Order / What is exeuted in a Processing program??

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terryking

Order / What is exeuted in a Processing program??

in Programming Questions • 3 years ago

I'm confused. Docs say that draw() is executed after setup() and loops unless controlled (noloop etc).

I am running the example: SerialCallResponse. The order on the page is:

Declarations
setup()
draw()
void serialEvent(Serial myPort)

What actually happens is that BOTH draw() and the serialEvent functions run in a loop. So the program works fine.

BUT I expected anything in the main loop to have to be INSIDE draw()

I searched examples and docs and still confused.

Can you straighten me out??

Regards, Terry King ..On the Red Sea at KAUST.edu.sa
terry@terryking.us
Newsletter: http://redseanews.info Community Information: http://redseainfo.info

Replies(4)

Jo Wood

Re: Order / What is exeuted in a Processing program??

3 years ago

It is true that anything inside the draw() method will run in a loop (unless you tell it otherwise with noLoop()), and that anything inside setup() will only run once.

That doesn't mean however that you cannot have other threaded loops in a sketch. When you use the Serial library and create a Serial object, that will create its own thread that will call serialEvent() if you create the method and there is data to process on the serial port. The documentation for serialEvent() hopefully makes this clear.

terryking

Re: Order / What is exeuted in a Processing program??

3 years ago

Jo, thanks very much for the quick reply.

OK, I understand about this, although the documentation could say something like "Called in it's own thread when a byte is received" or something like that,

General question (should it be another post?): Is there general information about threads and multithreading in Processing? Can I create a function that runs in it's own thread? etc..

Thanks!

[I deleted those other posts :-)]

Jo Wood

Re: Order / What is exeuted in a Processing program??

3 years ago

There's space on the Processing Wiki for a tutorial on threading, but as yet we don't have anything. Threading and concurrency is a massive topic and there's plenty on threading with Java, which is equally applicable to Processing - e.g. the Java tutorial on concurrency. So yes, you could create a method that ran in its own thread.

If I was to offer one tip on threading and Processing specifically, it would be, try to avoid creating your own threads unless you have very good reason to do so. The reason being that you can end up with problems synchronising other threads with the draw() and keyboard/mouse threads. If I do need to put something in a thread that has an effect on drawing behaviour, it is best to use the thread to set some object-wide boolean variable which is then responded to inside the draw() method. Others may have different views on this though.

terryking

Re: Order / What is exeuted in a Processing program??

3 years ago

Hey Jo,

OK, I would like to stay connected with this subject. Right now I'm pushing to get some young people's hands onto Arduino and heads around some concepts.

I understand multiprocessing/multithreading pretty well, I have written and modified Real Time Operating System stuff, starting back on the IBM EDX product and etc. So I hope I can contribute to some discussion in this area, if only in some GrayBeard capacity. Let me know if you see some discussion start up again....

I have no immediate need for multiple threads, I just don't want to get tangled up in them :-) Most everything I've done in micros has been just looped / interrupts anyway. That said, there is a certain arcane elegance to systems designed for concurrency.

Thanks for your work in monitoring the Forum!

Regards, Terry King ..On the Red Sea at KAUST.edu.sa
terry@terryking.us

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