readDataset: use step selection from time of enqueuing

Author: franzpoeschel

include/openPMD/IO/ADIOS/ADIOS2File.hpp

@@ -67,6 +67,7 @@ struct BufferedGet : BufferedAction
 {
     std::string name;
     Parameter<Operation::READ_DATASET> param;
+    std::optional<size_t> stepSelection;
 
     void run(ADIOS2File &) override;
 };

src/IO/ADIOS/ADIOS2File.cpp

@@ -146,7 +146,7 @@ void BufferedGet::run(ADIOS2File &ba)
         ba.m_IO,
         ba.getEngine(),
         ba.m_file,
-        ba.stepSelection());
+        this->stepSelection);
 }
 
 void BufferedPut::run(ADIOS2File &ba)

src/IO/ADIOS/ADIOS2IOHandler.cpp

@@ -1079,6 +1079,9 @@ void ADIOS2IOHandlerImpl::readDataset(
     detail::BufferedGet bg;
     bg.name = nameOfVariable(writable);
     bg.param = parameters;
+    // need to store the current step selection for deferred reads as the step
+    // selection might change again before flushing
+    bg.stepSelection = ba.stepSelection();
     ba.enqueue(std::move(bg));
     m_dirty.emplace(std::move(file));
 }