Refs #20706: Fix

Signed-off-by: Mario Dominguez <mariodominguez@eprosima.com>

include/fastdds/dds/subscriber/DataReader.hpp

@@ -785,7 +785,9 @@ class DataReader : public DomainEntity
             const void* instance) const;
 
     /**
-     * @brief Returns information about the first untaken sample.
+     * @brief Returns information about the first untaken sample. This method is meant to be called prior to
+     * a read() or take() operation as it does not modify the status condition of the entity.
+     *
      *
      * @param [out] info Pointer to a SampleInfo_t structure to store first untaken sample information.
      *

src/cpp/fastdds/subscriber/DataReaderImpl.hpp

@@ -199,7 +199,8 @@ class DataReaderImpl
             SampleInfoSeq& sample_infos);
 
     /**
-     * @brief Returns information about the first untaken sample.
+     * @brief Returns information about the first untaken sample. This method is meant to be called prior to
+     * a read() or take() operation as it does not modify the status condition of the entity.
      * @param [out] info Pointer to a SampleInfo structure to store first untaken sample information.
      * @return true if sample info was returned. false if there is no sample to take.
      */

src/cpp/fastdds/subscriber/history/DataReaderHistory.cpp

@@ -356,9 +356,20 @@ bool DataReaderHistory::get_first_untaken_info(
     for (auto& it : data_available_instances_)
     {
         auto& instance_changes = it.second->cache_changes;
-        if (!instance_changes.empty())
+        for (auto& instance_change : instance_changes)
         {
-            ReadTakeCommand::generate_info(info, *(it.second), instance_changes.front());
+            WriterProxy* wp;
+            bool is_future_change = false;
+
+            {
+                std::lock_guard<RecursiveTimedMutex> _(mp_reader->getMutex());
+                if (mp_reader->begin_sample_access_nts(instance_change, wp, is_future_change) && is_future_change)
+                {
+                    continue;
+                }
+            }
+
+            ReadTakeCommand::generate_info(info, *(it.second), instance_change);
             return true;
         }
     }