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Paho (java) concurrency model [message #1743416]

Thu, 15 September 2016 09:14

Alberto Anguita

Messages: 4
Registered: September 2016

Junior Member

Hi,

I recently started using the Paho java client. I am using the asynch client. I have searched about the concurrency model used by paho, but I found little info.

- Are received messages handled by a single thread, or one thread per topic, or one thread per message?
- Are published messages queued and processed by a single thread, or are they processed in parallel by different threads?
- May I perform operations on the client in the connect success callback (i.e. subscribe to topics)?
- May I publish a message in the subscribe success callback?

Thanks in advance.

Regards.

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Re: Paho (java) concurrency model [message #1744285 is a reply to message #1743416]

Fri, 23 September 2016 21:22

Ian Craggs

Messages: 83
Registered: March 2013

Member

I can give you some answers.

There are multiple threads for each client object: sending thread, receiving thread, callback thread. Despite this I think there are limitations on what operations you can make in the callbacks. I'll ask James to explain further.

Ian

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Re: Paho (java) concurrency model [message #1744344 is a reply to message #1743416]

Mon, 26 September 2016 08:25

James Sutton

Messages: 71
Registered: July 2015

Member

Hi,

1) Received messages are handled by a single thread, keep in mind that the messageArrived callback that you implement will block that thread, so you will want to handle the message quickly (If handling the message may take a while, you might want to pass incoming messages off to a new thread for your application to process)
- See: https://www.eclipse.org/paho/files/javadoc/org/eclipse/paho/client/mqttv3/IMqttMessageListener.html and https://www.eclipse.org/paho/files/javadoc/org/eclipse/paho/client/mqttv3/MqttCallback.html#messageArrived-java.lang.String-org.eclipse.paho.client.mqttv3.MqttMessage-

2) Published messages are handed off to a synchronous thread as well and will be queued and published in order, this is because there is only a single communications thread with direct control of the socket.

3) Yes you can. You won't be blocking anything either.

4) Again, you can, no problems there. You won't be blocking anything either.

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