gecko-dev/xpcom/threads/nsTimerImpl.h

/* -*- 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 nsTimerImpl_h___
#define nsTimerImpl_h___

#include "nsITimer.h"
#include "nsIEventTarget.h"
#include "nsIObserver.h"

#include "nsCOMPtr.h"

#include "mozilla/Attributes.h"
#include "mozilla/Mutex.h"
#include "mozilla/TimeStamp.h"
#include "mozilla/Variant.h"

#ifdef MOZ_TASK_TRACER
#  include "TracedTaskCommon.h"
#endif

extern mozilla::LogModule* GetTimerLog();

#define NS_TIMER_CID                                 \
  { /* 5ff24248-1dd2-11b2-8427-fbab44f29bc8 */       \
    0x5ff24248, 0x1dd2, 0x11b2, {                    \
      0x84, 0x27, 0xfb, 0xab, 0x44, 0xf2, 0x9b, 0xc8 \
    }                                                \
  }

class nsIObserver;
class nsTimerImplHolder;

namespace mozilla {
class LogModule;
}

// TimerThread, nsTimerEvent, and nsTimer have references to these. nsTimer has
// a separate lifecycle so we can Cancel() the underlying timer when the user of
// the nsTimer has let go of its last reference.
class nsTimerImpl {
  ~nsTimerImpl() { MOZ_ASSERT(!mHolder); }

 public:
  typedef mozilla::TimeStamp TimeStamp;

  nsTimerImpl(nsITimer* aTimer, nsIEventTarget* aTarget);
  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(nsTimerImpl)
  NS_DECL_NON_VIRTUAL_NSITIMER

  static nsresult Startup();
  static void Shutdown();

  void SetDelayInternal(uint32_t aDelay, TimeStamp aBase = TimeStamp::Now());
  void CancelImpl(bool aClearITimer);

  void Fire(int32_t aGeneration);

#ifdef MOZ_TASK_TRACER
  void GetTLSTraceInfo();
  mozilla::tasktracer::TracedTaskCommon GetTracedTask();
#endif

  int32_t GetGeneration() { return mGeneration; }

  struct Callback {
    Callback() : mType(Type::Unknown), mName(Nothing), mClosure(nullptr) {
      mCallback.c = nullptr;
    }

    Callback(const Callback& other) : Callback() { *this = other; }

    enum class Type : uint8_t {
      Unknown = 0,
      Interface = 1,
      Function = 2,
      Observer = 3,
    };

    Callback& operator=(const Callback& other) {
      if (this != &other) {
        clear();
        mType = other.mType;
        switch (mType) {
          case Type::Unknown:
            break;
          case Type::Interface:
            mCallback.i = other.mCallback.i;
            NS_ADDREF(mCallback.i);
            break;
          case Type::Function:
            mCallback.c = other.mCallback.c;
            break;
          case Type::Observer:
            mCallback.o = other.mCallback.o;
            NS_ADDREF(mCallback.o);
            break;
        }
        mName = other.mName;
        mClosure = other.mClosure;
      }
      return *this;
    }

    ~Callback() { clear(); }

    void clear() {
      if (mType == Type::Interface) {
        NS_RELEASE(mCallback.i);
      } else if (mType == Type::Observer) {
        NS_RELEASE(mCallback.o);
      }
      mType = Type::Unknown;
    }

    void swap(Callback& other) {
      std::swap(mType, other.mType);
      std::swap(mCallback, other.mCallback);
      std::swap(mName, other.mName);
      std::swap(mClosure, other.mClosure);
    }

    Type mType;

    union CallbackUnion {
      nsTimerCallbackFunc c;
      // These refcounted references are managed manually, as they are in a
      // union
      nsITimerCallback* MOZ_OWNING_REF i;
      nsIObserver* MOZ_OWNING_REF o;
    } mCallback;

    // |Name| is a tagged union type representing one of (a) nothing, (b) a
    // string, or (c) a function. mozilla::Variant doesn't naturally handle the
    // "nothing" case, so we define a dummy type and value (which is unused and
    // so the exact value doesn't matter) for it.
    typedef const int NameNothing;
    typedef const char* NameString;
    typedef nsTimerNameCallbackFunc NameFunc;
    typedef mozilla::Variant<NameNothing, NameString, NameFunc> Name;
    static const NameNothing Nothing;
    Name mName;

    void* mClosure;
  };

  nsresult InitCommon(uint32_t aDelayMS, uint32_t aType,
                      Callback&& newCallback);

  nsresult InitCommon(const mozilla::TimeDuration& aDelay, uint32_t aType,
                      Callback&& newCallback);

  Callback& GetCallback() {
    mMutex.AssertCurrentThreadOwns();
    return mCallback;
  }

  bool IsRepeating() const {
    static_assert(nsITimer::TYPE_ONE_SHOT < nsITimer::TYPE_REPEATING_SLACK,
                  "invalid ordering of timer types!");
    static_assert(
        nsITimer::TYPE_REPEATING_SLACK < nsITimer::TYPE_REPEATING_PRECISE,
        "invalid ordering of timer types!");
    static_assert(nsITimer::TYPE_REPEATING_PRECISE <
                      nsITimer::TYPE_REPEATING_PRECISE_CAN_SKIP,
                  "invalid ordering of timer types!");
    return mType >= nsITimer::TYPE_REPEATING_SLACK &&
           mType < nsITimer::TYPE_ONE_SHOT_LOW_PRIORITY;
  }

  bool IsLowPriority() const {
    return mType == nsITimer::TYPE_ONE_SHOT_LOW_PRIORITY ||
           mType == nsITimer::TYPE_REPEATING_SLACK_LOW_PRIORITY;
  }

  bool IsSlack() const {
    return mType == nsITimer::TYPE_REPEATING_SLACK ||
           mType == nsITimer::TYPE_REPEATING_SLACK_LOW_PRIORITY;
  }

  void GetName(nsACString& aName);

  void SetHolder(nsTimerImplHolder* aHolder);

  nsCOMPtr<nsIEventTarget> mEventTarget;

  void LogFiring(const Callback& aCallback, uint8_t aType, uint32_t aDelay);

  nsresult InitWithFuncCallbackCommon(nsTimerCallbackFunc aFunc, void* aClosure,
                                      uint32_t aDelay, uint32_t aType,
                                      const Callback::Name& aName);

  // This weak reference must be cleared by the nsTimerImplHolder by calling
  // SetHolder(nullptr) before the holder is destroyed.
  nsTimerImplHolder* mHolder;

  // These members are set by the initiating thread, when the timer's type is
  // changed and during the period where it fires on that thread.
  uint8_t mType;

  // The generation number of this timer, re-generated each time the timer is
  // initialized so one-shot timers can be canceled and re-initialized by the
  // arming thread without any bad race conditions.
  // Updated only after this timer has been removed from the timer thread.
  int32_t mGeneration;

  mozilla::TimeDuration mDelay;
  // Updated only after this timer has been removed from the timer thread.
  mozilla::TimeStamp mTimeout;

#ifdef MOZ_TASK_TRACER
  mozilla::tasktracer::TracedTaskCommon mTracedTask;
#endif

  static double sDeltaSum;
  static double sDeltaSumSquared;
  static double sDeltaNum;
  RefPtr<nsITimer> mITimer;
  mozilla::Mutex mMutex;
  Callback mCallback;
  // Counter because in rare cases we can Fire reentrantly
  unsigned int mFiring;
};

class nsTimer final : public nsITimer {
  explicit nsTimer(nsIEventTarget* aTarget)
      : mImpl(new nsTimerImpl(this, aTarget)) {}

  virtual ~nsTimer();

 public:
  friend class TimerThread;
  friend class nsTimerEvent;

  NS_DECL_THREADSAFE_ISUPPORTS
  NS_FORWARD_SAFE_NSITIMER(mImpl);

  virtual size_t SizeOfIncludingThis(
      mozilla::MallocSizeOf aMallocSizeOf) const override;

  // Create a timer targeting the given target.  nullptr indicates that the
  // current thread should be used as the timer's target.
  static RefPtr<nsTimer> WithEventTarget(nsIEventTarget* aTarget);

  static nsresult XPCOMConstructor(nsISupports* aOuter, REFNSIID aIID,
                                   void** aResult);

 private:
  // nsTimerImpl holds a strong ref to us. When our refcount goes to 1, we will
  // null this to break the cycle.
  RefPtr<nsTimerImpl> mImpl;
};

// A class that holds on to an nsTimerImpl.  This lets the nsTimerImpl object
// directly instruct its holder to forget the timer, avoiding list lookups.
class nsTimerImplHolder {
 public:
  explicit nsTimerImplHolder(nsTimerImpl* aTimerImpl) : mTimerImpl(aTimerImpl) {
    if (mTimerImpl) {
      mTimerImpl->SetHolder(this);
    }
  }

  ~nsTimerImplHolder() {
    if (mTimerImpl) {
      mTimerImpl->SetHolder(nullptr);
    }
  }

  void Forget(nsTimerImpl* aTimerImpl) {
    if (MOZ_UNLIKELY(!mTimerImpl)) {
      return;
    }
    MOZ_ASSERT(aTimerImpl == mTimerImpl);
    mTimerImpl->SetHolder(nullptr);
    mTimerImpl = nullptr;
  }

 protected:
  RefPtr<nsTimerImpl> mTimerImpl;
};

#endif /* nsTimerImpl_h___ */