path: root/release_docs/RELEASE.txt

HDF5 version 1.13.0 currently under development
================================================================================


INTRODUCTION
============

This document describes the differences between this release and the previous
HDF5 release. It contains information on the platforms tested and known
problems in this release. For more details check the HISTORY*.txt files in the
HDF5 source.

Note that documentation in the links below will be updated at the time of each
final release.

Links to HDF5 documentation can be found on The HDF5 web page:

     https://portal.hdfgroup.org/display/HDF5/HDF5

The official HDF5 releases can be obtained from:

     https://www.hdfgroup.org/downloads/hdf5/

Changes from Release to Release and New Features in the HDF5-1.13.x release series
can be found at:

     https://portal.hdfgroup.org/display/HDF5/HDF5+Application+Developer%27s+Guide

If you have any questions or comments, please send them to the HDF Help Desk:

     help@hdfgroup.org


CONTENTS
========

- New Features
- Support for new platforms and languages
- Bug Fixes since HDF5-1.12.0
- Supported Platforms
- Tested Configuration Features Summary
- More Tested Platforms
- Known Problems
- CMake vs. Autotools installations


New Features
============

    Configuration:
    -------------
    - On macOS, Universal Binaries can now be built, allowing native execution on
      both Intel and Apple Silicon (ARM) based Macs.

      To do so, set CMAKE_OSX_ARCHITECTURES="x86_64;arm64"

      (SAM - 2021/02/07, https://github.com/HDFGroup/hdf5/issues/311)

    - Added a configure-time option to control certain compiler warnings
      diagnostics

      A new configure-time option was added that allows some compiler warnings
      diagnostics to have the default operation. This is mainly intended for
      library developers and currently only works for gcc 10 and above. The
      diagnostics flags apply to C, C++ and Fortran compilers and will appear
      in "H5 C Flags", H5 C++ Flags" and H5 Fortran Flags, respectively. They
      will NOT be exported to h5cc, etc.

      The default is OFF, which will disable the warnings URL and color attributes
      for the warnings output. ON will not add the flags and allow default behavior.

      Autotools:    --enable-diags

      CMake:        HDF5_ENABLE_BUILD_DIAGS

      (ADB - 2021/02/05, HDFFV-11213)

    - CMake option to build the HDF filter plugins project as an external project

        The HDF filter plugins project is a collection of registered compression
        filters that can be dynamically loaded when needed to access data stored
        in a hdf5 file. This CMake-only option allows the plugins to be built and
        distributed with the hdf5 library and tools. Like the options for szip and
        zlib, either a tgz file or a git repository can be specified for the source.

        The option was refactored to use the CMake FetchContent process. This allows
        more control over the filter targets, but required external project command
        options to be moved to a CMake include file, HDF5PluginCache.cmake. Also
        enabled the filter examples to be used as tests for operation of the
        filter plugins.

        (ADB - 2020/12/10, OESS-98)

    - FreeBSD Autotools configuration now defaults to 'cc' and 'c++' compilers

      On FreeBSD, the autotools defaulted to 'gcc' as the C compiler and did
      not process C++ options. Since FreeBSD 10, the default compiler has
      been clang (via 'cc').

      The default compilers have been set to 'cc' for C and 'c++' for C++,
      which will pick up clang and clang++ respectively on FreeBSD 10+.
      Additionally, clang options are now set correctly for both C and C++
      and g++ options will now be set if that compiler is being used (an
      omission from the former functionality).

      (DER - 2020/11/28, HDFFV-11193)

    - Fixed POSIX problems when building w/ gcc on Solaris

      When building on Solaris using gcc, the POSIX symbols were not
      being set correctly, which could lead to issues like clock_gettime()
      not being found.

      The standard is now set to gnu99 when building with gcc on Solaris,
      which allows POSIX things to be #defined and linked correctly. This
      differs slightly from the gcc norm, where we set the standard to c99
      and manually set POSIX #define symbols.

      (DER - 2020/11/25, HDFFV-11191)

    - Added a configure-time option to consider certain compiler warnings
      as errors

      A new configure-time option was added that converts some compiler warnings
      to errors. This is mainly intended for library developers and currently
      only works for gcc and clang. The warnings that are considered errors
      will appear in the generated libhdf5.settings file. These warnings apply
      to C and C++ code and will appear in "H5 C Flags" and H5 C++ Flags",
      respectively. They will NOT be exported to h5cc, etc.

      The default is OFF. Building with this option may fail when compiling
      on operating systems and with compiler versions not commonly used by
      the library developers. Compilation may also fail when headers not
      under the control of the library developers (e.g., mpi.h, hdfs.h) raise
      warnings.

      Autotools:    --enable-warnings-as-errors

      CMake:        HDF5_ENABLE_WARNINGS_AS_ERRORS

      (DER - 2020/11/23, HDFFV-11189)

    - Autotools and CMake target added to produce doxygen generated documentation

        The default is OFF or disabled.
        Autoconf option is '--enable-doxygen'
          autotools make target is 'doxygen' and will build all doxygen targets
        CMake configure option is 'HDF5_BUILD_DOC'.
          CMake target is 'doxygen' for all available doxygen targets
          CMake target is 'hdf5lib_doc' for the src subdirectory

        (ADB - 2020/11/03)

    - CMake option to use MSVC naming conventions with MinGW

        HDF5_MSVC_NAMING_CONVENTION option enable to use MSVC naming conventions
        when using a MinGW toolchain

        (xan - 2020/10/30)

    - CMake option to statically link gcc libs with MinGW

        HDF5_MINGW_STATIC_GCC_LIBS allows to statically link libg/libstdc++
        with the MinGW toolchain

        (xan - 2020/10/30)

    - CMake option to build the HDF filter plugins project as an external project

        The HDF filter plugins project is a collection of registered compression
        filters that can be dynamically loaded when needed to access data stored
        in a hdf5 file. This CMake-only option allows the plugins to be built and
        distributed with the hdf5 library and tools. Like the options for szip and
        zlib, either a tgz file or a git repository can be specified for the source.

        The necessary options are (see the INSTALL_CMake.txt file):
          HDF5_ENABLE_PLUGIN_SUPPORT
          PLUGIN_TGZ_NAME or PLUGIN_GIT_URL
        There are more options necessary for various filters and the plugin project
        documents should be referenced.

        (ADB - 2020/09/27, OESS-98)

    - Added CMake option to format source files

        HDF5_ENABLE_FORMATTERS option will enable creation of targets using the
        pattern - HDF5_*_SRC_FORMAT - where * corresponds to the source folder
        or tool folder. All sources can be formatted by executing the format target;
        make format

        (ADB - 2020/08/24)

    - Add file locking configure and CMake options

        HDF5 1.10.0 introduced a file locking scheme, primarily to help
        enforce SWMR setup. Formerly, the only user-level control of the scheme
        was via the HDF5_USE_FILE_LOCKING environment variable.

        This change introduces configure-time options that control whether
        or not file locking will be used and whether or not the library
        ignores errors when locking has been disabled on the file system
        (useful on some HPC Lustre installations).

        In both the Autotools and CMake, the settings have the effect of changing
        the default property list settings (see the H5Pset/get_file_locking()
        entry, below).

        The yes/no/best-effort file locking configure setting has also been
        added to the libhdf5.settings file.

        Autotools:

            An --enable-file-locking=(yes|no|best-effort) option has been added.

            yes:          Use file locking.
            no:           Do not use file locking.
            best-effort:  Use file locking and ignore "disabled" errors.

        CMake:

            Two self-explanatory options have been added:

            HDF5_USE_FILE_LOCKING
            HDF5_IGNORE_DISABLED_FILE_LOCKS

            Setting both of these to ON is the equivalent to the Autotools'
            best-effort setting.

        NOTE:
        The precedence order of the various file locking control mechanisms is:

            1) HDF5_USE_FILE_LOCKING environment variable (highest)

            2) H5Pset_file_locking()

            3) configure/CMake options (which set the property list defaults)

            4) library defaults (currently best-effort)

        (DER - 2020/07/30, HDFFV-11092)

    - CMake option to link the generated Fortran MOD files into the include
      directory.

        The Fortran generation of MOD files by a Fortran compile can produce
        different binary files between SHARED and STATIC compiles with different
        compilers and/or different platforms. Note that it has been found that
        different versions of Fortran compilers will produce incompatible MOD
        files. Currently, CMake will locate these MOD files in subfolders of
        the include directory and add that path to the Fortran library target
        in the CMake config file, which can be used by the CMake find library
        process. For other build systems using the binary from a CMake install,
        a new CMake configuration can be used to copy the pre-chosen version
        of the Fortran MOD files into the install include directory.

        The default will depend on the configuration of
        BUILD_STATIC_LIBS and BUILD_SHARED_LIBS:
            YES                   YES         Default to SHARED
            YES                   NO          Default to STATIC
            NO                    YES         Default to SHARED
            NO                    NO          Default to SHARED
        The defaults can be overriden by setting the config option
            HDF5_INSTALL_MOD_FORTRAN to one of NO, SHARED, or STATIC

        (ADB - 2020/07/09, HDFFV-11116)

    - CMake option to use AEC (open source SZip) library instead of SZip

        The open source AEC library is a replacement library for SZip. In
        order to use it for hdf5 the libaec CMake source was changed to add
        "-fPIC" and exclude test files. Autotools does not build the
        compression libraries within hdf5 builds. New option USE_LIBAEC is
        required to compensate for the different files produced by AEC build.

        (ADB - 2020/04/22, OESS-65)

    - CMake ConfigureChecks.cmake file now uses CHECK_STRUCT_HAS_MEMBER

        Some handcrafted tests in HDFTests.c has been removed and the CMake
        CHECK_STRUCT_HAS_MEMBER module has been used.

        (ADB - 2020/03/24, TRILAB-24)

    - Both build systems use same set of warnings flags

        GNU C, C++ and gfortran warnings flags were moved to files in a config
        sub-folder named gnu-warnings. Flags that only are available for a specific
        version of the compiler are in files named with that version.
        Clang C warnings flags were moved to files in a config sub-folder
        named clang-warnings.
        Intel C, Fortran warnings flags were moved to files in a config sub-folder
        named intel-warnings.

        There are flags in named "error-xxx" files with warnings that may
        be promoted to errors. Some source files may still need fixes.

        There are also pairs of files named "developer-xxx" and "no-developer-xxx"
        that are chosen by the CMake option:HDF5_ENABLE_DEV_WARNINGS or the
        configure option:--enable-developer-warnings.

        In addition, CMake no longer applies these warnings for examples.

        (ADB - 2020/03/24, TRILAB-192)

    - Added test script for file size compare

        If CMake minimum version is at least 3.14, the fileCompareTest.cmake
        script will compare file sizes.

        (ADB - 2020/02/24, HDFFV-11036)

    - Update CMake minimum version to 3.12

        Updated CMake minimum version to 3.12 and added version checks
        for Windows features.

        (ADB - 2020/02/05, TRILABS-142)

    - Fixed CMake include properties for Fortran libraries

        Corrected the library properties for Fortran to use the
        correct path for the Fortran module files.

        (ADB - 2020/02/04, HDFFV-11012)

    - Added common warnings files for gnu and intel

        Added warnings files to use one common set of flags
        during configure for both autotools and CMake build
        systems. The initial implementation only affects a
        general set of flags for gnu and intel compilers.

        (ADB - 2020/01/17)

    - Added new options to CMake for control of testing

        Added CMake options (default ON);
          HDF5_TEST_SERIAL AND/OR HDF5_TEST_PARALLEL
          combined with:
            HDF5_TEST_TOOLS
            HDF5_TEST_EXAMPLES
            HDF5_TEST_SWMR
            HDF5_TEST_FORTRAN
            HDF5_TEST_CPP
            HDF5_TEST_JAVA

        (ADB - 2020/01/15, HDFFV-11001)

    - Added Clang sanitizers to CMake for analyzer support if compiler is clang.

        Added CMake code and files to execute the Clang sanitizers if
        HDF5_ENABLE_SANITIZERS is enabled and the USE_SANITIZER option
        is set to one of the following:
          Address
          Memory
          MemoryWithOrigins
          Undefined
          Thread
          Leak
          'Address;Undefined'

        (ADB - 2019/12/12, TRILAB-135)

    - Update CMake for VS2019 support

        CMake added support for VS2019 in version 3.15. Changes to the CMake
        generator setting required changes to scripts. Also updated version
        references in CMake files as necessary.

        (ADB - 2019/11/18, HDFFV-10962)

    - Update CMake options to match new autotools options

        Add configure options (autotools - CMake):
            enable-asserts       HDF5_ENABLE_ASSERTS
            enable-symbols       HDF5_ENABLE_SYMBOLS
            enable-profiling     HDF5_ENABLE_PROFILING
            enable-optimization  HDF5_ENABLE_OPTIMIZATION
        In addition NDEBUG is no longer forced defined and relies on the CMake
        process.

        (ADB - 2019/10/07, HDFFV-100901, HDFFV-10637, TRILAB-97)


    Library:
    --------
    - H5Epush_ret() now requires a trailing semi-colon

        H5Epush_ret() is a function-like macro that has been changed to
        contain a `do {} while(0)` loop. Consequently, a trailing semi-colon
        is now required to end the `while` statement. Previously, a trailing
        semi would work, but was not mandatory. This change was made to allow
        clang-format to correctly format the source code.

        (SAM - 2021/03-03)

    - Improved performance of H5Sget_select_elem_pointlist

        Modified library to cache the point after the last block of points
        retrieved by H5Sget_select_elem_pointlist, so a subsequent call to the
        same function to retrieve the next block of points from the list can
        proceed immediately without needing to iterate over the point list.

        (NAF - 2021/01/19)

    - Replaced H5E_ATOM with H5E_ID in H5Epubgen.h

      The term "atom" is archaic and not in line with current HDF5 library
      terminology, which uses "ID" instead. "Atom" has mostly been purged
      from the library internals and this change removes H5E_ATOM from
      the H5Epubgen.h (exposed via H5Epublic.h) and replaces it with
      H5E_ID.

      (DER - 2020/11/24, HDFFV-11190)

    - Add new public function H5Ssel_iter_reset

        This function resets a dataspace selection iterator back to an
        initial state so that it may be used for iteration once more.
        This can be useful when needing to iterate over a selection
        multiple times without having to repeatedly create/destroy
        a selection iterator for that dataspace selection.

        (JTH - 2020/09/18)

    - Remove HDFS VFD stubs

        The original implementation of the HDFS VFD included non-functional
        versions of the following public API calls when the HDFS VFD is
        not built as a part of the HDF5 library:

        * H5FD_hdfs_init()
        * H5Pget_fapl_hdfs()
        * H5Pset_fapl_hdfs()

        They will remain present in HDF5 1.10 and HDF5 1.12 releases
        for binary compatibility purposes but have been removed as of 1.14.0.

        Note that this has nothing to do with the real HDFS VFD API calls
        that are fully functional when the HDFS VFD is configured and built.

        We simply changed:

          #ifdef LIBHDFS
            <real API call>
          #else
            <useless stub>
          #endif

        to:

          #ifdef LIBHDFS
            <real API call>
          #endif

        Which is how the other optional VFDs are handled.

        (DER - 2020/08/27)

    - Add Mirror VFD

        Use TCP/IP sockets to perform write-only (W/O) file I/O on a remote
        machine. Must be used in conjunction with the Splitter VFD.

        (JOS - 2020/03/13, TBD)

    - Add Splitter VFD

        Maintain separate R/W and W/O channels for "concurrent" file writes
        to two files using a single HDF5 file handle.

        (JOS - 2020/03/13, TBD)

    - Refactored public exposure of haddr_t type in favor of "object tokens"

        To better accommodate HDF5 VOL connectors where "object addresses in a file"
        may not make much sense, the following changes were made to the library:

        * Introduced new H5O_token_t "object token" type, which represents a
          unique and permanent identifier for referencing an HDF5 object within
          a container; these "object tokens" are meant to replace object addresses.
          Along with the new type, a new H5Oopen_by_token API call was introduced
          to open an object by a token, similar to how object addresses were
          previously used with H5Oopen_by_addr.

        * Introduced new H5Lget_info2, H5Lget_info_by_idx2, H5Literate2, H5Literate_by_name2,
          H5Lvisit2 and H5Lvisit_by_name2 API calls, along with their associated H5L_info2_t
          struct and H5L_iterate2_t callback function, which work with the newly-introduced
          object tokens, instead of object addresses. The original functions have been
          renamed to version 1 functions and are deprecated in favor of the new version 2
          functions. The H5L_info_t and H5L_iterate_t types have been renamed to version 1
          types and are now deprecated in favor of their version 2 counterparts. For each of
          the functions and types, compatibility macros take place of the original symbols.

        * Introduced new H5Oget_info3, H5Oget_info_by_name3, H5Oget_info_by_idx3,
          H5Ovisit3 and H5Ovisit_by_name3 API calls, along with their associated H5O_info2_t
          struct and H5O_iterate2_t callback function, which work with the newly-introduced
          object tokens, instead of object addresses. The version 2 functions are now
          deprecated in favor of the version 3 functions. The H5O_info_t and H5O_iterate_t
          types have been renamed to version 1 types and are now deprecated in favor of their
          version 2 counterparts. For each, compatibility macros take place of the original
          symbols.

        * Introduced new H5Oget_native_info, H5Oget_native_info_by_name and
          H5Oget_native_info_by_idx API calls, along with their associated H5O_native_info_t
          struct, which are used to retrieve the native HDF5 file format-specific information
          about an object. This information (such as object header info and B-tree/heap info)
          has been removed from the new H5O_info2_t struct so that the more generic
          H5Oget_info(_by_name/_by_idx)3 routines will not try to retrieve it for non-native
          VOL connectors.

        * Added new H5Otoken_cmp, H5Otoken_to_str and H5Otoken_from_str routines to compare
          two object tokens, convert an object token into a nicely-readable string format and
          to convert an object token string back into a real object token, respectively.

        (DER, QAK, JTH - 2020/01/16)

    - Add new public function H5Sselect_adjust.

        This function shifts a dataspace selection by a specified logical offset
        within the dataspace extent.  This can be useful for VOL developers to
        implement chunked datasets.

        (NAF - 2019/11/18)

    - Add new public function H5Sselect_project_intersection.

        This function computes the intersection between two dataspace selections
        and projects that intersection into a third selection.  This can be useful
        for VOL developers to implement chunked or virtual datasets.

        (NAF - 2019/11/13, ID-148)

    - Add new public function H5VLget_file_type.

        This function returns a datatype equivalent to the supplied datatype but
        with the location set to be in the file.  This datatype can then be used
        with H5Tconvert to convert data between file and in-memory representation.
        This funcition is intended for use only by VOL connector developers.

        (NAF - 2019/11/08, ID-127)


    Parallel Library:
    -----------------
    -


    Fortran Library:
    ----------------
    - Add wrappers for H5Pset/get_file_locking() API calls

        h5pget_file_locking_f()
        h5pset_file_locking_f()

        See the configure option discussion for HDFFV-11092 (above) for more
        information on the file locking feature and how it's controlled.

        (DER - 2020/07/30, HDFFV-11092)

    C++ Library:
    ------------
    - Add wrappers for H5Pset/get_file_locking() API calls

        FileAccPropList::setFileLocking()
        FileAccPropList::getFileLocking()

        See the configure option discussion for HDFFV-11092 (above) for more
        information on the file locking feature and how it's controlled.

        (DER - 2020/07/30, HDFFV-11092)


    Java Library:
    -------------
    - Replaced HDF5AtomException with HDF5IdException

      Since H5E_ATOM changed to H5E_ID in the C library, the Java exception
      that wraps the error category was also renamed. Its functionality
      remains unchanged aside from the name.

      (See also the HDFFV-11190 note in the C library section)

      (DER - 2020/11/24, HDFFV-11190)

    - Added new H5S functions.

        H5Sselect_copy, H5Sselect_shape_same, H5Sselect_adjust,
        H5Sselect_intersect_block, H5Sselect_project_intersection,
        H5Scombine_hyperslab, H5Smodify_select, H5Scombine_select
        wrapper functions added.

        (ADB - 2020/10/27, HDFFV-10868)

    - Add wrappers for H5Pset/get_file_locking() API calls

        H5Pset_file_locking()
        H5Pget_use_file_locking()
        H5Pget_ignore_disabled_file_locking()

        Unlike the C++ and Fortran wrappers, there are separate getters for the
        two file locking settings, each of which returns a boolean value.

        See the configure option discussion for HDFFV-11092 (above) for more
        information on the file locking feature and how it's controlled.

        (DER - 2020/07/30, HDFFV-11092)

    - Added ability to test java library with VOLs.

        Created new CMake script that combines the java and vol test scripts.

        (ADB - 2020/02/03, HDFFV-10996)

    - Tests fail for non-English locale.

        In the JUnit tests with a non-English locale, only the part before
        the decimal comma is replaced by XXXX and this leads to a comparison
        error. Changed the regex for the Time substitution.

        (ADB - 2020/01/09, HDFFV-10995)


    Tools:
    ------
    - h5repack added help text for user-defined filters.

        Added help text line that states the valid values of the filter flag
        for user-defined filters;
            filter_flag: 1 is OPTIONAL or 0 is MANDATORY

        (ADB - 2021/01/14, HDFFV-11099)

    - Added h5delete tool

        Deleting HDF5 storage when using the VOL can be tricky when the VOL
        does not create files. The h5delete tool is a simple wrapper around
        the H5Fdelete() API call that uses the VOL specified in the
        HDF5_VOL_CONNECTOR environment variable to delete a "file". If
        the call to H5Fdelete() fails, the tool will attempt to use
        the POSIX remove(3) call to remove the file.

        Note that the HDF5 library does currently have support for
        H5Fdelete() in the native VOL connector.

        (DER - 2020/12/16)

    - h5repack added options to control how external links are handled.

        Currently h5repack preserves external links and cannot copy and merge
        data from the external files. Two options, merge and prune, were added to
        control how to merge data from an external link into the resulting file.
            --merge             Follow external soft link recursively and merge data.
            --prune             Do not follow external soft links and remove link.
            --merge --prune     Follow external link, merge data and remove dangling link.

        (ADB - 2020/08/05, HDFFV-9984)

    - h5repack was fixed to repack the reference attributes properly.
        The code line that checks if the update of reference inside a compound
        datatype is misplaced outside the code block loop that carries out the
        check. In consequence, the next attribute that is not the reference
        type was repacked again as the reference type and caused the failure of
        repacking. The fix is to move the corresponding code line to the correct
        code block.

        (KY -2020/02/07, HDFFV-11014)

    - h5diff was updated to use the new reference APIs.

        h5diff uses the new reference APIs to compare references.
        Attribute references can also be compared.

        (ADB - 2019/12/19, HDFFV-10980)

    - h5dump and h5ls were updated to use the new reference APIs.

        The tools library now use the new reference APIs to inspect a
        file. Also the DDL spec was updated to reflect the format
        changes produced with the new APIs. The export API and support
        functions in the JNI were updated to match.

        (ADB - 2019/12/06, HDFFV-10876 and HDFFV-10877)


    High-Level APIs:
    ----------------
    -

    C Packet Table API:
    -------------------
    -

    Internal header file:
    ---------------------
    -

    Documentation:
    --------------
    -

Support for new platforms, languages and compilers
==================================================
    -

Bug Fixes since HDF5-1.12.0 release
===================================
    Library
    -------
    - Remove underscores on header file guards

        Header file guards used a variety of underscores at the beginning the define.

        Removed all leading (some trailing) underscores from header file guards.

        (ADB - 2021/03/03, #361)

    - Fixed issue with MPI communicator and info object not being
      copied into new FAPL retrieved from H5F_get_access_plist

        Added logic to copy the MPI communicator and info object into
        the output FAPL. MPI communicator is retrieved from the VFD, while
        the MPI info object is retrieved from the file's original FAPL.

        (JTH - 2021/02/15, HDFFV-11109)

    - Fixed problems with vlens and refs inside compound using
      H5VLget_file_type()

        Modified library to properly ref count H5VL_object_t structs and only
        consider file vlen and reference types to be equal if their files are
        the same.

        (NAF - 2021/01/22)

    - Creation of dataset with optional filter

        When the combination of type, space, etc doesn't work for filter
        and the filter is optional, it was supposed to be skipped but it was
        not skipped and the creation failed.

        Allowed the creation of the dataset in such situation.

        (BMR - 2020/08/13, HDFFV-10933)

    - Explicitly declared dlopen to use RTLD_LOCAL

        dlopen documentation states that if neither RTLD_GLOBAL nor
        RTLD_LOCAL are specified, then the default behavior is unspecified.
        The default on linux is usually RTLD_LOCAL while macos will default
        to RTLD_GLOBAL.

        (ADB - 2020/08/12, HDFFV-11127)

    - H5Sset_extent_none() sets the dataspace class to H5S_NO_CLASS which
      causes asserts/errors when passed to other dataspace API calls.

        H5S_NO_CLASS is an internal class value that should not have been
        exposed via a public API call.

        In debug builds of the library, this can cause asserts to trip. In
        non-debug builds, it will produce normal library errors.

        The new library behavior is for H5Sset_extent_none() to convert
        the dataspace into one of type H5S_NULL, which is better handled
        by the library and easier for developers to reason about.

        (DER - 2020/07/27, HDFFV-11027)

    - Fixed issues CVE-2018-13870 and CVE-2018-13869

        When a buffer overflow occurred because a name length was corrupted
        and became very large, h5dump crashed on memory access violation.

        A check for reading pass the end of the buffer was added to multiple
        locations to prevent the crashes and h5dump now simply fails with an
        error message when this error condition occurs.

        (BMR - 2020/07/22, HDFFV-11120 and HDFFV-11121)

    - Fixed the segmentation fault when reading attributes with multiple threads

        It was reported that the reading of attributes with variable length string
        datatype will crash with segmentation fault particularly when the number of
        threads is high (>16 threads).  The problem was due to the file pointer that
        was set in the variable length string datatype for the attribute.  That file
        pointer was already closed when the attribute was accessed.

        The problem was fixed by setting the file pointer to the current opened file pointer
        when the attribute was accessed.  Similar patch up was done before when reading
        dataset with variable length string datatype.

        (VC - 2020/07/13, HDFFV-11080)

    - Fixed CVE-2020-10810

        The tool h5clear produced a segfault during an error recovery in
        the superblock decoding.  An internal pointer was reset to prevent
        further accessing when it is not assigned with a value.

        (BMR - 2020/06/29, HDFFV-11053)

    - Fixed CVE-2018-17435

        The tool h52gif produced a segfault when the size of an attribute
        message was corrupted and caused a buffer overflow.

        The problem was fixed by verifying the attribute message's size
        against the buffer size before accessing the buffer.  h52gif was
        also fixed to display the failure instead of silently exiting
        after the segfault was eliminated.

        (BMR - 2020/06/19, HDFFV-10591)


    Java Library
    ------------
    - JNI utility function does not handle new references.

        The JNI utility function for converting reference data to string did
        not use the new APIs. In addition to fixing that function, added new
        java tests for using the new APIs.

        (ADB - 2021/02/16, HDFFV-11212)

    - The H5FArray.java class, in which virtually the entire execution time
        is spent using the HDFNativeData method that converts from an array
        of bytes to an array of the destination Java type.

        1. Convert the entire byte array into a 1-d array of the desired type,
           rather than performing 1 conversion per row;
        2. Use the Java Arrays method copyOfRange to grab the section of the
           array from (1) that is desired to be inserted into the destination array.

        (PGT,ADB - 2020/12/13, HDFFV-10865)

    - Added ability to test java library with VOLs.

        Created new CMake script that combines the java and vol test scripts.

        (ADB - 2020/02/03, HDFFV-10996)

    - Tests fail for non-English locale.

        In the JUnit tests with a non-English locale, only the part before
        the decimal comma is replaced by XXXX and this leads to a comparison
        error. Changed the regex for the Time substitution.

        (ADB - 2020/01/09, HDFFV-10995)


    Configuration
    -------------
    - Reclassify CMake messages, to allow new modes and --log-level option

      CMake message commands have a mode argument. By default, STATUS mode
      was chosen for any non-error message. CMake version 3.15 added additional
      modes, NOTICE, VERBOSE, DEBUG and TRACE. All message commands with a mode
      of STATUS were reviewed and most were reclassified as VERBOSE. The new
      mode was protected by a check for a CMake version of at least 3.15. If CMake
      version 3.17 or above is used, the user can use the command line option
      of "--log-level" to further restrict which message commands are displayed.

      (ADB - 2021/01/11, HDFFV-11144)

    - Fixes Autotools determination of the stat struct having an st_blocks field

      A missing parenthesis in an autoconf macro prevented building the test
      code used to determine if the stat struct contains the st_blocks field.
      Now that the test functions correctly, the H5_HAVE_STAT_ST_BLOCKS #define
      found in H5pubconf.h will be defined correctly on both the Autotools and
      CMake. This #define is only used in the tests and does not affect the
      HDF5 C library.

      (DER - 2021/01/07, HDFFV-11201)


    Tools
    -----
    - Fixed tools argument parsing.

        Tools parsing used the length of the option from the long array to match
        the option from the command line. This incorrectly matched a shorter long
        name option that was happened to be a subset of another long option.
        Changed to match whole names.

        (ADB - 2021/01/19, HDFFV-11106)

    - The tools library was updated by standardizing the error stack process.

        General sequence is:
          h5tools_setprogname(PROGRAMNAME);
          h5tools_setstatus(EXIT_SUCCESS);
          h5tools_init();
          ... process the command-line (check for error-stack enable) ...
          h5tools_error_report();
          ... (do work) ...
          h5diff_exit(ret);

        (ADB - 2020/07/20, HDFFV-11066)

    - h5diff fixed a command line parsing error.

        h5diff would ignore the argument to -d (delta) if it is smaller than DBL_EPSILON.
        The macro H5_DBL_ABS_EQUAL was removed and a direct value comparision was used.

        (ADB - 2020/07/20, HDFFV-10897)

    - h5diff added a command line option to ignore attributes.

        h5diff would ignore all objects with a supplied path if the exclude-path argument is used.
        Adding the exclude-attribute argument will only eclude attributes, with the supplied path,
        from comparision.

        (ADB - 2020/07/20, HDFFV-5935)

    - h5diff added another level to the verbose argument to print filenames.

        Added verbose level 3 that is level 2 plus the filenames. The levels are:
          0 : Identical to '-v' or '--verbose'
          1 : All level 0 information plus one-line attribute status summary
          2 : All level 1 information plus extended attribute status report
          3 : All level 2 information plus file names

        (ADB - 2020/07/20, HDFFV-10005)

    - h5repack was fixed to repack the reference attributes properly.

        The code line that checks if the update of reference inside a compound
        datatype is misplaced outside the code block loop that carries out the
        check. In consequence, the next attribute that is not the reference
        type was repacked again as the reference type and caused the failure of
        repacking. The fix is to move the corresponding code line to the correct
        code block.

        (KY -2020/02/10, HDFFV-11014)

    - h5diff was updated to use the new reference APIs.

        h5diff uses the new reference APIs to compare references.
        Attribute references can also be compared.

        (ADB - 2019/12/19, HDFFV-10980)

    - h5dump and h5ls were updated to use the new reference APIs.

        The tools library now use the new reference APIs to inspect a
        file. Also the DDL spec was updated to reflect the format
        changes produced with the new APIs. The export API and support
        functions in the JNI were updated to match.

        (ADB - 2019/12/06, HDFFV-10876 and HDFFV-10877)


    Performance
    -------------
    -


    Fortran API
    -----------
    - Corrected INTERFACE INTENT(IN) to INTENT(OUT) for buf_size in h5fget_file_image_f.

        (MSB - 2020/02/18, HDFFV-11029)


    High-Level Library
    ------------------
    -


    Fortran High-Level APIs
    -----------------------
    -


    Documentation
    -------------
    -


    F90 APIs
    --------
    -


    C++ APIs
    --------
    -


    Testing
    -------
    - Stopped java/test/junit.sh.in installing libs for testing under ${prefix}

        Lib files needed are now copied to a subdirectory in the java/test
        directory, and on Macs the loader path for libhdf5.xxxs.so is changed
        in the temporary copy of libhdf5_java.dylib.

        (LRK, 2020/07/02, HDFFV-11063)


Supported Platforms
===================

    Linux 2.6.32-696.16.1.el6.ppc64 gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-18)
    #1 SMP ppc64 GNU/Linux        g++ (GCC) 4.4.7 20120313 (Red Hat 4.4.7-18)
    (ostrich)                     GNU Fortran (GCC) 4.4.7 20120313 (Red Hat 4.4.7-18)
                                  IBM XL C/C++ V13.1
                                  IBM XL Fortran V15.1

    Linux 3.10.0-327.10.1.el7   GNU C (gcc), Fortran (gfortran), C++ (g++)
    #1 SMP x86_64 GNU/Linux       compilers:
    (kituo/moohan)                Version 4.8.5 20150623 (Red Hat 4.8.5-4)
                                    Version 4.9.3, Version 5.2.0,
                                  Intel(R) C (icc), C++ (icpc), Fortran (icc)
                                  compilers:
                                     Version 17.0.0.098 Build 20160721
                                  MPICH 3.1.4 compiled with GCC 4.9.3

    SunOS 5.11 32- and 64-bit     Sun C 5.12 SunOS_sparc
    (emu)                         Sun Fortran 95 8.6 SunOS_sparc
                                  Sun C++ 5.12 SunOS_sparc

    Windows 10 x64                Visual Studio 2015 w/ Intel Fortran 18 (cmake)
                                  Visual Studio 2017 w/ Intel Fortran 19 (cmake)
                                  Visual Studio 2019 w/ Intel Fortran 19 (cmake)
                                  Visual Studio 2019 w/ MSMPI 10.1 (cmake)

    Mac OS X Yosemite 10.10.5     Apple clang/clang++ version 6.1 from Xcode 7.0
    64-bit                        gfortran GNU Fortran (GCC) 4.9.2
    (osx1010dev/osx1010test)      Intel icc/icpc/ifort version 15.0.3

    Mac OS X El Capitan 10.11.6   Apple clang/clang++ version 7.3.0 from Xcode 7.3
    64-bit                        gfortran GNU Fortran (GCC) 5.2.0
    (osx1011dev/osx1011test)      Intel icc/icpc/ifort version 16.0.2

    Mac OS Sierra 10.12.6         Apple LLVM version 8.1.0 (clang/clang++-802.0.42)
    64-bit                        gfortran GNU Fortran (GCC) 7.1.0
    (swallow/kite)                Intel icc/icpc/ifort version 17.0.2


Tested Configuration Features Summary
=====================================

    In the tables below
          y   = tested
          n   = not tested in this release
          C   = Cluster
          W   = Workstation
          x   = not working in this release
          dna = does not apply
          ( ) = footnote appears below second table
          <blank> = testing incomplete on this feature or platform

Platform                              C         F90/   F90      C++  zlib  SZIP
                                      parallel  F2003  parallel
Solaris2.11 32-bit                      n        y/y    n        y    y     y
Solaris2.11 64-bit                      n        y/n    n        y    y     y
Windows 10                              y        y/y    n        y    y     y
Windows 10 x64                          y        y/y    n        y    y     y
Mac OS X Mountain Lion 10.8.5 64-bit    n        y/y    n        y    y     y
Mac OS X Mavericks 10.9.5 64-bit        n        y/y    n        y    y     ?
Mac OS X Yosemite 10.10.5 64-bit        n        y/y    n        y    y     ?
Mac OS X El Capitan 10.11.6 64-bit      n        y/y    n        y    y     ?
CentOS 6.7 Linux 2.6.18 x86_64 GNU      n        y/y    n        y    y     y
CentOS 6.7 Linux 2.6.18 x86_64 Intel    n        y/y    n        y    y     y
CentOS 6.7 Linux 2.6.32 x86_64 PGI      n        y/y    n        y    y     y
CentOS 7.2 Linux 2.6.32 x86_64 GNU      y        y/y    y        y    y     y
CentOS 7.2 Linux 2.6.32 x86_64 Intel    n        y/y    n        y    y     y
Linux 2.6.32-573.18.1.el6.ppc64         n        y/n    n        y    y     y


Platform                                 Shared  Shared    Shared    Thread-
                                         C libs  F90 libs  C++ libs  safe
Solaris2.11 32-bit                         y       y         y         y
Solaris2.11 64-bit                         y       y         y         y
Windows 10                                 y       y         y         y
Windows 10 x64                             y       y         y         y
Mac OS X Mountain Lion 10.8.5 64-bit       y       n         y         y
Mac OS X Mavericks 10.9.5 64-bit           y       n         y         y
Mac OS X Yosemite 10.10.5 64-bit           y       n         y         y
Mac OS X El Capitan 10.11.6 64-bit         y       n         y         y
CentOS 6.7 Linux 2.6.18 x86_64 GNU         y       y         y         y
CentOS 6.7 Linux 2.6.18 x86_64 Intel       y       y         y         n
CentOS 6.7 Linux 2.6.32 x86_64 PGI         y       y         y         n
CentOS 7.2 Linux 2.6.32 x86_64 GNU         y       y         y         n
CentOS 7.2 Linux 2.6.32 x86_64 Intel       y       y         y         n
Linux 2.6.32-573.18.1.el6.ppc64            y       y         y         n

Compiler versions for each platform are listed in the preceding
"Supported Platforms" table.


More Tested Platforms
=====================
The following platforms are not supported but have been tested for this release.

    Linux 2.6.32-573.22.1.el6    GNU C (gcc), Fortran (gfortran), C++ (g++)
    #1 SMP x86_64 GNU/Linux       compilers:
    (mayll/platypus)                 Version 4.4.7 20120313
                                     Version 4.9.3, 5.3.0, 6.2.0
                                  PGI C, Fortran, C++ for 64-bit target on
                                  x86-64;
                                      Version 17.10-0
                                  Intel(R) C (icc), C++ (icpc), Fortran (icc)
                                  compilers:
                                     Version 17.0.4.196 Build 20170411
                                  MPICH 3.1.4 compiled with GCC 4.9.3

    Linux 3.10.0-327.18.2.el7     GNU C (gcc) and C++ (g++) compilers
    #1 SMP x86_64 GNU/Linux          Version 4.8.5 20150623 (Red Hat 4.8.5-4)
    (jelly)                       with NAG Fortran Compiler Release 6.1(Tozai)
                                  GCC Version 7.1.0
                                  OpenMPI 3.0.0-GCC-7.2.0-2.29
                                  Intel(R) C (icc) and C++ (icpc) compilers
                                     Version 17.0.0.098 Build 20160721
                                  with NAG Fortran Compiler Release 6.1(Tozai)

    Linux 3.10.0-327.10.1.el7     MPICH 3.2 compiled with GCC 5.3.0
    #1 SMP x86_64 GNU/Linux
    (moohan)

    Linux 2.6.32-573.18.1.el6.ppc64  MPICH mpich 3.1.4 compiled with
    #1 SMP ppc64 GNU/Linux           IBM XL C/C++ for Linux, V13.1
    (ostrich)                        and IBM XL Fortran for Linux, V15.1

    Fedora33 5.10.10-200.fc33.x86_64
    #1 SMP x86_64  GNU/Linux         GNU gcc (GCC) 10.2.1 20201125 (Red Hat 10.2.1-9)
                                     GNU Fortran (GCC) 10.2.1 20201125 (Red Hat 10.2.1-9)
                                     clang version 11.0.0 (Fedora 11.0.0-2.fc33)
                                     (cmake and autotools)

    Ubuntu20.10 5.8.0-41-generic-x86_64
    #46-Ubuntu SMP x86_64  GNU/Linux GNU gcc (GCC) 10.2.0-13ubuntu1
                                     GNU Fortran (GCC) 10.2.0-13ubuntu1
                                     (cmake and autotools)

    SUSE15sp2 5.3.18-22-default
    #1 SMP x86_64  GNU/Linux         GNU gcc (SUSE Linux) 7.5.0
                                     GNU Fortran (SUSE Linux) 7.5.0
                                     clang version 7.0.1 (tags/RELEASE_701/final 349238)
                                     (cmake and autotools)


Known Problems
==============
    CMake files do not behave correctly with paths containing spaces.
    Do not use spaces in paths because the required escaping for handling spaces
    results in very complex and fragile build files.
    ADB - 2019/05/07

    At present, metadata cache images may not be generated by parallel
    applications.  Parallel applications can read files with metadata cache
    images, but since this is a collective operation, a deadlock is possible
    if one or more processes do not participate.

    CPP ptable test fails on both VS2017 and VS2019 with Intel compiler, JIRA
    issue: HDFFV-10628.  This test will pass with VS2015 with Intel compiler.

    Known problems in previous releases can be found in the HISTORY*.txt files
    in the HDF5 source. Please report any new problems found to
    help@hdfgroup.org.


CMake vs. Autotools installations
=================================
While both build systems produce similar results, there are differences.
Each system produces the same set of folders on linux (only CMake works
on standard Windows); bin, include, lib and share. Autotools places the
COPYING and RELEASE.txt file in the root folder, CMake places them in
the share folder.

The bin folder contains the tools and the build scripts. Additionally, CMake
creates dynamic versions of the tools with the suffix "-shared". Autotools
installs one set of tools depending on the "--enable-shared" configuration
option.
  build scripts
  -------------
  Autotools: h5c++, h5cc, h5fc
  CMake: h5c++, h5cc, h5hlc++, h5hlcc

The include folder holds the header files and the fortran mod files. CMake
places the fortran mod files into separate shared and static subfolders,
while Autotools places one set of mod files into the include folder. Because
CMake produces a tools library, the header files for tools will appear in
the include folder.

The lib folder contains the library files, and CMake adds the pkgconfig
subfolder with the hdf5*.pc files used by the bin/build scripts created by
the CMake build. CMake separates the C interface code from the fortran code by
creating C-stub libraries for each Fortran library. In addition, only CMake
installs the tools library. The names of the szip libraries are different
between the build systems.

The share folder will have the most differences because CMake builds include
a number of CMake specific files for support of CMake's find_package and support
for the HDF5 Examples CMake project.