Add GC library to python

[yannis300307]

Problem you'd like to fix

Sometimes, we need to allocate a lot of memory, but if the garbage collector doesn't delete old variables quickly enough, we can run into a memory allocation error.

Describe the solution you'd like

Add the gc lib to python to free the memory.

Describe alternatives you've considered

Make the del keyword forcing the garbage collection.

[adri1numworks]

Thanks for your suggestion. The gc lib is a bit too advanced for our students needs, we don't plan on adding it in future versions at the moment.

Make the del keyword forcing the garbage collection.

Do you have examples where del function is not working as you want it to ?

[yannis300307]

I've made a project in which I have to store images as bytes. Sometimes, the memory is not cleared quickly enough between the images' loading despite the use of del. Moreover, the memory is not always cleared between programs executions. You can see this project here. It makes the emulator bugging, and it crashes on actual hardware (N0110) after 1 or 2 lignes rendered.

[EmilieNumworks]

MicroPython's garbage collector is triggered when the allocator runs out of memory. There shouldn't be such things as "it doesn't delete old variables quickly enough". The objects in the pool aren't deleted if some pointers still refer to them... What you're describing might be a bug but I cannot reproduce it (neither on the emulator nor the actual devices). Could you give the versions of your device or a video of the emulator bugging?

[yannis300307]

I've a N0110 and the OS version is 22.2.0. I will send a video at the evening.

[Volcanio18]

Hi, I've also encountered the same problem. You can easily reproduce this bug using this program :

a="" while True; ‎ ‎ ‎ ‎ a+="0" ‎ ‎ ‎ ‎ if len(a)%100==0: print(len(a))

You will see that every time you run this script it will run out of memory with "a" having reached a different length each time, because the ram was not cleared proprely.

[yannis300307]

In this case, you never clear a during the execution, so you will always run into a MemoryAllocationError.

[yannis300307]

I've reproduced the bug in this video: https://github.com/numworks/epsilon/assets/52321382/cb96bfb5-b80f-41d6-8ac4-cac5d3890c8b

As you can see, I clear a at the end of my for loop with del but the memory is not correctly cleared and it causes the error.

[EmilieNumworks]

Hi, I think @Volcanio18 is pointing at a heap leakage which I can indeed observe by enabling the MICROPY_MEM_STATS macro. @yannis300307 you implying that the del keyword doesn't work as intended. I'm opening issues internally for both topic and will keep you posted.