BLE APIs are not thread safe

[filipnavara]

BLE APIs are not thread safe

[Danappelxx]

This is a pretty serious issue. Since it's doesn't seem to be fixed in the firmware, what would be a "good enough" workaround on the application side? Wrap all ble calls in a 0-delay timer? Add a simple delay(<some reasonable amount>) after ble.init?

[filipnavara]

Unfortunately due to the way the callback registration works there's no reliable workaround from application code. You cannot register callbacks before ble.init because it resets them. At the same time it also starts the Bluetooth module and the background thread, so by registering them later you may miss some of the events. There are ways to call the ble functions on the right worker thread, but none of them are reliable during the initialization.

I managed to fry one of my boards by accident so I don't have a way to test this anymore.

[Danappelxx]

Appreciate the quick response. So you're saying there's not really a way to prevent race conditions? That's pretty unfortunate...

[filipnavara]

I recompiled my firmware to solve this, but obviously that's not a solution for everyone. There were other problems which I submitted pull requests for (#40, #41) and the latest version of the firmware solves at least that bits. Then RedBear was acquired by Particle and this whole repository was scheduled to get merged into the official Particle firmware (particle-iot#1505). So far that didn't happen. My hope was that the BLE API gets more attention as Particle is going to release their own Bluetooth products (https://www.particle.io/mesh/).

[Danappelxx]

Are your modifications by any chance open source? I’m already recompiling the firmware to get around other limitations (#45) so it wouldn’t be a huge leap for me.

Edit: Also, I mirror your wishes for the future of particle Bluetooth, hopefully it gets more attention!

[filipnavara]

I am afraid I never pushed that branch to my GitHub, so it's probably lost for good :-/ I tried all the three approaches above, but in the end I settled on implementing ble.waitForEvents and getting rid of the worker thread. It was by far the easiest one to implement and to reason about its correctness.