path: root/xpcom/threads/TimerThread.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 "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 <math.h>

using namespace mozilla;

// 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");
}

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

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)) {
    nsAutoCString name;
    mTimer->GetName(name);
    PROFILER_MARKER_TEXT(
        "PostTimerEvent", OTHER,
        MarkerOptions(MOZ_LIKELY(mInitTime)
                          ? MarkerTiming::IntervalUntilNowFrom(mInitTime)
                          : MarkerTiming::InstantNow(),
                      MarkerThreadId(mTimerThreadId)),
        name);
  }

  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.
    for (const UniquePtr<Entry>& entry : mTimers) {
      timers.AppendElement(entry->Take());
    }

    mTimers.Clear();
  }

  for (const RefPtr<nsTimerImpl>& timer : timers) {
    if (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

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;

  while (!mShutdown) {
    // Have to use PRIntervalTime here, since PR_WaitCondVar takes it
    TimeDuration waitFor;
    bool forceRunThisTimer = forceRunNextTimer;
    forceRunNextTimer = false;

    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();

      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.
          {
            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();

        if (ChaosMode::isActive(ChaosFeature::TimerScheduling)) {
          // 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 const float sFractions[] = {0.0f, 0.25f, 0.5f, 0.75f,
                                             1.0f, 1.75f, 2.75f};
          microseconds *= sFractions[ChaosMode::randomUint32LessThan(
              ArrayLength(sFractions))];
          forceRunNextTimer = true;
        }

        if (microseconds < mAllowedEarlyFiringMicroseconds) {
          forceRunNextTimer = false;
          goto next;  // round down; execute event now
        }
        waitFor = TimeDuration::FromMicroseconds(microseconds);
        if (waitFor.IsZero()) {
          // round up, wait the minimum time we can wait
          waitFor = TimeDuration::FromMicroseconds(1);
        }
      }

      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()));
      }
    }

    mWaiting = true;
    mNotified = false;
    {
      AUTO_PROFILER_TRACING_MARKER("TimerThread", "Wait", OTHER);
      mMonitor.Wait(waitFor);
    }
    if (mNotified) {
      forceRunNextTimer = false;
    }
    mWaiting = false;
  }

  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;
  }

  // Add the timer to our list.
  if (!AddTimerInternal(aTimer)) {
    return NS_ERROR_OUT_OF_MEMORY;
  }

  // Awaken the timer thread if:
  // - This is the new front timer, which may require the TimerThread to wake up
  //   earlier than previously planned. 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!
  if (mWaiting && (mTimers[0]->Value() == aTimer || aTimer->mDelay.IsZero())) {
    mNotified = true;
    mMonitor.Notify();
  }

  if (profiler_thread_is_being_profiled_for_markers(mProfilerThreadId)) {
    struct TimerMarker {
      static constexpr Span<const char> MarkerTypeName() {
        return MakeStringSpan("Timer");
      }
      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;
      }
    };

    nsAutoCString name;
    aTimer->GetName(name, aProofOfLock);

    nsLiteralCString prefix("Anonymous_");
    profiler_add_marker(
        "AddTimer", geckoprofiler::category::OTHER,
        MarkerOptions(MarkerThreadId(mProfilerThreadId),
                      MarkerStack::MaybeCapture(
                          StringHead(name, prefix.Length()) == prefix)),
        TimerMarker{}, 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;
  }

  // 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_");
    PROFILER_MARKER_TEXT(
        "RemoveTimer", OTHER,
        MarkerOptions(MarkerThreadId(mProfilerThreadId),
                      MarkerStack::MaybeCapture(
                          StringHead(name, prefix.Length()) == prefix)),
        name);
  }

  return NS_OK;
}

TimeStamp TimerThread::FindNextFireTimeForCurrentThread(TimeStamp aDefault,
                                                        uint32_t aSearchBound) {
  MonitorAutoLock lock(mMonitor);
  AUTO_TIMERS_STATS(TimerThread_FindNextFireTimeForCurrentThread);
  TimeStamp timeStamp = aDefault;
  uint32_t index = 0;

#ifdef DEBUG
  TimeStamp firstTimeStamp;
  Entry* initialFirstEntry = nullptr;
  if (!mTimers.IsEmpty()) {
    initialFirstEntry = mTimers[0].get();
    firstTimeStamp = mTimers[0]->Timeout();
  }
#endif

  auto end = mTimers.end();
  while (end != mTimers.begin()) {
    nsTimerImpl* timer = mTimers[0]->Value();
    if (timer) {
      if (timer->mTimeout > aDefault) {
        timeStamp = aDefault;
        break;
      }

      // 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) {
          timeStamp = timer->mTimeout;
          break;
        }
      }

      if (++index > aSearchBound) {
        // Track the currently highest timeout so that we can bail out when we
        // reach the bound or when we find a timer for the current thread.
        // 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.
        timeStamp = timer->mTimeout;
        break;
      }
    }

    std::pop_heap(mTimers.begin(), end, Entry::UniquePtrLessThan);
    --end;
  }

  while (end != mTimers.end()) {
    ++end;
    std::push_heap(mTimers.begin(), end, Entry::UniquePtrLessThan);
  }

#ifdef DEBUG
  if (!mTimers.IsEmpty()) {
    if (firstTimeStamp != mTimers[0]->Timeout()) {
      TimeStamp now = TimeStamp::Now();
      printf_stderr(
          "firstTimeStamp %f, mTimers[0]->Timeout() %f, "
          "initialFirstTimer %p, current first %p\n",
          (firstTimeStamp - now).ToMilliseconds(),
          (mTimers[0]->Timeout() - now).ToMilliseconds(), initialFirstEntry,
          mTimers[0].get());
    }
  }
  MOZ_ASSERT_IF(!mTimers.IsEmpty(), firstTimeStamp == mTimers[0]->Timeout());
#endif

  return timeStamp;
}

// 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;
  }

  TimeStamp now = TimeStamp::Now();

  LogTimerEvent::LogDispatch(aTimer);

  UniquePtr<Entry>* entry = mTimers.AppendElement(
      MakeUnique<Entry>(now, aTimer->mTimeout, aTimer), mozilla::fallible);
  if (!entry) {
    return false;
  }

  std::push_heap(mTimers.begin(), mTimers.end(), Entry::UniquePtrLessThan);

  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) {
    COUNT_TIMERS_STATS(TimerThread_RemoveTimerInternal_nullptr);
    return false;
  }
  if (!aTimer->mHolder) {
    COUNT_TIMERS_STATS(TimerThread_RemoveTimerInternal_not_in_list);
    return false;
  }
  AUTO_TIMERS_STATS(TimerThread_RemoveTimerInternal_in_list);
  aTimer->mHolder->Forget(aTimer);
  return true;
}

void TimerThread::RemoveLeadingCanceledTimersInternal() {
  mMonitor.AssertCurrentThreadOwns();
  AUTO_TIMERS_STATS(TimerThread_RemoveLeadingCanceledTimersInternal);

  // Move all canceled timers from the front of the list to
  // the back of the list using std::pop_heap().  We do this
  // without actually removing them from the list so we can
  // modify the nsTArray in a single bulk operation.
  auto sortedEnd = mTimers.end();
  while (sortedEnd != mTimers.begin() && !mTimers[0]->Value()) {
    std::pop_heap(mTimers.begin(), sortedEnd, Entry::UniquePtrLessThan);
    --sortedEnd;
  }

  // If there were no canceled timers then we are done.
  if (sortedEnd == mTimers.end()) {
    return;
  }

  // Finally, remove the canceled timers from the back of the
  // nsTArray.
  mTimers.RemoveLastElements(mTimers.end() - sortedEnd);
}

void TimerThread::RemoveFirstTimerInternal() {
  mMonitor.AssertCurrentThreadOwns();
  AUTO_TIMERS_STATS(TimerThread_RemoveFirstTimerInternal);
  MOZ_ASSERT(!mTimers.IsEmpty());
  std::pop_heap(mTimers.begin(), mTimers.end(), Entry::UniquePtrLessThan);
  mTimers.RemoveLastElement();
}

void TimerThread::PostTimerEvent(already_AddRefed<nsTimerImpl> aTimerRef) {
  mMonitor.AssertCurrentThreadOwns();
  AUTO_TIMERS_STATS(TimerThread_PostTimerEvent);

  RefPtr<nsTimerImpl> timer(aTimerRef);
  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
      MutexAutoLock lock1(timer.get()->mMutex);
      MonitorAutoLock lock2(mMonitor);
      RemoveTimerInternal(timer.get());
    }
  }
}

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;
}