1 files changed, 247 insertions, 0 deletions
diff --git a/xpcom/threads/TimerThread.h b/xpcom/threads/TimerThread.h
new file mode 100644
index 0000000000..f6a5827b94
--- /dev/null
+++ b/xpcom/threads/TimerThread.h
@@ -0,0 +1,247 @@
+/* -*- 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/. */
+
+#ifndef TimerThread_h___
+#define TimerThread_h___
+
+#include "nsIObserver.h"
+#include "nsIRunnable.h"
+#include "nsIThread.h"
+
+#include "nsTimerImpl.h"
+#include "nsThreadUtils.h"
+
+#include "nsTArray.h"
+
+#include "mozilla/Attributes.h"
+#include "mozilla/HalTypes.h"
+#include "mozilla/Monitor.h"
+#include "mozilla/ProfilerUtils.h"
+
+// Enable this to compute lots of interesting statistics and print them out when
+// PrintStatistics() is called.
+#define TIMER_THREAD_STATISTICS 0
+
+class TimerThread final : public mozilla::Runnable, public nsIObserver {
+ public:
+  typedef mozilla::Monitor Monitor;
+  typedef mozilla::MutexAutoLock MutexAutoLock;
+  typedef mozilla::TimeStamp TimeStamp;
+  typedef mozilla::TimeDuration TimeDuration;
+
+  TimerThread();
+
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_NSIRUNNABLE
+  NS_DECL_NSIOBSERVER
+
+  nsresult Shutdown();
+
+  nsresult AddTimer(nsTimerImpl* aTimer, const MutexAutoLock& aProofOfLock)
+      MOZ_REQUIRES(aTimer->mMutex);
+  nsresult RemoveTimer(nsTimerImpl* aTimer, const MutexAutoLock& aProofOfLock)
+      MOZ_REQUIRES(aTimer->mMutex);
+  // Considering only the first 'aSearchBound' timers (in firing order), returns
+  // the timeout of the first non-low-priority timer, on the current thread,
+  // that will fire before 'aDefault'. If no such timer exists, 'aDefault' is
+  // returned.
+  TimeStamp FindNextFireTimeForCurrentThread(TimeStamp aDefault,
+                                             uint32_t aSearchBound);
+
+  void DoBeforeSleep();
+  void DoAfterSleep();
+
+  bool IsOnTimerThread() const { return mThread->IsOnCurrentThread(); }
+
+  uint32_t AllowedEarlyFiringMicroseconds();
+  nsresult GetTimers(nsTArray<RefPtr<nsITimer>>& aRetVal);
+
+ private:
+  ~TimerThread();
+
+  bool mInitialized;
+
+  // These internal helper methods must be called while mMonitor is held.
+  // AddTimerInternal returns false if the insertion failed.
+  bool AddTimerInternal(nsTimerImpl& aTimer) MOZ_REQUIRES(mMonitor);
+  bool RemoveTimerInternal(nsTimerImpl& aTimer)
+      MOZ_REQUIRES(mMonitor, aTimer.mMutex);
+  void RemoveLeadingCanceledTimersInternal() MOZ_REQUIRES(mMonitor);
+  void RemoveFirstTimerInternal() MOZ_REQUIRES(mMonitor);
+  nsresult Init() MOZ_REQUIRES(mMonitor);
+
+  void PostTimerEvent(already_AddRefed<nsTimerImpl> aTimerRef)
+      MOZ_REQUIRES(mMonitor);
+
+  // Using atomic because this value is written to in one place, and read from
+  // in another, and those two locations are likely to be executed from separate
+  // threads. Reads/writes to an aligned value this size should be atomic even
+  // without using std::atomic, but doing this explicitly provides a good
+  // reminder that this is accessed from multiple threads.
+  std::atomic<mozilla::hal::ProcessPriority> mCachedPriority =
+      mozilla::hal::PROCESS_PRIORITY_UNKNOWN;
+
+  nsCOMPtr<nsIThread> mThread;
+  // Lock ordering requirements:
+  // (optional) ThreadWrapper::sMutex ->
+  // (optional) nsTimerImpl::mMutex   ->
+  // TimerThread::mMonitor
+  Monitor mMonitor;
+
+  bool mShutdown MOZ_GUARDED_BY(mMonitor);
+  bool mWaiting MOZ_GUARDED_BY(mMonitor);
+  bool mNotified MOZ_GUARDED_BY(mMonitor);
+  bool mSleeping MOZ_GUARDED_BY(mMonitor);
+
+  class Entry final {
+   public:
+    explicit Entry(nsTimerImpl& aTimerImpl)
+        : mTimeout(aTimerImpl.mTimeout),
+          mDelay(aTimerImpl.mDelay),
+          mTimerImpl(&aTimerImpl) {
+      aTimerImpl.SetIsInTimerThread(true);
+    }
+
+    // Create an already-canceled entry with the given timeout.
+    explicit Entry(TimeStamp aTimeout)
+        : mTimeout(std::move(aTimeout)), mTimerImpl(nullptr) {}
+
+    // Don't allow copies, otherwise which one would manage `IsInTimerThread`?
+    Entry(const Entry&) = delete;
+    Entry& operator=(const Entry&) = delete;
+
+    // Move-only.
+    Entry(Entry&&) = default;
+    Entry& operator=(Entry&&) = default;
+
+    ~Entry() {
+      if (mTimerImpl) {
+        mTimerImpl->mMutex.AssertCurrentThreadOwns();
+        mTimerImpl->SetIsInTimerThread(false);
+      }
+    }
+
+    nsTimerImpl* Value() const { return mTimerImpl; }
+
+    void Forget() {
+      if (MOZ_UNLIKELY(!mTimerImpl)) {
+        return;
+      }
+      mTimerImpl->mMutex.AssertCurrentThreadOwns();
+      mTimerImpl->SetIsInTimerThread(false);
+      mTimerImpl = nullptr;
+    }
+
+    // Called with the Monitor held, but not the TimerImpl's mutex
+    already_AddRefed<nsTimerImpl> Take() {
+      if (MOZ_LIKELY(mTimerImpl)) {
+        MOZ_ASSERT(mTimerImpl->IsInTimerThread());
+        mTimerImpl->SetIsInTimerThread(false);
+      }
+      return mTimerImpl.forget();
+    }
+
+    const TimeStamp& Timeout() const { return mTimeout; }
+    const TimeDuration& Delay() const { return mDelay; }
+
+   private:
+    // These values are simply cached from the timer. Keeping them here is good
+    // for cache usage and allows us to avoid worrying about locking conflicts
+    // with the timer.
+    TimeStamp mTimeout;
+    TimeDuration mDelay;
+
+    RefPtr<nsTimerImpl> mTimerImpl;
+  };
+
+  // Computes and returns the index in mTimers at which a new timer with the
+  // specified timeout should be inserted in order to maintain "sorted" order.
+  size_t ComputeTimerInsertionIndex(const TimeStamp& timeout) const
+      MOZ_REQUIRES(mMonitor);
+
+  // Computes and returns when we should next try to wake up in order to handle
+  // the triggering of the timers in mTimers. Currently this is very simple and
+  // we always just plan to wake up for the next timer in the list. In the
+  // future this will be more sophisticated.
+  TimeStamp ComputeWakeupTimeFromTimers() const MOZ_REQUIRES(mMonitor);
+
+  // Computes how late a timer can acceptably fire.
+  // timerDuration is the duration of the timer whose delay we are calculating.
+  // Longer timers can tolerate longer firing delays.
+  // minDelay is an amount by which any timer can be delayed.
+  // This function will never return a value smaller than minDelay (unless this
+  // conflicts with maxDelay). maxDelay is the upper limit on the amount by
+  // which we will ever delay any timer. Takes precedence over minDelay if there
+  // is a conflict. (Zero will effectively disable timer coalescing.)
+  TimeDuration ComputeAcceptableFiringDelay(TimeDuration timerDuration,
+                                            TimeDuration minDelay,
+                                            TimeDuration maxDelay) const;
+
+#ifdef XP_WIN
+  UINT ComputeDesiredTimerPeriod() const;
+#endif
+
+#ifdef DEBUG
+  // Checks mTimers to see if any entries are out of order or any cached
+  // timeouts are incorrect and will assert if any inconsistency is found. Has
+  // no side effects other than asserting so has no use in non-DEBUG builds.
+  void VerifyTimerListConsistency() const MOZ_REQUIRES(mMonitor);
+#endif
+
+  // mTimers is maintained in a "pseudo-sorted" order wrt the timeouts.
+  // Specifcally, mTimers is sorted according to the timeouts *if you ignore the
+  // canceled entries* (those whose mTimerImpl is nullptr). Notably this means
+  // that you cannot use a binary search on this list.
+  nsTArray<Entry> mTimers MOZ_GUARDED_BY(mMonitor);
+
+  // Set only at the start of the thread's Run():
+  uint32_t mAllowedEarlyFiringMicroseconds MOZ_GUARDED_BY(mMonitor);
+
+  ProfilerThreadId mProfilerThreadId MOZ_GUARDED_BY(mMonitor);
+
+  // Time at which we were intending to wake up the last time that we slept.
+  // Is "null" if we have never slept or if our last sleep was "forever".
+  TimeStamp mIntendedWakeupTime;
+
+#if TIMER_THREAD_STATISTICS
+  static constexpr size_t sTimersFiredPerWakeupBucketCount = 16;
+  static inline constexpr std::array<size_t, sTimersFiredPerWakeupBucketCount>
+      sTimersFiredPerWakeupThresholds = {
+          0, 1, 2, 3, 4, 5, 6, 7, 8, 12, 20, 30, 40, 50, 70, (size_t)(-1)};
+
+  mutable AutoTArray<size_t, sTimersFiredPerWakeupBucketCount>
+      mTimersFiredPerWakeup MOZ_GUARDED_BY(mMonitor) = {0, 0, 0, 0, 0, 0, 0, 0,
+                                                        0, 0, 0, 0, 0, 0, 0, 0};
+  mutable AutoTArray<size_t, sTimersFiredPerWakeupBucketCount>
+      mTimersFiredPerUnnotifiedWakeup MOZ_GUARDED_BY(mMonitor) = {
+          0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+  mutable AutoTArray<size_t, sTimersFiredPerWakeupBucketCount>
+      mTimersFiredPerNotifiedWakeup MOZ_GUARDED_BY(mMonitor) = {
+          0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+
+  mutable size_t mTotalTimersAdded MOZ_GUARDED_BY(mMonitor) = 0;
+  mutable size_t mTotalTimersRemoved MOZ_GUARDED_BY(mMonitor) = 0;
+  mutable size_t mTotalTimersFiredNotified MOZ_GUARDED_BY(mMonitor) = 0;
+  mutable size_t mTotalTimersFiredUnnotified MOZ_GUARDED_BY(mMonitor) = 0;
+
+  mutable size_t mTotalWakeupCount MOZ_GUARDED_BY(mMonitor) = 0;
+  mutable size_t mTotalUnnotifiedWakeupCount MOZ_GUARDED_BY(mMonitor) = 0;
+  mutable size_t mTotalNotifiedWakeupCount MOZ_GUARDED_BY(mMonitor) = 0;
+
+  mutable double mTotalActualTimerFiringDelayNotified MOZ_GUARDED_BY(mMonitor) =
+      0.0;
+  mutable double mTotalActualTimerFiringDelayUnnotified
+      MOZ_GUARDED_BY(mMonitor) = 0.0;
+
+  mutable TimeStamp mFirstTimerAdded MOZ_GUARDED_BY(mMonitor);
+
+  mutable size_t mEarlyWakeups MOZ_GUARDED_BY(mMonitor) = 0;
+  mutable double mTotalEarlyWakeupTime MOZ_GUARDED_BY(mMonitor) = 0.0;
+
+  void PrintStatistics() const;
+#endif
+};
+#endif /* TimerThread_h___ */