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What are tasks?

Tasks are a great tool to do multiple things at once, but they can be difficult to use properly. The most important thing to remember when using tasks is that tasks aren’t truly running in the background - they are run one at a time and swapped out by the PROS scheduler. If your task performs some repeated action (e.g. a while loop), you should include a delay() or task_delay_until(). Without a delay() statement, your task could starve the processor of resources and prevent the kernel from running properly.

-Pros Documentation.

How to create tasks using lighting

In lightning, you can create and manage task using the TaskManager class.

Creating a TaskManager object.​

To create a TaskManager object, simply do the following:

main.cpp
lightning::TaskManager task_manager_name;

Creating and Running tasks​

Creating the task​

The first thing to be aware of is that you need to create the function you want to run in the background.

Commonly, this function is in a while loop.

note

Remember to set a delay time. Not using a delay time will cause problems with the V5 Brain and lead to unexpected behavior.

The second thing is very important, your function must to be of type void name_function (void*).

Example​

In the next example, we will crate a function. The objetive of this function is to sense something.

main.cpp
void sensing_something(void*){
    while (1) {
    sense_sensors(); 
    pros::delay(util::DELAY_TIME); //10 milliseconds of delay.   
  }
}

Note that our function meets the following:

  • It is of type void (void*).
  • It is inside of a loop.
  • Has delay time.

Running the task​

Now that we have our function, it is time to run it as a task using the start_task() function.

How to use it?​

We need to understand parameters of this function:

Parameters
task_nameThe name key that you want for your task.
functionThe void function that will pass.

First, we need to provide a name for this task. The name is important because it is useful for referencing and managing that particular task.

Then we need to provide the designated function.

As a result, we have the following:

main.cpp
task_manager_name.start_task("key_name", function);

Example, running a task.​

In the next example, we will running the previous example function in the autonomous function.

main.cpp
void sensing_something(void*){
    while (1) {
    sense_sensors(); 
    pros::delay(util::DELAY_TIME); //10 milliseconds of delay.   
  }
}

lightning::TaskManager autonomous_task_manager; //Our task manager 

void autonomous(){
    autonomous_task_manager.start_task("SENSING", sensing_something); 
    //WE WOULD RUNNING THE sensing_something function in the autonomous routine as a task. 
}

Example, running multiple tasks.​

You can create more than just one task.

main.cpp

/////////////////////////////////Our functions:
void sensing_something(void*){
    while (1) {
    sense_sensors(); 
    pros::delay(util::DELAY_TIME); //10 milliseconds of delay.   
  }
}

void printing_stuff(void*){
    while(1){
        some_printing_function(); 
        pros::delay(util::DELAY_TIME); //10 milliseconds of delay.
    }
}

void timer(void*){
    while(1){
        some_clock_function();
        pros::delay(util::DELAY_TIME); //10 milliseconds of delay.
    }
}
//////////////////////////////////////////////////////////////////

lightning::TaskManager autonomous_task_manager; //Our task manager 

void autonomous(){
    autonomous_task_manager.start_task("SENSING", sensing_something); //FIRST TASK 
    autonomous_task_manager.start_task("PRINTING", printing_stuff);  //SECOND TASK
    autonomous_task_manager.start_task("CLOCK",timer); //THIRD TASK
}

Considerations​

  • You can create more than just one task.
  • You can create different task manager (example: One task manager for the driver period and another for the autonomous period).

Deleting tasks​

To delete tasks use the kill_task() method.

For this function you just need to provide the task name that you want delete.

main.cpp
task_manager.kill_task("TASK NAME");

Example​

Let´s suppose that after using a task we want to delete it.

main.cpp
void sensing_something(void*){
    while (1) {
    sense_sensors(); 
    pros::delay(util::DELAY_TIME); //10 milliseconds of delay.   
  }
}

lightning::TaskManager autonomous_task_manager; //Our task manager 

void autonomous(){
    autonomous_task_manager.start_task("SENSING", sensing_something); 
    //AFTER USING THE TASK SOME AMOUNT OF TIME 
    ///
    ///
    ///
    autonomous_task_manager.kill_task("SENSING"); //KILLING THE TASK. 
}

Delete the task when it is no longer required.

Considerations​

One important thing to keep in mind. The tasks belong to the TaskManager object. This means that if the task manager is deleted, all the task will be deleted as well.

Printing current tasks​

You can print the current tasks that are running in the integrated PROS terminal . To do this you can use two different ways:

  1. Using the print_current_tasks().
main.cpp
lightning::TaskManager autonomous_task_manager; //Our task manager 
void autonomous(){
   autonomous_task_manager.start_task("SENSING", sensing_something); //FIRST TASK 
   autonomous_task_manager.start_task("PRINTING", printing_stuff);  //SECOND TASK
   autonomous_task_manager.start_task("CLOCK",timer); //THIRD TASK

   autonomous_task_manager.print_current_tasks(); 
   /* OUTPUT
    SENSING
    PRINTING
    CLOCK
   */ 
}
  1. Or using std::cout.
main.cpp
lightning::TaskManager autonomous_task_manager; //Our task manager 
void autonomous(){
   autonomous_task_manager.start_task("SENSING", sensing_something); //FIRST TASK 
   autonomous_task_manager.start_task("PRINTING", printing_stuff);  //SECOND TASK
   autonomous_task_manager.start_task("CLOCK",timer); //THIRD TASK

   std::cout<<autonomous_task_manager; 
   /* OUTPUT
    SENSING
    PRINTING
    CLOCK
   */ 
}

Congratulations! 🎉​

You finished the tutorial! Now you can start creating task in your code.

For more information check the TaskManager Documentation.