Confusing problems with `shutdown_reply` being received on iopub

[gibiansky]

Note #1: The IPython kernel sends a status: "ok" key with the shutdown_reply, which is not documented in the messaging spec. Extra keys are generally not a problem but could also be documented if they play any role (or it can also be documented that extra keys should never be rejected).

More serious issue:

I am getting the shutdown_reply sent on the iopub channel, which can break client libraries. This seems to be somewhat tricky to reproduce, which has me confused.

Here is how you I can reproduce it:

Start a kernel:

python -m ipykernel

Find the absolute path to kernel-DDDDD.json in the stdout of that process.

Then, run jupyter console, and enter the following code (substituting in kernel-DDDDD.json as appropriate):

from pprint import pprint
from jupyter_client.consoleapp import JupyterConsoleApp
import time

class MyKernelApp(JupyterConsoleApp):
    def __init__(self, connection_file, runtime_dir):
        self._dispatching = False
        self.existing = connection_file
        self.runtime_dir = runtime_dir
        self.initialize()

app = MyKernelApp("/Users/silver/Library/Jupyter/runtime/kernel-23605.json", "/tmp")
kc = app.kernel_client
# Clear status messages
time.sleep(0.5)
kc.iopub_channel.get_msgs()

kc.shutdown()
time.sleep(0.5)
[m["header"]["msg_type"] for m in kc.iopub_channel.get_msgs()]

This will result in a list of message types which include shutdown_reply, which does not make sense, because this is the iopub channel.

Similarly, the following code reproduces the problem for me:

multimanager = MultiKernelManager()
manager = multimanager.get_kernel(multimanager.start_kernel("python3"))
client = manager.client()
time.sleep(0.5)
print(client.iopub_channel.get_msgs())
client.shutdown()
time.sleep(0.5)
print([m["header"]["msg_type"] for m in client.iopub_channel.get_msgs()])

However, the following code does not reproduce the issue:

multimanager = MultiKernelManager()
manager = multimanager.get_kernel(multimanager.start_kernel("python3"))
client = manager.client()
client.shutdown()
print(client.get_shell_msg())
print(client.get_iopub_msg())

Instead, it just blocks on get_iopub_msg, after returning the shutdown_reply message on the shell channel.

Can you help me figure out what's going on? Is the shutdown_reply being sent on both channels? Why is it being received on iopub at all?

I am quite confused. (The real issue I'm having is on a Haskell codebase, but hopefully these code snippets are enough to reproduce it.)

Here are some versions:

Python 3.5.0 (default, Oct  3 2015, 11:20:34)
[GCC 4.2.1 Compatible Apple LLVM 7.0.0 (clang-700.0.72)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import ipykernel; print(ipykernel.__version__)
4.3.1
>>> import jupyter_client; print(jupyter_client.__version__)
4.3.0

[gibiansky]

To add yet another little bit of data, in the Haskell implementation I am receiving the shutdown_reply on both shell and iopub, with different times in the headers:

Iopub: {"session":"59cdd707-0a40-4e37-a3f7-096ea2e87d7c","date":"2016-08-02T23:28:31.346912","version":"5.0","msg_id":"43ee94bc-d874-4ce5-8857-506b18ddbc96","username":"silver","msg_type":"shutdown_reply"}
Shell: {"session":"59cdd707-0a40-4e37-a3f7-096ea2e87d7c","date":"2016-08-02T23:28:31.346758","version":"5.0","msg_id":"dab5b281-8ecc-4335-8c5c-d87f6aed17b9","username":"silver","msg_type":"shutdown_reply"}

[gibiansky]

Now that I am thinking about it, it would make sense if this were consistent and on purpose, to re-broadcast the shutdown to all connected clients.

And, now that I am looking at it, we discussed this a few weeks ago here: jupyter/jupyter_client#170

So yes, this is the shutdown_reply just being rebroadcast consistently on iopub, and this simply needing to be documented in the spec.

In that case, this can be boiled down to two things:

• Document shutdown_reply on iopub (or a similar message) eventually, but the shutdown reply for the current messaging spec version
• Document the status key of the shutdown_reply

[minrk]

Document the status key of the shutdown_reply

It is documented that all replies should have a status field, with the value either 'ok' or 'error' in most cases though this is rarely checked, so omitting it will likely not be noticed by clients. In fact, as I look at IPython, I see we are omitting it in a few places.

Document shutdown_reply on iopub (or a similar message) eventually, but the shutdown reply for the current messaging spec version

👍 while I would prefer replacing shutdown_reply with a dedicated IOPub message, documenting what we currently do is probably the right thing now.

[gibiansky]

Good point, I missed that!

Yes, it would be great if all the messages IPython sends followed that, but it seems pretty reasonable to just assume that status is "ok" unless otherwise specified.

[minrk]

Yes, it would be great if all the messages IPython sends followed that

understatement :) and should be fixed by #171

it seems pretty reasonable to just assume that status is "ok" unless otherwise specified.

that's what clients have done so far, and I suppose we can encourage them to do so.