workunit.h

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// The DAGFrameScheduler is a Multi-Threaded lock free and wait free scheduling library.
// © Copyright 2010 - 2014 BlackTopp Studios Inc.
/* This file is part of The DAGFrameScheduler.

    The DAGFrameScheduler is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    The DAGFrameScheduler is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with The DAGFrameScheduler.  If not, see <http://www.gnu.org/licenses/>.
*/
/* The original authors have included a copy of the license specified above in the
   'doc' folder. See 'gpl.txt'
*/
/* We welcome the use of the DAGFrameScheduler to anyone, including companies who wish to
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   Joseph Toppi - toppij@gmail.com
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*/
#ifndef _workunit_h
#define _workunit_h

#include "datatypes.h"

#if !defined(SWIG) || defined(SWIG_THREADING) // Do not read when in swig and not in the threading module
#include "framescheduler.h"
#include "mutex.h"
#include "rollingaverage.h"
#include "threadingenumerations.h"
#include "thread.h"
#include "workunitkey.h"
#endif

/// @file
/// @brief This file has the definition of the workunit.

namespace Mezzanine
{
    namespace Threading
    {
        /// @brief Interface of a WorkUnit. This represents on piece of work through time.
        /// @details This has no real substance, use the DefaultWorkUnit class is you
        /// want to inherit from something ready for easy integration. Implement this
        /// if you want to make heavy changes to the algorithm or maximize performance.
        class MEZZ_LIB iWorkUnit
        {
            public:
                /////////////////////////////////////////////////////////////////////////////////////////////
                // Work with the dependents as in what WorkUnits must not start until this finishes.

                /// @brief This returns the count workunits that depend on this work unit.
                /// @param SchedulerToCount The @ref FrameScheduler has a cache of this data, it is impossible to calculate without the complete list of WorkUnits on it either.
                /// @details Because Dependents are not tracked this iterates over entry in the FrameScheduler it is passed.
                /// @return A Whole is returned containing the count.
                virtual Whole GetDependentCount(FrameScheduler &SchedulerToCount) = 0;


                /////////////////////////////////////////////////////////////////////////////////////////////
                // Work with the dependencies as in what must finish before we can run this work unit.

                /// @brief This is used to iterate of all the dependencies.
                /// @param Index The 0 based index of the dependency you are trying to retrieve. No ordering is guaranteed, just that counting from 0 to @ref GetImmediateDependencyCount() with access each iWorkUnit once.
                /// @return A pointer to an iWorkUnit.
                virtual iWorkUnit* GetDependency(Whole Index) const = 0;

                /// @brief Get the amount of dependencies that directly count on this for access purposes.
                /// @return The amount of accessable WorkUnit from this WorkUnits dependency list.
                virtual Whole GetImmediateDependencyCount() const = 0;

                /// @brief How many other WorkUnits does this one depend on?
                /// @details This is what the @ref FrameScheduler uses to calculate the
                /// sorting order of WorkUnits. In the default implmentation it counts
                /// some units twice if they depend on this WorkUnit through Multiple
                /// dependency chains.
                /// @return A Whole containing the answer.
                virtual Whole GetDependencyCount() const = 0;

                /// @brief Force this WorkUnit to Start after another has completed.
                /// @param NewDependency The WorkUnit that must start after this one has completed.
                /// @warning Changing this outside the schedule, once the scheduler has started can cause undefined behavior.
                virtual void AddDependency(iWorkUnit* NewDependency) = 0;

                /// @brief Remove a dependency.
                /// @param RemoveDependency A pointer to the WorkUnit to remove as a dependency.
                virtual void RemoveDependency(iWorkUnit* RemoveDependency) = 0;

                /// @brief Drop any information about what work units this one depends on.
                virtual void ClearDependencies() = 0;

                /// @brief Check if this WorkUnit could concievably run right now.
                /// @return This returns true if all of this WorkUnits dependencies have completed execution and false otherwise.
                virtual bool IsEveryDependencyComplete() = 0;


                /////////////////////////////////////////////////////////////////////////////////////////////
                // Work with the ownership and RunningState

                /// @brief Attempts to atomically start the work unit in the current thread.
                /// @return Returns RunningState::Starting if this thread was able to gain ownership and start the workunit, returns RunningState::NotStarted otherwise.
                virtual RunningState TakeOwnerShip() = 0;

                /// @brief Retrieves the current RunningState of the thread.
                /// @return A RunningState that indicates if the thread is running, started, etc... This information can be changed at any time and should be considered stale immediately after retrieval.
                virtual RunningState GetRunningState() const = 0;

                /// @brief This resets the running state and takes any further action required to use the WorkUnit again.
                virtual void PrepareForNextFrame() = 0;


                /////////////////////////////////////////////////////////////////////////////////////////////
                // Work with the preformance log

                /// @brief Get the internal rolling average for querying.
                /// @return A whole that represents this WorkUnits Performance.
                virtual Whole GetPerformance() const = 0;


                /////////////////////////////////////////////////////////////////////////////////////////////
                // Deciding when to and doing the work

                /// @brief This tracks work unit metadata, then calls DoWork.
                /// @param CurrentThreadStorage The @ref ThreadSpecificStorage that this WorkUnit will operate with when executing.
                virtual void operator() (DefaultThreadSpecificStorage::Type& CurrentThreadStorage) = 0;

                /// @brief Get the sorting metadata.
                /// @param SchedulerToCount This uses the metadata on the @ref FrameScheduler to generate the Dependency listing required.
                /// @return A WorkUnitKey suitable for sorting this workunit.
                virtual WorkUnitKey GetSortingKey(FrameScheduler &SchedulerToCount) = 0;

                /// @brief WorkUnits Must implement these to do the work.
                virtual void DoWork(DefaultThreadSpecificStorage::Type& CurrentThreadStorage) = 0;

                /// @brief Virtual destructor.
                virtual ~iWorkUnit(){}
        };//iWorkUnit


        /// @brief Default implementation of WorkUnit. This represents on piece of work through time.
        class MEZZ_LIB DefaultWorkUnit : public iWorkUnit
        {
                /////////////////////////////////////////////////////////////////////////////////////////////
                // Data Members
            protected:
                /// @brief A collection of of workunits that must be complete before this one can start.
                std::vector<iWorkUnit*> Dependencies;

                /// @brief A rolling average of execution times.
                DefaultRollingAverage<Whole>::Type PerformanceLog;

                /// @brief This controls do work with this after it has.
                Int32 CurrentRunningState;

                /////////////////////////////////////////////////////////////////////////////////////////////
                // The Simple Stuff
            private:
                /// @brief Remove Copy constructor, Copying a work unit does not make sense, it breaks scheduling, made private.
                DefaultWorkUnit(const DefaultWorkUnit&);

                /// @brief Assignment operator, Assignment on a WorkUnit Does Not make sense, it breaks scheduling, made private.
                DefaultWorkUnit& operator=(DefaultWorkUnit& Unused);

            public:
#ifndef SWIG
                /// @brief Simple constructor.
                DefaultWorkUnit();
#endif
                /// @brief Virtual destructor, doesn't actually do much.
                virtual ~DefaultWorkUnit();

                /////////////////////////////////////////////////////////////////////////////////////////////
                // Work with the dependents as in what must not start until this finishes.
            public:
                virtual Whole GetDependentCount(FrameScheduler &SchedulerToCount);

                /////////////////////////////////////////////////////////////////////////////////////////////
                // Work with the dependents as in what WorkUnits must not start until this finishes.
            public:
                virtual iWorkUnit* GetDependency(Whole Index) const;

                virtual Whole GetImmediateDependencyCount() const;

                virtual Whole GetDependencyCount() const;

            public:
                virtual void AddDependency(iWorkUnit* NewDependency);

                virtual void RemoveDependency(iWorkUnit* RemoveDependency);

                virtual void ClearDependencies();

                virtual bool IsEveryDependencyComplete();

                /////////////////////////////////////////////////////////////////////////////////////////////
                // Work with the ownership and RunningState
            public:
                virtual RunningState TakeOwnerShip();

                virtual RunningState GetRunningState() const;

                virtual void PrepareForNextFrame();

                /////////////////////////////////////////////////////////////////////////////////////////////
                // Work with the performance log
            public:
                virtual Whole GetPerformance() const;

                /// @brief Get the internal rolling average for querying.
                /// @return A const reference to the internal Rolling Average.
                virtual RollingAverage<Whole>& GetPerformanceLog();

                /////////////////////////////////////////////////////////////////////////////////////////////
                // Deciding when to and doing the work
            public:
                /// @brief This does everything required to track metadata and log work
                /// @param CurrentThreadStorage The FrameScheduler passes this in
                /// @details This wraps the log output in a WorkUnit element with a unique ID
                /// as and an attribute. This causes all the log output to be valid xml as long
                /// no '<' or '>' are emitted.
                /// @n @n
                ///
                virtual void operator() (DefaultThreadSpecificStorage::Type& CurrentThreadStorage);

                virtual WorkUnitKey GetSortingKey(FrameScheduler &SchedulerToCount);

        };//DefaultWorkUnit
    }//Threading
}//Mezzanine

#endif