Resizable Datasets

include/openPMD/Dataset.hpp

@@ -40,6 +40,14 @@ class Dataset
 public:
     Dataset(Datatype, Extent, std::string options = "{}");
 
+    /**
+     * @brief Constructor that sets the datatype to undefined.
+     *
+     * Helpful for resizing datasets, since datatypes need not be given twice.
+     *
+     */
+    Dataset( Extent );
+
     Dataset& extend(Extent newExtent);
     Dataset& setChunkSize(Extent const&);
     Dataset& setCompression(std::string const&, uint8_t const);

include/openPMD/IO/IOTask.hpp

@@ -281,8 +281,7 @@ template<>
 struct OPENPMDAPI_EXPORT Parameter< Operation::EXTEND_DATASET > : public AbstractParameter
 {
     Parameter() = default;
-    Parameter(Parameter const & p) : AbstractParameter(),
-        name(p.name), extent(p.extent) {}
+    Parameter(Parameter const & p) : AbstractParameter(), extent(p.extent) {}
 
     std::unique_ptr< AbstractParameter >
     clone() const override
@@ -291,7 +290,6 @@ struct OPENPMDAPI_EXPORT Parameter< Operation::EXTEND_DATASET > : public Abstrac
             new Parameter< Operation::EXTEND_DATASET >(*this));
     }
 
-    std::string name = "";
     Extent extent = {};
 };
 

include/openPMD/RecordComponent.hpp

@@ -100,7 +100,26 @@ class RecordComponent : public BaseRecordComponent
 
     RecordComponent& setUnitSI(double);
 
-    RecordComponent& resetDataset(Dataset);
+    /**
+     * @brief Declare the dataset's type and extent.
+     *
+     * Calling this again after flushing will require resizing the dataset.
+     * Support for this depends on the backend.
+     * Unsupported are:
+     * * Changing the datatype.
+     * * Shrinking any dimension's extent.
+     * * Changing the number of dimensions.
+     *
+     * Backend support for resizing datasets:
+     * * JSON: Supported
+     * * ADIOS1: Unsupported
+     * * ADIOS2: Supported as of ADIOS2 2.7.0
+     * * HDF5: (Currently) unsupported.
+     *   Will be probably supported as soon as chunking is supported in HDF5.
+     *
+     * @return RecordComponent&
+     */
+    RecordComponent & resetDataset( Dataset );
 
     uint8_t getDimensionality() const;
     Extent getExtent() const;
@@ -196,6 +215,10 @@ class RecordComponent : public BaseRecordComponent
     std::shared_ptr< std::queue< IOTask > > m_chunks;
     std::shared_ptr< Attribute > m_constantValue;
     std::shared_ptr< bool > m_isEmpty = std::make_shared< bool >( false );
+    // User has extended the dataset, but the EXTEND task must yet be flushed
+    // to the backend
+    std::shared_ptr< bool > m_hasBeenExtended =
+        std::make_shared< bool >( false );
 
 private:
     void flush(std::string const&);

src/Dataset.cpp

@@ -34,8 +34,12 @@ Dataset::Dataset(Datatype d, Extent e, std::string options_in)
           options{std::move(options_in)}
 { }
 
-Dataset&
-Dataset::extend(Extent newExtents)
+Dataset::Dataset( Extent e ) : Dataset( Datatype::UNDEFINED, std::move( e ) )
+{
+}
+
+Dataset &
+Dataset::extend( Extent newExtents )
 {
     if( newExtents.size() != rank )
         throw std::runtime_error("Dimensionality of extended Dataset must match the original dimensionality");

src/IO/ADIOS/ADIOS2IOHandler.cpp

@@ -403,15 +403,58 @@ void ADIOS2IOHandlerImpl::createDataset(
     }
 }
 
-void ADIOS2IOHandlerImpl::extendDataset(
-    Writable *, const Parameter< Operation::EXTEND_DATASET > & )
+namespace detail
+{
+    struct DatasetExtender
+    {
+        template< typename T, typename... Args >
+        void
+        operator()(
+            adios2::IO & IO,
+            std::string const & variable,
+            Extent const & newShape )
+        {
+            auto var = IO.InquireVariable< T >( variable );
+            if( !var )
+            {
+                throw std::runtime_error(
+                    "[ADIOS2] Unable to retrieve variable for resizing: '" +
+                    variable + "'." );
+            }
+            adios2::Dims dims;
+            dims.reserve( newShape.size() );
+            for( auto ext : newShape )
+            {
+                dims.push_back( ext );
+            }
+            var.SetShape( dims );
+        }
+
+        std::string errorMsg = "ADIOS2: extendDataset()";
+    };
+} // namespace detail
+
+void
+ADIOS2IOHandlerImpl::extendDataset(
+    Writable * writable,
+    const Parameter< Operation::EXTEND_DATASET > & parameters )
 {
-    throw std::runtime_error(
-        "[ADIOS2] Dataset extension not implemented in ADIOS backend" );
+    VERIFY_ALWAYS(
+        m_handler->m_backendAccess != Access::READ_ONLY,
+        "[ADIOS2] Cannot extend datasets in read-only mode." );
+    setAndGetFilePosition( writable );
+    auto file = refreshFileFromParent( writable );
+    std::string name = nameOfVariable( writable );
+    auto & filedata = getFileData( file );
+    static detail::DatasetExtender de;
+    Datatype dt = detail::fromADIOS2Type( filedata.m_IO.VariableType( name ) );
+    switchAdios2VariableType( dt, de, filedata.m_IO, name, parameters.extent );
 }
 
-void ADIOS2IOHandlerImpl::openFile(
-    Writable * writable, const Parameter< Operation::OPEN_FILE > & parameters )
+void
+ADIOS2IOHandlerImpl::openFile(
+    Writable * writable,
+    const Parameter< Operation::OPEN_FILE > & parameters )
 {
     if ( !auxiliary::directory_exists( m_handler->directory ) )
     {

src/IO/HDF5/HDF5IOHandler.cpp

@@ -346,25 +346,36 @@ HDF5IOHandlerImpl::extendDataset(Writable* writable,
     if( !writable->written )
         throw std::runtime_error("[HDF5] Extending an unwritten Dataset is not possible.");
 
-    auto file = getFile(writable->parent).get();
-    hid_t node_id, dataset_id;
-    node_id = H5Gopen(file.id,
-                      concrete_h5_file_position(writable->parent).c_str(),
-                      H5P_DEFAULT);
-    VERIFY(node_id >= 0, "[HDF5] Internal error: Failed to open HDF5 group during dataset extension");
-
-    /* Sanitize name */
-    std::string name = parameters.name;
-    if( auxiliary::starts_with(name, '/') )
-        name = auxiliary::replace_first(name, "/", "");
-    if( !auxiliary::ends_with(name, '/') )
-        name += '/';
-
-    dataset_id = H5Dopen(node_id,
-                         name.c_str(),
+    auto res = getFile( writable );
+    if( !res )
+        res = getFile( writable->parent );
+    hid_t dataset_id = H5Dopen(res.get().id,
+                         concrete_h5_file_position(writable).c_str(),
                          H5P_DEFAULT);
     VERIFY(dataset_id >= 0, "[HDF5] Internal error: Failed to open HDF5 dataset during dataset extension");
 
+    // Datasets may only be extended if they have chunked layout, so let's see
+    // whether this one does
+    {
+        hid_t dataset_space = H5Dget_space( dataset_id );
+        int ndims = H5Sget_simple_extent_ndims( dataset_space );
+        VERIFY(
+            ndims >= 0,
+            "[HDF5]: Internal error: Failed to retrieve dimensionality of "
+            "dataset "
+            "during dataset read." );
+        hid_t propertyList = H5Dget_create_plist( dataset_id );
+        std::vector< hsize_t > chunkExtent( ndims, 0 );
+        int chunkDimensionality =
+            H5Pget_chunk( propertyList, ndims, chunkExtent.data() );
+        if( chunkDimensionality < 0 )
+        {
+            throw std::runtime_error(
+                "[HDF5] Cannot extend datasets unless written with chunked "
+                "layout (currently unsupported)." );
+        }
+    }
+
     std::vector< hsize_t > size;
     for( auto const& val : parameters.extent )
         size.push_back(static_cast< hsize_t >(val));
@@ -375,8 +386,6 @@ HDF5IOHandlerImpl::extendDataset(Writable* writable,
 
     status = H5Dclose(dataset_id);
     VERIFY(status == 0, "[HDF5] Internal error: Failed to close HDF5 dataset during dataset extension");
-    status = H5Gclose(node_id);
-    VERIFY(status == 0, "[HDF5] Internal error: Failed to close HDF5 group during dataset extension");
 }
 
 void

src/IO/JSON/JSONIOHandlerImpl.cpp

@@ -248,18 +248,42 @@ namespace openPMD
         }
     }
 
+    namespace
+    {
+        void
+        mergeInto( nlohmann::json & into, nlohmann::json & from );
+        void
+        mergeInto( nlohmann::json & into, nlohmann::json & from )
+        {
+            if( !from.is_array() )
+            {
+                into = from; // copy
+            }
+            else
+            {
+                size_t size = from.size();
+                for( size_t i = 0; i < size; ++i )
+                {
+                    if( !from[ i ].is_null() )
+                    {
+                        mergeInto( into[ i ], from[ i ] );
+                    }
+                }
+            }
+        }
+    } // namespace
 
-    void JSONIOHandlerImpl::extendDataset(
+    void
+    JSONIOHandlerImpl::extendDataset(
         Writable * writable,
-        Parameter< Operation::EXTEND_DATASET > const & parameters
-    )
+        Parameter< Operation::EXTEND_DATASET > const & parameters )
     {
-        VERIFY_ALWAYS(m_handler->m_backendAccess != Access::READ_ONLY,
+        VERIFY_ALWAYS(
+            m_handler->m_backendAccess != Access::READ_ONLY,
             "[JSON] Cannot extend a dataset in read-only mode." )
-        refreshFileFromParent( writable );
         setAndGetFilePosition( writable );
-        auto name = removeSlashes( parameters.name );
-        auto & j = obtainJsonContents( writable )[name];
+        refreshFileFromParent( writable );
+        auto & j = obtainJsonContents( writable );
 
         try
         {
@@ -280,25 +304,32 @@ namespace openPMD
             }
         } catch( json::basic_json::type_error & )
         {
-            throw std::runtime_error( "[JSON] The specified location contains no valid dataset" );
+            throw std::runtime_error(
+                "[JSON] The specified location contains no valid dataset" );
         }
         switch( stringToDatatype( j[ "datatype" ].get< std::string >() ) )
         {
             case Datatype::CFLOAT:
             case Datatype::CDOUBLE:
             case Datatype::CLONG_DOUBLE:
             {
+                // @todo test complex resizing
                 auto complexExtent = parameters.extent;
                 complexExtent.push_back( 2 );
-                j["data"] = initializeNDArray( complexExtent );
+                nlohmann::json newData = initializeNDArray( complexExtent );
+                nlohmann::json & oldData = j[ "data" ];
+                mergeInto( newData, oldData );
+                j[ "data" ] = newData;
                 break;
             }
             default:
-                j["data"] = initializeNDArray( parameters.extent );
+                nlohmann::json newData = initializeNDArray( parameters.extent );
+                nlohmann::json & oldData = j[ "data" ];
+                mergeInto( newData, oldData );
+                j[ "data" ] = newData;
                 break;
         }
         writable->written = true;
-
     }
 
     namespace