⏳ A simple way to run Threads on Arduino
Arduino does not support isolated parallel tasks (Threads),
but we can make the main loop
switch function execution conditionally and
thus simulate threading with Protothread mechanism.
This library implements it and helps you to:
Blinking an LED is often the very first thing an Arduino user learns. And this demonstrates that periodically performing one single task, like toggling the LED state, is really easy. However, one may quickly discover that managing multiple periodic tasks is not so simple if the tasks have different schedule.
The user defines a Thread object for each of those tasks, then lets the library manage their scheduled execution.
It should be noted that these are not “threads” in the real computer-science meaning of the term:
tasks are implemented as functions that are run periodically.
On the one hand, this means that the only way a task can yield the CPU is by returning to the caller,
and it is thus inadvisable to delay()
or do long waits inside any task.
On the other hand, this makes ArduinoThreads memory friendly, as no stack need to be allocated per task.
Libraries
folder inside Sketchbooks or Arduino software).If you are here just because another library requires a class from ArduinoThread, then you are done now .
There are many examples showing many ways to use it. We will explain Class itself, what it does and how it does.
There are three main classes included in the library:
Thread
, ThreadController
and StaticThreadController
(both controllers inherit from Thread
).
Thread
: Basic class, witch contains methods to set and run callbacks,
check if the Thread should be run, and also creates a unique ThreadID on the instantiation.
ThreadController
: Responsible for managing multiple Threads. Can also be thought of
as "a group of Threads", and is used to perform run
in every Thread ONLY when needed.
StaticThreadController
: Slightly faster and smaller version of the ThreadController
.
It works similar to ThreadController
, but once constructed it can't add or remove threads to run.
Thread myThread = Thread();
// or, if initializing a pointer
Thread* myThread = new Thread();
You can configure many things:
myThread.enabled = true; // Default enabled value is true
myThread.setInterval(10); // Setts the wanted interval to be 10ms
/*
This is useful for debugging
(Thread Name is disabled by default, to use less memory)
(Enable it by definint USE_THREAD_NAMES on 'Thread.h')
*/
myThread.ThreadName = "myThread tag";
// This will set the callback of the Thread: "What should I run"?
myThread.onRun(callback_function); // callback_function is the name of the function
Ok, creating threads isn't too hard, but what do we do with them?
// First check if our Thread should be run
if(myThread.shouldRun()){
// Yes, the Thread should run, let's run it
myThread.run();
}
If you had 3, 5 or 100 threads, managing them manually could become tedious.
That's when ThreadController
or StaticThreadController
comes into play and saves you the repetitive thread management parts of code.
// Instantiate new ThreadController
ThreadController controller = ThreadController();
// Now, put bunch of Threads inside it, FEED it!
controller.add(&myThread); // Notice the '&' sign before the thread, IF it's not instantied as a pointer.
controller.add(&hisThread);
controller.add(&sensorReadings);
...
or
// Instantiate a new StaticThreadController with the number of threads to be supplied as template parameter
StaticThreadController<3> controller (&myThread, &hisThread, &sensorReadings);
// You don't need to do anything else, controller now contains all the threads.
...
You have created, configured, grouped it. What is missing? Yes, whe should RUN it! The following will run all the threads that NEED to run.
// call run on a Thread, a ThreadController or a StaticThreadController to run it
controller.run();
Congratulations, you have learned the basics of the ArduinoThread
library. If you want to learn more, see bellow.
ThreadController
is not of a dynamic size (like a LinkedList
). The maximum number of threads that it can manage
is defined in ThreadController.h
(default is 15)
☢ When extending the Thread
class and overriding the run()
function,
remember to always call runned();
at the end, otherwise the thread will hang forever.
It's a good idea, to create a Timer
interrupt and call a ThreadController.run()
there.
That way, you don't need to worry about reading sensors and doing time-sensitive stuff
in your main code (loop
). Check ControllerWithTimer
example.
Inheriting from Thread
or even ThreadController
is always a good idea.
For example, I always create base classes of sensors that extends Thread
,
so that I can "register" the sensors inside a ThreadController
, and forget
about reading sensors, just having the values available in my main code.
Check the SensorThread
example.
Remember that ThreadController
is in fact, a Thread
itself. If you want to group threads and
manage them together (enable or disable), think about putting all of them inside a ThreadController
,
and adding this ThreadController
to another ThreadController
(YES! One inside another).
Check ControllerInController
example.
StaticThreadController
is optimal when you know the exact number of
threads to run. You cannot add or remove threads at runtime, but it
doesn't require additional memory to keep all the treads together, doesn't limit the number of thread
(except for available memory) and the code may be slightly
better optimized because all the threads always exist and no need to do any runtime checks.
Check the full example CustomTimedThread
for a cool application of threads that run
for a period, after a button is pressed.
Running tasks on the Timer
interrupts must be thought though REALLY carefully
You mustn't use sleep()
inside an interrupt, because it would cause an infinite loop.
Things execute quickly. Waiting too loooong on a interrupt, means waiting too
loooong on the main code (loop
)
Things might get "scrambled". Since Timers interrupts actually "BREAK" your code in half
and start running the interrupt, you might want to call noInterrupts
and interrupts
on places where cannot be interrupted:
noInterrupts();
// Put the code that CANNOT be interrupted...
interrupts(); // This will enable the interrupts egain. DO NOT FORGET!
bool Thread::enabled
- Enables or disables the thread. (doesn't prevent it from running, but will
return false
when shouldRun()
is called)void Thread::setInterval()
- Schedules the thread run interval in millisecondsbool Thread::shouldRun()
- Returns true, if the thread should be run.
(Basically,the logic is: (reached time AND is enabled?).void Thread::onRun(<function>)
- The target callback function to be called.void Thread::run()
- Runs the thread (executes the callback function).int Thread::ThreadID
- Theoretically, it's the memory address. It's unique, and can
be used to compare if two threads are identical.int Thread::ThreadName
- A human-readable thread name.
Default is "Thread ThreadID", eg.: "Thread 141515".
Note that to enable this attribute, you must uncomment the line that disables it on Thread.h
void Thread::runned()
- Used to reset internal timer of the thread.
This is automatically called AFTER a call to run()
.void ThreadController::run()
- Runs the all threads grouped by the controller,
but only if needed (if shouldRun()
returns true);bool ThreadController::add(Thread* _thread)
- Adds a the thread to the controller,
and returns true
if succeeded (returns false if the array is full).void ThreadController::remove(Thread* _thread)
- Removes the thread from the controllervoid ThreadController::remove(int index)
- Removes the thread at the index
positionvoid ThreadController::clear()
- Removes ALL threads from the controllerint ThreadController::size(bool cached = true)
- Returns number of threads allocated
in the ThreadController. Re-calculates thread count if cached
is false
Thread* ThreadController::get(int index)
- Returns the thread at the index
positionvoid StaticThreadController::run()
- Runs all the threads within the controller,
but only if needed (if shouldRun()
returns true);int StaticThreadController::size()
- Returns how many Threads are allocated inside the controller.Thread* ThreadController::get(int index)
- Returns the thread at the index
position - or nullptr
if index
is out of bounds.