TaskScheduler

Arduino library of a simple task scheduler for cooperative multitasking without the use of interrupt nor delay functions. Each task can queue and unqueue itself, as well as other tasks, on demand. The developer must be aware of what is queued at every given moment for a correct synchronization.

Description

This library allows to schedule the execution of tasks. It creates a circular queue of tasks that execute one after another. Features:

• Add a task to the queue.
• Remove a task from the queue.
• Modify the periodicity at which a task is executed.

The terms add and remove are used instead of queue and unqueue to make the abstraction independent of the underlining data structure.

Files

• TaskScheduler.h: c++ header file containing the declaration of two classes: class Task and class Scheduler. Only the last one needs to be invoqued. See bellow: Usage.
• TaskScheduler.cpp: c++ class code with the implementation of both classes.
• TaskScheduler.ino: Arduino project file with and example of a fictional usage (not a real case scenario).

Usage

Libraries

Include the TaskScheduler library. Example:

#include "TaskScheduler.h"

IMPORTANT: There is a dependency of the Arduino.h file.

Object instantiation

Declare an object of class Scheduler. For example:

Scheduler task;

Loop

Declare inside the loop function a declaration to the run() method (no arguments). For example:

task.run();

Adding and removing tasks

Tasks can be enqueued to the end of the queue to be executed periodically as soon as possible using the add method. Add the name of the function as the first parameter. Example:

task.add(foo);

Tasks can also be added to run every set period of time －by default in microseconds－ set in the second parameter (optional) of type uint_64. Example:

task.add(foo, 1000);

Tasks can be unqueued with the remove method. Example:

task.remove(foo);

Call the remove method with no arguments to remove the present task. For example, the following call will remove function foo from the scheduler.

void foo() { task.remove(); }

Change periodicity

Use the ´setPeriod´ method to change the period at which a task is executed. The first argument must contain the name of the function, the second parameter the new period. Set to '0' if the task must run as soon as possible. Example:

task.setPeriod(foo, 0);

Macros

#define PRECISION micros

Defines the unit of meassurement of time. Time related arguments in this library (such as adding tasks or setting their periodicity) depend on the unit here selected. The possible values are:

1. micros (microseconds).

2. millis (milliseconds).

#define LOOP_PREVENTION

As tasks can call each other this can eventually lead to and infinite loop in which a couple of task call each other and prevent other tasks from being executed. To prevent this situation enable this feature by defining this macro. It requires no tokens.

Notes.

Use this code at your own risk. There could be bugs or performance issues. Feel free to report any bug or send your feedback in the following forum post: https://forum.arduino.cc/index.php?topic=684393.0