Best way to poll for latest sample of an instance?

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Best way to poll for latest sample of an instance?

What is the best method to poll a reader for the latest sample of a given instance?

I can think of a several ways to do it, but I'm not sure which is 'best':

1) Call plain read, manually compare key fields for each sample, starting from the end of the sequence.

2) Call read_w_condition with a query condition that compares the key fields.  Is this any different than 1?

3) Call read_instance.  This requires additional logic to lookup_instance on each poll iteration untill lookup_instance returns non-nil.  The polling will occur before publisher have come online.


Constraints:

1) No content filter is used, this reader is used to read for more than this one instance.

2) It should return the most recent valid_data sample from the reader's cache, even if the instance has since become not-alive.

3) Reader history depth is set to KeepLast(1).  I only ever care about the latest value for this application.

4) I don't need low-latency or to react to every published sample.  The additional complexity of listeners or waitsets is not required.

 

 

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@seymour33: Have you gotten this question resolved? I'm also looking fo a solution to the same question.

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This: https://community.rti.com/static/documentation/connext-dds/5.2.3/doc/api/connext_dds/api_cpp2/classdds_1_1sub_1_1DataReader_1_1Selector.html#a68edc8af79f33deaf685e9423fe5fb41

Iterate with this: https://community.rti.com/static/documentation/connext-dds/5.2.3/doc/api/connext_dds/api_cpp2/classdds_1_1sub_1_1LoanedSamples.html#a5417c8de7de7098e10ead01915b1b0cf