client.py deadlocks on BlockingKernelClient.get_iopub_msg()

It seems client.py sometimes deadlocks waiting on the lost messages for IOPub channel.

The IPython doc[1] says that IOPub is a "broadcast channel" which I think implies that there will be no guarantee that the messages get actually delivered to client.py, and indeed they get quite often lost in my setup ([Emacs on macbook] <=[ssh tunnel]=> [IPython kernel on a VM instance in the GCP cloud])

A quickest hack to work around the deadlocks would be to change the first "while True:" to "while False:", in the function msg_router, at the cost of losing all the stdout/stderr outputs. But at least this gets the code executed without blocking indefinitely, and we have historical data of stdout/stderr available any time from the shell channel.

I guess the correct solution would be to regard any message from IOPub as a bonus that could get lost at any time, and only wait for history data from the shell channel.

[1]: https://ipython.org/ipython-doc/3/development/messaging.html