gecko-dev/dom/base/TimeoutManager.cpp

/* -*- 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/StaticPrefs.h"
#include "mozilla/Telemetry.h"
#include "mozilla/ThrottledEventQueue.h"
#include "mozilla/TimeStamp.h"
#include "nsIDocShell.h"
#include "nsINamed.h"
#include "nsITimeoutHandler.h"
#include "mozilla/dom/DocGroup.h"
#include "mozilla/dom/PopupBlocker.h"
#include "mozilla/dom/TabGroup.h"
#include "TimeoutExecutor.h"
#include "TimeoutBudgetManager.h"
#include "mozilla/net/WebSocketEventService.h"
#include "mozilla/MediaManager.h"

using namespace mozilla;
using namespace mozilla::dom;

static LazyLogModule gLog("Timeout");

static int32_t gRunningTimeoutDepth = 0;

// The default shortest interval/timeout we permit
#define DEFAULT_MIN_CLAMP_TIMEOUT_VALUE 4                   // 4ms
#define DEFAULT_MIN_BACKGROUND_TIMEOUT_VALUE 1000           // 1000ms
#define DEFAULT_MIN_TRACKING_TIMEOUT_VALUE 4                // 4ms
#define DEFAULT_MIN_TRACKING_BACKGROUND_TIMEOUT_VALUE 1000  // 1000ms
static int32_t gMinClampTimeoutValue = 0;
static int32_t gMinBackgroundTimeoutValue = 0;
static int32_t gMinTrackingTimeoutValue = 0;
static int32_t gMinTrackingBackgroundTimeoutValue = 0;
static int32_t gTimeoutThrottlingDelay = 0;

#define DEFAULT_BACKGROUND_BUDGET_REGENERATION_FACTOR 100  // 1ms per 100ms
#define DEFAULT_FOREGROUND_BUDGET_REGENERATION_FACTOR 1    // 1ms per 1ms
#define DEFAULT_BACKGROUND_THROTTLING_MAX_BUDGET 50        // 50ms
#define DEFAULT_FOREGROUND_THROTTLING_MAX_BUDGET -1        // infinite
#define DEFAULT_BUDGET_THROTTLING_MAX_DELAY 15000          // 15s
#define DEFAULT_ENABLE_BUDGET_TIMEOUT_THROTTLING false
static int32_t gBackgroundBudgetRegenerationFactor = 0;
static int32_t gForegroundBudgetRegenerationFactor = 0;
static int32_t gBackgroundThrottlingMaxBudget = 0;
static int32_t gForegroundThrottlingMaxBudget = 0;
static int32_t gBudgetThrottlingMaxDelay = 0;
static bool gEnableBudgetTimeoutThrottling = false;

// 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 ? gBackgroundBudgetRegenerationFactor
                             : gForegroundBudgetRegenerationFactor,
               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 ? gBackgroundThrottlingMaxBudget
                                    : gForegroundThrottlingMaxBudget;
  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(
      -gBudgetThrottlingMaxDelay /
      std::max(aIsBackground ? gBackgroundBudgetRegenerationFactor
                             : gForegroundBudgetRegenerationFactor,
               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.AsInner()->IsPlayingAudio()) {
    return true;
  }

  return false;
}

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
  // gBudgetThrottlingMaxDelay 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(gMinBackgroundTimeoutValue)
                   : TimeDuration();
  if (BudgetThrottlingEnabled(isBackground) &&
      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));
  }
  //
  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.
    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. HTML5 says 1, WebKit
// uses 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) {
    result = TimeDuration::Max(
        result, TimeDuration::FromMilliseconds(gMinClampTimeoutValue));
  }

  return result;
}

PerformanceCounter* TimeoutManager::GetPerformanceCounter() {
  if (!StaticPrefs::dom_performance_enable_scheduler_timing()) {
    return nullptr;
  }
  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) {
  if (!StaticPrefs::dom_performance_enable_scheduler_timing() &&
      mWindow.IsChromeWindow()) {
    return;
  }

  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;
}

#define DEFAULT_TIMEOUT_THROTTLING_DELAY \
  -1  // Only positive integers cause us to introduce a delay for
      // timeout throttling.

// 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;

namespace {

// The maximum number of milliseconds to allow consecutive timer callbacks
// to run in a single event loop runnable.
#define DEFAULT_MAX_CONSECUTIVE_CALLBACKS_MILLISECONDS 4
uint32_t gMaxConsecutiveCallbacksMilliseconds;

// Only propagate the open window click permission if the setTimeout() is equal
// to or less than this value.
#define DEFAULT_DISABLE_OPEN_CLICK_DELAY 0
int32_t gDisableOpenClickDelay;

}  // anonymous namespace

TimeoutManager::TimeoutManager(nsGlobalWindowInner& aWindow)
    : mWindow(aWindow),
      mExecutor(new TimeoutExecutor(this)),
      mTimeouts(*this),
      mTimeoutIdCounter(1),
      mNextFiringId(InvalidFiringId + 1),
      mRunningTimeout(nullptr),
      mIdleCallbackTimeoutCounter(1),
      mLastBudgetUpdate(TimeStamp::Now()),
      mExecutionBudget(GetMaxBudget(mWindow.IsBackgroundInternal())),
      mThrottleTimeouts(false),
      mThrottleTrackingTimeouts(false),
      mBudgetThrottleTimeouts(false) {
  MOZ_LOG(gLog, 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();

  MOZ_LOG(gLog, LogLevel::Debug, ("TimeoutManager %p destroyed\n", this));
}

/* static */
void TimeoutManager::Initialize() {
  Preferences::AddIntVarCache(&gMinClampTimeoutValue, "dom.min_timeout_value",
                              DEFAULT_MIN_CLAMP_TIMEOUT_VALUE);
  Preferences::AddIntVarCache(&gMinBackgroundTimeoutValue,
                              "dom.min_background_timeout_value",
                              DEFAULT_MIN_BACKGROUND_TIMEOUT_VALUE);
  Preferences::AddIntVarCache(&gMinTrackingTimeoutValue,
                              "dom.min_tracking_timeout_value",
                              DEFAULT_MIN_TRACKING_TIMEOUT_VALUE);
  Preferences::AddIntVarCache(&gMinTrackingBackgroundTimeoutValue,
                              "dom.min_tracking_background_timeout_value",
                              DEFAULT_MIN_TRACKING_BACKGROUND_TIMEOUT_VALUE);
  Preferences::AddIntVarCache(&gTimeoutThrottlingDelay,
                              "dom.timeout.throttling_delay",
                              DEFAULT_TIMEOUT_THROTTLING_DELAY);

  Preferences::AddUintVarCache(&gMaxConsecutiveCallbacksMilliseconds,
                               "dom.timeout.max_consecutive_callbacks_ms",
                               DEFAULT_MAX_CONSECUTIVE_CALLBACKS_MILLISECONDS);

  Preferences::AddIntVarCache(&gDisableOpenClickDelay,
                              "dom.disable_open_click_delay",
                              DEFAULT_DISABLE_OPEN_CLICK_DELAY);
  Preferences::AddIntVarCache(&gBackgroundBudgetRegenerationFactor,
                              "dom.timeout.background_budget_regeneration_rate",
                              DEFAULT_BACKGROUND_BUDGET_REGENERATION_FACTOR);
  Preferences::AddIntVarCache(&gForegroundBudgetRegenerationFactor,
                              "dom.timeout.foreground_budget_regeneration_rate",
                              DEFAULT_FOREGROUND_BUDGET_REGENERATION_FACTOR);
  Preferences::AddIntVarCache(&gBackgroundThrottlingMaxBudget,
                              "dom.timeout.background_throttling_max_budget",
                              DEFAULT_BACKGROUND_THROTTLING_MAX_BUDGET);
  Preferences::AddIntVarCache(&gForegroundThrottlingMaxBudget,
                              "dom.timeout.foreground_throttling_max_budget",
                              DEFAULT_FOREGROUND_THROTTLING_MAX_BUDGET);
  Preferences::AddIntVarCache(&gBudgetThrottlingMaxDelay,
                              "dom.timeout.budget_throttling_max_delay",
                              DEFAULT_BUDGET_THROTTLING_MAX_DELAY);
  Preferences::AddBoolVarCache(&gEnableBudgetTimeoutThrottling,
                               "dom.timeout.enable_budget_timer_throttling",
                               DEFAULT_ENABLE_BUDGET_TIMEOUT_THROTTLING);
}

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(nsITimeoutHandler* 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();
  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 <= gDisableOpenClickDelay) {
      timeout->mPopupState = PopupBlocker::GetPopupControlState();
    }
  }

  Timeouts::SortBy sort(mWindow.IsFrozen() ? Timeouts::SortBy::TimeRemaining
                                           : Timeouts::SortBy::TimeWhen);
  mTimeouts.Insert(timeout, sort);

  timeout->mTimeoutId = GetTimeoutId(aReason);
  *aReturn = timeout->mTimeoutId;

  MOZ_LOG(
      gLog, 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;
}

void TimeoutManager::ClearTimeout(int32_t aTimerId, Timeout::Reason aReason) {
  uint32_t timerId = (uint32_t)aTimerId;

  bool firstTimeout = true;
  bool deferredDeletion = false;

  mTimeouts.ForEachAbortable([&](Timeout* aTimeout) {
    MOZ_LOG(gLog, LogLevel::Debug,
            ("Clear%s(TimeoutManager=%p, timeout=%p, aTimerId=%u, ID=%u)\n",
             aTimeout->mIsInterval ? "Interval" : "Timeout", this, aTimeout,
             timerId, aTimeout->mTimeoutId));

    if (aTimeout->mTimeoutId == timerId && aTimeout->mReason == aReason) {
      if (aTimeout->mRunning) {
        /* We're running from inside the aTimeout. Mark this
           aTimeout for deferred deletion by the code in
           RunTimeout() */
        aTimeout->mIsInterval = false;
        deferredDeletion = true;
      } else {
        /* Delete the aTimeout from the pending aTimeout list */
        aTimeout->remove();
      }
      return true;  // abort!
    }

    firstTimeout = false;

    return false;
  });

  // 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;
  }

  // Stop the executor and restart it at the next soonest deadline.
  mExecutor->Cancel();

  Timeout* nextTimeout = mTimeouts.GetFirst();
  if (nextTimeout) {
    MOZ_ALWAYS_SUCCEEDS(MaybeSchedule(nextTimeout->When()));
  }
}

void TimeoutManager::RunTimeout(const TimeStamp& aNow,
                                const TimeStamp& aTargetDeadline) {
  MOZ_DIAGNOSTIC_ASSERT(!aNow.IsNull());
  MOZ_DIAGNOSTIC_ASSERT(!aTargetDeadline.IsNull());

  MOZ_ASSERT_IF(mWindow.IsFrozen(), mWindow.IsSuspended());
  if (mWindow.IsSuspended()) {
    return;
  }

  // Limit the overall time spent in RunTimeout() to reduce jank.
  uint32_t totalTimeLimitMS =
      std::max(1u, gMaxConsecutiveCallbacksMilliseconds);
  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
  nsCOMPtr<nsIScriptGlobalObject> windowKungFuDeathGrip(&mWindow);
  // Silence the static analysis error about windowKungFuDeathGrip.  Accessing
  // members of mWindow here is safe, because the lifetime of TimeoutManager is
  // the same as the lifetime of the containing nsGlobalWindow.
  Unused << windowKungFuDeathGrip;

  // 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 = mTimeouts.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;
        }
      }
    }
  }

  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());
    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 = mTimeouts.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.  Just
        // skip it.
        if (IsValidFiringId(timeout->mFiringId)) {
          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.

      // 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;
      }

      // This timeout is good to run
      bool timeout_was_cleared = mWindow.RunTimeoutHandler(timeout, scx);

      MOZ_LOG(gLog, 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.
        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 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;

  // 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(gLog, LogLevel::Debug,
          ("ClearAllTimeouts(TimeoutManager=%p)\n", this));

  if (mThrottleTimeoutsTimer) {
    mThrottleTimeoutsTimer->Cancel();
    mThrottleTimeoutsTimer = nullptr;
  }

  mExecutor->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 list
  mTimeouts.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) {
    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(gLog, LogLevel::Debug, ("Suspend(TimeoutManager=%p)\n", this));

  if (mThrottleTimeoutsTimer) {
    mThrottleTimeoutsTimer->Cancel();
    mThrottleTimeoutsTimer = nullptr;
  }

  mExecutor->Cancel();
}

void TimeoutManager::Resume() {
  MOZ_LOG(gLog, 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.AsInner()->IsDocumentLoaded() && !mThrottleTimeouts) {
    MaybeStartThrottleTimeout();
  }

  Timeout* nextTimeout = mTimeouts.GetFirst();
  if (nextTimeout) {
    MOZ_ALWAYS_SUCCEEDS(MaybeSchedule(nextTimeout->When()));
  }
}

void TimeoutManager::Freeze() {
  MOZ_LOG(gLog, 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(gLog, 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()));
    }
  }
}

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() {}

 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->AsInner()->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 ? gBackgroundThrottlingMaxBudget
                     : gForegroundThrottlingMaxBudget) < 0) {
    return false;
  }

  if (!mBudgetThrottleTimeouts || IsActive()) {
    return false;
  }

  // Check if there are any active IndexedDB databases
  if (mWindow.AsInner()->HasActiveIndexedDBDatabases()) {
    return false;
  }

  // Check if we have active PeerConnection
  if (mWindow.AsInner()->HasActivePeerConnections()) {
    return false;
  }

  if (mWindow.AsInner()->HasOpenWebSockets()) {
    return false;
  }

  return true;
}

void TimeoutManager::StartThrottlingTimeouts() {
  MOZ_ASSERT(NS_IsMainThread());
  MOZ_DIAGNOSTIC_ASSERT(mThrottleTimeoutsTimer);

  MOZ_LOG(gLog, LogLevel::Debug,
          ("TimeoutManager %p started to throttle tracking timeouts\n", this));

  MOZ_DIAGNOSTIC_ASSERT(!mThrottleTimeouts);
  mThrottleTimeouts = true;
  mThrottleTrackingTimeouts = true;
  mBudgetThrottleTimeouts = gEnableBudgetTimeoutThrottling;
  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 (gTimeoutThrottlingDelay <= 0 || mWindow.IsDying() ||
      mWindow.IsSuspended()) {
    return;
  }

  MOZ_DIAGNOSTIC_ASSERT(!mThrottleTimeouts);

  MOZ_LOG(gLog, LogLevel::Debug,
          ("TimeoutManager %p delaying tracking timeout throttling by %dms\n",
           this, gTimeoutThrottlingDelay));

  nsCOMPtr<nsITimerCallback> callback = new ThrottleTimeoutsCallback(&mWindow);

  NS_NewTimerWithCallback(getter_AddRefs(mThrottleTimeoutsTimer), callback,
                          gTimeoutThrottlingDelay, 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.EventTargetFor(TaskCategory::Timer);
}