Basic question regarding yarp::os::BufferedPort::read()!

[paliasgh]

Hello and sorry for bothering you again,

I have a basic question about something I came across and I could not fix. Let's say I have a rf module that runs every 0.1 seconds and reads from a port in every update through messageRsPos = rsPos.read(false); in updateModule(). Data in the port, however, is published much slower (let's say every 0.5 seconds). In this case, i.e., when no new data has come, messageRsPos returns a null pointer. Is this expected? How can I make it read the last message regardless (repeat the last message if there is no new one)? Thanks.

[pattacini]

Hi @paliasgh

Never mind, we're here to help.

In this case, i.e., when no new data has come, messageRsPos returns a null pointer. Is this expected?

Yep.

How can I make it read the last message regardless (repeat the last message if there is no new one)?

An easy solution consists in latching the value in a class data member for example.
Something like the following:

messageRsPos = rsPos.read(false);
if (messageRsPos != nullptr) {
  messageRsPosLatch = *messageRsPos; 
}

In your code, you'll be using messageRsPosLatch, which gets updated only when a new message is retrieved via polling. Just make sure to initialize messageRsPosLatch with a value that is sensible for your application.

This should address your use case.
Instead, if you aim to query the BufferedPort to return the last data received, lastRead() should do the job.