gecko-dev/dom/clients/manager/ClientThing.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_dom_ClientThing_h
#define _mozilla_dom_ClientThing_h

#include "nsTArray.h"

namespace mozilla::dom {

// Base class representing various Client "things" such as ClientHandle,
// ClientSource, and ClientManager.  Currently it provides a common set
// of code for handling activation and shutdown of IPC actors.
template <typename ActorType>
class ClientThing {
#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
  static const uint32_t kMagic1 = 0xC9FE2C9C;
  static const uint32_t kMagic2 = 0x832072D4;
#endif

  ActorType* mActor;
#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
  uint32_t mMagic1;
  uint32_t mMagic2;
#endif
  bool mShutdown;

 protected:
  ClientThing()
      : mActor(nullptr)
#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
        ,
        mMagic1(kMagic1),
        mMagic2(kMagic2)
#endif
        ,
        mShutdown(false) {
  }

  ~ClientThing() {
    AssertIsValid();
    ShutdownThing();
#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
    mMagic1 = 0;
    mMagic2 = 0;
#endif
  }

  void AssertIsValid() const {
    MOZ_DIAGNOSTIC_ASSERT(mMagic1 == kMagic1);
    MOZ_DIAGNOSTIC_ASSERT(mMagic2 == kMagic2);
  }

  // Return the current actor.
  ActorType* GetActor() const {
    AssertIsValid();
    return mActor;
  }

  // Returns true if ShutdownThing() has been called.
  bool IsShutdown() const {
    AssertIsValid();
    return mShutdown;
  }

  // Conditionally execute the given callable based on the current state.
  template <typename Callable>
  void MaybeExecute(
      const Callable& aSuccess, const std::function<void()>& aFailure = [] {}) {
    AssertIsValid();
    if (mShutdown) {
      aFailure();
      return;
    }
    MOZ_DIAGNOSTIC_ASSERT(mActor);
    aSuccess(mActor);
  }

  // Attach activate the thing by attaching its underlying IPC actor.  This
  // will make the thing register as the actor's owner as well.  The actor
  // must call RevokeActor() to clear this weak back reference before its
  // destroyed.
  void ActivateThing(ActorType* aActor) {
    AssertIsValid();
    MOZ_DIAGNOSTIC_ASSERT(aActor);
    MOZ_DIAGNOSTIC_ASSERT(!mActor);
    MOZ_DIAGNOSTIC_ASSERT(!mShutdown);
    mActor = aActor;
    mActor->SetOwner(this);
  }

  // Start destroying the underlying actor and disconnect the thing.
  void ShutdownThing() {
    AssertIsValid();
    if (mShutdown) {
      return;
    }
    mShutdown = true;

    // If we are shutdown before the actor, then clear the weak references
    // between the actor and the thing.
    if (mActor) {
      mActor->RevokeOwner(this);
      mActor->MaybeStartTeardown();
      mActor = nullptr;
    }

    OnShutdownThing();
  }

  // Allow extending classes to take action when shutdown.
  virtual void OnShutdownThing() {
    // by default do nothing
  }

 public:
  // Clear the weak references between the thing and its IPC actor.
  void RevokeActor(ActorType* aActor) {
    AssertIsValid();
    MOZ_DIAGNOSTIC_ASSERT(mActor);
    MOZ_DIAGNOSTIC_ASSERT(mActor == aActor);
    mActor->RevokeOwner(this);
    mActor = nullptr;

    // Also consider the ClientThing shutdown.  We simply set the flag
    // instead of calling ShutdownThing() to avoid calling MaybeStartTeardown()
    // on the destroyed actor.
    mShutdown = true;

    OnShutdownThing();
  }
};

}  // namespace mozilla::dom

#endif  // _mozilla_dom_ClientThing_h