Backport 0.14.4: automatically deactive span-based API

docs/source/details/backendconfig.rst

@@ -77,6 +77,11 @@ Explanation of the single keys:
 
   * ``type`` supported ADIOS operator type, e.g. zfp, sz
   * ``parameters`` is an associative map of string parameters for the operator (e.g. compression levels)
+* ``adios2.use_span_based_put``: The openPMD-api exposes the `span-based Put() API <https://adios2.readthedocs.io/en/latest/components/components.html#put-modes-and-memory-contracts>`_ of ADIOS2 via an overload of ``RecordComponent::storeChunk()``.
+  This API is incompatible with compression operators as described above.
+  The openPMD-api will automatically use a fallback implementation for the span-based Put() API if any operator is added to a dataset.
+  This workaround is enabled on a per-dataset level.
+  The workaround can be completely deactivated by specifying ``{"adios2": {"use_span_based_put": true}}`` or it can alternatively be activated indiscriminately for all datasets by specifying ``{"adios2": {"use_span_based_put": false}}``.
 
 Any setting specified under ``adios2.dataset`` is applicable globally as well as on a per-dataset level.
 Any setting under ``adios2.engine`` is applicable globally only.

include/openPMD/IO/ADIOS/ADIOS2IOHandler.hpp

@@ -236,6 +236,15 @@ class ADIOS2IOHandlerImpl
     std::string m_engineType;
     ADIOS2Schema::schema_t m_schema = ADIOS2Schema::schema_0000_00_00;
 
+    enum class UseSpan : char
+    {
+        Yes,
+        No,
+        Auto
+    };
+
+    UseSpan m_useSpanBasedPutByDefault = UseSpan::Auto;
+
     enum class AttributeLayout : char
     {
         ByAdiosAttributes,

src/IO/ADIOS/ADIOS2IOHandler.cpp

@@ -132,6 +132,14 @@ ADIOS2IOHandlerImpl::init( nlohmann::json cfg )
                 m_config[ "schema" ].json().get< ADIOS2Schema::schema_t >();
         }
 
+        if( m_config.json().contains( "use_span_based_put" ) )
+        {
+            m_useSpanBasedPutByDefault =
+                m_config[ "use_span_based_put" ].json().get< bool >()
+                ? UseSpan::Yes
+                : UseSpan::No;
+        }
+
         auto engineConfig = config( ADIOS2Defaults::str_engine );
         if( !engineConfig.json().is_null() )
         {
@@ -704,6 +712,22 @@ struct GetSpan
 
     std::string errorMsg = "ADIOS2: getBufferView()";
 };
+
+struct HasOperators
+{
+    template< typename T >
+    bool operator()( std::string const & name, adios2::IO & IO ) const
+    {
+        adios2::Variable< T > variable = IO.InquireVariable< T >( name );
+        if( !variable )
+        {
+            return false;
+        }
+        return !variable.Operations().empty();
+    }
+
+    std::string errorMsg = "ADIOS2: getBufferView()";
+};
 } // namespace detail
 
 void
@@ -721,6 +745,28 @@ ADIOS2IOHandlerImpl::getBufferView(
     auto file = refreshFileFromParent( writable, /* preferParentFile = */ false );
     detail::BufferedActions & ba =
         getFileData( file, IfFileNotOpen::ThrowError );
+
+    std::string name = nameOfVariable( writable );
+    switch( m_useSpanBasedPutByDefault )
+    {
+    case UseSpan::No:
+        parameters.out->backendManagedBuffer = false;
+        return;
+    case UseSpan::Auto:
+    {
+        detail::HasOperators hasOperators;
+        if( switchAdios2VariableType(
+            parameters.dtype, hasOperators, name, ba.m_IO ) )
+        {
+            parameters.out->backendManagedBuffer = false;
+            return;
+        }
+        break;
+    }
+    case UseSpan::Yes:
+        break;
+    }
+
     if( parameters.update )
     {
         detail::I_UpdateSpan &updater =
@@ -731,7 +777,6 @@ ADIOS2IOHandlerImpl::getBufferView(
     else
     {
         static detail::GetSpan gs;
-        std::string name = nameOfVariable( writable );
         switchAdios2VariableType( parameters.dtype, gs, this, parameters, ba, name );
     }
 }