Need help with MultiPort

[autosavemidi]

I am working in a program that autosaves MIDI messages as they are played, and everything is working really well when using a single input port.
I want to extend to use 2 or 3 simultaneous ports (the app is aimed at VST piano players, and some use the piano as one MIDI device, and the sustain pedal as a second device in another USB slot). I was able to get it to work using two separate input ports, and then using 2 iter_pending() loops. The basic code is something like this:

ports = mido.get_input_names()
port_A = mido.open_input(ports[0])
port_B = mido.open_input(ports[1])

for msg_A in port_A.iter_pending():
...
for msg_B in port_B.iter_pending():
...

The problem with this is that the loops are sequential. When I test by sending the same midi message through the 2 ports, the same event when entering through port_B is processed with a few milliseconds of delay.

I want to test if the mido.ports.MultiPort() helps. My problem is that I cannot make it to work.

If I try:

multi = mido.ports.MultiPort([port_A, port_B])
for msg in multi:
print (msg)

as suggested in the documentation, no msg is printed...

I have done all sorts of syntax combinations for the ports in multi, but nothing seems to work.

EDIT:

I posted the same question at stackoverflow and received an helpful suggestion as a workaround:

open_ports = [port_A, port_B]
for port in open_ports:
msg = port.poll()

Now the same MIDI message sent through both ports arrive simultaneously.

[rdoursenaud]

Thanks for sharing your solution.

I guess one could also use callbacks instead of polling depending on the requirements.
This would lighten the loop load at the cost of having to handle thread synchronisation according to the docs.