gecko-dev/xpcom/threads/SchedulerGroup.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 mozilla_SchedulerGroup_h
#define mozilla_SchedulerGroup_h

#include "mozilla/AlreadyAddRefed.h"
#include "mozilla/TaskCategory.h"
#include "mozilla/TimeStamp.h"
#include "nsCOMPtr.h"
#include "nsISupportsImpl.h"
#include "nsThreadUtils.h"

class nsIEventTarget;
class nsIRunnable;
class nsISerialEventTarget;

namespace mozilla {
class AbstractThread;
namespace dom {
class TabGroup;
}

#define NS_SCHEDULERGROUPRUNNABLE_IID \
{ 0xd31b7420, 0x872b, 0x4cfb, \
  { 0xa9, 0xc6, 0xae, 0x4c, 0x0f, 0x06, 0x36, 0x74 } }

// The "main thread" in Gecko will soon be a set of cooperatively scheduled
// "fibers". Global state in Gecko will be partitioned into a series of "groups"
// (with roughly one group per tab). Runnables will be annotated with the set of
// groups that they touch. Two runnables may run concurrently on different
// fibers as long as they touch different groups.
//
// A SchedulerGroup is an abstract class to represent a "group". Essentially the
// only functionality offered by a SchedulerGroup is the ability to dispatch
// runnables to the group. TabGroup, DocGroup, and SystemGroup are the concrete
// implementations of SchedulerGroup.
class SchedulerGroup
{
public:
  SchedulerGroup();

  NS_INLINE_DECL_PURE_VIRTUAL_REFCOUNTING

  // This method returns true if all members of the "group" are in a
  // "background" state.
  virtual bool IsBackground() const { return false; }

  class MOZ_STACK_CLASS AutoProcessEvent final {
  public:
    AutoProcessEvent();
    ~AutoProcessEvent();

  private:
    SchedulerGroup* mPrevRunningDispatcher;
  };

  // This function returns true if it's currently safe to run code associated
  // with this SchedulerGroup. It will return true either if we're inside an
  // unlabeled runnable or if we're inside a runnable labeled with this
  // SchedulerGroup.
  bool IsSafeToRun() const
  {
    return !sRunningDispatcher || mAccessValid;
  }

  // Ensure that it's valid to access the TabGroup at this time.
  void ValidateAccess() const
  {
    MOZ_ASSERT(IsSafeToRun());
  }

  class Runnable final : public mozilla::Runnable
  {
  public:
    Runnable(already_AddRefed<nsIRunnable>&& aRunnable,
             SchedulerGroup* aGroup);

    SchedulerGroup* Group() const { return mGroup; }

    NS_IMETHOD GetName(nsACString& aName) override;

    bool IsBackground() const { return mGroup->IsBackground(); }

    NS_DECL_ISUPPORTS_INHERITED
    NS_DECL_NSIRUNNABLE

    NS_DECLARE_STATIC_IID_ACCESSOR(NS_SCHEDULERGROUPRUNNABLE_IID);

 private:
    ~Runnable() = default;

    nsCOMPtr<nsIRunnable> mRunnable;
    RefPtr<SchedulerGroup> mGroup;
  };
  friend class Runnable;

  bool* GetValidAccessPtr() { return &mAccessValid; }

  virtual nsresult Dispatch(const char* aName,
                            TaskCategory aCategory,
                            already_AddRefed<nsIRunnable>&& aRunnable);

  virtual nsISerialEventTarget* EventTargetFor(TaskCategory aCategory) const;

  // Must always be called on the main thread. The returned AbstractThread can
  // always be used off the main thread.
  AbstractThread* AbstractMainThreadFor(TaskCategory aCategory);

  // This method performs a safe cast. It returns null if |this| is not of the
  // requested type.
  virtual dom::TabGroup* AsTabGroup() { return nullptr; }

  static nsresult UnlabeledDispatch(const char* aName,
                                    TaskCategory aCategory,
                                    already_AddRefed<nsIRunnable>&& aRunnable);

  static void MarkVsyncReceived();

  static void MarkVsyncRan();

protected:
  // Implementations are guaranteed that this method is called on the main
  // thread.
  virtual AbstractThread* AbstractMainThreadForImpl(TaskCategory aCategory);

  // Helper method to create an event target specific to a particular TaskCategory.
  virtual already_AddRefed<nsISerialEventTarget>
  CreateEventTargetFor(TaskCategory aCategory);

  // Given an event target returned by |dispatcher->CreateEventTargetFor|, this
  // function returns |dispatcher|.
  static SchedulerGroup* FromEventTarget(nsIEventTarget* aEventTarget);

  nsresult LabeledDispatch(const char* aName,
                           TaskCategory aCategory,
                           already_AddRefed<nsIRunnable>&& aRunnable);

  void CreateEventTargets(bool aNeedValidation);

  // Shuts down this dispatcher. If aXPCOMShutdown is true, invalidates this
  // dispatcher.
  void Shutdown(bool aXPCOMShutdown);

  enum ValidationType {
    StartValidation,
    EndValidation,
  };
  void SetValidatingAccess(ValidationType aType);

  static SchedulerGroup* sRunningDispatcher;
  bool mAccessValid;

  nsCOMPtr<nsISerialEventTarget> mEventTargets[size_t(TaskCategory::Count)];
  RefPtr<AbstractThread> mAbstractThreads[size_t(TaskCategory::Count)];
};

NS_DEFINE_STATIC_IID_ACCESSOR(SchedulerGroup::Runnable, NS_SCHEDULERGROUPRUNNABLE_IID);

} // namespace mozilla

#endif // mozilla_SchedulerGroup_h