Thread safety in set_value

[thomaspurchas]

@ikalchev do you have any docs covering thread safety? I know elaborated about how threads are used in #74, but it looks like characteristics set_value() is not really thread safe, while being called from multiple threads.

Also do you offer guidance anywhere for how an accessories run() loop should interact with requests from py-HAP in a thread safe manner?

[cdce8p]

Regarding set_value: You might be right here. What if the user calls set_value at the same time, when the value is changed in HomeKit and set_characteristics calls set_value?

Regarding run(): I don't think there is currently. Although set_value might not be threadsafe as described above, I think this method should be the point of connection here.

[ikalchev]

set_value is not thread-safe that's true - the server thread can set that as part of handling a user request, while in the same time the Accessory thread can set it. Ops.

[ikalchev]

The chars are the only shared state, which are solely manipulated through set_value. At least I cannot recall another such place.

[shred86]

Could this possibly be an explanation to an issue I’m having with Home Assistant and HomeKit?

home-assistant/core#19604

I noticed in the logs when I’m having the issue mentioned in that post, set_value is not executed. When everything works as expected, I can see set_value being executed.