1 files changed, 779 insertions, 0 deletions
diff --git a/xpcom/threads/TimerThread.cpp b/xpcom/threads/TimerThread.cpp
new file mode 100644
index 0000000000..9cd60e1bae
--- /dev/null
+++ b/xpcom/threads/TimerThread.cpp
@@ -0,0 +1,779 @@
+/* -*- 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 "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 <math.h>
+
+using namespace mozilla;
+#ifdef MOZ_TASK_TRACER
+#  include "GeckoTaskTracerImpl.h"
+using namespace mozilla::tasktracer;
+#endif
+
+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");
+}
+
+nsresult TimerThread::InitLocks() { return NS_OK; }
+
+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;
+  FreeEntry* mFirstFree;
+  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)
+      : mozilla::CancelableRunnable("nsTimerEvent"),
+        mTimer(aTimer),
+        mGeneration(mTimer->GetGeneration()) {
+    // Note: We override operator new for this class, and the override is
+    // fallible!
+    sAllocatorUsers++;
+
+    if (MOZ_LOG_TEST(GetTimerLog(), LogLevel::Debug)) {
+      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);
+    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");
+    sAllocatorUsers--;
+  }
+
+  TimeStamp mInitTime;
+  RefPtr<nsTimerImpl> mTimer;
+  const int32_t mGeneration;
+
+  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()));
+  }
+
+  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 Thread", getter_AddRefs(mThread), this);
+    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() {
+  NS_SetCurrentThreadName("Timer");
+
+  MonitorAutoLock lock(mMonitor);
+
+  // 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());
+            timerRef = PostTimerEvent(timerRef.forget());
+          }
+
+          if (timerRef) {
+            // We got our reference back due to an error.
+            // Unhook the nsRefPtr, and release manually so we can get the
+            // refcount.
+            nsrefcnt rc = timerRef.forget().take()->Release();
+            (void)rc;
+
+            // The nsITimer interface requires that its users keep a reference
+            // to the timers they use while those timers are initialized but
+            // have not yet fired.  If this ever happens, it is a bug in the
+            // code that created and used the timer.
+            //
+            // Further, note that this should never happen even with a
+            // misbehaving user, because nsTimerImpl::Release checks for a
+            // refcount of 1 with an armed timer (a timer whose only reference
+            // is from the timer thread) and when it hits this will remove the
+            // timer from the timer thread and thus destroy the last reference,
+            // preventing this situation from occurring.
+            MOZ_ASSERT(rc != 0, "destroyed timer off its target thread!");
+          }
+
+          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).ToMilliseconds() * 1000;
+
+        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;
+    mMonitor.Wait(waitFor);
+    if (mNotified) {
+      forceRunNextTimer = false;
+    }
+    mWaiting = false;
+  }
+
+  return NS_OK;
+}
+
+nsresult TimerThread::AddTimer(nsTimerImpl* aTimer) {
+  MonitorAutoLock lock(mMonitor);
+
+  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 (mWaiting && mTimers[0]->Value() == aTimer) {
+    mNotified = true;
+    mMonitor.Notify();
+  }
+
+  return NS_OK;
+}
+
+nsresult TimerThread::RemoveTimer(nsTimerImpl* aTimer) {
+  MonitorAutoLock lock(mMonitor);
+
+  // 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;
+  }
+
+  // Awaken the timer thread.
+  if (mWaiting) {
+    mNotified = true;
+    mMonitor.Notify();
+  }
+
+  return NS_OK;
+}
+
+TimeStamp TimerThread::FindNextFireTimeForCurrentThread(TimeStamp aDefault,
+                                                        uint32_t aSearchBound) {
+  MonitorAutoLock lock(mMonitor);
+  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
+bool TimerThread::AddTimerInternal(nsTimerImpl* aTimer) {
+  mMonitor.AssertCurrentThreadOwns();
+  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);
+
+#ifdef MOZ_TASK_TRACER
+  // Caller of AddTimer is the parent task of its timer event, so we store the
+  // TraceInfo here for later used.
+  aTimer->GetTLSTraceInfo();
+#endif
+
+  return true;
+}
+
+bool TimerThread::RemoveTimerInternal(nsTimerImpl* aTimer) {
+  mMonitor.AssertCurrentThreadOwns();
+  if (!aTimer || !aTimer->mHolder) {
+    return false;
+  }
+  aTimer->mHolder->Forget(aTimer);
+  return true;
+}
+
+void TimerThread::RemoveLeadingCanceledTimersInternal() {
+  mMonitor.AssertCurrentThreadOwns();
+
+  // 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();
+  MOZ_ASSERT(!mTimers.IsEmpty());
+  std::pop_heap(mTimers.begin(), mTimers.end(), Entry::UniquePtrLessThan);
+  mTimers.RemoveLastElement();
+}
+
+already_AddRefed<nsTimerImpl> TimerThread::PostTimerEvent(
+    already_AddRefed<nsTimerImpl> aTimerRef) {
+  mMonitor.AssertCurrentThreadOwns();
+
+  RefPtr<nsTimerImpl> timer(aTimerRef);
+  if (!timer->mEventTarget) {
+    NS_ERROR("Attempt to post timer event to NULL event target");
+    return timer.forget();
+  }
+
+  // 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.
+
+#ifdef MOZ_TASK_TRACER
+  // During the dispatch of TimerEvent, we overwrite the current TraceInfo
+  // partially with the info saved in timer earlier, and restore it back by
+  // AutoSaveCurTraceInfo.
+  AutoSaveCurTraceInfo saveCurTraceInfo;
+  (timer->GetTracedTask()).SetTLSTraceInfo();
+#endif
+
+  nsCOMPtr<nsIEventTarget> target = timer->mEventTarget;
+
+  void* p = nsTimerEvent::operator new(sizeof(nsTimerEvent));
+  if (!p) {
+    return timer.forget();
+  }
+  RefPtr<nsTimerEvent> event =
+      ::new (KnownNotNull, p) nsTimerEvent(timer.forget());
+
+  nsresult rv;
+  {
+    // We release mMonitor around the Dispatch because if this timer is targeted
+    // at the TimerThread we'll deadlock.
+    MonitorAutoUnlock unlock(mMonitor);
+    rv = target->Dispatch(event, NS_DISPATCH_NORMAL);
+  }
+
+  if (NS_FAILED(rv)) {
+    timer = event->ForgetTimer();
+    RemoveTimerInternal(timer);
+    return timer.forget();
+  }
+
+  return nullptr;
+}
+
+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;
+  mMonitor.Notify();
+}
+
+NS_IMETHODIMP
+TimerThread::Observe(nsISupports* /* aSubject */, const char* aTopic,
+                     const char16_t* /* aData */) {
+  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() const {
+  return mAllowedEarlyFiringMicroseconds;
+}