stk_strategy_edf.h

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/*
 * SuperTinyKernel(TM) RTOS: Lightweight High-Performance Deterministic C++ RTOS for Embedded Systems.
 *
 * Source: https://github.com/SuperTinyKernel-RTOS
 *
 * Copyright (c) 2022-2026 Neutron Code Limited <stk@neutroncode.com>. All Rights Reserved.
 * License: MIT License, see LICENSE for a full text.
 */
 
#ifndef STK_STRATEGY_EDF_H_
#define STK_STRATEGY_EDF_H_

 
#include "stk_common.h"
 
namespace stk {

class SwitchStrategyEDF final : public ITaskSwitchStrategy
{
public:
    enum EConfig
    {
        WEIGHT_API               = 0, 
        SLEEP_EVENT_API          = 1, 
        DEADLINE_MISSED_API      = 0, 
        PRIORITY_INHERITANCE_API = 0, 
        NOSLEEP_YIELD_API        = 0, 
        TIMESLICE_API            = 0  
    };

    explicit SwitchStrategyEDF() : m_tasks(), m_sleep()
    {}

    STK_VIRT_DTOR ~SwitchStrategyEDF() = default;

    void AddTask(IKernelTask *task) override
    {
        STK_ASSERT(task != nullptr);
        STK_ASSERT(task->GetHead() == nullptr);
 
        m_tasks.LinkBack(task);
    }

    void RemoveTask(IKernelTask *task) override
    {
        STK_ASSERT(task != nullptr);
        STK_ASSERT(GetSize() != 0U);
        STK_ASSERT((task->GetHead() == &m_tasks) || (task->GetHead() == &m_sleep));
 
        if (task->GetHead() == &m_tasks)
        {
            m_tasks.Unlink(task);
        }
        else
        {
            m_sleep.Unlink(task);
        }
    }

    IKernelTask *GetNext() override
    {
        IKernelTask *next = nullptr;
 
        if (!m_tasks.IsEmpty())
        {
            IKernelTask *const start = (*m_tasks.GetFirst());
 
            next = start; // initialize earliest found task to the first one
 
            Timeout earliest = next->GetHrtRelativeDeadline();
            IKernelTask *itr = (*start->GetNext());
 
            while (itr != start)
            {
                const Timeout deadline = itr->GetHrtRelativeDeadline();
 
                if (deadline < earliest)
                {
                    earliest = deadline;
                    next     = itr;
                }
 
                itr = (*itr->GetNext());
            }
        }
 
        return next;
    }

    IKernelTask *GetFirst() override
    {
        STK_ASSERT(GetSize() != 0U);
        
        return (*(!m_tasks.IsEmpty() ? m_tasks.GetFirst() : m_sleep.GetFirst()));
    }

    size_t GetSize() const override
    {
        return m_tasks.GetSize() + m_sleep.GetSize();
    }

    void OnTaskSleep(IKernelTask *task) override
    {
        STK_ASSERT(task != nullptr);
        STK_ASSERT(task->IsSleeping());
        STK_ASSERT(task->GetHead() == &m_tasks);
 
        m_tasks.Unlink(task);
        m_sleep.LinkBack(task);
    }

    void OnTaskWake(IKernelTask *task) override
    {
        STK_ASSERT(task != nullptr);
        STK_ASSERT(!task->IsSleeping());
        STK_ASSERT(task->GetHead() == &m_sleep);
 
        m_sleep.Unlink(task);
        m_tasks.LinkBack(task);
    }
 
protected:
    STK_NONCOPYABLE_CLASS(SwitchStrategyEDF);
 
    IKernelTask::ListHeadType m_tasks; 
    IKernelTask::ListHeadType m_sleep; 
};
 
} // namespace stk
 
#endif /* STK_STRATEGY_EDF_H_ */