/* -*- 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_GFX_TASKSCHEDULER_H_

#define MOZILLA_GFX_TASKSCHEDULER_H_

#include "mozilla/RefPtr.h"

#include "mozilla/gfx/Types.h"

#include "mozilla/RefCounted.h"

#ifdef WIN32

#include "mozilla/gfx/JobScheduler_win32.h"

#else

#include "mozilla/gfx/JobScheduler_posix.h"

#endif

#include <vector>

namespace mozilla {

namespace gfx {

class MultiThreadedJobQueue;

class SyncObject;

class WorkerThread;

class JobScheduler {

public:

  /// Return one of the queues that the drawing worker threads pull from, chosen

  /// pseudo-randomly.

  static MultiThreadedJobQueue* GetDrawingQueue()

  {

    return sSingleton->mDrawingQueues[

      sSingleton->mNextQueue++ % sSingleton->mDrawingQueues.size()

    ];

  }

  /// Return one of the queues that the drawing worker threads pull from with a

  /// hash to choose the queue.

  ///

  /// Calling this function several times with the same hash will yield the same queue.

  static MultiThreadedJobQueue* GetDrawingQueue(uint32_t aHash)

  {

    return sSingleton->mDrawingQueues[

      aHash % sSingleton->mDrawingQueues.size()

    ];

  }

  /// Return the task queue associated to the worker the task is pinned to if

  /// the task is pinned to a worker, or a random queue.

  static MultiThreadedJobQueue* GetQueueForJob(Job* aJob);

  /// Initialize the task scheduler with aNumThreads worker threads for drawing

  /// and aNumQueues task queues.

  ///

  /// The number of threads must be superior or equal to the number of queues

  /// (since for now a worker thread only pulls from one queue).

  static bool Init(uint32_t aNumThreads, uint32_t aNumQueues);

  /// Shut the scheduler down.

  ///

  /// This will block until worker threads are joined and deleted.

  static void ShutDown();

  /// Returns true if there is a successfully initialized JobScheduler singleton.

  static bool IsEnabled() { return !!sSingleton; }

  /// Submit a task buffer to its associated queue.

  ///

  /// The caller looses ownership of the task buffer.

  static void SubmitJob(Job* aJobs);

  /// Convenience function to block the current thread until a given SyncObject

  /// is in the signaled state.

  ///

  /// The current thread will first try to steal jobs before blocking.

  static void Join(SyncObject* aCompletionSync);

  /// Process commands until the command buffer needs to block on a sync object,

  /// completes, yields, or encounters an error.

  ///

  /// Can be used on any thread. Worker threads basically loop over this, but the

  /// main thread can also dequeue pending task buffers and process them alongside

  /// the worker threads if it is about to block until completion anyway.

  ///

  /// The caller looses ownership of the task buffer.

  static JobStatus ProcessJob(Job* aJobs);

protected:

  static JobScheduler* sSingleton;

  // queues of Job that are ready to be processed

  std::vector<MultiThreadedJobQueue*> mDrawingQueues;

  std::vector<WorkerThread*> mWorkerThreads;

  Atomic<uint32_t> mNextQueue;

};

/// Jobs are not reference-counted because they don't have shared ownership.

/// The ownership of tasks can change when they are passed to certain methods

/// of JobScheduler and SyncObject. See the docuumentaion of these classes.

class Job {

public:

  Job(SyncObject* aStart, SyncObject* aCompletion, WorkerThread* aThread = nullptr);

  virtual ~Job();

  virtual JobStatus Run() = 0;

  /// For use in JobScheduler::SubmitJob. Don't use it anywhere else.

  //already_AddRefed<SyncObject> GetAndResetStartSync();

  SyncObject* GetStartSync() { return mStartSync; }

  bool IsPinnedToAThread() const { return !!mPinToThread; }

  WorkerThread* GetWorkerThread() { return mPinToThread; }

protected:

  // An intrusive linked list of tasks waiting for a sync object to enter the

  // signaled state. When the task is not waiting for a sync object, mNextWaitingJob

  // should be null. This is only accessed from the thread that owns the task.

  Job* mNextWaitingJob;

  RefPtr<SyncObject> mStartSync;

  RefPtr<SyncObject> mCompletionSync;

  WorkerThread* mPinToThread;

  friend class SyncObject;

};

class EventObject;

/// This task will set an EventObject.

///

/// Typically used as the final task, so that the main thread can block on the

/// corresponfing EventObject until all of the tasks are processed.

class SetEventJob : public Job

{

public:

  explicit SetEventJob(EventObject* aEvent,

                        SyncObject* aStart, SyncObject* aCompletion = nullptr,

                        WorkerThread* aPinToWorker = nullptr);

  ~SetEventJob();

  JobStatus Run() override;

  EventObject* GetEvent() { return mEvent; }

protected:

  RefPtr<EventObject> mEvent;

};

/// A synchronization object that can be used to express dependencies and ordering between

/// tasks.

///

/// Jobs can register to SyncObjects in order to asynchronously wait for a signal.

/// In practice, Job objects usually start with a sync object (startSyc) and end

/// with another one (completionSync).

/// a Job never gets processed before its startSync is in the signaled state, and

/// signals its completionSync as soon as it finishes. This is how dependencies

/// between tasks is expressed.

class SyncObject final : public external::AtomicRefCounted<SyncObject> {

public:

  MOZ_DECLARE_REFCOUNTED_TYPENAME(SyncObject)

  /// Create a synchronization object.

  ///

  /// aNumPrerequisites represents the number of times the object must be signaled

  /// before actually entering the signaled state (in other words, it means the

  /// number of dependencies of this sync object).

  ///

  /// Explicitly specifying the number of prerequisites when creating sync objects

  /// makes it easy to start scheduling some of the prerequisite tasks while

  /// creating the others, which is how we typically use the task scheduler.

  /// Automatically determining the number of prerequisites using Job's constructor

  /// brings the risk that the sync object enters the signaled state while we

  /// are still adding prerequisites which is hard to fix without using muteces.

  explicit SyncObject(uint32_t aNumPrerequisites = 1);

  ~SyncObject();

  /// Attempt to register a task.

  ///

  /// If the sync object is already in the signaled state, the buffer is *not*

  /// registered and the sync object does not take ownership of the task.

  /// If the object is not yet in the signaled state, it takes ownership of

  /// the task and places it in a list of pending tasks.

  /// Pending tasks will not be processed by the worker thread.

  /// When the SyncObject reaches the signaled state, it places the pending

  /// tasks back in the available buffer queue, so that they can be

  /// scheduled again.

  ///

  /// Returns true if the SyncOject is not already in the signaled state.

  /// This means that if this method returns true, the SyncObject has taken

  /// ownership of the Job.

  bool Register(Job* aJob);

  /// Signal the SyncObject.

  ///

  /// This decrements an internal counter. The sync object reaches the signaled

  /// state when the counter gets to zero.

  void Signal();

  /// Returns true if mSignals is equal to zero. In other words, returns true

  /// if all prerequisite tasks have already signaled the sync object.

  bool IsSignaled();

  /// Asserts that the number of added prerequisites is equal to the number

  /// specified in the constructor (does nothin in release builds).

  void FreezePrerequisites();

private:

  // Called by Job's constructor

  void AddSubsequent(Job* aJob);

  void AddPrerequisite(Job* aJob);

  void AddWaitingJob(Job* aJob);

  void SubmitWaitingJobs();

  Atomic<int32_t> mSignals;

  Atomic<Job*> mFirstWaitingJob;

#ifdef DEBUG

  uint32_t mNumPrerequisites;

  Atomic<uint32_t> mAddedPrerequisites;

#endif

  friend class Job;

  friend class JobScheduler;

};

/// Base class for worker threads.

class WorkerThread

{

public:

  static WorkerThread* Create(MultiThreadedJobQueue* aJobQueue);

  virtual ~WorkerThread() {}

  void Run();

  MultiThreadedJobQueue* GetJobQueue() { return mQueue; }

protected:

  explicit WorkerThread(MultiThreadedJobQueue* aJobQueue);

  virtual void SetName(const char* aName) {}

  MultiThreadedJobQueue* mQueue;

};

} // namespace

} // namespace

#endif