gecko-dev/xpcom/threads/nsThreadUtils.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 nsThreadUtils_h__
#define nsThreadUtils_h__

#include "prthread.h"
#include "prinrval.h"
#include "MainThreadUtils.h"
#include "nsICancelableRunnable.h"
#include "nsIIdlePeriod.h"
#include "nsIIdleRunnable.h"
#include "nsINamed.h"
#include "nsIRunnable.h"
#include "nsIThreadManager.h"
#include "nsITimer.h"
#include "nsIThread.h"
#include "nsString.h"
#include "nsCOMPtr.h"
#include "nsAutoPtr.h"
#include "xpcpublic.h"
#include "mozilla/AbstractEventQueue.h"
#include "mozilla/Atomics.h"
#include "mozilla/Likely.h"
#include "mozilla/Maybe.h"
#include "mozilla/Move.h"
#include "mozilla/TimeStamp.h"
#include "mozilla/Tuple.h"
#include "mozilla/TypeTraits.h"

#include <utility>

//-----------------------------------------------------------------------------
// These methods are alternatives to the methods on nsIThreadManager, provided
// for convenience.

/**
 * Create a new thread, and optionally provide an initial event for the thread.
 *
 * @param aResult
 *   The resulting nsIThread object.
 * @param aInitialEvent
 *   The initial event to run on this thread.  This parameter may be null.
 * @param aStackSize
 *   The size in bytes to reserve for the thread's stack.
 *
 * @returns NS_ERROR_INVALID_ARG
 *   Indicates that the given name is not unique.
 */
extern nsresult NS_NewThread(
    nsIThread** aResult, nsIRunnable* aInitialEvent = nullptr,
    uint32_t aStackSize = nsIThreadManager::DEFAULT_STACK_SIZE);

/**
 * Creates a named thread, otherwise the same as NS_NewThread
 */
extern nsresult NS_NewNamedThread(
    const nsACString& aName, nsIThread** aResult,
    nsIRunnable* aInitialEvent = nullptr,
    uint32_t aStackSize = nsIThreadManager::DEFAULT_STACK_SIZE);

template <size_t LEN>
inline nsresult NS_NewNamedThread(
    const char (&aName)[LEN], nsIThread** aResult,
    nsIRunnable* aInitialEvent = nullptr,
    uint32_t aStackSize = nsIThreadManager::DEFAULT_STACK_SIZE) {
  static_assert(LEN <= 16, "Thread name must be no more than 16 characters");
  return NS_NewNamedThread(nsDependentCString(aName, LEN - 1), aResult,
                           aInitialEvent, aStackSize);
}

/**
 * Get a reference to the current thread, creating it if it does not exist yet.
 *
 * @param aResult
 *   The resulting nsIThread object.
 */
extern nsresult NS_GetCurrentThread(nsIThread** aResult);

/**
 * Dispatch the given event to the current thread.
 *
 * @param aEvent
 *   The event to dispatch.
 *
 * @returns NS_ERROR_INVALID_ARG
 *   If event is null.
 */
extern nsresult NS_DispatchToCurrentThread(nsIRunnable* aEvent);
extern nsresult NS_DispatchToCurrentThread(
    already_AddRefed<nsIRunnable>&& aEvent);

/**
 * Dispatch the given event to the main thread.
 *
 * @param aEvent
 *   The event to dispatch.
 * @param aDispatchFlags
 *   The flags to pass to the main thread's dispatch method.
 *
 * @returns NS_ERROR_INVALID_ARG
 *   If event is null.
 */
extern nsresult NS_DispatchToMainThread(
    nsIRunnable* aEvent, uint32_t aDispatchFlags = NS_DISPATCH_NORMAL);
extern nsresult NS_DispatchToMainThread(
    already_AddRefed<nsIRunnable>&& aEvent,
    uint32_t aDispatchFlags = NS_DISPATCH_NORMAL);

extern nsresult NS_DelayedDispatchToCurrentThread(
    already_AddRefed<nsIRunnable>&& aEvent, uint32_t aDelayMs);

/**
 * Dispatch the given event to the specified queue of the current thread.
 *
 * @param aEvent The event to dispatch.
 * @param aQueue The event queue for the thread to use
 *
 * @returns NS_ERROR_INVALID_ARG
 *   If event is null.
 * @returns NS_ERROR_UNEXPECTED
 *   If the thread is shutting down.
 */
extern nsresult NS_DispatchToCurrentThreadQueue(
    already_AddRefed<nsIRunnable>&& aEvent, mozilla::EventQueuePriority aQueue);

/**
 * Dispatch the given event to the specified queue of the main thread.
 *
 * @param aEvent The event to dispatch.
 * @param aQueue The event queue for the thread to use
 *
 * @returns NS_ERROR_INVALID_ARG
 *   If event is null.
 * @returns NS_ERROR_UNEXPECTED
 *   If the thread is shutting down.
 */
extern nsresult NS_DispatchToMainThreadQueue(
    already_AddRefed<nsIRunnable>&& aEvent, mozilla::EventQueuePriority aQueue);

/**
 * Dispatch the given event to an idle queue of the current thread.
 *
 * @param aEvent The event to dispatch. If the event implements
 *   nsIIdleRunnable, it will receive a call on
 *   nsIIdleRunnable::SetTimer when dispatched, with the value of
 *   aTimeout.
 *
 * @param aTimeout The time in milliseconds until the event should be
 *   moved from an idle queue to the regular queue, if it hasn't been
 *   executed. If aEvent is also an nsIIdleRunnable, it is expected
 *   that it should handle the timeout itself, after a call to
 *   nsIIdleRunnable::SetTimer.
 *
 * @param aQueue
 *   The event queue for the thread to use.  Must be an idle queue
 *   (Idle or DeferredTimers)
 *
 * @returns NS_ERROR_INVALID_ARG
 *   If event is null.
 * @returns NS_ERROR_UNEXPECTED
 *   If the thread is shutting down.
 */
extern nsresult NS_DispatchToCurrentThreadQueue(
    already_AddRefed<nsIRunnable>&& aEvent, uint32_t aTimeout,
    mozilla::EventQueuePriority aQueue);

/**
 * Dispatch the given event to a queue of a thread.
 *
 * @param aEvent The event to dispatch.
 * @param aThread The target thread for the dispatch.
 * @param aQueue The event queue for the thread to use.
 *
 * @returns NS_ERROR_INVALID_ARG
 *   If event is null.
 * @returns NS_ERROR_UNEXPECTED
 *   If the thread is shutting down.
 */
extern nsresult NS_DispatchToThreadQueue(already_AddRefed<nsIRunnable>&& aEvent,
                                         nsIThread* aThread,
                                         mozilla::EventQueuePriority aQueue);

/**
 * Dispatch the given event to an idle queue of a thread.
 *
 * @param aEvent The event to dispatch. If the event implements
 *   nsIIdleRunnable, it will receive a call on
 *   nsIIdleRunnable::SetTimer when dispatched, with the value of
 *   aTimeout.
 *
 * @param aTimeout The time in milliseconds until the event should be
 *   moved from an idle queue to the regular queue, if it hasn't been
 *   executed. If aEvent is also an nsIIdleRunnable, it is expected
 *   that it should handle the timeout itself, after a call to
 *   nsIIdleRunnable::SetTimer.
 *
 * @param aThread The target thread for the dispatch.
 *
 * @param aQueue
 *   The event queue for the thread to use.  Must be an idle queue
 *   (Idle or DeferredTimers)
 *
 * @returns NS_ERROR_INVALID_ARG
 *   If event is null.
 * @returns NS_ERROR_UNEXPECTED
 *   If the thread is shutting down.
 */
extern nsresult NS_DispatchToThreadQueue(already_AddRefed<nsIRunnable>&& aEvent,
                                         uint32_t aTimeout, nsIThread* aThread,
                                         mozilla::EventQueuePriority aQueue);

#ifndef XPCOM_GLUE_AVOID_NSPR
/**
 * Process all pending events for the given thread before returning.  This
 * method simply calls ProcessNextEvent on the thread while HasPendingEvents
 * continues to return true and the time spent in NS_ProcessPendingEvents
 * does not exceed the given timeout value.
 *
 * @param aThread
 *   The thread object for which to process pending events.  If null, then
 *   events will be processed for the current thread.
 * @param aTimeout
 *   The maximum number of milliseconds to spend processing pending events.
 *   Events are not pre-empted to honor this timeout.  Rather, the timeout
 *   value is simply used to determine whether or not to process another event.
 *   Pass PR_INTERVAL_NO_TIMEOUT to specify no timeout.
 */
extern nsresult NS_ProcessPendingEvents(
    nsIThread* aThread, PRIntervalTime aTimeout = PR_INTERVAL_NO_TIMEOUT);
#endif

/**
 * Shortcut for nsIThread::HasPendingEvents.
 *
 * It is an error to call this function when the given thread is not the
 * current thread.  This function will return false if called from some
 * other thread.
 *
 * @param aThread
 *   The current thread or null.
 *
 * @returns
 *   A boolean value that if "true" indicates that there are pending events
 *   in the current thread's event queue.
 */
extern bool NS_HasPendingEvents(nsIThread* aThread = nullptr);

/**
 * Shortcut for nsIThread::ProcessNextEvent.
 *
 * It is an error to call this function when the given thread is not the
 * current thread.  This function will simply return false if called
 * from some other thread.
 *
 * @param aThread
 *   The current thread or null.
 * @param aMayWait
 *   A boolean parameter that if "true" indicates that the method may block
 *   the calling thread to wait for a pending event.
 *
 * @returns
 *   A boolean value that if "true" indicates that an event from the current
 *   thread's event queue was processed.
 */
extern bool NS_ProcessNextEvent(nsIThread* aThread = nullptr,
                                bool aMayWait = true);

// A wrapper for nested event loops.
//
// This function is intended to make code more obvious (do you remember
// what NS_ProcessNextEvent(nullptr, true) means?) and slightly more
// efficient, as people often pass nullptr or NS_GetCurrentThread to
// NS_ProcessNextEvent, which results in needless querying of the current
// thread every time through the loop.
//
// You should use this function in preference to NS_ProcessNextEvent inside
// a loop unless one of the following is true:
//
// * You need to pass `false` to NS_ProcessNextEvent; or
// * You need to do unusual things around the call to NS_ProcessNextEvent,
//   such as unlocking mutexes that you are holding.
//
// If you *do* need to call NS_ProcessNextEvent manually, please do call
// NS_GetCurrentThread() outside of your loop and pass the returned pointer
// into NS_ProcessNextEvent for a tiny efficiency win.
namespace mozilla {

// You should normally not need to deal with this template parameter.  If
// you enjoy esoteric event loop details, read on.
//
// If you specify that NS_ProcessNextEvent wait for an event, it is possible
// for NS_ProcessNextEvent to return false, i.e. to indicate that an event
// was not processed.  This can only happen when the thread has been shut
// down by another thread, but is still attempting to process events outside
// of a nested event loop.
//
// This behavior is admittedly strange.  The scenario it deals with is the
// following:
//
// * The current thread has been shut down by some owner thread.
// * The current thread is spinning an event loop waiting for some condition
//   to become true.
// * Said condition is actually being fulfilled by another thread, so there
//   are timing issues in play.
//
// Thus, there is a small window where the current thread's event loop
// spinning can check the condition, find it false, and call
// NS_ProcessNextEvent to wait for another event.  But we don't actually
// want it to wait indefinitely, because there might not be any other events
// in the event loop, and the current thread can't accept dispatched events
// because it's being shut down.  Thus, actually blocking would hang the
// thread, which is bad.  The solution, then, is to detect such a scenario
// and not actually block inside NS_ProcessNextEvent.
//
// But this is a problem, because we want to return the status of
// NS_ProcessNextEvent to the caller of SpinEventLoopUntil if possible.  In
// the above scenario, however, we'd stop spinning prematurely and cause
// all sorts of havoc.  We therefore have this template parameter to
// control whether errors are ignored or passed out to the caller of
// SpinEventLoopUntil.  The latter is the default; if you find yourself
// wanting to use the former, you should think long and hard before doing
// so, and write a comment like this defending your choice.

enum class ProcessFailureBehavior {
  IgnoreAndContinue,
  ReportToCaller,
};

template <
    ProcessFailureBehavior Behavior = ProcessFailureBehavior::ReportToCaller,
    typename Pred>
bool SpinEventLoopUntil(Pred&& aPredicate, nsIThread* aThread = nullptr) {
  nsIThread* thread = aThread ? aThread : NS_GetCurrentThread();

  // From a latency perspective, spinning the event loop is like leaving script
  // and returning to the event loop. Tell the watchdog we stopped running
  // script (until we return).
  mozilla::Maybe<xpc::AutoScriptActivity> asa;
  if (NS_IsMainThread()) {
    asa.emplace(false);
  }

  while (!aPredicate()) {
    bool didSomething = NS_ProcessNextEvent(thread, true);

    if (Behavior == ProcessFailureBehavior::IgnoreAndContinue) {
      // Don't care what happened, continue on.
      continue;
    } else if (!didSomething) {
      return false;
    }
  }

  return true;
}

}  // namespace mozilla

/**
 * Returns true if we're in the compositor thread.
 *
 * We declare this here because the headers required to invoke
 * CompositorThreadHolder::IsInCompositorThread() also pull in a bunch of system
 * headers that #define various tokens in a way that can break the build.
 */
extern bool NS_IsInCompositorThread();

extern bool NS_IsInVRThread();

//-----------------------------------------------------------------------------
// Helpers that work with nsCOMPtr:

inline already_AddRefed<nsIThread> do_GetCurrentThread() {
  nsIThread* thread = nullptr;
  NS_GetCurrentThread(&thread);
  return already_AddRefed<nsIThread>(thread);
}

inline already_AddRefed<nsIThread> do_GetMainThread() {
  nsIThread* thread = nullptr;
  NS_GetMainThread(&thread);
  return already_AddRefed<nsIThread>(thread);
}

//-----------------------------------------------------------------------------

#ifdef MOZILLA_INTERNAL_API
// Fast access to the current thread.  Will create an nsIThread if one does not
// exist already!  Do not release the returned pointer!  If you want to use this
// pointer from some other thread, then you will need to AddRef it.  Otherwise,
// you should only consider this pointer valid from code running on the current
// thread.
extern nsIThread* NS_GetCurrentThread();

// Exactly the same as NS_GetCurrentThread, except it will not create an
// nsThread if one does not exist yet. This is useful in cases where you have
// code that runs on threads that may or may not not be driven by an nsThread
// event loop, and wish to avoid inadvertently creating a superfluous nsThread.
extern nsIThread* NS_GetCurrentThreadNoCreate();

/**
 * Set the name of the current thread. Prefer this function over
 * PR_SetCurrentThreadName() if possible. The name will also be included in the
 * crash report.
 *
 * @param aName
 *   Name of the thread. A C language null-terminated string.
 */
extern void NS_SetCurrentThreadName(const char* aName);
#endif

//-----------------------------------------------------------------------------

#ifndef XPCOM_GLUE_AVOID_NSPR

namespace mozilla {

// This class is designed to be subclassed.
class IdlePeriod : public nsIIdlePeriod {
 public:
  NS_DECL_THREADSAFE_ISUPPORTS
  NS_DECL_NSIIDLEPERIOD

  IdlePeriod() {}

 protected:
  virtual ~IdlePeriod() {}

 private:
  IdlePeriod(const IdlePeriod&) = delete;
  IdlePeriod& operator=(const IdlePeriod&) = delete;
  IdlePeriod& operator=(const IdlePeriod&&) = delete;
};

// Cancelable runnable methods implement nsICancelableRunnable, and
// Idle and IdleWithTimer also nsIIdleRunnable.
enum class RunnableKind { Standard, Cancelable, Idle, IdleWithTimer };

// Implementing nsINamed on Runnable bloats vtables for the hundreds of
// Runnable subclasses that we have, so we want to avoid that overhead
// when we're not using nsINamed for anything.
#  ifndef RELEASE_OR_BETA
#    define MOZ_COLLECTING_RUNNABLE_TELEMETRY
#  endif

// This class is designed to be subclassed.
class Runnable : public nsIRunnable
#  ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
    ,
                 public nsINamed
#  endif
{
 public:
  // Runnable refcount changes are preserved when recording/replaying to ensure
  // that they are destroyed at consistent points.
  NS_DECL_THREADSAFE_ISUPPORTS_WITH_RECORDING(recordreplay::Behavior::Preserve)
  NS_DECL_NSIRUNNABLE
#  ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
  NS_DECL_NSINAMED
#  endif

  Runnable() = delete;

#  ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
  explicit Runnable(const char* aName) : mName(aName) {}
#  else
  explicit Runnable(const char* aName) {}
#  endif

 protected:
  virtual ~Runnable() {}

#  ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
  const char* mName = nullptr;
#  endif

 private:
  Runnable(const Runnable&) = delete;
  Runnable& operator=(const Runnable&) = delete;
  Runnable& operator=(const Runnable&&) = delete;
};

// This class is designed to be subclassed.
class CancelableRunnable : public Runnable, public nsICancelableRunnable {
 public:
  NS_DECL_ISUPPORTS_INHERITED
  // nsICancelableRunnable
  virtual nsresult Cancel() override;

  CancelableRunnable() = delete;
  explicit CancelableRunnable(const char* aName) : Runnable(aName) {}

 protected:
  virtual ~CancelableRunnable() {}

 private:
  CancelableRunnable(const CancelableRunnable&) = delete;
  CancelableRunnable& operator=(const CancelableRunnable&) = delete;
  CancelableRunnable& operator=(const CancelableRunnable&&) = delete;
};

// This class is designed to be subclassed.
class IdleRunnable : public CancelableRunnable, public nsIIdleRunnable {
 public:
  NS_DECL_ISUPPORTS_INHERITED

  IdleRunnable() : CancelableRunnable("IdleRunnable") {}
  explicit IdleRunnable(const char* aName) : CancelableRunnable(aName) {}

 protected:
  virtual ~IdleRunnable() {}

 private:
  IdleRunnable(const IdleRunnable&) = delete;
  IdleRunnable& operator=(const IdleRunnable&) = delete;
  IdleRunnable& operator=(const IdleRunnable&&) = delete;
};

// This class is designed to be a wrapper of a real runnable to support event
// prioritizable.
class PrioritizableRunnable : public Runnable, public nsIRunnablePriority {
 public:
  PrioritizableRunnable(already_AddRefed<nsIRunnable>&& aRunnable,
                        uint32_t aPriority);

#  ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
  NS_IMETHOD GetName(nsACString& aName) override;
#  endif

  NS_DECL_ISUPPORTS_INHERITED
  NS_DECL_NSIRUNNABLE
  NS_DECL_NSIRUNNABLEPRIORITY

 protected:
  virtual ~PrioritizableRunnable(){};
  nsCOMPtr<nsIRunnable> mRunnable;
  uint32_t mPriority;
};

extern already_AddRefed<nsIRunnable> CreateMediumHighRunnable(
    already_AddRefed<nsIRunnable>&& aRunnable);

namespace detail {

// An event that can be used to call a C++11 functions or function objects,
// including lambdas. The function must have no required arguments, and must
// return void.
template <typename StoredFunction>
class RunnableFunction : public Runnable {
 public:
  template <typename F>
  explicit RunnableFunction(const char* aName, F&& aFunction)
      : Runnable(aName), mFunction(std::forward<F>(aFunction)) {}

  NS_IMETHOD Run() override {
    static_assert(IsVoid<decltype(mFunction())>::value,
                  "The lambda must return void!");
    mFunction();
    return NS_OK;
  }

 private:
  StoredFunction mFunction;
};

// Type alias for NS_NewRunnableFunction
template <typename Function>
using RunnableFunctionImpl =
    // Make sure we store a non-reference in nsRunnableFunction.
    typename detail::RunnableFunction<typename RemoveReference<Function>::Type>;
}  // namespace detail

namespace detail {

template <typename CVRemoved>
struct IsRefcountedSmartPointerHelper : FalseType {};

template <typename Pointee>
struct IsRefcountedSmartPointerHelper<RefPtr<Pointee>> : TrueType {};

template <typename Pointee>
struct IsRefcountedSmartPointerHelper<nsCOMPtr<Pointee>> : TrueType {};

}  // namespace detail

template <typename T>
struct IsRefcountedSmartPointer
    : detail::IsRefcountedSmartPointerHelper<typename RemoveCV<T>::Type> {};

namespace detail {

template <typename T, typename CVRemoved>
struct RemoveSmartPointerHelper {
  typedef T Type;
};

template <typename T, typename Pointee>
struct RemoveSmartPointerHelper<T, RefPtr<Pointee>> {
  typedef Pointee Type;
};

template <typename T, typename Pointee>
struct RemoveSmartPointerHelper<T, nsCOMPtr<Pointee>> {
  typedef Pointee Type;
};

}  // namespace detail

template <typename T>
struct RemoveSmartPointer
    : detail::RemoveSmartPointerHelper<T, typename RemoveCV<T>::Type> {};

namespace detail {

template <typename T, typename CVRemoved>
struct RemoveRawOrSmartPointerHelper {
  typedef T Type;
};

template <typename T, typename Pointee>
struct RemoveRawOrSmartPointerHelper<T, Pointee*> {
  typedef Pointee Type;
};

template <typename T, typename Pointee>
struct RemoveRawOrSmartPointerHelper<T, RefPtr<Pointee>> {
  typedef Pointee Type;
};

template <typename T, typename Pointee>
struct RemoveRawOrSmartPointerHelper<T, nsCOMPtr<Pointee>> {
  typedef Pointee Type;
};

}  // namespace detail

template <typename T>
struct RemoveRawOrSmartPointer
    : detail::RemoveRawOrSmartPointerHelper<T, typename RemoveCV<T>::Type> {};

}  // namespace mozilla

inline nsISupports* ToSupports(mozilla::Runnable* p) {
  return static_cast<nsIRunnable*>(p);
}

template <typename Function>
already_AddRefed<mozilla::Runnable> NS_NewRunnableFunction(
    const char* aName, Function&& aFunction) {
  // We store a non-reference in RunnableFunction, but still forward aFunction
  // to move if possible.
  return do_AddRef(new mozilla::detail::RunnableFunctionImpl<Function>(
      aName, std::forward<Function>(aFunction)));
}

namespace mozilla {
namespace detail {

template <RunnableKind Kind>
class TimerBehaviour {
 public:
  nsITimer* GetTimer() { return nullptr; }
  void CancelTimer() {}

 protected:
  ~TimerBehaviour() {}
};

template <>
class TimerBehaviour<RunnableKind::IdleWithTimer> {
 public:
  nsITimer* GetTimer() {
    if (!mTimer) {
      mTimer = NS_NewTimer();
    }

    return mTimer;
  }

  void CancelTimer() {
    if (mTimer) {
      mTimer->Cancel();
    }
  }

 protected:
  ~TimerBehaviour() { CancelTimer(); }

 private:
  nsCOMPtr<nsITimer> mTimer;
};

}  // namespace detail
}  // namespace mozilla

// An event that can be used to call a method on a class.  The class type must
// support reference counting. This event supports Revoke for use
// with nsRevocableEventPtr.
template <class ClassType, typename ReturnType = void, bool Owning = true,
          mozilla::RunnableKind Kind = mozilla::RunnableKind::Standard>
class nsRunnableMethod
    : public mozilla::Conditional<
          Kind == mozilla::RunnableKind::Standard, mozilla::Runnable,
          typename mozilla::Conditional<
              Kind == mozilla::RunnableKind::Cancelable,
              mozilla::CancelableRunnable, mozilla::IdleRunnable>::Type>::Type,
      protected mozilla::detail::TimerBehaviour<Kind> {
  using BaseType = typename mozilla::Conditional<
      Kind == mozilla::RunnableKind::Standard, mozilla::Runnable,
      typename mozilla::Conditional<Kind == mozilla::RunnableKind::Cancelable,
                                    mozilla::CancelableRunnable,
                                    mozilla::IdleRunnable>::Type>::Type;

 public:
  nsRunnableMethod(const char* aName) : BaseType(aName) {}

  virtual void Revoke() = 0;

  // These ReturnTypeEnforcer classes set up a blacklist for return types that
  // we know are not safe. The default ReturnTypeEnforcer compiles just fine but
  // already_AddRefed will not.
  template <typename OtherReturnType>
  class ReturnTypeEnforcer {
   public:
    typedef int ReturnTypeIsSafe;
  };

  template <class T>
  class ReturnTypeEnforcer<already_AddRefed<T>> {
    // No ReturnTypeIsSafe makes this illegal!
  };

  // Make sure this return type is safe.
  typedef typename ReturnTypeEnforcer<ReturnType>::ReturnTypeIsSafe check;
};

template <class ClassType, bool Owning>
struct nsRunnableMethodReceiver {
  RefPtr<ClassType> mObj;
  explicit nsRunnableMethodReceiver(ClassType* aObj) : mObj(aObj) {}
  ~nsRunnableMethodReceiver() { Revoke(); }
  ClassType* Get() const { return mObj.get(); }
  void Revoke() { mObj = nullptr; }
};

template <class ClassType>
struct nsRunnableMethodReceiver<ClassType, false> {
  ClassType* MOZ_NON_OWNING_REF mObj;
  explicit nsRunnableMethodReceiver(ClassType* aObj) : mObj(aObj) {}
  ClassType* Get() const { return mObj; }
  void Revoke() { mObj = nullptr; }
};

static inline constexpr bool IsIdle(mozilla::RunnableKind aKind) {
  return aKind == mozilla::RunnableKind::Idle ||
         aKind == mozilla::RunnableKind::IdleWithTimer;
}

template <typename PtrType, typename Method, bool Owning,
          mozilla::RunnableKind Kind>
struct nsRunnableMethodTraits;

template <typename PtrType, class C, typename R, bool Owning,
          mozilla::RunnableKind Kind, typename... As>
struct nsRunnableMethodTraits<PtrType, R (C::*)(As...), Owning, Kind> {
  typedef typename mozilla::RemoveRawOrSmartPointer<PtrType>::Type class_type;
  static_assert(mozilla::IsBaseOf<C, class_type>::value,
                "Stored class must inherit from method's class");
  typedef R return_type;
  typedef nsRunnableMethod<C, R, Owning, Kind> base_type;
  static const bool can_cancel = Kind == mozilla::RunnableKind::Cancelable;
};

template <typename PtrType, class C, typename R, bool Owning,
          mozilla::RunnableKind Kind, typename... As>
struct nsRunnableMethodTraits<PtrType, R (C::*)(As...) const, Owning, Kind> {
  typedef const typename mozilla::RemoveRawOrSmartPointer<PtrType>::Type
      class_type;
  static_assert(mozilla::IsBaseOf<C, class_type>::value,
                "Stored class must inherit from method's class");
  typedef R return_type;
  typedef nsRunnableMethod<C, R, Owning, Kind> base_type;
  static const bool can_cancel = Kind == mozilla::RunnableKind::Cancelable;
};

#  ifdef NS_HAVE_STDCALL
template <typename PtrType, class C, typename R, bool Owning,
          mozilla::RunnableKind Kind, typename... As>
struct nsRunnableMethodTraits<PtrType, R (__stdcall C::*)(As...), Owning,
                              Kind> {
  typedef typename mozilla::RemoveRawOrSmartPointer<PtrType>::Type class_type;
  static_assert(mozilla::IsBaseOf<C, class_type>::value,
                "Stored class must inherit from method's class");
  typedef R return_type;
  typedef nsRunnableMethod<C, R, Owning, Kind> base_type;
  static const bool can_cancel = Kind == mozilla::RunnableKind::Cancelable;
};

template <typename PtrType, class C, typename R, bool Owning,
          mozilla::RunnableKind Kind>
struct nsRunnableMethodTraits<PtrType, R (NS_STDCALL C::*)(), Owning, Kind> {
  typedef typename mozilla::RemoveRawOrSmartPointer<PtrType>::Type class_type;
  static_assert(mozilla::IsBaseOf<C, class_type>::value,
                "Stored class must inherit from method's class");
  typedef R return_type;
  typedef nsRunnableMethod<C, R, Owning, Kind> base_type;
  static const bool can_cancel = Kind == mozilla::RunnableKind::Cancelable;
};

template <typename PtrType, class C, typename R, bool Owning,
          mozilla::RunnableKind Kind, typename... As>
struct nsRunnableMethodTraits<PtrType, R (__stdcall C::*)(As...) const, Owning,
                              Kind> {
  typedef const typename mozilla::RemoveRawOrSmartPointer<PtrType>::Type
      class_type;
  static_assert(mozilla::IsBaseOf<C, class_type>::value,
                "Stored class must inherit from method's class");
  typedef R return_type;
  typedef nsRunnableMethod<C, R, Owning, Kind> base_type;
  static const bool can_cancel = Kind == mozilla::RunnableKind::Cancelable;
};

template <typename PtrType, class C, typename R, bool Owning,
          mozilla::RunnableKind Kind>
struct nsRunnableMethodTraits<PtrType, R (NS_STDCALL C::*)() const, Owning,
                              Kind> {
  typedef const typename mozilla::RemoveRawOrSmartPointer<PtrType>::Type
      class_type;
  static_assert(mozilla::IsBaseOf<C, class_type>::value,
                "Stored class must inherit from method's class");
  typedef R return_type;
  typedef nsRunnableMethod<C, R, Owning, Kind> base_type;
  static const bool can_cancel = Kind == mozilla::RunnableKind::Cancelable;
};
#  endif

// IsParameterStorageClass<T>::value is true if T is a parameter-storage class
// that will be recognized by NS_New[NonOwning]RunnableMethodWithArg[s] to
// force a specific storage&passing strategy (instead of inferring one,
// see ParameterStorage).
// When creating a new storage class, add a specialization for it to be
// recognized.
template <typename T>
struct IsParameterStorageClass : public mozilla::FalseType {};

// StoreXPassByY structs used to inform nsRunnableMethodArguments how to
// store arguments, and how to pass them to the target method.

template <typename T>
struct StoreCopyPassByValue {
  typedef typename mozilla::Decay<T>::Type stored_type;
  typedef stored_type passed_type;
  stored_type m;
  template <typename A>
  MOZ_IMPLICIT StoreCopyPassByValue(A&& a) : m(std::forward<A>(a)) {}
  passed_type PassAsParameter() { return m; }
};
template <typename S>
struct IsParameterStorageClass<StoreCopyPassByValue<S>>
    : public mozilla::TrueType {};

template <typename T>
struct StoreCopyPassByConstLRef {
  typedef typename mozilla::Decay<T>::Type stored_type;
  typedef const stored_type& passed_type;
  stored_type m;
  template <typename A>
  MOZ_IMPLICIT StoreCopyPassByConstLRef(A&& a) : m(std::forward<A>(a)) {}
  passed_type PassAsParameter() { return m; }
};
template <typename S>
struct IsParameterStorageClass<StoreCopyPassByConstLRef<S>>
    : public mozilla::TrueType {};

template <typename T>
struct StoreCopyPassByLRef {
  typedef typename mozilla::Decay<T>::Type stored_type;
  typedef stored_type& passed_type;
  stored_type m;
  template <typename A>
  MOZ_IMPLICIT StoreCopyPassByLRef(A&& a) : m(std::forward<A>(a)) {}
  passed_type PassAsParameter() { return m; }
};
template <typename S>
struct IsParameterStorageClass<StoreCopyPassByLRef<S>>
    : public mozilla::TrueType {};

template <typename T>
struct StoreCopyPassByRRef {
  typedef typename mozilla::Decay<T>::Type stored_type;
  typedef stored_type&& passed_type;
  stored_type m;
  template <typename A>
  MOZ_IMPLICIT StoreCopyPassByRRef(A&& a) : m(std::forward<A>(a)) {}
  passed_type PassAsParameter() { return std::move(m); }
};
template <typename S>
struct IsParameterStorageClass<StoreCopyPassByRRef<S>>
    : public mozilla::TrueType {};

template <typename T>
struct StoreRefPassByLRef {
  typedef T& stored_type;
  typedef T& passed_type;
  stored_type m;
  template <typename A>
  MOZ_IMPLICIT StoreRefPassByLRef(A& a) : m(a) {}
  passed_type PassAsParameter() { return m; }
};
template <typename S>
struct IsParameterStorageClass<StoreRefPassByLRef<S>>
    : public mozilla::TrueType {};

template <typename T>
struct StoreConstRefPassByConstLRef {
  typedef const T& stored_type;
  typedef const T& passed_type;
  stored_type m;
  template <typename A>
  MOZ_IMPLICIT StoreConstRefPassByConstLRef(const A& a) : m(a) {}
  passed_type PassAsParameter() { return m; }
};
template <typename S>
struct IsParameterStorageClass<StoreConstRefPassByConstLRef<S>>
    : public mozilla::TrueType {};

template <typename T>
struct StoreRefPtrPassByPtr {
  typedef RefPtr<T> stored_type;
  typedef T* passed_type;
  stored_type m;
  template <typename A>
  MOZ_IMPLICIT StoreRefPtrPassByPtr(A&& a) : m(std::forward<A>(a)) {}
  passed_type PassAsParameter() { return m.get(); }
};
template <typename S>
struct IsParameterStorageClass<StoreRefPtrPassByPtr<S>>
    : public mozilla::TrueType {};

template <typename T>
struct StorePtrPassByPtr {
  typedef T* stored_type;
  typedef T* passed_type;
  stored_type m;
  template <typename A>
  MOZ_IMPLICIT StorePtrPassByPtr(A a) : m(a) {}
  passed_type PassAsParameter() { return m; }
};
template <typename S>
struct IsParameterStorageClass<StorePtrPassByPtr<S>>
    : public mozilla::TrueType {};

template <typename T>
struct StoreConstPtrPassByConstPtr {
  typedef const T* stored_type;
  typedef const T* passed_type;
  stored_type m;
  template <typename A>
  MOZ_IMPLICIT StoreConstPtrPassByConstPtr(A a) : m(a) {}
  passed_type PassAsParameter() { return m; }
};
template <typename S>
struct IsParameterStorageClass<StoreConstPtrPassByConstPtr<S>>
    : public mozilla::TrueType {};

template <typename T>
struct StoreCopyPassByConstPtr {
  typedef T stored_type;
  typedef const T* passed_type;
  stored_type m;
  template <typename A>
  MOZ_IMPLICIT StoreCopyPassByConstPtr(A&& a) : m(std::forward<A>(a)) {}
  passed_type PassAsParameter() { return &m; }
};
template <typename S>
struct IsParameterStorageClass<StoreCopyPassByConstPtr<S>>
    : public mozilla::TrueType {};

template <typename T>
struct StoreCopyPassByPtr {
  typedef T stored_type;
  typedef T* passed_type;
  stored_type m;
  template <typename A>
  MOZ_IMPLICIT StoreCopyPassByPtr(A&& a) : m(std::forward<A>(a)) {}
  passed_type PassAsParameter() { return &m; }
};
template <typename S>
struct IsParameterStorageClass<StoreCopyPassByPtr<S>>
    : public mozilla::TrueType {};

namespace detail {

template <typename>
struct SFINAE1True : mozilla::TrueType {};

template <class T>
static auto HasRefCountMethodsTest(int)
    -> SFINAE1True<decltype(mozilla::DeclVal<T>().AddRef(),
                            mozilla::DeclVal<T>().Release())>;
template <class>
static auto HasRefCountMethodsTest(long) -> mozilla::FalseType;

template <class T>
struct HasRefCountMethods : decltype(HasRefCountMethodsTest<T>(0)) {};

template <typename TWithoutPointer>
struct NonnsISupportsPointerStorageClass
    : mozilla::Conditional<
          mozilla::IsConst<TWithoutPointer>::value,
          StoreConstPtrPassByConstPtr<
              typename mozilla::RemoveConst<TWithoutPointer>::Type>,
          StorePtrPassByPtr<TWithoutPointer>> {};

template <typename TWithoutPointer>
struct PointerStorageClass
    : mozilla::Conditional<
          HasRefCountMethods<TWithoutPointer>::value,
          StoreRefPtrPassByPtr<TWithoutPointer>,
          typename NonnsISupportsPointerStorageClass<TWithoutPointer>::Type> {};

template <typename TWithoutRef>
struct LValueReferenceStorageClass
    : mozilla::Conditional<
          mozilla::IsConst<TWithoutRef>::value,
          StoreConstRefPassByConstLRef<
              typename mozilla::RemoveConst<TWithoutRef>::Type>,
          StoreRefPassByLRef<TWithoutRef>> {};

template <typename T>
struct SmartPointerStorageClass
    : mozilla::Conditional<
          mozilla::IsRefcountedSmartPointer<T>::value,
          StoreRefPtrPassByPtr<typename mozilla::RemoveSmartPointer<T>::Type>,
          StoreCopyPassByConstLRef<T>> {};

template <typename T>
struct NonLValueReferenceStorageClass
    : mozilla::Conditional<
          mozilla::IsRvalueReference<T>::value,
          StoreCopyPassByRRef<typename mozilla::RemoveReference<T>::Type>,
          typename SmartPointerStorageClass<T>::Type> {};

template <typename T>
struct NonPointerStorageClass
    : mozilla::Conditional<
          mozilla::IsLvalueReference<T>::value,
          typename LValueReferenceStorageClass<
              typename mozilla::RemoveReference<T>::Type>::Type,
          typename NonLValueReferenceStorageClass<T>::Type> {};

template <typename T>
struct NonParameterStorageClass
    : mozilla::Conditional<mozilla::IsPointer<T>::value,
                           typename PointerStorageClass<
                               typename mozilla::RemovePointer<T>::Type>::Type,
                           typename NonPointerStorageClass<T>::Type> {};

// Choose storage&passing strategy based on preferred storage type:
// - If IsParameterStorageClass<T>::value is true, use as-is.
// - RC*       -> StoreRefPtrPassByPtr<RC>       :Store RefPtr<RC>, pass RC*
//   ^^ RC quacks like a ref-counted type (i.e., has AddRef and Release methods)
// - const T*  -> StoreConstPtrPassByConstPtr<T> :Store const T*, pass const T*
// - T*        -> StorePtrPassByPtr<T>           :Store T*, pass T*.
// - const T&  -> StoreConstRefPassByConstLRef<T>:Store const T&, pass const T&.
// - T&        -> StoreRefPassByLRef<T>          :Store T&, pass T&.
// - T&&       -> StoreCopyPassByRRef<T>         :Store T, pass std::move(T).
// - RefPtr<T>, nsCOMPtr<T>
//             -> StoreRefPtrPassByPtr<T>        :Store RefPtr<T>, pass T*
// - Other T   -> StoreCopyPassByConstLRef<T>    :Store T, pass const T&.
// Other available explicit options:
// -              StoreCopyPassByValue<T>        :Store T, pass T.
// -              StoreCopyPassByLRef<T>         :Store T, pass T& (of copy!)
// -              StoreCopyPassByConstPtr<T>     :Store T, pass const T*
// -              StoreCopyPassByPtr<T>          :Store T, pass T* (of copy!)
// Or create your own class with PassAsParameter() method, optional
// clean-up in destructor, and with associated IsParameterStorageClass<>.
template <typename T>
struct ParameterStorage
    : mozilla::Conditional<IsParameterStorageClass<T>::value, T,
                           typename NonParameterStorageClass<T>::Type> {};

template <class T>
static auto HasSetDeadlineTest(int) -> SFINAE1True<decltype(
    mozilla::DeclVal<T>().SetDeadline(mozilla::DeclVal<mozilla::TimeStamp>()))>;

template <class T>
static auto HasSetDeadlineTest(long) -> mozilla::FalseType;

template <class T>
struct HasSetDeadline : decltype(HasSetDeadlineTest<T>(0)) {};

template <class T>
typename mozilla::EnableIf<::detail::HasSetDeadline<T>::value>::Type
SetDeadlineImpl(T* aObj, mozilla::TimeStamp aTimeStamp) {
  aObj->SetDeadline(aTimeStamp);
}

template <class T>
typename mozilla::EnableIf<!::detail::HasSetDeadline<T>::value>::Type
SetDeadlineImpl(T* aObj, mozilla::TimeStamp aTimeStamp) {}
} /* namespace detail */

namespace mozilla {
namespace detail {

// struct used to store arguments and later apply them to a method.
template <typename... Ts>
struct RunnableMethodArguments final {
  Tuple<typename ::detail::ParameterStorage<Ts>::Type...> mArguments;
  template <typename... As>
  explicit RunnableMethodArguments(As&&... aArguments)
      : mArguments(std::forward<As>(aArguments)...) {}
  template <typename C, typename M, typename... Args, size_t... Indices>
  static auto applyImpl(C* o, M m, Tuple<Args...>& args,
                        std::index_sequence<Indices...>)
      -> decltype(((*o).*m)(Get<Indices>(args).PassAsParameter()...)) {
    return ((*o).*m)(Get<Indices>(args).PassAsParameter()...);
  }
  template <class C, typename M>
  auto apply(C* o, M m)
      -> decltype(applyImpl(o, m, mArguments,
                            std::index_sequence_for<Ts...>{})) {
    return applyImpl(o, m, mArguments, std::index_sequence_for<Ts...>{});
  }
};

template <typename PtrType, typename Method, bool Owning, RunnableKind Kind,
          typename... Storages>
class RunnableMethodImpl final
    : public ::nsRunnableMethodTraits<PtrType, Method, Owning,
                                      Kind>::base_type {
  typedef typename ::nsRunnableMethodTraits<PtrType, Method, Owning, Kind>
      Traits;

  typedef typename Traits::class_type ClassType;
  typedef typename Traits::base_type BaseType;
  ::nsRunnableMethodReceiver<ClassType, Owning> mReceiver;
  Method mMethod;
  RunnableMethodArguments<Storages...> mArgs;
  using BaseType::CancelTimer;
  using BaseType::GetTimer;

 private:
  virtual ~RunnableMethodImpl() { Revoke(); };
  static void TimedOut(nsITimer* aTimer, void* aClosure) {
    static_assert(IsIdle(Kind), "Don't use me!");
    RefPtr<IdleRunnable> r = static_cast<IdleRunnable*>(aClosure);
    r->SetDeadline(TimeStamp());
    r->Run();
    r->Cancel();
  }

 public:
  template <typename ForwardedPtrType, typename... Args>
  explicit RunnableMethodImpl(const char* aName, ForwardedPtrType&& aObj,
                              Method aMethod, Args&&... aArgs)
      : BaseType(aName),
        mReceiver(std::forward<ForwardedPtrType>(aObj)),
        mMethod(aMethod),
        mArgs(std::forward<Args>(aArgs)...) {
    static_assert(sizeof...(Storages) == sizeof...(Args),
                  "Storages and Args should have equal sizes");
  }

  NS_IMETHOD Run() {
    CancelTimer();

    if (MOZ_LIKELY(mReceiver.Get())) {
      mArgs.apply(mReceiver.Get(), mMethod);
    }

    return NS_OK;
  }

  nsresult Cancel() {
    static_assert(Kind >= RunnableKind::Cancelable, "Don't use me!");
    Revoke();
    return NS_OK;
  }

  void Revoke() {
    CancelTimer();
    mReceiver.Revoke();
  }

  void SetDeadline(TimeStamp aDeadline) {
    if (MOZ_LIKELY(mReceiver.Get())) {
      ::detail::SetDeadlineImpl(mReceiver.Get(), aDeadline);
    }
  }

  void SetTimer(uint32_t aDelay, nsIEventTarget* aTarget) {
    MOZ_ASSERT(aTarget);

    if (nsCOMPtr<nsITimer> timer = GetTimer()) {
      timer->Cancel();
      timer->SetTarget(aTarget);
      timer->InitWithNamedFuncCallback(TimedOut, this, aDelay,
                                       nsITimer::TYPE_ONE_SHOT,
                                       "detail::RunnableMethodImpl::SetTimer");
    }
  }
};

// Type aliases for NewRunnableMethod.
template <typename PtrType, typename Method>
using OwningRunnableMethod =
    typename ::nsRunnableMethodTraits<typename RemoveReference<PtrType>::Type,
                                      Method, true,
                                      RunnableKind::Standard>::base_type;
template <typename PtrType, typename Method, typename... Storages>
using OwningRunnableMethodImpl =
    RunnableMethodImpl<typename RemoveReference<PtrType>::Type, Method, true,
                       RunnableKind::Standard, Storages...>;

// Type aliases for NewCancelableRunnableMethod.
template <typename PtrType, typename Method>
using CancelableRunnableMethod =
    typename ::nsRunnableMethodTraits<typename RemoveReference<PtrType>::Type,
                                      Method, true,
                                      RunnableKind::Cancelable>::base_type;
template <typename PtrType, typename Method, typename... Storages>
using CancelableRunnableMethodImpl =
    RunnableMethodImpl<typename RemoveReference<PtrType>::Type, Method, true,
                       RunnableKind::Cancelable, Storages...>;

// Type aliases for NewIdleRunnableMethod.
template <typename PtrType, typename Method>
using IdleRunnableMethod =
    typename ::nsRunnableMethodTraits<typename RemoveReference<PtrType>::Type,
                                      Method, true,
                                      RunnableKind::Idle>::base_type;
template <typename PtrType, typename Method, typename... Storages>
using IdleRunnableMethodImpl =
    RunnableMethodImpl<typename RemoveReference<PtrType>::Type, Method, true,
                       RunnableKind::Idle, Storages...>;

// Type aliases for NewIdleRunnableMethodWithTimer.
template <typename PtrType, typename Method>
using IdleRunnableMethodWithTimer =
    typename ::nsRunnableMethodTraits<typename RemoveReference<PtrType>::Type,
                                      Method, true,
                                      RunnableKind::IdleWithTimer>::base_type;
template <typename PtrType, typename Method, typename... Storages>
using IdleRunnableMethodWithTimerImpl =
    RunnableMethodImpl<typename RemoveReference<PtrType>::Type, Method, true,
                       RunnableKind::IdleWithTimer, Storages...>;

// Type aliases for NewNonOwningRunnableMethod.
template <typename PtrType, typename Method>
using NonOwningRunnableMethod =
    typename ::nsRunnableMethodTraits<typename RemoveReference<PtrType>::Type,
                                      Method, false,
                                      RunnableKind::Standard>::base_type;
template <typename PtrType, typename Method, typename... Storages>
using NonOwningRunnableMethodImpl =
    RunnableMethodImpl<typename RemoveReference<PtrType>::Type, Method, false,
                       RunnableKind::Standard, Storages...>;

// Type aliases for NonOwningCancelableRunnableMethod
template <typename PtrType, typename Method>
using NonOwningCancelableRunnableMethod =
    typename ::nsRunnableMethodTraits<typename RemoveReference<PtrType>::Type,
                                      Method, false,
                                      RunnableKind::Cancelable>::base_type;
template <typename PtrType, typename Method, typename... Storages>
using NonOwningCancelableRunnableMethodImpl =
    RunnableMethodImpl<typename RemoveReference<PtrType>::Type, Method, false,
                       RunnableKind::Cancelable, Storages...>;

// Type aliases for NonOwningIdleRunnableMethod
template <typename PtrType, typename Method>
using NonOwningIdleRunnableMethod =
    typename ::nsRunnableMethodTraits<typename RemoveReference<PtrType>::Type,
                                      Method, false,
                                      RunnableKind::Idle>::base_type;
template <typename PtrType, typename Method, typename... Storages>
using NonOwningIdleRunnableMethodImpl =
    RunnableMethodImpl<typename RemoveReference<PtrType>::Type, Method, false,
                       RunnableKind::Idle, Storages...>;

// Type aliases for NewIdleRunnableMethodWithTimer.
template <typename PtrType, typename Method>
using NonOwningIdleRunnableMethodWithTimer =
    typename ::nsRunnableMethodTraits<typename RemoveReference<PtrType>::Type,
                                      Method, false,
                                      RunnableKind::IdleWithTimer>::base_type;
template <typename PtrType, typename Method, typename... Storages>
using NonOwningIdleRunnableMethodWithTimerImpl =
    RunnableMethodImpl<typename RemoveReference<PtrType>::Type, Method, false,
                       RunnableKind::IdleWithTimer, Storages...>;

}  // namespace detail

// NewRunnableMethod and friends
//
// Very often in Gecko, you'll find yourself in a situation where you want
// to invoke a method (with or without arguments) asynchronously.  You
// could write a small helper class inheriting from nsRunnable to handle
// all these details, or you could let NewRunnableMethod take care of all
// those details for you.
//
// The simplest use of NewRunnableMethod looks like:
//
//   nsCOMPtr<nsIRunnable> event =
//     mozilla::NewRunnableMethod("description", myObject,
//                                &MyClass::HandleEvent);
//   NS_DispatchToCurrentThread(event);
//
// Statically enforced constraints:
//  - myObject must be of (or implicitly convertible to) type MyClass
//  - MyClass must define AddRef and Release methods
//
// The "description" string should specify a human-readable name for the
// runnable; the provided string is used by various introspection tools
// in the browser.
//
// The created runnable will take a strong reference to `myObject`.  For
// non-refcounted objects, or refcounted objects with unusual refcounting
// requirements, and if and only if you are 110% certain that `myObject`
// will live long enough, you can use NewNonOwningRunnableMethod instead,
// which will, as its name implies, take a non-owning reference.  If you
// find yourself having to use this function, you should accompany your use
// with a proof comment describing why the runnable will not lead to
// use-after-frees.
//
// (If you find yourself writing contorted code to Release() an object
// asynchronously on a different thread, you should use the
// NS_ProxyRelease function.)
//
// Invoking a method with arguments takes a little more care.  The
// natural extension of the above:
//
//   nsCOMPtr<nsIRunnable> event =
//     mozilla::NewRunnableMethod("description", myObject,
//                                &MyClass::HandleEvent,
//                                arg1, arg2, ...);
//
// can lead to security hazards (e.g. passing in raw pointers to refcounted
// objects and storing those raw pointers in the runnable).  We therefore
// require you to specify the storage types used by the runnable, just as
// you would if you were writing out the class by hand:
//
//   nsCOMPtr<nsIRunnable> event =
//     mozilla::NewRunnableMethod<RefPtr<T>, nsTArray<U>>
//         ("description", myObject, &MyClass::HandleEvent, arg1, arg2);
//
// Please note that you do not have to pass the same argument type as you
// specify in the template arguments.  For example, if you want to transfer
// ownership to a runnable, you can write:
//
//   RefPtr<T> ptr = ...;
//   nsTArray<U> array = ...;
//   nsCOMPtr<nsIRunnable> event =
//     mozilla::NewRunnableMethod<RefPtr<T>, nsTArray<U>>
//         ("description", myObject, &MyClass::DoSomething,
//          std::move(ptr), std::move(array));
//
// and there will be no extra AddRef/Release traffic, or copying of the array.
//
// Each type that you specify as a template argument to NewRunnableMethod
// comes with its own style of storage in the runnable and its own style
// of argument passing to the invoked method.  See the comment for
// ParameterStorage above for more details.
//
// If you need to customize the storage type and/or argument passing type,
// you can write your own class to use as a template argument to
// NewRunnableMethod.  If you find yourself having to do that frequently,
// please file a bug in Core::XPCOM about adding the custom type to the
// core code in this file, and/or for custom rules for ParameterStorage
// to select that strategy.
//
// For places that require you to use cancelable runnables, such as
// workers, there's also NewCancelableRunnableMethod and its non-owning
// counterpart.  The runnables returned by these methods additionally
// implement nsICancelableRunnable.
//
// Finally, all of the functions discussed above have additional overloads
// that do not take a `const char*` as their first parameter; you may see
// these in older code.  The `const char*` overload is preferred and
// should be used in new code exclusively.

template <typename PtrType, typename Method>
already_AddRefed<detail::OwningRunnableMethod<PtrType, Method>>
NewRunnableMethod(const char* aName, PtrType&& aPtr, Method aMethod) {
  return do_AddRef(new detail::OwningRunnableMethodImpl<PtrType, Method>(
      aName, std::forward<PtrType>(aPtr), aMethod));
}

template <typename PtrType, typename Method>
already_AddRefed<detail::CancelableRunnableMethod<PtrType, Method>>
NewCancelableRunnableMethod(const char* aName, PtrType&& aPtr, Method aMethod) {
  return do_AddRef(new detail::CancelableRunnableMethodImpl<PtrType, Method>(
      aName, std::forward<PtrType>(aPtr), aMethod));
}

template <typename PtrType, typename Method>
already_AddRefed<detail::IdleRunnableMethod<PtrType, Method>>
NewIdleRunnableMethod(const char* aName, PtrType&& aPtr, Method aMethod) {
  return do_AddRef(new detail::IdleRunnableMethodImpl<PtrType, Method>(
      aName, std::forward<PtrType>(aPtr), aMethod));
}

template <typename PtrType, typename Method>
already_AddRefed<detail::IdleRunnableMethodWithTimer<PtrType, Method>>
NewIdleRunnableMethodWithTimer(const char* aName, PtrType&& aPtr,
                               Method aMethod) {
  return do_AddRef(new detail::IdleRunnableMethodWithTimerImpl<PtrType, Method>(
      aName, std::forward<PtrType>(aPtr), aMethod));
}

template <typename PtrType, typename Method>
already_AddRefed<detail::NonOwningRunnableMethod<PtrType, Method>>
NewNonOwningRunnableMethod(const char* aName, PtrType&& aPtr, Method aMethod) {
  return do_AddRef(new detail::NonOwningRunnableMethodImpl<PtrType, Method>(
      aName, std::forward<PtrType>(aPtr), aMethod));
}

template <typename PtrType, typename Method>
already_AddRefed<detail::NonOwningCancelableRunnableMethod<PtrType, Method>>
NewNonOwningCancelableRunnableMethod(const char* aName, PtrType&& aPtr,
                                     Method aMethod) {
  return do_AddRef(
      new detail::NonOwningCancelableRunnableMethodImpl<PtrType, Method>(
          aName, std::forward<PtrType>(aPtr), aMethod));
}

template <typename PtrType, typename Method>
already_AddRefed<detail::NonOwningIdleRunnableMethod<PtrType, Method>>
NewNonOwningIdleRunnableMethod(const char* aName, PtrType&& aPtr,
                               Method aMethod) {
  return do_AddRef(new detail::NonOwningIdleRunnableMethodImpl<PtrType, Method>(
      aName, std::forward<PtrType>(aPtr), aMethod));
}

template <typename PtrType, typename Method>
already_AddRefed<detail::NonOwningIdleRunnableMethodWithTimer<PtrType, Method>>
NewNonOwningIdleRunnableMethodWithTimer(const char* aName, PtrType&& aPtr,
                                        Method aMethod) {
  return do_AddRef(
      new detail::NonOwningIdleRunnableMethodWithTimerImpl<PtrType, Method>(
          aName, std::forward<PtrType>(aPtr), aMethod));
}

// Similar to NewRunnableMethod. Call like so:
// nsCOMPtr<nsIRunnable> event =
//   NewRunnableMethod<Types,...>(myObject, &MyClass::HandleEvent, myArg1,...);
// 'Types' are the stored type for each argument, see ParameterStorage for
// details.
template <typename... Storages, typename PtrType, typename Method,
          typename... Args>
already_AddRefed<detail::OwningRunnableMethod<PtrType, Method>>
NewRunnableMethod(const char* aName, PtrType&& aPtr, Method aMethod,
                  Args&&... aArgs) {
  static_assert(sizeof...(Storages) == sizeof...(Args),
                "<Storages...> size should be equal to number of arguments");
  return do_AddRef(
      new detail::OwningRunnableMethodImpl<PtrType, Method, Storages...>(
          aName, std::forward<PtrType>(aPtr), aMethod,
          std::forward<Args>(aArgs)...));
}

template <typename... Storages, typename PtrType, typename Method,
          typename... Args>
already_AddRefed<detail::NonOwningRunnableMethod<PtrType, Method>>
NewNonOwningRunnableMethod(const char* aName, PtrType&& aPtr, Method aMethod,
                           Args&&... aArgs) {
  static_assert(sizeof...(Storages) == sizeof...(Args),
                "<Storages...> size should be equal to number of arguments");
  return do_AddRef(
      new detail::NonOwningRunnableMethodImpl<PtrType, Method, Storages...>(
          aName, std::forward<PtrType>(aPtr), aMethod,
          std::forward<Args>(aArgs)...));
}

template <typename... Storages, typename PtrType, typename Method,
          typename... Args>
already_AddRefed<detail::CancelableRunnableMethod<PtrType, Method>>
NewCancelableRunnableMethod(const char* aName, PtrType&& aPtr, Method aMethod,
                            Args&&... aArgs) {
  static_assert(sizeof...(Storages) == sizeof...(Args),
                "<Storages...> size should be equal to number of arguments");
  return do_AddRef(
      new detail::CancelableRunnableMethodImpl<PtrType, Method, Storages...>(
          aName, std::forward<PtrType>(aPtr), aMethod,
          std::forward<Args>(aArgs)...));
}

template <typename... Storages, typename PtrType, typename Method,
          typename... Args>
already_AddRefed<detail::NonOwningCancelableRunnableMethod<PtrType, Method>>
NewNonOwningCancelableRunnableMethod(const char* aName, PtrType&& aPtr,
                                     Method aMethod, Args&&... aArgs) {
  static_assert(sizeof...(Storages) == sizeof...(Args),
                "<Storages...> size should be equal to number of arguments");
  return do_AddRef(
      new detail::NonOwningCancelableRunnableMethodImpl<PtrType, Method,
                                                        Storages...>(
          aName, std::forward<PtrType>(aPtr), aMethod,
          std::forward<Args>(aArgs)...));
}

template <typename... Storages, typename PtrType, typename Method,
          typename... Args>
already_AddRefed<detail::IdleRunnableMethod<PtrType, Method>>
NewIdleRunnableMethod(const char* aName, PtrType&& aPtr, Method aMethod,
                      Args&&... aArgs) {
  static_assert(sizeof...(Storages) == sizeof...(Args),
                "<Storages...> size should be equal to number of arguments");
  return do_AddRef(
      new detail::IdleRunnableMethodImpl<PtrType, Method, Storages...>(
          aName, std::forward<PtrType>(aPtr), aMethod,
          std::forward<Args>(aArgs)...));
}

template <typename... Storages, typename PtrType, typename Method,
          typename... Args>
already_AddRefed<detail::NonOwningIdleRunnableMethod<PtrType, Method>>
NewNonOwningIdleRunnableMethod(const char* aName, PtrType&& aPtr,
                               Method aMethod, Args&&... aArgs) {
  static_assert(sizeof...(Storages) == sizeof...(Args),
                "<Storages...> size should be equal to number of arguments");
  return do_AddRef(
      new detail::NonOwningIdleRunnableMethodImpl<PtrType, Method, Storages...>(
          aName, std::forward<PtrType>(aPtr), aMethod,
          std::forward<Args>(aArgs)...));
}

}  // namespace mozilla

#endif  // XPCOM_GLUE_AVOID_NSPR

// This class is designed to be used when you have an event class E that has a
// pointer back to resource class R.  If R goes away while E is still pending,
// then it is important to "revoke" E so that it does not try use R after R has
// been destroyed.  nsRevocableEventPtr makes it easy for R to manage such
// situations:
//
//   class R;
//
//   class E : public mozilla::Runnable {
//   public:
//     void Revoke() {
//       mResource = nullptr;
//     }
//   private:
//     R *mResource;
//   };
//
//   class R {
//   public:
//     void EventHandled() {
//       mEvent.Forget();
//     }
//   private:
//     nsRevocableEventPtr<E> mEvent;
//   };
//
//   void R::PostEvent() {
//     // Make sure any pending event is revoked.
//     mEvent->Revoke();
//
//     nsCOMPtr<nsIRunnable> event = new E();
//     if (NS_SUCCEEDED(NS_DispatchToCurrentThread(event))) {
//       // Keep pointer to event so we can revoke it.
//       mEvent = event;
//     }
//   }
//
//   NS_IMETHODIMP E::Run() {
//     if (!mResource)
//       return NS_OK;
//     ...
//     mResource->EventHandled();
//     return NS_OK;
//   }
//
template <class T>
class nsRevocableEventPtr {
 public:
  nsRevocableEventPtr() : mEvent(nullptr) {}
  ~nsRevocableEventPtr() { Revoke(); }

  const nsRevocableEventPtr& operator=(RefPtr<T>&& aEvent) {
    if (mEvent != aEvent) {
      Revoke();
      mEvent = std::move(aEvent);
    }
    return *this;
  }

  void Revoke() {
    if (mEvent) {
      mEvent->Revoke();
      mEvent = nullptr;
    }
  }

  void Forget() { mEvent = nullptr; }
  bool IsPending() { return mEvent != nullptr; }
  T* get() { return mEvent; }

 private:
  // Not implemented
  nsRevocableEventPtr(const nsRevocableEventPtr&);
  nsRevocableEventPtr& operator=(const nsRevocableEventPtr&);

  RefPtr<T> mEvent;
};

template <class T>
inline already_AddRefed<T> do_AddRef(nsRevocableEventPtr<T>& aObj) {
  return do_AddRef(aObj.get());
}

/**
 * A simple helper to suffix thread pool name
 * with incremental numbers.
 */
class nsThreadPoolNaming {
 public:
  nsThreadPoolNaming() : mCounter(0) {}

  /**
   * Returns a thread name as "<aPoolName> #<n>" and increments the counter.
   */
  nsCString GetNextThreadName(const nsACString& aPoolName);

  template <size_t LEN>
  nsCString GetNextThreadName(const char (&aPoolName)[LEN]) {
    return GetNextThreadName(nsDependentCString(aPoolName, LEN - 1));
  }

 private:
  mozilla::Atomic<uint32_t> mCounter;

  nsThreadPoolNaming(const nsThreadPoolNaming&) = delete;
  void operator=(const nsThreadPoolNaming&) = delete;
};

/**
 * Thread priority in most operating systems affect scheduling, not IO.  This
 * helper is used to set the current thread to low IO priority for the lifetime
 * of the created object.  You can only use this low priority IO setting within
 * the context of the current thread.
 */
class MOZ_STACK_CLASS nsAutoLowPriorityIO {
 public:
  nsAutoLowPriorityIO();
  ~nsAutoLowPriorityIO();

 private:
  bool lowIOPrioritySet;
#if defined(XP_MACOSX)
  int oldPriority;
#endif
};

void NS_SetMainThread();

// Used only on cooperatively scheduled "main" threads. Causes the thread to be
// considered a main thread and also causes GetCurrentVirtualThread to return
// aVirtualThread.
void NS_SetMainThread(PRThread* aVirtualThread);

// Used only on cooperatively scheduled "main" threads. Causes the thread to no
// longer be considered a main thread. Also causes GetCurrentVirtualThread() to
// return a unique value.
void NS_UnsetMainThread();

/**
 * Return the expiration time of the next timer to run on the current
 * thread.  If that expiration time is greater than aDefault, then
 * return aDefault.  aSearchBound specifies a maximum number of timers
 * to examine to find a timer on the current thread.  If no timer that
 * will run on the current thread is found after examining
 * aSearchBound timers, return the highest seen expiration time as a
 * best effort guess.
 *
 * Timers with either the type nsITimer::TYPE_ONE_SHOT_LOW_PRIORITY or
 * nsITIMER::TYPE_REPEATING_SLACK_LOW_PRIORITY will be skipped when
 * searching for the next expiration time.  This enables timers to
 * have lower priority than callbacks dispatched from
 * nsIThread::IdleDispatch.
 */
extern mozilla::TimeStamp NS_GetTimerDeadlineHintOnCurrentThread(
    mozilla::TimeStamp aDefault, uint32_t aSearchBound);

namespace mozilla {

/**
 * Cooperative thread scheduling is governed by two rules:
 * - Only one thread in the pool of cooperatively scheduled threads runs at a
 *   time.
 * - Thread switching happens at well-understood safe points.
 *
 * In some cases we may want to treat all the threads in a cooperative pool as a
 * single thread, while other parts of the code may want to view them as
 * separate threads. GetCurrentVirtualThread() will return the same value for
 * all threads in a cooperative thread pool. GetCurrentPhysicalThread will
 * return a different value for each thread in the pool.
 *
 * Thread safety assertions are a concrete example where GetCurrentVirtualThread
 * should be used. An object may want to assert that it only can be used on the
 * thread that created it. Such assertions would normally prevent the object
 * from being used on different cooperative threads. However, the object might
 * really only care that it's used atomically. Cooperative scheduling guarantees
 * that it will be (assuming we don't yield in the middle of modifying the
 * object). So we can weaken the assertion to compare the virtual thread the
 * object was created on to the virtual thread on which it's being used. This
 * assertion allows the object to be used across threads in a cooperative thread
 * pool while preventing accesses across preemptively scheduled threads (which
 * would be unsafe).
 */

// Returns the PRThread on which this code is running.
PRThread* GetCurrentPhysicalThread();

// Returns a "virtual" PRThread that should only be used for comparison with
// other calls to GetCurrentVirtualThread. Two threads in the same cooperative
// thread pool will return the same virtual thread. Threads that are not
// cooperatively scheduled will have their own unique virtual PRThread (which
// will be equal to their physical PRThread).
//
// The return value of GetCurrentVirtualThread() is guaranteed not to change
// throughout the lifetime of a thread.
//
// Note that the original main thread (the first one created in the process) is
// considered as part of the pool of cooperative threads, so the return value of
// GetCurrentVirtualThread() for this thread (throughout its lifetime, even
// during shutdown) is the same as the return value from any other thread in the
// cooperative pool.
PRThread* GetCurrentVirtualThread();

// These functions return event targets that can be used to dispatch to the
// current or main thread. They can also be used to test if you're on those
// threads (via IsOnCurrentThread). These functions should be used in preference
// to the nsIThread-based NS_Get{Current,Main}Thread functions since they will
// return more useful answers in the case of threads sharing an event loop.

nsIEventTarget* GetCurrentThreadEventTarget();

nsIEventTarget* GetMainThreadEventTarget();

// These variants of the above functions assert that the given thread has a
// serial event target (i.e., that it's not part of a thread pool) and returns
// that.

nsISerialEventTarget* GetCurrentThreadSerialEventTarget();

nsISerialEventTarget* GetMainThreadSerialEventTarget();

// Returns the number of CPUs, like PR_GetNumberOfProcessors, except
// that it can return a cached value on platforms where sandboxing
// would prevent reading the current value (currently Linux).  CPU
// hotplugging is uncommon, so this is unlikely to make a difference
// in practice.
size_t GetNumberOfProcessors();

}  // namespace mozilla

#endif  // nsThreadUtils_h__