Obtain samples which do not match a querycondition

I have a FooDataReader with a QueryCondition.  Foo is keyed.  

During my read loop, I need to process all NOT_READ samples, and perform a database update if the last received sample of Foo matches the QueryCondition, and a database deletion if the last read sample does NOT match the queryCondition.

The first case is easy.  I call read_w_condition(), and the condition specifies DDS_NOT_READ_SAMPLE_STATE.

The latter case is messy...

• I could read_w_condition all the matching samples, and then read all the remaining NOT_READ samples, which should all be mismatches.
  ...But new samples can arrive between the two read() calls.  So I end up getting false negatives that I have to manually test and handle.
  
  
• I could do the two reads above, atomically...  Perhaps by using FooDataReader.lock()/unlock(), which... might... keep new samples from coming in between my read calls???
  ...But lock() is undocmented, so it might not even do what I expect, and it's also not part of the OMG DDS API.  There doesn't seem to be any OMG DDS API method to do an atomic set of read() calls.
  
  
• I could read NOT_READ samples, using no QueryCondition at all, and filter them myself
  ...But there's no API support to do that, so I can't actually use the SQL filter I defined, meaning I have to implement it myself in software.
  
  
• I could make a second QueryCondition, with a query string that is inverse of my criteria.
  ...But this results in extra processing since the filter is evaluated redundantly, twice

Is there another alternative model I could use that will do what I need?