hdf5: support HDF5_PREFER_PARELLEL cmake option

modules/hdf/CMakeLists.txt

@@ -25,11 +25,23 @@ if(NOT HDF5_FOUND)
     ocv_module_disable(hdf) # no return
 endif()
 
-set(HAVE_HDF5 1)
+# See https://github.com/opencv/opencv_contrib/issues/3858
+# If HDF5_PREFER_PARALLEL is enabled, find_package(HDF5) sets HDF5_IS_PARALLEL=ON.
+if(HDF5_IS_PARALLEL)
+  find_package(MPI)
+  if(NOT MPI_FOUND)
+    message(STATUS "Module opencv_hdf disabled because the following dependency is not found: MPI")
+    ocv_module_disable(hdf) # no return
+  endif()
+else()
+  unset(MPI_CXX_LIBRARIES)
+  unset(MPI_CXX_INCLUDE_DIRS)
+endif()
 
+set(HAVE_HDF5 1)
 ocv_warnings_disable(CMAKE_CXX_FLAGS -Winvalid-offsetof)
 
 set(the_description "Hierarchical Data Format I/O")
 ocv_define_module(hdf opencv_core WRAP python)
-ocv_target_link_libraries(${the_module} ${HDF5_LIBRARIES})
-ocv_include_directories(${HDF5_INCLUDE_DIRS})
+ocv_target_link_libraries(${the_module} ${HDF5_LIBRARIES} ${MPI_CXX_LIBRARIES})
+ocv_include_directories(${HDF5_INCLUDE_DIRS} ${MPI_CXX_INCLUDE_DIRS})

modules/hdf/include/opencv2/hdf.hpp

@@ -49,6 +49,10 @@ This module provides storage routines for Hierarchical Data Format objects.
 
     In order to use it, the hdf5 library has to be installed, which
     means cmake should find it using `find_package(HDF5)`.
+
+    You can use parallel hdf5 library with `-DHDF5_PREFER_PARELLEL=ON` cmake option.
+    Depended MPI library(e.g. Open MPI or MPICH) is detected in `find_package(MPI)`.
+    To set prefer MPI library, `update-alternatives` command is helpful for your Ubuntu.
 @}
 */