Quelle WorkerRef.h Sprache: C

/* -*- 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_workers_WorkerRef_h
#define mozilla_dom_workers_WorkerRef_h

#include "mozilla/dom/WorkerStatus.h"
#include "mozilla/MoveOnlyFunction.h"
#include "mozilla/RefPtr.h"
#include "nsISupports.h"
#include "nsTString.h"

#ifdef DEBUG
#  include "mozilla/Mutex.h"
#endif

namespace mozilla::dom {

/*
* If you want to play with a DOM Worker, you must know that it can go away
* at any time if nothing prevents its shutting down. This documentation helps
* to understand how to play with DOM Workers correctly.
*
* There are several reasons why a DOM Worker could go away. Here is the
* complete list:
*
* a. GC/CC - If the DOM Worker thread is idle and the Worker object is garbage
*    collected, it goes away.
* b. The worker script can call self.close()
* c. The Worker object calls worker.terminate()
* d. Firefox is shutting down.
*
* When a DOM Worker goes away, it does several steps. See more in
* WorkerStatus.h. The DOM Worker thread will basically stop scheduling
* WorkerRunnables, and eventually WorkerControlRunnables. But if there is
* something preventing the shutting down, it will always possible to dispatch
* WorkerControlRunnables.  Of course, at some point, the worker _must_ be
* released, otherwise firefox will leak it and the browser shutdown will hang.
*
* WeakWorkerRef is a refcounted, NON thread-safe object.
*
* From this object, you can obtain a WorkerPrivate, calling
* WeakWorkerRef::GetPrivate(). It returns nullptr if the worker is shutting
* down or if it is already gone away.
*
* If you want to know when a DOM Worker starts the shutting down procedure,
* pass a callback to the mozilla::dom::WeakWorkerRef::Create() method.
* Your function will be called. Note that _after_ the callback,
* WeakWorkerRef::GetPrivate() will return nullptr.
*
* How to keep a DOM Worker alive?
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* If you need to keep the worker alive, you must use StrongWorkerRef.
* You can have this refcounted, NON thread-safe object, calling
* mozilla::dom::StrongWorkerRef::Create(WorkerPrivate* aWorkerPrivate);
*
* If you have a StrongWorkerRef:
* a. the DOM Worker is kept alive.
* b. you can have access to the WorkerPrivate, calling: Private().
* c. WorkerControlRunnable can be dispatched.
*
* Note that the DOM Worker shutdown can start at any time, but having a
* StrongWorkerRef prevents the full shutdown. Also with StrongWorkerRef, you
* can pass a callback when calling mozilla::dom::StrongWorkerRef::Create().
*
* When the DOM Worker shutdown starts, WorkerRunnable cannot be dispatched
* anymore. At this point, you should dispatch WorkerControlRunnable just to
* release resources.
*
* How to have a thread-safe DOM Worker reference?
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* Sometimes you need to play with threads and you need a thread-safe worker
* reference. ThreadSafeWorkerRef is what you want.
*
* Just because this object can be sent to different threads, we don't allow the
* setting of a callback. It would be confusing.
*
* ThreadSafeWorkerRef can be destroyed in any thread. Internally it keeps a
* reference to its StrongWorkerRef creator and this ref will be dropped on the
* correct thread when the ThreadSafeWorkerRef is deleted.
*
* IPC WorkerRef
* ~~~~~~~~~~~~~
*
* IPDL protocols require a correct shutdown sequence. Because of this, they
* need a special configuration:
* 1. they need to be informed when the Worker starts the shutting down
* 2. they don't want to prevent the shutdown
* 3. but at the same time, they need to block the shutdown until the WorkerRef
*    is not longer alive.
*
* Point 1 is a standard feature of WorkerRef; point 2 is similar to
* WeakWorkerRef; point 3 is similar to StrongWorkerRef.
*
* You can create a special IPC WorkerRef using this static method:
* mozilla::dom::IPCWorkerRef::Create(WorkerPrivate* aWorkerPrivate,
*                                    const char* * aName);
*/

class WorkerPrivate;
class StrongWorkerRef;
class ThreadSafeWorkerRef;

#ifdef DEBUG  // In debug mode, provide a way for clients to annotate WorkerRefs
#  define SET_WORKERREF_DEBUG_STATUS(workerref, str) \
    ((workerref)->DebugSetWorkerRefStatus(str))
#  define GET_WORKERREF_DEBUG_STATUS(workerref) \
    ((workerref)->DebugGetWorkerRefStatus())
#else
#  define SET_WORKERREF_DEBUG_STATUS(workerref, str) (void())
#  define GET_WORKERREF_DEBUG_STATUS(workerref) (EmptyCString())
#endif

class WorkerRef {
  friend class WorkerPrivate;

public:
  NS_INLINE_DECL_REFCOUNTING(WorkerRef)

#ifdef DEBUG
  mutable Mutex mDebugMutex;
  nsCString mDebugStatus MOZ_GUARDED_BY(mDebugMutex);

  void DebugSetWorkerRefStatus(const nsCString& aStatus) {
    MutexAutoLock lock(mDebugMutex);
    mDebugStatus = aStatus;
  }

  const nsCString DebugGetWorkerRefStatus() const {
    MutexAutoLock lock(mDebugMutex);
    return mDebugStatus;
  }
#endif

protected:
  WorkerRef(WorkerPrivate* aWorkerPrivate, const char* aName,
            bool aIsPreventingShutdown);
  virtual ~WorkerRef();

  virtual void Notify();

  bool HoldWorker(WorkerStatus aStatus);
  void ReleaseWorker();

  bool IsPreventingShutdown() const { return mIsPreventingShutdown; }

  const char* Name() const { return mName; }

  WorkerPrivate* mWorkerPrivate;

  MoveOnlyFunction<void()> mCallback;
  const char* const mName;
  const bool mIsPreventingShutdown;

  // True if this WorkerRef has been added to a WorkerPrivate.
  bool mHolding;
};

class WeakWorkerRef final : public WorkerRef {
public:
  static already_AddRefed<WeakWorkerRef> Create(
      WorkerPrivate* aWorkerPrivate,
      MoveOnlyFunction<void()>&& aCallback = nullptr);

  WorkerPrivate* GetPrivate() const;

  // This can be called on any thread. It's racy and, in general, the wrong
  // choice.
  WorkerPrivate* GetUnsafePrivate() const;

private:
  friend class ThreadSafeWeakWorkerRef;

  explicit WeakWorkerRef(WorkerPrivate* aWorkerPrivate);
  ~WeakWorkerRef();

  void Notify() override;
};

class StrongWorkerRef final : public WorkerRef {
public:
  static already_AddRefed<StrongWorkerRef> Create(
      WorkerPrivate* aWorkerPrivate, const char* aName,
      MoveOnlyFunction<void()>&& aCallback = nullptr);

  // This function creates a StrongWorkerRef even when in the Canceling state of
  // the worker's lifecycle. It's intended to be used by system code, e.g. code
  // that needs to perform IPC.
  //
  // This method should only be used in cases where the StrongWorkerRef will be
  // used for an extremely bounded duration that cannot be impacted by content.
  // For example, IPCStreams use this type of ref in order to immediately
  // migrate to an actor on another thread. Whether the IPCStream ever actually
  // is streamed does not matter; the ref will be dropped once the new actor is
  // created. For this reason, this method does not take a callback. It's
  // expected and required that callers will drop the reference when they are
  // done.
  static already_AddRefed<StrongWorkerRef> CreateForcibly(
      WorkerPrivate* aWorkerPrivate, const char* aName);

  WorkerPrivate* Private() const;

private:
  friend class WeakWorkerRef;
  friend class ThreadSafeWorkerRef;

  static already_AddRefed<StrongWorkerRef> CreateImpl(
      WorkerPrivate* aWorkerPrivate, const char* aName,
      WorkerStatus aFailStatus);

  StrongWorkerRef(WorkerPrivate* aWorkerPrivate, const char* aName);
  ~StrongWorkerRef();
};

class ThreadSafeWorkerRef final {
public:
  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ThreadSafeWorkerRef)

  explicit ThreadSafeWorkerRef(StrongWorkerRef* aRef);

  WorkerPrivate* Private() const;

#ifdef DEBUG
  RefPtr<StrongWorkerRef>& Ref() { return mRef; }
#endif

private:
  friend class StrongWorkerRef;

  ~ThreadSafeWorkerRef();

  RefPtr<StrongWorkerRef> mRef;
};

class IPCWorkerRef final : public WorkerRef {
public:
  static already_AddRefed<IPCWorkerRef> Create(
      WorkerPrivate* aWorkerPrivate, const char* aName,
      MoveOnlyFunction<void()>&& aCallback = nullptr);

  WorkerPrivate* Private() const;

  void SetActorCount(uint32_t aCount);

private:
  IPCWorkerRef(WorkerPrivate* aWorkerPrivate, const char* aName);
  ~IPCWorkerRef();

  // The count of background actors which binding with this IPCWorkerRef.
  uint32_t mActorCount;
};

// Template class to keep an Actor pointer, as a raw pointer, in a ref-counted
// way when passed to lambdas.
template <class ActorPtr>
class IPCWorkerRefHelper final {
public:
  NS_INLINE_DECL_REFCOUNTING(IPCWorkerRefHelper);

  explicit IPCWorkerRefHelper(ActorPtr* aActor) : mActor(aActor) {}

  ActorPtr* Actor() const { return mActor; }

private:
  ~IPCWorkerRefHelper() = default;

  // Raw pointer
  ActorPtr* mActor;
};

}  // namespace mozilla::dom

#endif /* mozilla_dom_workers_WorkerRef_h */

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