Read from parallel rank table

Author: franzpoeschel

include/openPMD/Series.hpp

@@ -188,8 +188,7 @@ class SeriesInterface : public AttributableInterface
      * @return  Vector with a String per (writing) MPI rank, indicating user-
      *          defined meta information per rank. Example: host name.
      */
-    chunk_assignment::RankMeta
-    mpiRanksMetaInfo() const;
+    chunk_assignment::RankMeta mpiRanksMetaInfo();
 
     /**
      * @brief Set the Mpi Ranks Meta Info attribute, i.e. a Vector with

src/Series.cpp

@@ -165,25 +165,61 @@ SeriesInterface::setMeshesPath(std::string const& mp)
     return *this;
 }
 
-chunk_assignment::RankMeta
-SeriesInterface::mpiRanksMetaInfo() const
+chunk_assignment::RankMeta SeriesInterface::mpiRanksMetaInfo()
 {
-    auto attribute = getAttribute( "rankMetaInfo" );
-    std::vector< std::string > asContiguousVector;
-    try
+    auto & series = get();
+    Parameter< Operation::OPEN_DATASET > openDataset;
+    openDataset.name = "hostTable";
+    IOHandler()->enqueue( IOTask( &series.m_rankTable, openDataset ) );
+
+    IOHandler()->flush();
+    if( openDataset.extent->size() != 2 )
+    {
+        // @todo use better error type
+        throw std::runtime_error( "[Series] rankTable must be 2D." );
+    }
+    if( *openDataset.dtype != Datatype::CHAR &&
+        *openDataset.dtype != Datatype::UCHAR )
     {
-        asContiguousVector = attribute.get< std::vector< std::string > >();
+        // @todo use better error type
+        throw std::runtime_error( "[Series] rankTable must have char type." );
     }
-    catch( std::runtime_error const & )
+
+    auto writerRanks = ( *openDataset.extent )[ 0 ];
+    auto lineWidth = ( *openDataset.extent )[ 1 ];
+
+    if( lineWidth < 1 )
     {
-        // workaround: if vector has length 1, some backends may report a
-        // single value instead of a vector
-        asContiguousVector = { attribute.get< std::string >() };
+        // Check this because our indexing logic later relies on this
+        // @todo use better error type
+        throw std::runtime_error(
+            "[Series] rankTable lines must not be empty." );
     }
+
+    Parameter< Operation::READ_DATASET > readDataset;
+    // read the whole thing
+    readDataset.offset.resize( 2 );
+    readDataset.extent = *openDataset.extent;
+    readDataset.dtype = Datatype::CHAR;
+    std::shared_ptr< char > get{
+        new char[ writerRanks * lineWidth ],
+        []( char const * ptr ) { delete[] ptr; } };
+    readDataset.data = get;
+
+    IOHandler()->enqueue( IOTask( &series.m_rankTable, readDataset ) );
+    IOHandler()->flush();
+
     chunk_assignment::RankMeta res;
-    for( size_t i = 0; i < asContiguousVector.size(); ++i )
+    for( size_t i = 0; i < writerRanks; ++i )
     {
-        res[ i ] = std::move( asContiguousVector[ i ] );
+        if( get.get()[ ( i + 1 ) * lineWidth - 1 ] != 0 )
+        {
+            throw std::runtime_error(
+                "[Series] rankTable lines must be null-terminated strings." );
+        }
+        // Use C-String constructor for std::string in the following line
+        // std::string::string(char const*);
+        res[ i ] = get.get() + i * lineWidth;
     }
     return res;
 }