1 files changed, 1512 insertions, 0 deletions
diff --git a/xpcom/threads/TimerThread.cpp b/xpcom/threads/TimerThread.cpp
new file mode 100644
index 0000000000..0d672ac7b0
--- /dev/null
+++ b/xpcom/threads/TimerThread.cpp
@@ -0,0 +1,1512 @@
+/* -*- 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 "nsTimerImpl.h"
+#include "TimerThread.h"
+
+#include "GeckoProfiler.h"
+#include "nsThreadUtils.h"
+#include "pratom.h"
+
+#include "nsIObserverService.h"
+#include "mozilla/Services.h"
+#include "mozilla/ChaosMode.h"
+#include "mozilla/ArenaAllocator.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/BinarySearch.h"
+#include "mozilla/OperatorNewExtensions.h"
+#include "mozilla/StaticPrefs_timer.h"
+
+#include "mozilla/glean/GleanMetrics.h"
+
+#include <math.h>
+
+using namespace mozilla;
+
+// Bug 1829983 reports an assertion failure that (so far) has only failed once
+// in over a month of the assert existing. This #define enables some additional
+// output that should get printed out if the assert fails again.
+#if defined(XP_WIN) && defined(DEBUG)
+#  define HACK_OUTPUT_FOR_BUG_1829983
+#endif
+
+// Uncomment the following line to enable runtime stats during development.
+// #define TIMERS_RUNTIME_STATS
+
+#ifdef TIMERS_RUNTIME_STATS
+// This class gathers durations and displays some basic stats when destroyed.
+// It is intended to be used as a static variable (see `AUTO_TIMERS_STATS`
+// below), to display stats at the end of the program.
+class StaticTimersStats {
+ public:
+  explicit StaticTimersStats(const char* aName) : mName(aName) {}
+
+  ~StaticTimersStats() {
+    // Using unsigned long long for computations and printfs.
+    using ULL = unsigned long long;
+    ULL n = static_cast<ULL>(mCount);
+    if (n == 0) {
+      printf("[%d] Timers stats `%s`: (nothing)\n",
+             int(profiler_current_process_id().ToNumber()), mName);
+    } else if (ULL sumNs = static_cast<ULL>(mSumDurationsNs); sumNs == 0) {
+      printf("[%d] Timers stats `%s`: %llu\n",
+             int(profiler_current_process_id().ToNumber()), mName, n);
+    } else {
+      printf("[%d] Timers stats `%s`: %llu ns / %llu = %llu ns, max %llu ns\n",
+             int(profiler_current_process_id().ToNumber()), mName, sumNs, n,
+             sumNs / n, static_cast<ULL>(mLongestDurationNs));
+    }
+  }
+
+  void AddDurationFrom(TimeStamp aStart) {
+    // Duration between aStart and now, rounded to the nearest nanosecond.
+    DurationNs duration = static_cast<DurationNs>(
+        (TimeStamp::Now() - aStart).ToMicroseconds() * 1000 + 0.5);
+    mSumDurationsNs += duration;
+    ++mCount;
+    // Update mLongestDurationNs if this one is longer.
+    for (;;) {
+      DurationNs longest = mLongestDurationNs;
+      if (MOZ_LIKELY(longest >= duration)) {
+        // This duration is not the longest, nothing to do.
+        break;
+      }
+      if (MOZ_LIKELY(mLongestDurationNs.compareExchange(longest, duration))) {
+        // Successfully updated `mLongestDurationNs` with the new value.
+        break;
+      }
+      // Otherwise someone else just updated `mLongestDurationNs`, we need to
+      // try again by looping.
+    }
+  }
+
+  void AddCount() {
+    MOZ_ASSERT(mSumDurationsNs == 0, "Don't mix counts and durations");
+    ++mCount;
+  }
+
+ private:
+  using DurationNs = uint64_t;
+  using Count = uint32_t;
+
+  Atomic<DurationNs> mSumDurationsNs{0};
+  Atomic<DurationNs> mLongestDurationNs{0};
+  Atomic<Count> mCount{0};
+  const char* mName;
+};
+
+// RAII object that measures its scoped lifetime duration and reports it to a
+// `StaticTimersStats`.
+class MOZ_RAII AutoTimersStats {
+ public:
+  explicit AutoTimersStats(StaticTimersStats& aStats)
+      : mStats(aStats), mStart(TimeStamp::Now()) {}
+
+  ~AutoTimersStats() { mStats.AddDurationFrom(mStart); }
+
+ private:
+  StaticTimersStats& mStats;
+  TimeStamp mStart;
+};
+
+// Macro that should be used to collect basic statistics from measurements of
+// block durations, from where this macro is, until the end of its enclosing
+// scope. The name is used in the static variable name and when displaying stats
+// at the end of the program; Another location could use the same name but their
+// stats will not be combined, so use different name if these locations should
+// be distinguished.
+#  define AUTO_TIMERS_STATS(name)                  \
+    static ::StaticTimersStats sStat##name(#name); \
+    ::AutoTimersStats autoStat##name(sStat##name);
+
+// This macro only counts the number of times it's used, not durations.
+// Don't mix with AUTO_TIMERS_STATS!
+#  define COUNT_TIMERS_STATS(name)                 \
+    static ::StaticTimersStats sStat##name(#name); \
+    sStat##name.AddCount();
+
+#else  // TIMERS_RUNTIME_STATS
+
+#  define AUTO_TIMERS_STATS(name)
+#  define COUNT_TIMERS_STATS(name)
+
+#endif  // TIMERS_RUNTIME_STATS else
+
+NS_IMPL_ISUPPORTS_INHERITED(TimerThread, Runnable, nsIObserver)
+
+TimerThread::TimerThread()
+    : Runnable("TimerThread"),
+      mInitialized(false),
+      mMonitor("TimerThread.mMonitor"),
+      mShutdown(false),
+      mWaiting(false),
+      mNotified(false),
+      mSleeping(false),
+      mAllowedEarlyFiringMicroseconds(0) {}
+
+TimerThread::~TimerThread() {
+  mThread = nullptr;
+
+  NS_ASSERTION(mTimers.IsEmpty(), "Timers remain in TimerThread::~TimerThread");
+
+#if TIMER_THREAD_STATISTICS
+  {
+    MonitorAutoLock lock(mMonitor);
+    PrintStatistics();
+  }
+#endif
+}
+
+namespace {
+
+class TimerObserverRunnable : public Runnable {
+ public:
+  explicit TimerObserverRunnable(nsIObserver* aObserver)
+      : mozilla::Runnable("TimerObserverRunnable"), mObserver(aObserver) {}
+
+  NS_DECL_NSIRUNNABLE
+
+ private:
+  nsCOMPtr<nsIObserver> mObserver;
+};
+
+NS_IMETHODIMP
+TimerObserverRunnable::Run() {
+  nsCOMPtr<nsIObserverService> observerService =
+      mozilla::services::GetObserverService();
+  if (observerService) {
+    observerService->AddObserver(mObserver, "sleep_notification", false);
+    observerService->AddObserver(mObserver, "wake_notification", false);
+    observerService->AddObserver(mObserver, "suspend_process_notification",
+                                 false);
+    observerService->AddObserver(mObserver, "resume_process_notification",
+                                 false);
+  }
+  return NS_OK;
+}
+
+}  // namespace
+
+namespace {
+
+// TimerEventAllocator is a thread-safe allocator used only for nsTimerEvents.
+// It's needed to avoid contention over the default allocator lock when
+// firing timer events (see bug 733277).  The thread-safety is required because
+// nsTimerEvent objects are allocated on the timer thread, and freed on another
+// thread.  Because TimerEventAllocator has its own lock, contention over that
+// lock is limited to the allocation and deallocation of nsTimerEvent objects.
+//
+// Because this is layered over ArenaAllocator, it never shrinks -- even
+// "freed" nsTimerEvents aren't truly freed, they're just put onto a free-list
+// for later recycling.  So the amount of memory consumed will always be equal
+// to the high-water mark consumption.  But nsTimerEvents are small and it's
+// unusual to have more than a few hundred of them, so this shouldn't be a
+// problem in practice.
+
+class TimerEventAllocator {
+ private:
+  struct FreeEntry {
+    FreeEntry* mNext;
+  };
+
+  ArenaAllocator<4096> mPool MOZ_GUARDED_BY(mMonitor);
+  FreeEntry* mFirstFree MOZ_GUARDED_BY(mMonitor);
+  mozilla::Monitor mMonitor;
+
+ public:
+  TimerEventAllocator()
+      : mPool(), mFirstFree(nullptr), mMonitor("TimerEventAllocator") {}
+
+  ~TimerEventAllocator() = default;
+
+  void* Alloc(size_t aSize);
+  void Free(void* aPtr);
+};
+
+}  // namespace
+
+// This is a nsICancelableRunnable because we can dispatch it to Workers and
+// those can be shut down at any time, and in these cases, Cancel() is called
+// instead of Run().
+class nsTimerEvent final : public CancelableRunnable {
+ public:
+  NS_IMETHOD Run() override;
+
+  nsresult Cancel() override {
+    mTimer->Cancel();
+    return NS_OK;
+  }
+
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
+  NS_IMETHOD GetName(nsACString& aName) override;
+#endif
+
+  explicit nsTimerEvent(already_AddRefed<nsTimerImpl> aTimer,
+                        ProfilerThreadId aTimerThreadId)
+      : mozilla::CancelableRunnable("nsTimerEvent"),
+        mTimer(aTimer),
+        mGeneration(mTimer->GetGeneration()),
+        mTimerThreadId(aTimerThreadId) {
+    // Note: We override operator new for this class, and the override is
+    // fallible!
+    sAllocatorUsers++;
+
+    if (MOZ_LOG_TEST(GetTimerLog(), LogLevel::Debug) ||
+        profiler_thread_is_being_profiled_for_markers(mTimerThreadId)) {
+      mInitTime = TimeStamp::Now();
+    }
+  }
+
+  static void Init();
+  static void Shutdown();
+  static void DeleteAllocatorIfNeeded();
+
+  static void* operator new(size_t aSize) noexcept(true) {
+    return sAllocator->Alloc(aSize);
+  }
+  void operator delete(void* aPtr) {
+    sAllocator->Free(aPtr);
+    sAllocatorUsers--;
+    DeleteAllocatorIfNeeded();
+  }
+
+  already_AddRefed<nsTimerImpl> ForgetTimer() { return mTimer.forget(); }
+
+ private:
+  nsTimerEvent(const nsTimerEvent&) = delete;
+  nsTimerEvent& operator=(const nsTimerEvent&) = delete;
+  nsTimerEvent& operator=(const nsTimerEvent&&) = delete;
+
+  ~nsTimerEvent() {
+    MOZ_ASSERT(!sCanDeleteAllocator || sAllocatorUsers > 0,
+               "This will result in us attempting to deallocate the "
+               "nsTimerEvent allocator twice");
+  }
+
+  TimeStamp mInitTime;
+  RefPtr<nsTimerImpl> mTimer;
+  const int32_t mGeneration;
+  ProfilerThreadId mTimerThreadId;
+
+  static TimerEventAllocator* sAllocator;
+
+  static Atomic<int32_t, SequentiallyConsistent> sAllocatorUsers;
+  static Atomic<bool, SequentiallyConsistent> sCanDeleteAllocator;
+};
+
+TimerEventAllocator* nsTimerEvent::sAllocator = nullptr;
+Atomic<int32_t, SequentiallyConsistent> nsTimerEvent::sAllocatorUsers;
+Atomic<bool, SequentiallyConsistent> nsTimerEvent::sCanDeleteAllocator;
+
+namespace {
+
+void* TimerEventAllocator::Alloc(size_t aSize) {
+  MOZ_ASSERT(aSize == sizeof(nsTimerEvent));
+
+  mozilla::MonitorAutoLock lock(mMonitor);
+
+  void* p;
+  if (mFirstFree) {
+    p = mFirstFree;
+    mFirstFree = mFirstFree->mNext;
+  } else {
+    p = mPool.Allocate(aSize, fallible);
+  }
+
+  return p;
+}
+
+void TimerEventAllocator::Free(void* aPtr) {
+  mozilla::MonitorAutoLock lock(mMonitor);
+
+  FreeEntry* entry = reinterpret_cast<FreeEntry*>(aPtr);
+
+  entry->mNext = mFirstFree;
+  mFirstFree = entry;
+}
+
+}  // namespace
+
+struct TimerMarker {
+  static constexpr Span<const char> MarkerTypeName() {
+    return MakeStringSpan("Timer");
+  }
+  static void StreamJSONMarkerData(baseprofiler::SpliceableJSONWriter& aWriter,
+                                   uint32_t aDelay, uint8_t aType,
+                                   MarkerThreadId aThreadId, bool aCanceled) {
+    aWriter.IntProperty("delay", aDelay);
+    if (!aThreadId.IsUnspecified()) {
+      // Tech note: If `ToNumber()` returns a uint64_t, the conversion to
+      // int64_t is "implementation-defined" before C++20. This is
+      // acceptable here, because this is a one-way conversion to a unique
+      // identifier that's used to visually separate data by thread on the
+      // front-end.
+      aWriter.IntProperty(
+          "threadId", static_cast<int64_t>(aThreadId.ThreadId().ToNumber()));
+    }
+    if (aCanceled) {
+      aWriter.BoolProperty("canceled", true);
+      // Show a red 'X' as a prefix on the marker chart for canceled timers.
+      aWriter.StringProperty("prefix", "❌");
+    }
+
+    // The string property for the timer type is not written when the type is
+    // one shot, as that's the type used almost all the time, and that would
+    // consume space in the profiler buffer and then in the profile JSON,
+    // getting in the way of capturing long power profiles.
+    // Bug 1815677 might make this cheap to capture.
+    if (aType != nsITimer::TYPE_ONE_SHOT) {
+      if (aType == nsITimer::TYPE_REPEATING_SLACK) {
+        aWriter.StringProperty("ttype", "repeating slack");
+      } else if (aType == nsITimer::TYPE_REPEATING_PRECISE) {
+        aWriter.StringProperty("ttype", "repeating precise");
+      } else if (aType == nsITimer::TYPE_REPEATING_PRECISE_CAN_SKIP) {
+        aWriter.StringProperty("ttype", "repeating precise can skip");
+      } else if (aType == nsITimer::TYPE_REPEATING_SLACK_LOW_PRIORITY) {
+        aWriter.StringProperty("ttype", "repeating slack low priority");
+      } else if (aType == nsITimer::TYPE_ONE_SHOT_LOW_PRIORITY) {
+        aWriter.StringProperty("ttype", "low priority");
+      }
+    }
+  }
+  static MarkerSchema MarkerTypeDisplay() {
+    using MS = MarkerSchema;
+    MS schema{MS::Location::MarkerChart, MS::Location::MarkerTable};
+    schema.AddKeyLabelFormat("delay", "Delay", MS::Format::Milliseconds);
+    schema.AddKeyLabelFormat("ttype", "Timer Type", MS::Format::String);
+    schema.AddKeyLabelFormat("canceled", "Canceled", MS::Format::String);
+    schema.SetChartLabel("{marker.data.prefix} {marker.data.delay}");
+    schema.SetTableLabel(
+        "{marker.name} - {marker.data.prefix} {marker.data.delay}");
+    return schema;
+  }
+};
+
+struct AddRemoveTimerMarker {
+  static constexpr Span<const char> MarkerTypeName() {
+    return MakeStringSpan("AddRemoveTimer");
+  }
+  static void StreamJSONMarkerData(baseprofiler::SpliceableJSONWriter& aWriter,
+                                   const ProfilerString8View& aTimerName,
+                                   uint32_t aDelay, MarkerThreadId aThreadId) {
+    aWriter.StringProperty("name", aTimerName);
+    aWriter.IntProperty("delay", aDelay);
+    if (!aThreadId.IsUnspecified()) {
+      // Tech note: If `ToNumber()` returns a uint64_t, the conversion to
+      // int64_t is "implementation-defined" before C++20. This is
+      // acceptable here, because this is a one-way conversion to a unique
+      // identifier that's used to visually separate data by thread on the
+      // front-end.
+      aWriter.IntProperty(
+          "threadId", static_cast<int64_t>(aThreadId.ThreadId().ToNumber()));
+    }
+  }
+  static MarkerSchema MarkerTypeDisplay() {
+    using MS = MarkerSchema;
+    MS schema{MS::Location::MarkerChart, MS::Location::MarkerTable};
+    schema.AddKeyLabelFormatSearchable("name", "Name", MS::Format::String,
+                                       MS::Searchable::Searchable);
+    schema.AddKeyLabelFormat("delay", "Delay", MS::Format::Milliseconds);
+    schema.SetTableLabel(
+        "{marker.name} - {marker.data.name} - {marker.data.delay}");
+    return schema;
+  }
+};
+
+void nsTimerEvent::Init() { sAllocator = new TimerEventAllocator(); }
+
+void nsTimerEvent::Shutdown() {
+  sCanDeleteAllocator = true;
+  DeleteAllocatorIfNeeded();
+}
+
+void nsTimerEvent::DeleteAllocatorIfNeeded() {
+  if (sCanDeleteAllocator && sAllocatorUsers == 0) {
+    delete sAllocator;
+    sAllocator = nullptr;
+  }
+}
+
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
+NS_IMETHODIMP
+nsTimerEvent::GetName(nsACString& aName) {
+  bool current;
+  MOZ_RELEASE_ASSERT(
+      NS_SUCCEEDED(mTimer->mEventTarget->IsOnCurrentThread(&current)) &&
+      current);
+
+  mTimer->GetName(aName);
+  return NS_OK;
+}
+#endif
+
+NS_IMETHODIMP
+nsTimerEvent::Run() {
+  if (MOZ_LOG_TEST(GetTimerLog(), LogLevel::Debug)) {
+    TimeStamp now = TimeStamp::Now();
+    MOZ_LOG(GetTimerLog(), LogLevel::Debug,
+            ("[this=%p] time between PostTimerEvent() and Fire(): %fms\n", this,
+             (now - mInitTime).ToMilliseconds()));
+  }
+
+  if (profiler_thread_is_being_profiled_for_markers(mTimerThreadId)) {
+    MutexAutoLock lock(mTimer->mMutex);
+    nsAutoCString name;
+    mTimer->GetName(name, lock);
+    // This adds a marker with the timer name as the marker name, to make it
+    // obvious which timers are being used. This marker will be useful to
+    // understand which timers might be added and firing excessively often.
+    profiler_add_marker(
+        name, geckoprofiler::category::TIMER,
+        MarkerOptions(MOZ_LIKELY(mInitTime)
+                          ? MarkerTiming::Interval(
+                                mTimer->mTimeout - mTimer->mDelay, mInitTime)
+                          : MarkerTiming::IntervalUntilNowFrom(
+                                mTimer->mTimeout - mTimer->mDelay),
+                      MarkerThreadId(mTimerThreadId)),
+        TimerMarker{}, mTimer->mDelay.ToMilliseconds(), mTimer->mType,
+        MarkerThreadId::CurrentThread(), false);
+    // This marker is meant to help understand the behavior of the timer thread.
+    profiler_add_marker(
+        "PostTimerEvent", geckoprofiler::category::OTHER,
+        MarkerOptions(MOZ_LIKELY(mInitTime)
+                          ? MarkerTiming::IntervalUntilNowFrom(mInitTime)
+                          : MarkerTiming::InstantNow(),
+                      MarkerThreadId(mTimerThreadId)),
+        AddRemoveTimerMarker{}, name, mTimer->mDelay.ToMilliseconds(),
+        MarkerThreadId::CurrentThread());
+  }
+
+  mTimer->Fire(mGeneration);
+
+  return NS_OK;
+}
+
+nsresult TimerThread::Init() {
+  mMonitor.AssertCurrentThreadOwns();
+  MOZ_LOG(GetTimerLog(), LogLevel::Debug,
+          ("TimerThread::Init [%d]\n", mInitialized));
+
+  if (!mInitialized) {
+    nsTimerEvent::Init();
+
+    // We hold on to mThread to keep the thread alive.
+    nsresult rv =
+        NS_NewNamedThread("Timer", getter_AddRefs(mThread), this,
+                          {.stackSize = nsIThreadManager::DEFAULT_STACK_SIZE,
+                           .blockDispatch = true});
+    if (NS_FAILED(rv)) {
+      mThread = nullptr;
+    } else {
+      RefPtr<TimerObserverRunnable> r = new TimerObserverRunnable(this);
+      if (NS_IsMainThread()) {
+        r->Run();
+      } else {
+        NS_DispatchToMainThread(r);
+      }
+    }
+
+    mInitialized = true;
+  }
+
+  if (!mThread) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+nsresult TimerThread::Shutdown() {
+  MOZ_LOG(GetTimerLog(), LogLevel::Debug, ("TimerThread::Shutdown begin\n"));
+
+  if (!mThread) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  nsTArray<RefPtr<nsTimerImpl>> timers;
+  {
+    // lock scope
+    MonitorAutoLock lock(mMonitor);
+
+    mShutdown = true;
+
+    // notify the cond var so that Run() can return
+    if (mWaiting) {
+      mNotified = true;
+      mMonitor.Notify();
+    }
+
+    // Need to copy content of mTimers array to a local array
+    // because call to timers' Cancel() (and release its self)
+    // must not be done under the lock. Destructor of a callback
+    // might potentially call some code reentering the same lock
+    // that leads to unexpected behavior or deadlock.
+    // See bug 422472.
+    timers.SetCapacity(mTimers.Length());
+    for (Entry& entry : mTimers) {
+      if (entry.Value()) {
+        timers.AppendElement(entry.Take());
+      }
+    }
+
+    mTimers.Clear();
+  }
+
+  for (const RefPtr<nsTimerImpl>& timer : timers) {
+    MOZ_ASSERT(timer);
+    timer->Cancel();
+  }
+
+  mThread->Shutdown();  // wait for the thread to die
+
+  nsTimerEvent::Shutdown();
+
+  MOZ_LOG(GetTimerLog(), LogLevel::Debug, ("TimerThread::Shutdown end\n"));
+  return NS_OK;
+}
+
+namespace {
+
+struct MicrosecondsToInterval {
+  PRIntervalTime operator[](size_t aMs) const {
+    return PR_MicrosecondsToInterval(aMs);
+  }
+};
+
+struct IntervalComparator {
+  int operator()(PRIntervalTime aInterval) const {
+    return (0 < aInterval) ? -1 : 1;
+  }
+};
+
+}  // namespace
+
+#ifdef DEBUG
+void TimerThread::VerifyTimerListConsistency() const {
+  mMonitor.AssertCurrentThreadOwns();
+
+  // Find the first non-canceled timer (and check its cached timeout if we find
+  // it).
+  const size_t timerCount = mTimers.Length();
+  size_t lastNonCanceledTimerIndex = 0;
+  while (lastNonCanceledTimerIndex < timerCount &&
+         !mTimers[lastNonCanceledTimerIndex].Value()) {
+    ++lastNonCanceledTimerIndex;
+  }
+  MOZ_ASSERT(lastNonCanceledTimerIndex == timerCount ||
+             mTimers[lastNonCanceledTimerIndex].Value());
+  MOZ_ASSERT(lastNonCanceledTimerIndex == timerCount ||
+             mTimers[lastNonCanceledTimerIndex].Value()->mTimeout ==
+                 mTimers[lastNonCanceledTimerIndex].Timeout());
+
+  // Verify that mTimers is sorted and the cached timeouts are consistent.
+  for (size_t timerIndex = lastNonCanceledTimerIndex + 1;
+       timerIndex < timerCount; ++timerIndex) {
+    if (mTimers[timerIndex].Value()) {
+      MOZ_ASSERT(mTimers[timerIndex].Timeout() ==
+                 mTimers[timerIndex].Value()->mTimeout);
+      MOZ_ASSERT(mTimers[timerIndex].Timeout() >=
+                 mTimers[lastNonCanceledTimerIndex].Timeout());
+      lastNonCanceledTimerIndex = timerIndex;
+    }
+  }
+}
+#endif
+
+size_t TimerThread::ComputeTimerInsertionIndex(const TimeStamp& timeout) const {
+  mMonitor.AssertCurrentThreadOwns();
+
+  const size_t timerCount = mTimers.Length();
+
+  size_t firstGtIndex = 0;
+  while (firstGtIndex < timerCount &&
+         (!mTimers[firstGtIndex].Value() ||
+          mTimers[firstGtIndex].Timeout() <= timeout)) {
+    ++firstGtIndex;
+  }
+
+  return firstGtIndex;
+}
+
+TimeStamp TimerThread::ComputeWakeupTimeFromTimers() const {
+  mMonitor.AssertCurrentThreadOwns();
+
+  // Timer list should be non-empty and first timer should always be
+  // non-canceled at this point and we rely on that here.
+  MOZ_ASSERT(!mTimers.IsEmpty());
+  MOZ_ASSERT(mTimers[0].Value());
+
+  // Overview: Find the last timer in the list that can be "bundled" together in
+  // the same wake-up with mTimers[0] and use its timeout as our target wake-up
+  // time.
+
+  // bundleWakeup is when we should wake up in order to be able to fire all of
+  // the timers in our selected bundle. It will always be the timeout of the
+  // last timer in the bundle.
+  TimeStamp bundleWakeup = mTimers[0].Timeout();
+
+  // cutoffTime is the latest that we can wake up for the timers currently
+  // accepted into the bundle. These needs to be updated as we go through the
+  // list because later timers may have more strict delay tolerances.
+  const TimeDuration minTimerDelay = TimeDuration::FromMilliseconds(
+      StaticPrefs::timer_minimum_firing_delay_tolerance_ms());
+  const TimeDuration maxTimerDelay = TimeDuration::FromMilliseconds(
+      StaticPrefs::timer_maximum_firing_delay_tolerance_ms());
+  TimeStamp cutoffTime =
+      bundleWakeup + ComputeAcceptableFiringDelay(mTimers[0].Delay(),
+                                                  minTimerDelay, maxTimerDelay);
+
+  const size_t timerCount = mTimers.Length();
+  for (size_t entryIndex = 1; entryIndex < timerCount; ++entryIndex) {
+    const Entry& curEntry = mTimers[entryIndex];
+    const nsTimerImpl* curTimer = curEntry.Value();
+    if (!curTimer) {
+      // Canceled timer - skip it
+      continue;
+    }
+
+    const TimeStamp curTimerDue = curEntry.Timeout();
+    if (curTimerDue > cutoffTime) {
+      // Can't include this timer in the bundle - it fires too late.
+      break;
+    }
+
+    // This timer can be included in the bundle. Update bundleWakeup and
+    // cutoffTime.
+    bundleWakeup = curTimerDue;
+    cutoffTime = std::min(
+        curTimerDue + ComputeAcceptableFiringDelay(
+                          curEntry.Delay(), minTimerDelay, maxTimerDelay),
+        cutoffTime);
+    MOZ_ASSERT(bundleWakeup <= cutoffTime);
+  }
+
+#ifdef HACK_OUTPUT_FOR_BUG_1829983
+  const bool assertCondition =
+      bundleWakeup - mTimers[0].Timeout() <=
+      ComputeAcceptableFiringDelay(mTimers[0].Delay(), minTimerDelay,
+                                   maxTimerDelay);
+  if (!assertCondition) {
+    printf_stderr("*** Special TimerThread debug output ***\n");
+    const int64_t tDMin = minTimerDelay.GetValue();
+    const int64_t tDMax = maxTimerDelay.GetValue();
+    printf_stderr("%16llx / %16llx\n", tDMin, tDMax);
+    const size_t l = mTimers.Length();
+    for (size_t i = 0; i < l; ++i) {
+      const Entry& e = mTimers[i];
+      const TimeStamp tS = e.Timeout();
+      const TimeStampValue tSV = tS.GetValue();
+      const TimeDuration d = e.Delay();
+      printf_stderr("[%5zu] %16llx / %16llx / %d / %d / %16llx\n", i, tSV.GTC(),
+                    tSV.QPC(), (int)tSV.IsNull(), (int)tSV.HasQPC(),
+                    d.GetValue());
+    }
+  }
+#endif
+  MOZ_ASSERT(bundleWakeup - mTimers[0].Timeout() <=
+             ComputeAcceptableFiringDelay(mTimers[0].Delay(), minTimerDelay,
+                                          maxTimerDelay));
+
+  return bundleWakeup;
+}
+
+TimeDuration TimerThread::ComputeAcceptableFiringDelay(
+    TimeDuration timerDuration, TimeDuration minDelay,
+    TimeDuration maxDelay) const {
+  // Use the timer's duration divided by this value as a base for how much
+  // firing delay a timer can accept. 8 was chosen specifically because it is a
+  // power of two which means that this division turns nicely into a shift.
+  constexpr int64_t timerDurationDivider = 8;
+  static_assert(IsPowerOfTwo(static_cast<uint64_t>(timerDurationDivider)));
+  const TimeDuration tmp = timerDuration / timerDurationDivider;
+  return std::min(std::max(minDelay, tmp), maxDelay);
+}
+
+NS_IMETHODIMP
+TimerThread::Run() {
+  MonitorAutoLock lock(mMonitor);
+
+  mProfilerThreadId = profiler_current_thread_id();
+
+  // We need to know how many microseconds give a positive PRIntervalTime. This
+  // is platform-dependent and we calculate it at runtime, finding a value |v|
+  // such that |PR_MicrosecondsToInterval(v) > 0| and then binary-searching in
+  // the range [0, v) to find the ms-to-interval scale.
+  uint32_t usForPosInterval = 1;
+  while (PR_MicrosecondsToInterval(usForPosInterval) == 0) {
+    usForPosInterval <<= 1;
+  }
+
+  size_t usIntervalResolution;
+  BinarySearchIf(MicrosecondsToInterval(), 0, usForPosInterval,
+                 IntervalComparator(), &usIntervalResolution);
+  MOZ_ASSERT(PR_MicrosecondsToInterval(usIntervalResolution - 1) == 0);
+  MOZ_ASSERT(PR_MicrosecondsToInterval(usIntervalResolution) == 1);
+
+  // Half of the amount of microseconds needed to get positive PRIntervalTime.
+  // We use this to decide how to round our wait times later
+  mAllowedEarlyFiringMicroseconds = usIntervalResolution / 2;
+  bool forceRunNextTimer = false;
+
+  // Queue for tracking of how many timers are fired on each wake-up. We need to
+  // buffer these locally and only send off to glean occasionally to avoid
+  // performance hit.
+  static constexpr size_t kMaxQueuedTimerFired = 128;
+  size_t queuedTimerFiredCount = 0;
+  AutoTArray<uint64_t, kMaxQueuedTimerFired> queuedTimersFiredPerWakeup;
+  queuedTimersFiredPerWakeup.SetLengthAndRetainStorage(kMaxQueuedTimerFired);
+
+  uint64_t timersFiredThisWakeup = 0;
+  while (!mShutdown) {
+    // Have to use PRIntervalTime here, since PR_WaitCondVar takes it
+    TimeDuration waitFor;
+    bool forceRunThisTimer = forceRunNextTimer;
+    forceRunNextTimer = false;
+
+#ifdef DEBUG
+    VerifyTimerListConsistency();
+#endif
+
+    if (mSleeping) {
+      // Sleep for 0.1 seconds while not firing timers.
+      uint32_t milliseconds = 100;
+      if (ChaosMode::isActive(ChaosFeature::TimerScheduling)) {
+        milliseconds = ChaosMode::randomUint32LessThan(200);
+      }
+      waitFor = TimeDuration::FromMilliseconds(milliseconds);
+    } else {
+      waitFor = TimeDuration::Forever();
+      TimeStamp now = TimeStamp::Now();
+
+#if TIMER_THREAD_STATISTICS
+      if (!mNotified && !mIntendedWakeupTime.IsNull() &&
+          now < mIntendedWakeupTime) {
+        ++mEarlyWakeups;
+        const double earlinessms = (mIntendedWakeupTime - now).ToMilliseconds();
+        mTotalEarlyWakeupTime += earlinessms;
+      }
+#endif
+
+      RemoveLeadingCanceledTimersInternal();
+
+      if (!mTimers.IsEmpty()) {
+        if (now >= mTimers[0].Value()->mTimeout || forceRunThisTimer) {
+        next:
+          // NB: AddRef before the Release under RemoveTimerInternal to avoid
+          // mRefCnt passing through zero, in case all other refs than the one
+          // from mTimers have gone away (the last non-mTimers[i]-ref's Release
+          // must be racing with us, blocked in gThread->RemoveTimer waiting
+          // for TimerThread::mMonitor, under nsTimerImpl::Release.
+
+          RefPtr<nsTimerImpl> timerRef(mTimers[0].Take());
+          RemoveFirstTimerInternal();
+          MOZ_LOG(GetTimerLog(), LogLevel::Debug,
+                  ("Timer thread woke up %fms from when it was supposed to\n",
+                   fabs((now - timerRef->mTimeout).ToMilliseconds())));
+
+          // We are going to let the call to PostTimerEvent here handle the
+          // release of the timer so that we don't end up releasing the timer
+          // on the TimerThread instead of on the thread it targets.
+          {
+            ++timersFiredThisWakeup;
+            LogTimerEvent::Run run(timerRef.get());
+            PostTimerEvent(timerRef.forget());
+          }
+
+          if (mShutdown) {
+            break;
+          }
+
+          // Update now, as PostTimerEvent plus the locking may have taken a
+          // tick or two, and we may goto next below.
+          now = TimeStamp::Now();
+        }
+      }
+
+      RemoveLeadingCanceledTimersInternal();
+
+      if (!mTimers.IsEmpty()) {
+        TimeStamp timeout = mTimers[0].Value()->mTimeout;
+
+        // Don't wait at all (even for PR_INTERVAL_NO_WAIT) if the next timer
+        // is due now or overdue.
+        //
+        // Note that we can only sleep for integer values of a certain
+        // resolution. We use mAllowedEarlyFiringMicroseconds, calculated
+        // before, to do the optimal rounding (i.e., of how to decide what
+        // interval is so small we should not wait at all).
+        double microseconds = (timeout - now).ToMicroseconds();
+
+        // The mean value of sFractions must be 1 to ensure that the average of
+        // a long sequence of timeouts converges to the actual sum of their
+        // times.
+        static constexpr double sChaosFractions[] = {0.0, 0.25, 0.5, 0.75,
+                                                     1.0, 1.75, 2.75};
+        if (ChaosMode::isActive(ChaosFeature::TimerScheduling)) {
+          microseconds *= sChaosFractions[ChaosMode::randomUint32LessThan(
+              ArrayLength(sChaosFractions))];
+          forceRunNextTimer = true;
+        }
+
+        if (microseconds < mAllowedEarlyFiringMicroseconds) {
+          forceRunNextTimer = false;
+          goto next;  // round down; execute event now
+        }
+
+        // TECHNICAL NOTE: Determining waitFor (by subtracting |now| from our
+        // desired wake-up time) at this point is not ideal. For one thing, the
+        // |now| that we have at this point is somewhat old. Secondly, there is
+        // quite a bit of code between here and where we actually use waitFor to
+        // request sleep. If I am thinking about this correctly, both of these
+        // will contribute to us requesting more sleep than is actually needed
+        // to wake up at our desired time. We could avoid this problem by only
+        // determining our desired wake-up time here and then calculating the
+        // wait time when we're actually about to sleep.
+        const TimeStamp wakeupTime = ComputeWakeupTimeFromTimers();
+        waitFor = wakeupTime - now;
+
+        // If this were to fail that would mean that we had more timers that we
+        // should have fired.
+        MOZ_ASSERT(!waitFor.IsZero());
+
+        if (ChaosMode::isActive(ChaosFeature::TimerScheduling)) {
+          // If chaos mode is active then mess with the amount of time that we
+          // request to sleep (without changing what we record as our expected
+          // wake-up time). This will simulate unintended early/late wake-ups.
+          const double waitInMs = waitFor.ToMilliseconds();
+          const double chaosWaitInMs =
+              waitInMs * sChaosFractions[ChaosMode::randomUint32LessThan(
+                             ArrayLength(sChaosFractions))];
+          waitFor = TimeDuration::FromMilliseconds(chaosWaitInMs);
+        }
+
+        mIntendedWakeupTime = wakeupTime;
+      } else {
+        mIntendedWakeupTime = TimeStamp{};
+      }
+
+      if (MOZ_LOG_TEST(GetTimerLog(), LogLevel::Debug)) {
+        if (waitFor == TimeDuration::Forever())
+          MOZ_LOG(GetTimerLog(), LogLevel::Debug, ("waiting forever\n"));
+        else
+          MOZ_LOG(GetTimerLog(), LogLevel::Debug,
+                  ("waiting for %f\n", waitFor.ToMilliseconds()));
+      }
+    }
+
+    {
+      // About to sleep - let's make note of how many timers we processed and
+      // see if we should send out a new batch of telemetry.
+      queuedTimersFiredPerWakeup[queuedTimerFiredCount] = timersFiredThisWakeup;
+      ++queuedTimerFiredCount;
+      if (queuedTimerFiredCount == kMaxQueuedTimerFired) {
+        glean::timer_thread::timers_fired_per_wakeup.AccumulateSamples(
+            queuedTimersFiredPerWakeup);
+        queuedTimerFiredCount = 0;
+      }
+    }
+
+#if TIMER_THREAD_STATISTICS
+    {
+      size_t bucketIndex = 0;
+      while (bucketIndex < sTimersFiredPerWakeupBucketCount - 1 &&
+             timersFiredThisWakeup >
+                 sTimersFiredPerWakeupThresholds[bucketIndex]) {
+        ++bucketIndex;
+      }
+      MOZ_ASSERT(bucketIndex < sTimersFiredPerWakeupBucketCount);
+      ++mTimersFiredPerWakeup[bucketIndex];
+
+      ++mTotalWakeupCount;
+      if (mNotified) {
+        ++mTimersFiredPerNotifiedWakeup[bucketIndex];
+        ++mTotalNotifiedWakeupCount;
+      } else {
+        ++mTimersFiredPerUnnotifiedWakeup[bucketIndex];
+        ++mTotalUnnotifiedWakeupCount;
+      }
+    }
+#endif
+
+    timersFiredThisWakeup = 0;
+
+    mWaiting = true;
+    mNotified = false;
+
+    {
+      AUTO_PROFILER_TRACING_MARKER("TimerThread", "Wait", OTHER);
+      mMonitor.Wait(waitFor);
+    }
+    if (mNotified) {
+      forceRunNextTimer = false;
+    }
+    mWaiting = false;
+  }
+
+  // About to shut down - let's send out the final batch of timers fired counts.
+  if (queuedTimerFiredCount != 0) {
+    queuedTimersFiredPerWakeup.SetLengthAndRetainStorage(queuedTimerFiredCount);
+    glean::timer_thread::timers_fired_per_wakeup.AccumulateSamples(
+        queuedTimersFiredPerWakeup);
+  }
+
+  return NS_OK;
+}
+
+nsresult TimerThread::AddTimer(nsTimerImpl* aTimer,
+                               const MutexAutoLock& aProofOfLock) {
+  MonitorAutoLock lock(mMonitor);
+  AUTO_TIMERS_STATS(TimerThread_AddTimer);
+
+  if (!aTimer->mEventTarget) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  nsresult rv = Init();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // Awaken the timer thread if:
+  // - This timer needs to fire *before* the Timer Thread is scheduled to wake
+  //   up.
+  // AND/OR
+  // - The delay is 0, which is usually meant to be run as soon as possible.
+  //   Note: Even if the thread is scheduled to wake up now/soon, on some
+  //   systems there could be a significant delay compared to notifying, which
+  //   is almost immediate; and some users of 0-delay depend on it being this
+  //   fast!
+  const TimeDuration minTimerDelay = TimeDuration::FromMilliseconds(
+      StaticPrefs::timer_minimum_firing_delay_tolerance_ms());
+  const TimeDuration maxTimerDelay = TimeDuration::FromMilliseconds(
+      StaticPrefs::timer_maximum_firing_delay_tolerance_ms());
+  const TimeDuration firingDelay = ComputeAcceptableFiringDelay(
+      aTimer->mDelay, minTimerDelay, maxTimerDelay);
+  const bool firingBeforeNextWakeup =
+      mIntendedWakeupTime.IsNull() ||
+      (aTimer->mTimeout + firingDelay < mIntendedWakeupTime);
+  const bool wakeUpTimerThread =
+      mWaiting && (firingBeforeNextWakeup || aTimer->mDelay.IsZero());
+
+#if TIMER_THREAD_STATISTICS
+  if (mTotalTimersAdded == 0) {
+    mFirstTimerAdded = TimeStamp::Now();
+  }
+  ++mTotalTimersAdded;
+#endif
+
+  // Add the timer to our list.
+  if (!AddTimerInternal(*aTimer)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  if (wakeUpTimerThread) {
+    mNotified = true;
+    mMonitor.Notify();
+  }
+
+  if (profiler_thread_is_being_profiled_for_markers(mProfilerThreadId)) {
+    nsAutoCString name;
+    aTimer->GetName(name, aProofOfLock);
+
+    nsLiteralCString prefix("Anonymous_");
+    profiler_add_marker(
+        "AddTimer", geckoprofiler::category::OTHER,
+        MarkerOptions(MarkerThreadId(mProfilerThreadId),
+                      MarkerStack::MaybeCapture(
+                          name.Equals("nonfunction:JS") ||
+                          StringHead(name, prefix.Length()) == prefix)),
+        AddRemoveTimerMarker{}, name, aTimer->mDelay.ToMilliseconds(),
+        MarkerThreadId::CurrentThread());
+  }
+
+  return NS_OK;
+}
+
+nsresult TimerThread::RemoveTimer(nsTimerImpl* aTimer,
+                                  const MutexAutoLock& aProofOfLock) {
+  MonitorAutoLock lock(mMonitor);
+  AUTO_TIMERS_STATS(TimerThread_RemoveTimer);
+
+  // Remove the timer from our array.  Tell callers that aTimer was not found
+  // by returning NS_ERROR_NOT_AVAILABLE.
+
+  if (!RemoveTimerInternal(*aTimer)) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+#if TIMER_THREAD_STATISTICS
+  ++mTotalTimersRemoved;
+#endif
+
+  // Note: The timer thread is *not* awoken.
+  // The removed-timer entry is just left null, and will be reused (by a new or
+  // re-set timer) or discarded (when the timer thread logic handles non-null
+  // timers around it).
+  // If this was the front timer, and in the unlikely case that its entry is not
+  // soon reused by a re-set timer, the timer thread will wake up at the
+  // previously-scheduled time, but will quickly notice that there is no actual
+  // pending timer, and will restart its wait until the following real timeout.
+
+  if (profiler_thread_is_being_profiled_for_markers(mProfilerThreadId)) {
+    nsAutoCString name;
+    aTimer->GetName(name, aProofOfLock);
+
+    nsLiteralCString prefix("Anonymous_");
+    // This marker is meant to help understand the behavior of the timer thread.
+    profiler_add_marker(
+        "RemoveTimer", geckoprofiler::category::OTHER,
+        MarkerOptions(MarkerThreadId(mProfilerThreadId),
+                      MarkerStack::MaybeCapture(
+                          name.Equals("nonfunction:JS") ||
+                          StringHead(name, prefix.Length()) == prefix)),
+        AddRemoveTimerMarker{}, name, aTimer->mDelay.ToMilliseconds(),
+        MarkerThreadId::CurrentThread());
+    // This adds a marker with the timer name as the marker name, to make it
+    // obvious which timers are being used. This marker will be useful to
+    // understand which timers might be added and removed excessively often.
+    profiler_add_marker(name, geckoprofiler::category::TIMER,
+                        MarkerOptions(MarkerTiming::IntervalUntilNowFrom(
+                                          aTimer->mTimeout - aTimer->mDelay),
+                                      MarkerThreadId(mProfilerThreadId)),
+                        TimerMarker{}, aTimer->mDelay.ToMilliseconds(),
+                        aTimer->mType, MarkerThreadId::CurrentThread(), true);
+  }
+
+  return NS_OK;
+}
+
+TimeStamp TimerThread::FindNextFireTimeForCurrentThread(TimeStamp aDefault,
+                                                        uint32_t aSearchBound) {
+  MonitorAutoLock lock(mMonitor);
+  AUTO_TIMERS_STATS(TimerThread_FindNextFireTimeForCurrentThread);
+
+  for (const Entry& entry : mTimers) {
+    const nsTimerImpl* timer = entry.Value();
+    if (timer) {
+      if (entry.Timeout() > aDefault) {
+        return aDefault;
+      }
+
+      // Don't yield to timers created with the *_LOW_PRIORITY type.
+      if (!timer->IsLowPriority()) {
+        bool isOnCurrentThread = false;
+        nsresult rv =
+            timer->mEventTarget->IsOnCurrentThread(&isOnCurrentThread);
+        if (NS_SUCCEEDED(rv) && isOnCurrentThread) {
+          return entry.Timeout();
+        }
+      }
+
+      if (aSearchBound == 0) {
+        // Return the currently highest timeout when we reach the bound.
+        // This won't give accurate information if we stop before finding
+        // any timer for the current thread, but at least won't report too
+        // long idle period.
+        return timer->mTimeout;
+      }
+
+      --aSearchBound;
+    }
+  }
+
+  // No timers for this thread, return the default.
+  return aDefault;
+}
+
+// This function must be called from within a lock
+// Also: we hold the mutex for the nsTimerImpl.
+bool TimerThread::AddTimerInternal(nsTimerImpl& aTimer) {
+  mMonitor.AssertCurrentThreadOwns();
+  aTimer.mMutex.AssertCurrentThreadOwns();
+  AUTO_TIMERS_STATS(TimerThread_AddTimerInternal);
+  if (mShutdown) {
+    return false;
+  }
+
+  LogTimerEvent::LogDispatch(&aTimer);
+
+  const TimeStamp& timeout = aTimer.mTimeout;
+  const size_t insertionIndex = ComputeTimerInsertionIndex(timeout);
+
+  if (insertionIndex != 0 && !mTimers[insertionIndex - 1].Value()) {
+    // Very common scenario in practice: The timer just before the insertion
+    // point is canceled, overwrite it.
+    AUTO_TIMERS_STATS(TimerThread_AddTimerInternal_overwrite_before);
+    mTimers[insertionIndex - 1] = Entry{aTimer};
+    return true;
+  }
+
+  const size_t length = mTimers.Length();
+  if (insertionIndex == length) {
+    // We're at the end (including it's the very first insertion), add new timer
+    // at the end.
+    AUTO_TIMERS_STATS(TimerThread_AddTimerInternal_append);
+    return mTimers.AppendElement(Entry{aTimer}, mozilla::fallible);
+  }
+
+  if (!mTimers[insertionIndex].Value()) {
+    // The timer at the insertion point is canceled, overwrite it.
+    AUTO_TIMERS_STATS(TimerThread_AddTimerInternal_overwrite);
+    mTimers[insertionIndex] = Entry{aTimer};
+    return true;
+  }
+
+  // The new timer has to be inserted.
+  AUTO_TIMERS_STATS(TimerThread_AddTimerInternal_insert);
+  // The capacity should be checked first, because if it needs to be increased
+  // and the memory allocation fails, only the new timer should be lost.
+  if (length == mTimers.Capacity() && mTimers[length - 1].Value()) {
+    // We have reached capacity, and the last entry is not canceled, so we
+    // really want to increase the capacity in case the extra slot is required.
+    // To force-expand the array, append a canceled-timer entry with a timestamp
+    // far in the future.
+    // This empty Entry may be used below to receive the moved-from previous
+    // entry. If not, it may be used in a later call if we need to append a new
+    // timer at the end.
+    AUTO_TIMERS_STATS(TimerThread_AddTimerInternal_insert_expand);
+    if (!mTimers.AppendElement(
+            Entry{mTimers[length - 1].Timeout() +
+                  TimeDuration::FromSeconds(365.0 * 24.0 * 60.0 * 60.0)},
+            mozilla::fallible)) {
+      return false;
+    }
+  }
+
+  // Extract the timer at the insertion point, and put the new timer in its
+  // place.
+  Entry extractedEntry = std::exchange(mTimers[insertionIndex], Entry{aTimer});
+  // Following entries can be pushed until we hit a canceled timer or the end.
+  for (size_t i = insertionIndex + 1; i < length; ++i) {
+    Entry& entryRef = mTimers[i];
+    if (!entryRef.Value()) {
+      // Canceled entry, overwrite it with the extracted entry from before.
+      COUNT_TIMERS_STATS(TimerThread_AddTimerInternal_insert_overwrite);
+      entryRef = std::move(extractedEntry);
+      return true;
+    }
+    // Write extracted entry from before, and extract current entry.
+    COUNT_TIMERS_STATS(TimerThread_AddTimerInternal_insert_shifts);
+    std::swap(entryRef, extractedEntry);
+  }
+  // We've reached the end of the list, with still one extracted entry to
+  // re-insert. We've checked the capacity above, this cannot fail.
+  COUNT_TIMERS_STATS(TimerThread_AddTimerInternal_insert_append);
+  mTimers.AppendElement(std::move(extractedEntry));
+  return true;
+}
+
+// This function must be called from within a lock
+// Also: we hold the mutex for the nsTimerImpl.
+bool TimerThread::RemoveTimerInternal(nsTimerImpl& aTimer) {
+  mMonitor.AssertCurrentThreadOwns();
+  aTimer.mMutex.AssertCurrentThreadOwns();
+  AUTO_TIMERS_STATS(TimerThread_RemoveTimerInternal);
+  if (!aTimer.IsInTimerThread()) {
+    COUNT_TIMERS_STATS(TimerThread_RemoveTimerInternal_not_in_list);
+    return false;
+  }
+  AUTO_TIMERS_STATS(TimerThread_RemoveTimerInternal_in_list);
+  for (auto& entry : mTimers) {
+    if (entry.Value() == &aTimer) {
+      entry.Forget();
+      return true;
+    }
+  }
+  MOZ_ASSERT(!aTimer.IsInTimerThread(),
+             "Not found in the list but it should be!?");
+  return false;
+}
+
+void TimerThread::RemoveLeadingCanceledTimersInternal() {
+  mMonitor.AssertCurrentThreadOwns();
+  AUTO_TIMERS_STATS(TimerThread_RemoveLeadingCanceledTimersInternal);
+
+  size_t toRemove = 0;
+  while (toRemove < mTimers.Length() && !mTimers[toRemove].Value()) {
+    ++toRemove;
+  }
+  mTimers.RemoveElementsAt(0, toRemove);
+}
+
+void TimerThread::RemoveFirstTimerInternal() {
+  mMonitor.AssertCurrentThreadOwns();
+  AUTO_TIMERS_STATS(TimerThread_RemoveFirstTimerInternal);
+  MOZ_ASSERT(!mTimers.IsEmpty());
+  mTimers.RemoveElementAt(0);
+}
+
+void TimerThread::PostTimerEvent(already_AddRefed<nsTimerImpl> aTimerRef) {
+  mMonitor.AssertCurrentThreadOwns();
+  AUTO_TIMERS_STATS(TimerThread_PostTimerEvent);
+
+  RefPtr<nsTimerImpl> timer(aTimerRef);
+
+#if TIMER_THREAD_STATISTICS
+  const double actualFiringDelay =
+      std::max((TimeStamp::Now() - timer->mTimeout).ToMilliseconds(), 0.0);
+  if (mNotified) {
+    ++mTotalTimersFiredNotified;
+    mTotalActualTimerFiringDelayNotified += actualFiringDelay;
+  } else {
+    ++mTotalTimersFiredUnnotified;
+    mTotalActualTimerFiringDelayUnnotified += actualFiringDelay;
+  }
+#endif
+
+  if (!timer->mEventTarget) {
+    NS_ERROR("Attempt to post timer event to NULL event target");
+    return;
+  }
+
+  // XXX we may want to reuse this nsTimerEvent in the case of repeating timers.
+
+  // Since we already addref'd 'timer', we don't need to addref here.
+  // We will release either in ~nsTimerEvent(), or pass the reference back to
+  // the caller. We need to copy the generation number from this timer into the
+  // event, so we can avoid firing a timer that was re-initialized after being
+  // canceled.
+
+  nsCOMPtr<nsIEventTarget> target = timer->mEventTarget;
+
+  void* p = nsTimerEvent::operator new(sizeof(nsTimerEvent));
+  if (!p) {
+    return;
+  }
+  RefPtr<nsTimerEvent> event =
+      ::new (KnownNotNull, p) nsTimerEvent(timer.forget(), mProfilerThreadId);
+
+  nsresult rv;
+  {
+    // We release mMonitor around the Dispatch because if the Dispatch interacts
+    // with the timer API we'll deadlock.
+    MonitorAutoUnlock unlock(mMonitor);
+    rv = target->Dispatch(event, NS_DISPATCH_NORMAL);
+    if (NS_FAILED(rv)) {
+      timer = event->ForgetTimer();
+      // We do this to avoid possible deadlock by taking the two locks in a
+      // different order than is used in RemoveTimer().  RemoveTimer() has
+      // aTimer->mMutex first.   We use timer.get() to keep static analysis
+      // happy
+      // NOTE: I'm not sure that any of the below is actually necessary. It
+      // seems to me that the timer that we're trying to fire will have already
+      // been removed prior to this.
+      MutexAutoLock lock1(timer.get()->mMutex);
+      MonitorAutoLock lock2(mMonitor);
+      RemoveTimerInternal(*timer);
+    }
+  }
+}
+
+void TimerThread::DoBeforeSleep() {
+  // Mainthread
+  MonitorAutoLock lock(mMonitor);
+  mSleeping = true;
+}
+
+// Note: wake may be notified without preceding sleep notification
+void TimerThread::DoAfterSleep() {
+  // Mainthread
+  MonitorAutoLock lock(mMonitor);
+  mSleeping = false;
+
+  // Wake up the timer thread to re-process the array to ensure the sleep delay
+  // is correct, and fire any expired timers (perhaps quite a few)
+  mNotified = true;
+  PROFILER_MARKER_UNTYPED("AfterSleep", OTHER,
+                          MarkerThreadId(mProfilerThreadId));
+  mMonitor.Notify();
+}
+
+NS_IMETHODIMP
+TimerThread::Observe(nsISupports* /* aSubject */, const char* aTopic,
+                     const char16_t* /* aData */) {
+  if (StaticPrefs::timer_ignore_sleep_wake_notifications()) {
+    return NS_OK;
+  }
+
+  if (strcmp(aTopic, "sleep_notification") == 0 ||
+      strcmp(aTopic, "suspend_process_notification") == 0) {
+    DoBeforeSleep();
+  } else if (strcmp(aTopic, "wake_notification") == 0 ||
+             strcmp(aTopic, "resume_process_notification") == 0) {
+    DoAfterSleep();
+  }
+
+  return NS_OK;
+}
+
+uint32_t TimerThread::AllowedEarlyFiringMicroseconds() {
+  MonitorAutoLock lock(mMonitor);
+  return mAllowedEarlyFiringMicroseconds;
+}
+
+#if TIMER_THREAD_STATISTICS
+void TimerThread::PrintStatistics() const {
+  mMonitor.AssertCurrentThreadOwns();
+
+  const TimeStamp freshNow = TimeStamp::Now();
+  const double timeElapsed = mFirstTimerAdded.IsNull()
+                                 ? 0.0
+                                 : (freshNow - mFirstTimerAdded).ToSeconds();
+  printf_stderr("TimerThread Stats (Total time %8.2fs)\n", timeElapsed);
+
+  printf_stderr("Added: %6llu Removed: %6llu Fired: %6llu\n", mTotalTimersAdded,
+                mTotalTimersRemoved,
+                mTotalTimersFiredNotified + mTotalTimersFiredUnnotified);
+
+  auto PrintTimersFiredBucket =
+      [](const AutoTArray<size_t, sTimersFiredPerWakeupBucketCount>& buckets,
+         const size_t wakeupCount, const size_t timersFiredCount,
+         const double totalTimerDelay, const char* label) {
+        printf_stderr("%s : [", label);
+        for (size_t bucketVal : buckets) {
+          printf_stderr(" %5llu", bucketVal);
+        }
+        printf_stderr(
+            " ] Wake-ups/timer %6llu / %6llu (%7.4f) Avg Timer Delay %7.4f\n",
+            wakeupCount, timersFiredCount,
+            static_cast<double>(wakeupCount) / timersFiredCount,
+            totalTimerDelay / timersFiredCount);
+      };
+
+  printf_stderr("Wake-ups:\n");
+  PrintTimersFiredBucket(
+      mTimersFiredPerWakeup, mTotalWakeupCount,
+      mTotalTimersFiredNotified + mTotalTimersFiredUnnotified,
+      mTotalActualTimerFiringDelayNotified +
+          mTotalActualTimerFiringDelayUnnotified,
+      "Total      ");
+  PrintTimersFiredBucket(mTimersFiredPerNotifiedWakeup,
+                         mTotalNotifiedWakeupCount, mTotalTimersFiredNotified,
+                         mTotalActualTimerFiringDelayNotified, "Notified   ");
+  PrintTimersFiredBucket(mTimersFiredPerUnnotifiedWakeup,
+                         mTotalUnnotifiedWakeupCount,
+                         mTotalTimersFiredUnnotified,
+                         mTotalActualTimerFiringDelayUnnotified, "Unnotified ");
+
+  printf_stderr("Early Wake-ups: %6llu Avg: %7.4fms\n", mEarlyWakeups,
+                mTotalEarlyWakeupTime / mEarlyWakeups);
+}
+#endif
+
+/* This nsReadOnlyTimer class is used for the values returned by the
+ * TimerThread::GetTimers method.
+ * It is not possible to return a strong reference to the nsTimerImpl
+ * instance (that could extend the lifetime of the timer and cause it to fire
+ * a callback pointing to already freed memory) or a weak reference
+ * (nsSupportsWeakReference doesn't support freeing the referee on a thread
+ * that isn't the thread that owns the weak reference), so instead the timer
+ * name, delay and type are copied to a new object. */
+class nsReadOnlyTimer final : public nsITimer {
+ public:
+  explicit nsReadOnlyTimer(const nsACString& aName, uint32_t aDelay,
+                           uint32_t aType)
+      : mName(aName), mDelay(aDelay), mType(aType) {}
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD Init(nsIObserver* aObserver, uint32_t aDelayInMs,
+                  uint32_t aType) override {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  NS_IMETHOD InitWithCallback(nsITimerCallback* aCallback, uint32_t aDelayInMs,
+                              uint32_t aType) override {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  NS_IMETHOD InitHighResolutionWithCallback(nsITimerCallback* aCallback,
+                                            const mozilla::TimeDuration& aDelay,
+                                            uint32_t aType) override {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  NS_IMETHOD Cancel(void) override { return NS_ERROR_NOT_IMPLEMENTED; }
+  NS_IMETHOD InitWithNamedFuncCallback(nsTimerCallbackFunc aCallback,
+                                       void* aClosure, uint32_t aDelay,
+                                       uint32_t aType,
+                                       const char* aName) override {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  NS_IMETHOD InitHighResolutionWithNamedFuncCallback(
+      nsTimerCallbackFunc aCallback, void* aClosure,
+      const mozilla::TimeDuration& aDelay, uint32_t aType,
+      const char* aName) override {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  NS_IMETHOD GetName(nsACString& aName) override {
+    aName = mName;
+    return NS_OK;
+  }
+  NS_IMETHOD GetDelay(uint32_t* aDelay) override {
+    *aDelay = mDelay;
+    return NS_OK;
+  }
+  NS_IMETHOD SetDelay(uint32_t aDelay) override {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  NS_IMETHOD GetType(uint32_t* aType) override {
+    *aType = mType;
+    return NS_OK;
+  }
+  NS_IMETHOD SetType(uint32_t aType) override {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  NS_IMETHOD GetClosure(void** aClosure) override {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  NS_IMETHOD GetCallback(nsITimerCallback** aCallback) override {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  NS_IMETHOD GetTarget(nsIEventTarget** aTarget) override {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  NS_IMETHOD SetTarget(nsIEventTarget* aTarget) override {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  NS_IMETHOD GetAllowedEarlyFiringMicroseconds(
+      uint32_t* aAllowedEarlyFiringMicroseconds) override {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) override {
+    return sizeof(*this);
+  }
+
+ private:
+  nsCString mName;
+  uint32_t mDelay;
+  uint32_t mType;
+  ~nsReadOnlyTimer() = default;
+};
+
+NS_IMPL_ISUPPORTS(nsReadOnlyTimer, nsITimer)
+
+nsresult TimerThread::GetTimers(nsTArray<RefPtr<nsITimer>>& aRetVal) {
+  nsTArray<RefPtr<nsTimerImpl>> timers;
+  {
+    MonitorAutoLock lock(mMonitor);
+    for (const auto& entry : mTimers) {
+      nsTimerImpl* timer = entry.Value();
+      if (!timer) {
+        continue;
+      }
+      timers.AppendElement(timer);
+    }
+  }
+
+  for (nsTimerImpl* timer : timers) {
+    nsAutoCString name;
+    timer->GetName(name);
+
+    uint32_t delay;
+    timer->GetDelay(&delay);
+
+    uint32_t type;
+    timer->GetType(&type);
+
+    aRetVal.AppendElement(new nsReadOnlyTimer(name, delay, type));
+  }
+
+  return NS_OK;
+}