workunitkey.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
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*/
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   'doc' folder. See 'gpl.txt'
*/
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*/
#ifndef _timeddagworkunitkey_h
#define _timeddagworkunitkey_h

#include "datatypes.h"

/// @file
/// @brief This file defines the metadata used to sort workunits.

namespace Mezzanine
{
    namespace Threading
    {
        class iWorkUnit;

        /// @brief Stores data about a single work unit so that it can easily be sorted.
        class MEZZ_LIB WorkUnitKey
        {
            public:
                /// @brief The WorkUnit this carries metadata for.
                iWorkUnit* Unit;
                
                /// @brief This stores how many things must run after the target workunit.
                /// @details This is most important sorting factor. In the Default algorithm.
                /// All of the Workunit that the most workunits depend on are run before the
                /// any others. Since this number is usually low (less than 10ish) in large
                /// groups of workunits, then there must be a tie-breaker. This should be
                /// calculated including the dependers of all the dependers (I don't think
                /// counting a workunit twice hurts, and it may even help if something
                /// actually depend on multiple workunits that depend on this.)
                /// @note I chose the word depender instead of dependent, to make the distinction between this field and dependencies more clear when communicated verbally. In some english dialects dependencies is pronounced Dee-pen-dent-sees only one syllable off from Dee-pen-dent.
                Whole Dependers;

                /// @brief Some representation of the time the target workunit takes to execute.
                /// @details In the default algorithm this is used to determine what executes
                /// first after dependents are counted. It is important to know what takes the longest time
                /// and start it first so that it might finish coterminously with shorter
                /// workunits. This is used second because length of execution of one workunit
                /// means nothing if many other workunits run serialized in one thread rather than
                /// in parrellel.
                Whole Time;

                /// @brief Default Constructor
                /// @details This creates an empty and quite useless Key, needs to be filled with data before being useful.
                WorkUnitKey();

                /// @brief Constructor
                /// @param Dependers_ How many items depend on this. This needs to be calculated the same for all WorkUnitKeys.
                /// @param Time_ How long is this workunit expected to execute for. This needs to be calculated the same for all WorkUnitKeys.
                /// @param WorkUnit_ A pointer to the workunit in question.
                WorkUnitKey(const Whole& Dependers_, const Whole& Time_, iWorkUnit* WorkUnit_);

                /// @brief Destructor
                virtual ~WorkUnitKey();

                /// @brief The function that does the comparison in most containers.
                /// @param rhs The right hand WorkUnitKey when using <.
                /// @details This enforces the algorithm that sorts workunits. The workunit with the most
                /// other work units depending on it is priotized first. Because the longest delays in
                /// execution time can be introduced if WorkUnits are waiting for a dependency and it is
                /// poorly scheduled, this can results in single threaded execution when more could have
                /// been possible. If there is a tie in dependent count, then the work unit that takes
                /// longer to execute is prioritized (this needs to be tested for correctness). This
                /// starts WorkUnits that take longer earlier in the frame, helping to minimize the
                /// length of the critical path. In the event that those are both tied, then the WorkUnit
                /// with the lowest pointer value is priotized to prevent any of WorkUnitKey from comparing
                /// identically.
                /// @return True if the left hand WorkUnit should be prioritized ahead of the right hand work unit.
                virtual bool operator< (const WorkUnitKey& rhs ) const;

                /// @brief Does this key point to the Same work unit as another?
                /// @param rhs The other key.
                /// @return True if the both keys are for the same unit, other parameters are ignored.
                virtual bool operator== (const WorkUnitKey& rhs ) const;
        };//WorkUnitKey
    }//Threading
}//Mezzanine
#endif