIsInterval ? "ClearInterval"
+                                  : "ClearTimeout",
+           this, timeout, timeout->mTimeoutId));
+
+  if (timeout->mRunning) {
+    /* We're running from inside the timeout. Mark this
+       timeout for deferred deletion by the code in
+       RunTimeout() */
+    timeout->mIsInterval = false;
+    deferredDeletion = true;
+  } else {
+    /* Delete the aTimeout from the pending aTimeout list */
+    timeout->remove();
+  }
+
+  // We don't need to reschedule the executor if any of the following are true:
+  //  * If the we weren't cancelling the first timeout, then the executor's
+  //    state doesn't need to change.  It will only reflect the next soonest
+  //    Timeout.
+  //  * If we did cancel the first Timeout, but its currently running, then
+  //    RunTimeout() will handle rescheduling the executor.
+  //  * If the window has become suspended then we should not start executing
+  //    Timeouts.
+  if (!firstTimeout || deferredDeletion || mWindow.IsSuspended()) {
+    return true;
+  }
+
+  // Stop the executor and restart it at the next soonest deadline.
+  executor->Cancel();
+
+  Timeout* nextTimeout = timeouts.GetFirst();
+  if (nextTimeout) {
+    if (aIsIdle) {
+      MOZ_ALWAYS_SUCCEEDS(
+          executor->MaybeSchedule(nextTimeout->When(), TimeDuration(0)));
+    } else {
+      MOZ_ALWAYS_SUCCEEDS(MaybeSchedule(nextTimeout->When()));
+    }
+  }
+  return true;
+}
+
+void TimeoutManager::RunTimeout(const TimeStamp& aNow,
+                                const TimeStamp& aTargetDeadline,
+                                bool aProcessIdle) {
+  MOZ_DIAGNOSTIC_ASSERT(!aNow.IsNull());
+  MOZ_DIAGNOSTIC_ASSERT(!aTargetDeadline.IsNull());
+
+  MOZ_ASSERT_IF(mWindow.IsFrozen(), mWindow.IsSuspended());
+  if (mWindow.IsSuspended()) {
+    return;
+  }
+
+  Timeouts& timeouts(aProcessIdle ? mIdleTimeouts : mTimeouts);
+
+  // Limit the overall time spent in RunTimeout() to reduce jank.
+  uint32_t totalTimeLimitMS =
+      std::max(1u, StaticPrefs::dom_timeout_max_consecutive_callbacks_ms());
+  const TimeDuration totalTimeLimit =
+      TimeDuration::Min(TimeDuration::FromMilliseconds(totalTimeLimitMS),
+                        TimeDuration::Max(TimeDuration(), mExecutionBudget));
+
+  // Allow up to 25% of our total time budget to be used figuring out which
+  // timers need to run.  This is the initial loop in this method.
+  const TimeDuration initialTimeLimit =
+      TimeDuration::FromMilliseconds(totalTimeLimit.ToMilliseconds() / 4);
+
+  // Ammortize overhead from from calling TimeStamp::Now() in the initial
+  // loop, though, by only checking for an elapsed limit every N timeouts.
+  const uint32_t kNumTimersPerInitialElapsedCheck = 100;
+
+  // Start measuring elapsed time immediately.  We won't potentially expire
+  // the time budget until at least one Timeout has run, though.
+  TimeStamp now(aNow);
+  TimeStamp start = now;
+
+  uint32_t firingId = CreateFiringId();
+  auto guard = MakeScopeExit([&] { DestroyFiringId(firingId); });
+
+  // Make sure that the window and the script context don't go away as
+  // a result of running timeouts
+  RefPtr<nsGlobalWindowInner> window(&mWindow);
+  // Accessing members of mWindow here is safe, because the lifetime of
+  // TimeoutManager is the same as the lifetime of the containing
+  // nsGlobalWindow.
+
+  // A native timer has gone off. See which of our timeouts need
+  // servicing
+  TimeStamp deadline;
+
+  if (aTargetDeadline > now) {
+    // The OS timer fired early (which can happen due to the timers
+    // having lower precision than TimeStamp does).  Set |deadline| to
+    // be the time when the OS timer *should* have fired so that any
+    // timers that *should* have fired *will* be fired now.
+
+    deadline = aTargetDeadline;
+  } else {
+    deadline = now;
+  }
+
+  TimeStamp nextDeadline;
+  uint32_t numTimersToRun = 0;
+
+  // The timeout list is kept in deadline order. Discover the latest timeout
+  // whose deadline has expired. On some platforms, native timeout events fire
+  // "early", but we handled that above by setting deadline to aTargetDeadline
+  // if the timer fired early.  So we can stop walking if we get to timeouts
+  // whose When() is greater than deadline, since once that happens we know
+  // nothing past that point is expired.
+
+  for (Timeout* timeout = timeouts.GetFirst(); timeout != nullptr;
+       timeout = timeout->getNext()) {
+    if (totalTimeLimit.IsZero() || timeout->When() > deadline) {
+      nextDeadline = timeout->When();
+      break;
+    }
+
+    if (IsInvalidFiringId(timeout->mFiringId)) {
+      // Mark any timeouts that are on the list to be fired with the
+      // firing depth so that we can reentrantly run timeouts
+      timeout->mFiringId = firingId;
+
+      numTimersToRun += 1;
+
+      // Run only a limited number of timers based on the configured maximum.
+      if (numTimersToRun % kNumTimersPerInitialElapsedCheck == 0) {
+        now = TimeStamp::Now();
+        TimeDuration elapsed(now - start);
+        if (elapsed >= initialTimeLimit) {
+          nextDeadline = timeout->When();
+          break;
+        }
+      }
+    }
+  }
+  if (aProcessIdle) {
+    MOZ_LOG(
+        gTimeoutLog, LogLevel::Debug,
+        ("Running %u deferred timeouts on idle (TimeoutManager=%p), "
+         "nextDeadline = %gms from now",
+         numTimersToRun, this,
+         nextDeadline.IsNull() ? 0.0 : (nextDeadline - now).ToMilliseconds()));
+  }
+
+  now = TimeStamp::Now();
+
+  // Wherever we stopped in the timer list, schedule the executor to
+  // run for the next unexpired deadline.  Note, this *must* be done
+  // before we start executing any content script handlers.  If one
+  // of them spins the event loop the executor must already be scheduled
+  // in order for timeouts to fire properly.
+  if (!nextDeadline.IsNull()) {
+    // Note, we verified the window is not suspended at the top of
+    // method and the window should not have been suspended while
+    // executing the loop above since it doesn't call out to js.
+    MOZ_DIAGNOSTIC_ASSERT(!mWindow.IsSuspended());
+    if (aProcessIdle) {
+      // We don't want to update timing budget for idle queue firings, and
+      // all timeouts in the IdleTimeouts list have hit their deadlines,
+      // and so should run as soon as possible.
+      MOZ_ALWAYS_SUCCEEDS(
+          mIdleExecutor->MaybeSchedule(nextDeadline, TimeDuration()));
+    } else {
+      MOZ_ALWAYS_SUCCEEDS(MaybeSchedule(nextDeadline, now));
+    }
+  }
+
+  // Maybe the timeout that the event was fired for has been deleted
+  // and there are no others timeouts with deadlines that make them
+  // eligible for execution yet. Go away.
+  if (!numTimersToRun) {
+    return;
+  }
+
+  // Now we need to search the normal and tracking timer list at the same
+  // time to run the timers in the scheduled order.
+
+  // We stop iterating each list when we go past the last expired timeout from
+  // that list that we have observed above.  That timeout will either be the
+  // next item after the last timeout we looked at or nullptr if we have
+  // exhausted the entire list while looking for the last expired timeout.
+  {
+    // Use a nested scope in order to make sure the strong references held while
+    // iterating are freed after the loop.
+
+    // The next timeout to run. This is used to advance the loop, but
+    // we cannot set it until we've run the current timeout, since
+    // running the current timeout might remove the immediate next
+    // timeout.
+    RefPtr<Timeout> next;
+
+    for (RefPtr<Timeout> timeout = timeouts.GetFirst(); timeout != nullptr;
+         timeout = next) {
+      next = timeout->getNext();
+      // We should only execute callbacks for the set of expired Timeout
+      // objects we computed above.
+      if (timeout->mFiringId != firingId) {
+        // If the FiringId does not match, but is still valid, then this is
+        // a Timeout for another RunTimeout() on the call stack (such as in
+        // the case of nested event loops, for alert() or more likely XHR).
+        // Just skip it.
+        if (IsValidFiringId(timeout->mFiringId)) {
+          MOZ_LOG(gTimeoutLog, LogLevel::Debug,
+                  ("Skipping Run%s(TimeoutManager=%p, timeout=%p) since "
+                   "firingId %d is valid (processing firingId %d)"
+#ifdef DEBUG
+                   " - FiringIndex %" PRId64 " (mLastFiringIndex %" PRId64 ")"
+#endif
+                   ,
+                   timeout->mIsInterval ? "Interval" : "Timeout", this,
+                   timeout.get(), timeout->mFiringId, firingId
+#ifdef DEBUG
+                   ,
+                   timeout->mFiringIndex, mFiringIndex
+#endif
+                   ));
+#ifdef DEBUG
+          // The old FiringIndex assumed no recursion; recursion can cause
+          // other timers to get fired "in the middle" of a sequence we've
+          // already assigned firingindexes to.  Since we're not going to
+          // run this timeout now, remove any FiringIndex that was already
+          // set.
+
+          // Since all timers that have FiringIndexes set *must* be ready
+          // to run and have valid FiringIds, all of them will be 'skipped'
+          // and reset if we recurse - we don't have to look through the
+          // list past where we'll stop on the first InvalidFiringId.
+          timeout->mFiringIndex = -1;
+#endif
+          continue;
+        }
+
+        // If, however, the FiringId is invalid then we have reached Timeout
+        // objects beyond the list we calculated above.  This can happen
+        // if the Timeout just beyond our last expired Timeout is cancelled
+        // by one of the callbacks we've just executed.  In this case we
+        // should just stop iterating.  We're done.
+        else {
+          break;
+        }
+      }
+
+      MOZ_ASSERT_IF(mWindow.IsFrozen(), mWindow.IsSuspended());
+      if (mWindow.IsSuspended()) {
+        break;
+      }
+
+      // The timeout is on the list to run at this depth, go ahead and
+      // process it.
+
+      // Record the first time we try to fire a timeout, and ensure that
+      // all actual firings occur in that order.  This ensures that we
+      // retain compliance with the spec language
+      // (https://html.spec.whatwg.org/#dom-settimeout) specifically items
+      // 15 ("If method context is a Window object, wait until the Document
+      // associated with method context has been fully active for a further
+      // timeout milliseconds (not necessarily consecutively)") and item 16
+      // ("Wait until any invocations of this algorithm that had the same
+      // method context, that started before this one, and whose timeout is
+      // equal to or less than this one's, have completed.").
+#ifdef DEBUG
+      if (timeout->mFiringIndex == -1) {
+        timeout->mFiringIndex = mFiringIndex++;
+      }
+#endif
+
+      if (mIsLoading && !aProcessIdle) {
+        // Any timeouts that would fire during a load will be deferred
+        // until the load event occurs, but if there's an idle time,
+        // they'll be run before the load event.
+        timeout->remove();
+        // MOZ_RELEASE_ASSERT(timeout->When() <= (TimeStamp::Now()));
+        mIdleTimeouts.InsertBack(timeout);
+        if (MOZ_LOG_TEST(gTimeoutLog, LogLevel::Debug)) {
+          uint32_t num = 0;
+          for (Timeout* t = mIdleTimeouts.GetFirst(); t != nullptr;
+               t = t->getNext()) {
+            num++;
+          }
+          MOZ_LOG(
+              gTimeoutLog, LogLevel::Debug,
+              ("Deferring Run%s(TimeoutManager=%p, timeout=%p (%gms in the "
+               "past)) (%u deferred)",
+               timeout->mIsInterval ? "Interval" : "Timeout", this,
+               timeout.get(), (now - timeout->When()).ToMilliseconds(), num));
+        }
+        MOZ_ALWAYS_SUCCEEDS(mIdleExecutor->MaybeSchedule(now, TimeDuration()));
+      } else {
+        // Get the script context (a strong ref to prevent it going away)
+        // for this timeout and ensure the script language is enabled.
+        nsCOMPtr<nsIScriptContext> scx = mWindow.GetContextInternal();
+
+        if (!scx) {
+          // No context means this window was closed or never properly
+          // initialized for this language.  This timer will never fire
+          // so just remove it.
+          timeout->remove();
+          continue;
+        }
+
+#ifdef DEBUG
+        if (timeout->mFiringIndex <= mLastFiringIndex) {
+          MOZ_LOG(gTimeoutLog, LogLevel::Debug,
+                  ("Incorrect firing index for Run%s(TimeoutManager=%p, "
+                   "timeout=%p) with "
+                   "firingId %d - FiringIndex %" PRId64
+                   " (mLastFiringIndex %" PRId64 ")",
+                   timeout->mIsInterval ? "Interval" : "Timeout", this,
+                   timeout.get(), timeout->mFiringId, timeout->mFiringIndex,
+                   mFiringIndex));
+        }
+        MOZ_ASSERT(timeout->mFiringIndex > mLastFiringIndex);
+        mLastFiringIndex = timeout->mFiringIndex;
+#endif
+        // This timeout is good to run.
+        bool timeout_was_cleared = window->RunTimeoutHandler(timeout, scx);
+        MOZ_LOG(gTimeoutLog, LogLevel::Debug,
+                ("Run%s(TimeoutManager=%p, timeout=%p) returned %d\n",
+                 timeout->mIsInterval ? "Interval" : "Timeout", this,
+                 timeout.get(), !!timeout_was_cleared));
+
+        if (timeout_was_cleared) {
+          // Make sure we're not holding any Timeout objects alive.
+          next = nullptr;
+
+          // Since ClearAllTimeouts() was called the lists should be empty.
+          MOZ_DIAGNOSTIC_ASSERT(!HasTimeouts());
+
+          return;
+        }
+
+        // If we need to reschedule a setInterval() the delay should be
+        // calculated based on when its callback started to execute.  So
+        // save off the last time before updating our "now" timestamp to
+        // account for its callback execution time.
+        TimeStamp lastCallbackTime = now;
+        now = TimeStamp::Now();
+
+        // If we have a regular interval timer, we re-schedule the
+        // timeout, accounting for clock drift.
+        bool needsReinsertion =
+            RescheduleTimeout(timeout, lastCallbackTime, now);
+
+        // Running a timeout can cause another timeout to be deleted, so
+        // we need to reset the pointer to the following timeout.
+        next = timeout->getNext();
+
+        timeout->remove();
+
+        if (needsReinsertion) {
+          // Insert interval timeout onto the corresponding list sorted in
+          // deadline order. AddRefs timeout.
+          // Always re-insert into the normal time queue!
+          mTimeouts.Insert(timeout, mWindow.IsFrozen()
+                                        ? Timeouts::SortBy::TimeRemaining
+                                        : Timeouts::SortBy::TimeWhen);
+        }
+      }
+      // Check to see if we have run out of time to execute timeout handlers.
+      // If we've exceeded our time budget then terminate the loop immediately.
+      TimeDuration elapsed = now - start;
+      if (elapsed >= totalTimeLimit) {
+        // We ran out of time.  Make sure to schedule the executor to
+        // run immediately for the next timer, if it exists.  Its possible,
+        // however, that the last timeout handler suspended the window.  If
+        // that happened then we must skip this step.
+        if (!mWindow.IsSuspended()) {
+          if (next) {
+            if (aProcessIdle) {
+              // We don't want to update timing budget for idle queue firings,
+              // and all timeouts in the IdleTimeouts list have hit their
+              // deadlines, and so should run as soon as possible.
+
+              // Shouldn't need cancelling since it never waits
+              MOZ_ALWAYS_SUCCEEDS(
+                  mIdleExecutor->MaybeSchedule(next->When(), TimeDuration()));
+            } else {
+              // If we ran out of execution budget we need to force a
+              // reschedule. By cancelling the executor we will not run
+              // immediately, but instead reschedule to the minimum
+              // scheduling delay.
+              if (mExecutionBudget < TimeDuration()) {
+                mExecutor->Cancel();
+              }
+
+              MOZ_ALWAYS_SUCCEEDS(MaybeSchedule(next->When(), now));
+            }
+          }
+        }
+        break;
+      }
+    }
+  }
+}
+
+bool TimeoutManager::RescheduleTimeout(Timeout* aTimeout,
+                                       const TimeStamp& aLastCallbackTime,
+                                       const TimeStamp& aCurrentNow) {
+  MOZ_DIAGNOSTIC_ASSERT(aLastCallbackTime <= aCurrentNow);
+
+  if (!aTimeout->mIsInterval) {
+    return false;
+  }
+
+  // Automatically increase the nesting level when a setInterval()
+  // is rescheduled just as if it was using a chained setTimeout().
+  if (aTimeout->mNestingLevel < DOM_CLAMP_TIMEOUT_NESTING_LEVEL) {
+    aTimeout->mNestingLevel += 1;
+  }
+
+  // Compute time to next timeout for interval timer.
+  // Make sure nextInterval is at least CalculateDelay().
+  TimeDuration nextInterval = CalculateDelay(aTimeout);
+
+  TimeStamp firingTime = aLastCallbackTime + nextInterval;
+  TimeDuration delay = firingTime - aCurrentNow;
+
+#ifdef DEBUG
+  aTimeout->mFiringIndex = -1;
+#endif
+  // And make sure delay is nonnegative; that might happen if the timer
+  // thread is firing our timers somewhat early or if they're taking a long
+  // time to run the callback.
+  if (delay < TimeDuration(0)) {
+    delay = TimeDuration(0);
+  }
+
+  aTimeout->SetWhenOrTimeRemaining(aCurrentNow, delay);
+
+  if (mWindow.IsSuspended()) {
+    return true;
+  }
+
+  nsresult rv = MaybeSchedule(aTimeout->When(), aCurrentNow);
+  NS_ENSURE_SUCCESS(rv, false);
+
+  return true;
+}
+
+void TimeoutManager::ClearAllTimeouts() {
+  bool seenRunningTimeout = false;
+
+  MOZ_LOG(gTimeoutLog, LogLevel::Debug,
+          ("ClearAllTimeouts(TimeoutManager=%p)\n", this));
+
+  if (mThrottleTimeoutsTimer) {
+    mThrottleTimeoutsTimer->Cancel();
+    mThrottleTimeoutsTimer = nullptr;
+  }
+
+  mExecutor->Cancel();
+  mIdleExecutor->Cancel();
+
+  ForEachUnorderedTimeout([&](Timeout* aTimeout) {
+    /* If RunTimeout() is higher up on the stack for this
+       window, e.g. as a result of document.write from a timeout,
+       then we need to reset the list insertion point for
+       newly-created timeouts in case the user adds a timeout,
+       before we pop the stack back to RunTimeout. */
+    if (mRunningTimeout == aTimeout) {
+      seenRunningTimeout = true;
+    }
+
+    // Set timeout->mCleared to true to indicate that the timeout was
+    // cleared and taken out of the list of timeouts
+    aTimeout->mCleared = true;
+  });
+
+  // Clear out our lists
+  mTimeouts.Clear();
+  mIdleTimeouts.Clear();
+}
+
+void TimeoutManager::Timeouts::Insert(Timeout* aTimeout, SortBy aSortBy) {
+  // Start at mLastTimeout and go backwards.  Stop if we see a Timeout with a
+  // valid FiringId since those timers are currently being processed by
+  // RunTimeout.  This optimizes for the common case of insertion at the end.
+  Timeout* prevSibling;
+  for (prevSibling = GetLast();
+       prevSibling &&
+       // This condition needs to match the one in SetTimeoutOrInterval that
+       // determines whether to set When() or TimeRemaining().
+       (aSortBy == SortBy::TimeRemaining
+            ? prevSibling->TimeRemaining() > aTimeout->TimeRemaining()
+            : prevSibling->When() > aTimeout->When()) &&
+       // Check the firing ID last since it will evaluate true in the vast
+       // majority of cases.
+       mManager.IsInvalidFiringId(prevSibling->mFiringId);
+       prevSibling = prevSibling->getPrevious()) {
+    /* Do nothing; just searching */
+  }
+
+  // Now link in aTimeout after prevSibling.
+  if (prevSibling) {
+    aTimeout->SetTimeoutContainer(mTimeouts);
+    prevSibling->setNext(aTimeout);
+  } else {
+    InsertFront(aTimeout);
+  }
+
+  aTimeout->mFiringId = InvalidFiringId;
+}
+
+Timeout* TimeoutManager::BeginRunningTimeout(Timeout* aTimeout) {
+  Timeout* currentTimeout = mRunningTimeout;
+  mRunningTimeout = aTimeout;
+  ++gRunningTimeoutDepth;
+
+  RecordExecution(currentTimeout, aTimeout);
+  return currentTimeout;
+}
+
+void TimeoutManager::EndRunningTimeout(Timeout* aTimeout) {
+  --gRunningTimeoutDepth;
+
+  RecordExecution(mRunningTimeout, aTimeout);
+  mRunningTimeout = aTimeout;
+}
+
+void TimeoutManager::UnmarkGrayTimers() {
+  ForEachUnorderedTimeout([](Timeout* aTimeout) {
+    if (aTimeout->mScriptHandler) {
+      aTimeout->mScriptHandler->MarkForCC();
+    }
+  });
+}
+
+void TimeoutManager::Suspend() {
+  MOZ_LOG(gTimeoutLog, LogLevel::Debug, ("Suspend(TimeoutManager=%p)\n", this));
+
+  if (mThrottleTimeoutsTimer) {
+    mThrottleTimeoutsTimer->Cancel();
+    mThrottleTimeoutsTimer = nullptr;
+  }
+
+  mExecutor->Cancel();
+  mIdleExecutor->Cancel();
+}
+
+void TimeoutManager::Resume() {
+  MOZ_LOG(gTimeoutLog, LogLevel::Debug, ("Resume(TimeoutManager=%p)\n", this));
+
+  // When Suspend() has been called after IsDocumentLoaded(), but the
+  // throttle tracking timer never managed to fire, start the timer
+  // again.
+  if (mWindow.IsDocumentLoaded() && !mThrottleTimeouts) {
+    MaybeStartThrottleTimeout();
+  }
+
+  Timeout* nextTimeout = mTimeouts.GetFirst();
+  if (nextTimeout) {
+    MOZ_ALWAYS_SUCCEEDS(MaybeSchedule(nextTimeout->When()));
+  }
+  nextTimeout = mIdleTimeouts.GetFirst();
+  if (nextTimeout) {
+    MOZ_ALWAYS_SUCCEEDS(
+        mIdleExecutor->MaybeSchedule(nextTimeout->When(), TimeDuration()));
+  }
+}
+
+void TimeoutManager::Freeze() {
+  MOZ_LOG(gTimeoutLog, LogLevel::Debug, ("Freeze(TimeoutManager=%p)\n", this));
+
+  TimeStamp now = TimeStamp::Now();
+  ForEachUnorderedTimeout([&](Timeout* aTimeout) {
+    // Save the current remaining time for this timeout.  We will
+    // re-apply it when the window is Thaw()'d.  This effectively
+    // shifts timers to the right as if time does not pass while
+    // the window is frozen.
+    TimeDuration delta(0);
+    if (aTimeout->When() > now) {
+      delta = aTimeout->When() - now;
+    }
+    aTimeout->SetWhenOrTimeRemaining(now, delta);
+    MOZ_DIAGNOSTIC_ASSERT(aTimeout->TimeRemaining() == delta);
+  });
+}
+
+void TimeoutManager::Thaw() {
+  MOZ_LOG(gTimeoutLog, LogLevel::Debug, ("Thaw(TimeoutManager=%p)\n", this));
+
+  TimeStamp now = TimeStamp::Now();
+
+  ForEachUnorderedTimeout([&](Timeout* aTimeout) {
+    // Set When() back to the time when the timer is supposed to fire.
+    aTimeout->SetWhenOrTimeRemaining(now, aTimeout->TimeRemaining());
+    MOZ_DIAGNOSTIC_ASSERT(!aTimeout->When().IsNull());
+  });
+}
+
+void TimeoutManager::UpdateBackgroundState() {
+  mExecutionBudget = GetMaxBudget(mWindow.IsBackgroundInternal());
+
+  // When the window moves to the background or foreground we should
+  // reschedule the TimeoutExecutor in case the MinSchedulingDelay()
+  // changed.  Only do this if the window is not suspended and we
+  // actually have a timeout.
+  if (!mWindow.IsSuspended()) {
+    Timeout* nextTimeout = mTimeouts.GetFirst();
+    if (nextTimeout) {
+      mExecutor->Cancel();
+      MOZ_ALWAYS_SUCCEEDS(MaybeSchedule(nextTimeout->When()));
+    }
+    // the Idle queue should all be past their firing time, so there we just
+    // need to restart the queue
+
+    // XXX May not be needed if we don't stop the idle queue, as
+    // MinSchedulingDelay isn't relevant here
+    nextTimeout = mIdleTimeouts.GetFirst();
+    if (nextTimeout) {
+      mIdleExecutor->Cancel();
+      MOZ_ALWAYS_SUCCEEDS(
+          mIdleExecutor->MaybeSchedule(nextTimeout->When(), TimeDuration()));
+    }
+  }
+}
+
+namespace {
+
+class ThrottleTimeoutsCallback final : public nsITimerCallback,
+                                       public nsINamed {
+ public:
+  explicit ThrottleTimeoutsCallback(nsGlobalWindowInner* aWindow)
+      : mWindow(aWindow) {}
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSITIMERCALLBACK
+
+  NS_IMETHOD GetName(nsACString& aName) override {
+    aName.AssignLiteral("ThrottleTimeoutsCallback");
+    return NS_OK;
+  }
+
+ private:
+  ~ThrottleTimeoutsCallback() = default;
+
+ private:
+  // The strong reference here keeps the Window and hence the TimeoutManager
+  // object itself alive.
+  RefPtr<nsGlobalWindowInner> mWindow;
+};
+
+NS_IMPL_ISUPPORTS(ThrottleTimeoutsCallback, nsITimerCallback, nsINamed)
+
+NS_IMETHODIMP
+ThrottleTimeoutsCallback::Notify(nsITimer* aTimer) {
+  mWindow->TimeoutManager().StartThrottlingTimeouts();
+  mWindow = nullptr;
+  return NS_OK;
+}
+
+}  // namespace
+
+bool TimeoutManager::BudgetThrottlingEnabled(bool aIsBackground) const {
+  // A window can be throttled using budget if
+  // * It isn't active
+  // * If it isn't using WebRTC
+  // * If it hasn't got open WebSockets
+  // * If it hasn't got active IndexedDB databases
+
+  // Note that we allow both foreground and background to be
+  // considered for budget throttling. What determines if they are if
+  // budget throttling is enabled is the max budget.
+  if ((aIsBackground
+           ? StaticPrefs::dom_timeout_background_throttling_max_budget()
+           : StaticPrefs::dom_timeout_foreground_throttling_max_budget()) < 0) {
+    return false;
+  }
+
+  if (!mBudgetThrottleTimeouts || IsActive()) {
+    return false;
+  }
+
+  // Check if there are any active IndexedDB databases
+  if (mWindow.HasActiveIndexedDBDatabases()) {
+    return false;
+  }
+
+  // Check if we have active PeerConnection
+  if (mWindow.HasActivePeerConnections()) {
+    return false;
+  }
+
+  if (mWindow.HasOpenWebSockets()) {
+    return false;
+  }
+
+  return true;
+}
+
+void TimeoutManager::StartThrottlingTimeouts() {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_DIAGNOSTIC_ASSERT(mThrottleTimeoutsTimer);
+
+  MOZ_LOG(gTimeoutLog, LogLevel::Debug,
+          ("TimeoutManager %p started to throttle tracking timeouts\n", this));
+
+  MOZ_DIAGNOSTIC_ASSERT(!mThrottleTimeouts);
+  mThrottleTimeouts = true;
+  mThrottleTrackingTimeouts = true;
+  mBudgetThrottleTimeouts =
+      StaticPrefs::dom_timeout_enable_budget_timer_throttling();
+  mThrottleTimeoutsTimer = nullptr;
+}
+
+void TimeoutManager::OnDocumentLoaded() {
+  // The load event may be firing again if we're coming back to the page by
+  // navigating through the session history, so we need to ensure to only call
+  // this when mThrottleTimeouts hasn't been set yet.
+  if (!mThrottleTimeouts) {
+    MaybeStartThrottleTimeout();
+  }
+}
+
+void TimeoutManager::MaybeStartThrottleTimeout() {
+  if (StaticPrefs::dom_timeout_throttling_delay() <= 0 || mWindow.IsDying() ||
+      mWindow.IsSuspended()) {
+    return;
+  }
+
+  MOZ_DIAGNOSTIC_ASSERT(!mThrottleTimeouts);
+
+  MOZ_LOG(gTimeoutLog, LogLevel::Debug,
+          ("TimeoutManager %p delaying tracking timeout throttling by %dms\n",
+           this, StaticPrefs::dom_timeout_throttling_delay()));
+
+  nsCOMPtr<nsITimerCallback> callback = new ThrottleTimeoutsCallback(&mWindow);
+
+  NS_NewTimerWithCallback(getter_AddRefs(mThrottleTimeoutsTimer), callback,
+                          StaticPrefs::dom_timeout_throttling_delay(),
+                          nsITimer::TYPE_ONE_SHOT, EventTarget());
+}
+
+void TimeoutManager::BeginSyncOperation() {
+  // If we're beginning a sync operation, the currently running
+  // timeout will be put on hold. To not get into an inconsistent
+  // state, where the currently running timeout appears to take time
+  // equivalent to the period of us spinning up a new event loop,
+  // record what we have and stop recording until we reach
+  // EndSyncOperation.
+  RecordExecution(mRunningTimeout, nullptr);
+}
+
+void TimeoutManager::EndSyncOperation() {
+  // If we're running a timeout, restart the measurement from here.
+  RecordExecution(nullptr, mRunningTimeout);
+}
+
+nsIEventTarget* TimeoutManager::EventTarget() {
+  return mWindow.GetBrowsingContextGroup()->GetTimerEventQueue();
+}