Avoid infinite loops if there is no stream active

The backends will explicitly report in their status if it is currently
random-accessing. The frontend will then fall back to stepping linearly.

Author: franzpoeschel

include/openPMD/IO/AbstractIOHandlerImpl.hpp

@@ -153,8 +153,10 @@ class AbstractIOHandlerImpl
    * The return status code shall be stored as parameters.status.
    */
   virtual void
-  advance( Writable *, Parameter< Operation::ADVANCE > & )
-  {}
+  advance( Writable *, Parameter< Operation::ADVANCE > & parameters )
+  {
+    *parameters.status = AdvanceStatus::RANDOMACCESS;
+  }
 
   /** Close an openPMD group.
    * 

include/openPMD/Streaming.hpp

@@ -19,8 +19,9 @@ namespace openPMD
  */
 enum class AdvanceStatus : unsigned char
 {
-    OK,  /* stream goes on */
-    OVER /* stream is over */
+    OK,   /* stream goes on */
+    OVER, /* stream is over */
+    RANDOMACCESS /* there is no stream, it will never be over */
 };
 
 /**

src/IO/ADIOS/ADIOS2IOHandler.cpp

@@ -2534,7 +2534,7 @@ namespace detail
             m_IO.DefineAttribute< bool_representation >(
                 ADIOS2Defaults::str_usesstepsAttribute, 0 );
             flush( /* writeAttributes = */ false );
-            return AdvanceStatus::OK;
+            return AdvanceStatus::RANDOMACCESS;
         }
 
         m_IO.DefineAttribute< bool_representation >(

src/ReadIterations.cpp

@@ -83,7 +83,8 @@ SeriesIterator::SeriesIterator( Series series )
             Iteration::BeginStepStatus::AvailableIterations_t
                 availableIterations;
             std::tie( status, availableIterations ) = it->second.beginStep();
-            if( availableIterations.has_value() )
+            if( availableIterations.has_value()
+                && status != AdvanceStatus::RANDOMACCESS )
             {
                 m_iterationsInCurrentStep = availableIterations.get();
                 if( !m_iterationsInCurrentStep.empty() )
@@ -188,7 +189,8 @@ SeriesIterator & SeriesIterator::operator++()
     AdvanceStatus status;
     Iteration::BeginStepStatus::AvailableIterations_t availableIterations;
     std::tie( status, availableIterations ) = currentIteration.beginStep();
-    if( availableIterations.has_value() )
+    if( availableIterations.has_value()
+        && status != AdvanceStatus::RANDOMACCESS )
     {
         m_iterationsInCurrentStep = availableIterations.get();
     }