A C++ template library for embedded applications
Designed and maintained by
Aster Consulting Ltd

Cooperative Scheduler

A lightweight cooperative multi-tasking scheduler.
Can be used stand-alone or in conjunction with a messaging system such as the ETL's message router or FSM as the back-
end handler. For use when a complex OS or RTOS is overkill.

Calls an 'idle' callback whenever the scheduler returns true.
Calls a 'watchdog' callback whenever the scheduler returns.

The scheduler makes use of etl::task.

Scheduling Policies

A number of built-in scheduling policies are available.
Note: The tasks are stored in decreasing priority id order. i.e. Higher id = higher priority.

Sequencial Single

etl::scheduler_policy_sequencial_single

A sequential algorithm that calls a task if it has work to do , starting from the highest priority task.
On return, it moves to the next task in the list. At the end of the list it returns the idle status.
If no tasks with work were found then the idle status is set to true.

Sequencial Multiple

scheduler_policy_sequencial_multiple

A sequential algorithm that calls a task if it has work to do , starting from the highest priority task.
On return, it calls the task again if it still has work, otherwise it moves to the next task in the list.
At the end of the list it returns the idle status.
If no tasks with work were found then the idle status is set to true.

Highest Priority

scheduler_policy_highest_priority

An algorithm that calls the highest priority task that has work to do.
Returns the idle status.
If no tasks with work were found then the idle status is set to true.

Most Work

scheduler_policy_most_work

An algorithm that calls the task that has the most work to do, starting from the highest priority task.
Returns the idle status.
If no tasks with work were found then the idle status is set to true.

Custom Scheduler

Creating a custom scheduler policy is simple.
Just create a structure with the following signature and add your own scheduling algorithm.
To get 'idle' callbacks then the policy must regularly return true.
To get 'watchdog' callbacks then the policy must regularly return.

struct scheduler_policy_custom
{
  bool schedule_tasks(etl::ivector<etl::task*>& task_list)
  {
    bool idle = true;

    //**************************************
    // Add your scheduling policy here.
    // Set 'idle' to false if any tasks were run.
    //**************************************

    return idle;
  }
};

etl::ischeduler

Can be used as a reference to all scheduler instances.


ischeduler()
Constructor

void set_idle_callback(etl::ifunction<void>& callback);
Sets the function to be called when idle.

void set_watchdog_callback(etl::ifunction<void>& callback);
Sets the function to be called to reset the watchdog.

void set_scheduler_running(bool scheduler_running);
Sets the running state of the scheduler.

bool scheduler_is_running() const;
Gets the running state of the scheduler.

void exit_scheduler()
Instructs the scheduler to exit after the next idle call.

void add_task(etl::task& task);
Adds a task to the task list.
The task list is in priority order where higher id = higher priority. Tasks with duplicate ids are in insert order.
Emits an etl::scheduler_too_many_tasks_exception if the task list is full.

template <typename TSize>
void add_task_list(etl::task** p_tasks, TSize size);
Emits an etl::scheduler_too_many_tasks_exception if the task list is full.
Emits an etl::scheduler_null_task_exception if any of the task pointers is null.

virtual void start()
Starts the scheduler.

etl::scheduler
Inherits from etl::ischeduler.

Template Parameters

TSchedulerPolicy The policy to use schedule tasks.
MAX_TASKS        The maximum number of tasks to schedule.

Member Functions

scheduler()
Constructor.
_______________________________________________________________________________________

void start()
Starts the scheduler.
Emits an etl::scheduler_no_tasks_exception if there are no tasks in the list.
_______________________________________________________________________________________

Errors

scheduler_exception
Inherits from etl::exception

scheduler_no_tasks_exception
Inherits from etl::scheduler_exception

scheduler_null_task_exception
Inherits from etl::scheduler_exception
scheduler.h