Re: [paho-dev] python paho-mqtt 1.1 connect() not blocking?

[Randy Forbes <randy.forbes@xxxxxxxxx>]

Thanks for the reply Roger.

My apologies up front as I'm quite the newbie to Python; long time C# developer; hopefully you won't hold that against me. ;-)  Based on your reply, I did a bit of studying up on the Python code and have a bit of a better understanding.

I'm not sure I'd mentioned, I'm using the AWS IoT. Here the code sample that I'm using: https://gist.github.com/shweta-nerake1/8684968ebacb5522c86a

What had me thinking async was putting a print("hello world") immediately after connect() and before subscribe(). That print was invoked prior to receiving the on_connect() callback. Would totally make sense in what you said that it's establishing the TCP connection but perhaps not receiving the CONNACK yet.

I'm still unable to get subscribe() working in having it immediately after connect() though. Moving the subscribe() into on_connect() definitely works.

Outside of the Gist above, I was able to find another web reference that this should work. At a bit of a loss. I was able to replicate the issue on my Mac so at least eliminated anything to do within the Raspberry Pi.

Any other thoughts or things to investigate, happy to do so. My Python debugging skills are essentially non-existent so it'll take me a bit to see what's really going on at the lower layers. Looking forward to learning that. I'll keep plugging away.

Thanks!

On Saturday, December 12, 2015, Roger Light <roger@xxxxxxxxxx> wrote:

Hi Randy,

connect() is definitely blocking, but maybe not in quite the way you are thinking. It blocks until the TCP connection with the server in complete, but this doesn't mean that the mqtt CONNECT/CONNACK flow is complete.

This shouldnt actually matter though, because calling subscribe() immediately after connect() should work fine. What error do you get?

Are you calling loop_start() or loop_forever() after the call to subscribe?

Cheers,

Roger

On 11 Dec 2015 01:29, "Randy Forbes" <randy.forbes@xxxxxxxxx> wrote:

python: 3.4.2

paho-mqtt: 1.1

os: raspian-jessie

According to the following documentation: https://pypi.python.org/pypi/paho-mqtt/1.1 the connect() call is supposed to be a blocking function.

**********
The connect() function connects the client to a broker. This is a blocking function.
**********

In my usage of the library, this appears to not be the case. I attempted to execute a subscribe() immediately after a connect but was not successful in getting subscribed. Moving the subscribe into onconnect() did work but indicated that the documentation may be incorrect.

In viewing the source, it appears that connect() calls into connect_async() which would make it a non-blocking call.

Am I correct in my observations?

Kind Regards.

Randy Forbes

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