Interface for a task switching strategy implementation. More...

#include <stk_common.h>

Inheritance diagram for stk::ITaskSwitchStrategy:

Public Member Functions
virtual void	AddTask (IKernelTask *task)=0
	Add task.
virtual void	RemoveTask (IKernelTask *task)=0
	Remove task.
virtual IKernelTask *	GetFirst () const =0
	Get first task.
virtual IKernelTask *	GetNext ()=0
	Advance the internal iterator and return the next runnable task.
virtual size_t	GetSize () const =0
	Get number of tasks currently managed by this strategy.
virtual void	OnTaskSleep (IKernelTask *task)=0
	Notification that a task has entered sleep/blocked state.
virtual void	OnTaskWake (IKernelTask *task)=0
	Notification that a task is becoming runnable again.
virtual bool	OnTaskDeadlineMissed (IKernelTask *task)=0
	Notification that a task has exceeded its HRT deadline; returns whether the strategy can recover without a hard fault.

Detailed Description

Interface for a task switching strategy implementation.

Note

Combines the Strategy and Iterator design patterns.

Strategy: concrete subclasses encapsulate the scheduling policy (round-robin, EDF, rate-monotonic, weighted round-robin, etc.) independently of the kernel.
Iterator: GetFirst() and GetNext() expose a stateful forward-iterator over the runnable task set. The cursor is owned by the concrete implementation and is not exposed directly, iteration is therefore not re-entrant.

Implementation must declare the following compile-time constants for reporting its capabilities to the kernel (place inside EConfig enum):

Example:

enum EConfig
{
    WEIGHT_API          = 0, // (1) if strategy needs Weight API of the kernel task, (0) otherwise (see \a IKernelTask and Weight API functions)
    SLEEP_EVENT_API     = 0, // (1) if strategy needs Sleep API events generated by the kernel, (0) otherwise (see \a ITaskSwitchStrategy::OnTaskSleep, \a ITaskSwitchStrategy::OnTaskWake)
    DEADLINE_MISSED_API = 0  // (1) if strategy implements OnTaskDeadlineMissed() and can absorb HRT deadline overruns, (0) otherwise (see \a ITaskSwitchStrategy::OnTaskDeadlineMissed)
};

Definition at line 781 of file stk_common.h.

Member Function Documentation

◆ AddTask()

virtual void stk::ITaskSwitchStrategy::AddTask ( IKernelTask * task )

pure virtual

Add task.

Note: Kernel tasks are added by the concrete implementation of IKernel.

Parameters

[in] task Pointer to the task to add.

Implemented in stk::SwitchStrategyEDF, stk::SwitchStrategyFixedPriority< MAX_PRIORITIES >, stk::SwitchStrategyFixedPriority< 32 >, stk::SwitchStrategyMonotonic< _Type >, stk::SwitchStrategyMonotonic< MSS_TYPE_DEADLINE >, stk::SwitchStrategyMonotonic< MSS_TYPE_RATE >, stk::SwitchStrategyRoundRobin, and stk::SwitchStrategySmoothWeightedRoundRobin.

◆ GetFirst()

virtual IKernelTask * stk::ITaskSwitchStrategy::GetFirst ( ) const

pure virtual

Get first task.

Returns: Pointer to the first task in the managed set, or NULL if no tasks have been added.

Implemented in stk::SwitchStrategyEDF, stk::SwitchStrategyFixedPriority< MAX_PRIORITIES >, stk::SwitchStrategyFixedPriority< 32 >, stk::SwitchStrategyMonotonic< _Type >, stk::SwitchStrategyMonotonic< MSS_TYPE_DEADLINE >, stk::SwitchStrategyMonotonic< MSS_TYPE_RATE >, stk::SwitchStrategyRoundRobin, and stk::SwitchStrategySmoothWeightedRoundRobin.

Referenced by stk::SchedulabilityCheck::IsSchedulableWCRT(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TestAlgorithm(), and stk::test::TestPriorityNext().

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◆ GetNext()

virtual IKernelTask * stk::ITaskSwitchStrategy::GetNext ( )

pure virtual

Advance the internal iterator and return the next runnable task.

Returns: Pointer to the next active task to schedule, or NULL if no runnable tasks are available (in which case the kernel transitions to FSM_STATE_SLEEPING).

Note: Implementations maintain an internal cursor. This method is not re-entrant, concurrent calls from multiple contexts are not supported.

Implemented in stk::SwitchStrategyEDF, stk::SwitchStrategyFixedPriority< MAX_PRIORITIES >, stk::SwitchStrategyFixedPriority< 32 >, stk::SwitchStrategyMonotonic< _Type >, stk::SwitchStrategyMonotonic< MSS_TYPE_DEADLINE >, stk::SwitchStrategyMonotonic< MSS_TYPE_RATE >, stk::SwitchStrategyRoundRobin, and stk::SwitchStrategySmoothWeightedRoundRobin.

Referenced by stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TestAlgorithm(), and stk::test::TestPriorityNext().

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◆ GetSize()

virtual size_t stk::ITaskSwitchStrategy::GetSize ( ) const

pure virtual

Get number of tasks currently managed by this strategy.

Returns: Total number of tasks in the set (runnable and idle).

Implemented in stk::SwitchStrategyEDF, stk::SwitchStrategyFixedPriority< MAX_PRIORITIES >, stk::SwitchStrategyFixedPriority< 32 >, stk::SwitchStrategyMonotonic< _Type >, stk::SwitchStrategyMonotonic< MSS_TYPE_DEADLINE >, stk::SwitchStrategyMonotonic< MSS_TYPE_RATE >, stk::SwitchStrategyRoundRobin, and stk::SwitchStrategySmoothWeightedRoundRobin.

Referenced by stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), and stk::test::TEST().

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◆ OnTaskDeadlineMissed()

virtual bool stk::ITaskSwitchStrategy::OnTaskDeadlineMissed ( IKernelTask * task )

pure virtual

Notification that a task has exceeded its HRT deadline; returns whether the strategy can recover without a hard fault.

Parameters

[in] task The task whose deadline was missed. Must not be nullptr.

Returns: true — the strategy has absorbed the overrun (e.g. by escalating its scheduling mode); the kernel must not call HrtHardFailDeadline() for this tick. false — the strategy cannot recover; the kernel must call HrtHardFailDeadline() as normal.

Note: Budget Overrun API. Called by the kernel from UpdateTaskState() within a tick, after GetNext() has already been called for that tick. Only invoked when DEADLINE_MISSED_API == 1 in the concrete strategy's EConfig. Strategies that set DEADLINE_MISSED_API = 0 do not need to implement this method; the kernel will not call it and will proceed directly to HrtHardFailDeadline().; Returning true carries no implicit side-effects on task sleep state or duration counters — normal tick-driven scheduling remains responsible for those. This call only communicates "do not hard-fault this tick."; The base implementation returns false (unrecoverable), which is the correct default for strategies that do not implement overrun recovery.

Implemented in stk::SwitchStrategyEDF, stk::SwitchStrategyFixedPriority< MAX_PRIORITIES >, stk::SwitchStrategyFixedPriority< 32 >, stk::SwitchStrategyMonotonic< _Type >, stk::SwitchStrategyMonotonic< MSS_TYPE_DEADLINE >, stk::SwitchStrategyMonotonic< MSS_TYPE_RATE >, stk::SwitchStrategyRoundRobin, and stk::SwitchStrategySmoothWeightedRoundRobin.

Referenced by stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), stk::test::TEST(), and stk::test::TEST().

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