ROS2 message duplicates

asked 2022-06-02 06:39:53 -0600

Mihai D
11 ●2 ●5 ●4

updated 2022-06-03 04:10:49 -0600

ljaniec

3064 ●14 ●297 ●50 https://www.linkedin.c...

Hello,

I am sending messages from a node, receiving them in another.

The message type is custom containing 4 float32 values.

I am sending using a QoS that contains "reliable".

Problem is, I am sending different values and receiving the same value over and over again for some time, then it changes, then again a lot of duplicates, etc.

In the attached 5 sec video you can see the sender and the receiver, they run in sync, simply printing out the message sent/received. The received message contains the duplicated values.

https://youtu.be/nWg6YaYQrPY

How is this possible, what could be wrong?

Thanks,

Mihai

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hard to tell without code. Can you provide a minimal working example?

CroCo ( 2022-06-02 07:25:40 -0600 )edit

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answered 2022-06-02 09:18:41 -0600

ljaniec

3064 ●14 ●297 ●50 https://www.linkedin.c...

updated 2022-06-03 02:39:46 -0600

QoS "reliable" means according to the documentation:

Reliability

Best effort: attempt to deliver samples, but may lose them if the network is not robust.

Reliable: guarantee that samples are delivered, may retry multiple times.

EDIT: That's not true, check @Mihai D and @gvdhoorn comments. I misunderstood the documentation.

This is what you observed here.

Do you have a Header in your messages? You could check the metadata to filter out repeated messages, using e.g.

# sequence ID: consecutively increasing ID 
uint32 seq

Maybe you could use a message_filters package to do it?

https://github.com/ros2/message_filters

@Mihai D Can you provide a minimal working example of your code? With this problem of overwriting values in messages that are NOT duplicates.

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The problem is I receive the exact number of messages I send. So there are no duplicates received, it is just the data fields in the messages that are somehow changed. Instead of receiving each individual value I send, I receive the same value over and over again, until at some point it changes, then I receive that value for some time, etc. The intermediate values are "overwritten" by some value to which the system is stuck for some time, that is my biggest problem.

Thanks,

Mihai

Mihai D ( 2022-06-03 01:39:24 -0600 )edit

Afaik, reliable QoS should not result in multiple message duplicates getting delivered to the application.

The "may retry multiple times" part describes the behaviour of the DDS layer. The application should still only see a single instance of a message.

gvdhoorn ( 2022-06-03 02:03:27 -0600 )edit

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1 Answer

EDIT: That's not true, check @Mihai D and @gvdhoorn comments. I misunderstood the documentation.

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ROS2 message duplicates edit

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1 Answer

EDIT: That's not true, check @Mihai D and @gvdhoorn comments. I misunderstood the documentation.

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ROS2 message duplicates