CyclicSendTask can no longer restart with socketcan

[hardbyte]

The CyclicSendTask which inherits from RestartableCyclicTaskABC closes the bcm socket when the tasks is stopped.

A replacement socket is created when the task is restarted... but if the user wants to modify the data while the task is stopped the modify_data method tries to use the closed bcm socket raising an exception (e.g. run examples/cyclic.py:

can.CanError: Couldn't send CAN BCM frame. OS Error 9: Bad file descriptor
The CAN socket appears to be closed.

I admit this is quite a corner case but perhaps we should keep the socket open until the task is garbage collected? What do you think @christiansandberg ?

[christiansandberg]

Oh, that's right. What do you think about having one BCM socket per bus instead? That would solve #292 too.

[felixdivo]

That would only solve that issue for socketcan, but seems to be a good change anyways! It might also be less resource demanding when having a lot of BCMs floating around, although that is probably a rare use case.

[christiansandberg]

It's only the socketcan interface that suffers from the garbage collector problem. Threads keep running even if there is no reference to it (but I'm not sure if that is a documented behaviour and they will fail ungracefully when the bus is shutdown). The IXXAT interface just tells the hardware to send a message periodically.

[felixdivo]

Okay, if you say so!

[hardbyte]

Yeah I like the idea of one BCM socket per socketcan bus. Both #409 and #412 seem fine to close this

[felixdivo]

Both #409 and #412 seem fine to close this.

Closing because #412 got merged.