path: root/release_docs/RELEASE.txt

HDF5 version 1.15.0 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 HDF5-1.16.x release series
can be found at:

     https://portal.hdfgroup.org/display/HDF5/Release+Specific+Information

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 HDF5-1.14.0
- Platforms Tested
- Known Problems
- CMake vs. Autotools installations


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

    Configuration:
    -------------
    - The CMake HDF5_ENABLE_DEBUG_H5B option has been removed

      This enabled some additional version-1 B-tree checks. These have been
      removed so the option is no longer necessary.

      This option was CMake-only and marked as advanced.

    - New option for building with static CRT in Windows

      The following option has been added:
        HDF5_BUILD_STATIC_CRT_LIBS    "Build With Static Windows CRT Libraries"          OFF
      Because our minimum CMake is 3.18, the macro to change runtime flags no longer
      works as CMake changed the default behavior in CMake 3.15.

      Fixes GitHub issue #3984

    - Added support for the new MSVC preprocessor

      Microsoft added support for a new, standards-conformant preprocessor
      to MSVC, which can be enabled with the /Zc:preprocessor option. This
      preprocessor would trip over our HDopen() variadic function-like
      macro, which uses a feature that only works with the legacy preprocessor.

      ifdefs have been added that select the correct HDopen() form and
      allow building HDF5 with the /Zc:preprocessor option.

      The HDopen() macro is located in an internal header file and only
      affects building the HDF5 library from source.

      Fixes GitHub #2515

    - Renamed HDF5_ENABLE_USING_MEMCHECKER to HDF5_USING_ANALYSIS_TOOL

      The HDF5_USING_ANALYSIS_TOOL is used to indicate to test macros that
      an analysis tool is being used and that the tests should not use
      the runTest.cmake macros and it's variations. The analysis tools,
      like valgrind, test the macro code instead of the program under test.

      HDF5_ENABLE_USING_MEMCHECKER is still used for controlling the HDF5
      define, H5_USING_MEMCHECKER.

    - New option for building and naming tools in CMake

      The following option has been added:
        HDF5_BUILD_STATIC_TOOLS    "Build Static Tools Not Shared Tools"          OFF

      The default will build shared tools unless BUILD_SHARED_LIBS = OFF.
      Tools will no longer have "-shared" as only one set of tools will be created.

    - Incorporated HDF5 examples repository into HDF5 library.

      The HDF5Examples folder is equivalent to the repository hdf5-examples.
      As such it can build and test the examples during library build or after
      the library is installed. Previously, the hdf5-repository archives were
      downloaded for packaging with the library. Now the examples can be built
      and tested without a packaged install of the library.

      However to maintain the ability to use the HDF5Examples with an installed
      library, it is necessary to translate or synch the option names from those
      used by the library to those used by the examples. The typical pattern is:
            <example option> = <library option>
            HDF_BUILD_FORTRAN = ${HDF5_BUILD_FORTRAN}

    - Added new option for CMake to mark tests as SKIPPED.

      HDF5_DISABLE_TESTS_REGEX is a REGEX string that will be checked with
      test names and if there is a match then that test's property will be
      set to DISABLED. HDF5_DISABLE_TESTS_REGEX can be initialized on the
      command line: "-DHDF5_DISABLE_TESTS_REGEX:STRING=<regex>"
      See CMake documentation for regex-specification.

    - Added defaults to CMake for long double conversion checks

      HDF5 performs a couple of checks at build time to see if long double
      values can be converted correctly (IBM's Power architecture uses a
      special format for long doubles). These checks were performed using
      TRY_RUN, which is a problem when cross-compiling.

      These checks now use default values appropriate for most non-Power
      systems when cross-compiling. The cache values can be pre-set if
      necessary, which will preempt both the TRY_RUN and the default.

      Affected values:
        H5_LDOUBLE_TO_LONG_SPECIAL      (default no)
        H5_LONG_TO_LDOUBLE_SPECIAL      (default no)
        H5_LDOUBLE_TO_LLONG_ACCURATE    (default yes)
        H5_LLONG_TO_LDOUBLE_CORRECT     (default yes)
        H5_DISABLE_SOME_LDOUBLE_CONV    (default no)

      Fixes GitHub #3585

    - Improved support for Intel oneAPI

      * Separates the old 'classic' Intel compiler settings and warnings
        from the oneAPI settings
      * Uses `-check nouninit` in debug builds to avoid false positives
        when building H5_buildiface with `-check all`
      * Both Autotools and CMake

    - Added new options for CMake and Autotools to control the Doxygen
      warnings as errors setting.

        * HDF5_ENABLE_DOXY_WARNINGS: ON/OFF (Default: ON)
        * --enable-doxygen-errors: enable/disable (Default: enable)

      The default will fail compile if the doxygen parsing generates warnings.
      The option can be disabled if certain versions of doxygen have parsing
      issues. i.e. 1.9.5, 1.9.8.

      Addresses GitHub issue #3398

    - Added support for AOCC and classic Flang w/ the Autotools

      * Adds a config/clang-fflags options file to support Flang
      * Corrects missing "-Wl," from linker options in the libtool wrappers
        when using Flang, the MPI Fortran compiler wrappers, and building
        the shared library. This would often result in unrecognized options
        like -soname.
      * Enable -nomp w/ Flang to avoid linking to the OpenMPI library.

      CMake can build the parallel, shared library w/ Fortran using AOCC
      and Flang, so no changes were needed for that build system.

      Fixes GitHub issues #3439, #1588, #366, #280

    - Converted the build of libaec and zlib to use FETCH_CONTENT with CMake.

      Using the CMake FetchContent module, the external filters can populate
      content at configure time via any method supported by the ExternalProject
      module. Whereas ExternalProject_Add() downloads at build time, the
      FetchContent module makes content available immediately, allowing the
      configure step to use the content in commands like add_subdirectory(),
      include() or file() operations.

      Removed HDF options for using FETCH_CONTENT explicitly:
          BUILD_SZIP_WITH_FETCHCONTENT:BOOL
          BUILD_ZLIB_WITH_FETCHCONTENT:BOOL

    - Thread-safety + static library disabled on Windows w/ CMake

      The thread-safety feature requires hooks in DllMain(), which is only
      present in the shared library.

      We previously just warned about this, but now any CMake configuration
      that tries to build thread-safety and the static library will fail.
      This cannot be overridden with ALLOW_UNSUPPORTED.

      Fixes GitHub issue #3613

    - Autotools builds now build the szip filter by default when an appropriate
      library is found

      Since libaec is prevalent and BSD-licensed for both encoding and
      decoding, we build the szip filter by default now.

      Both autotools and CMake build systems will process the szip filter the same as
      the zlib filter is processed.

    - Removed CMake cross-compiling variables

      * HDF5_USE_PREGEN
      * HDF5_BATCH_H5DETECT

      These were used to work around H5detect and H5make_libsettings and
      are no longer required.

    - Running H5make_libsettings is no longer required for cross-compiling

      The functionality of H5make_libsettings is now handled via template files,
      so H5make_libsettings has been removed.

    - Running H5detect is no longer required for cross-compiling

      The functionality of H5detect is now exercised at library startup,
      so H5detect has been removed.

    - Updated HDF5 API tests CMake code to support VOL connectors

      * Implemented support for fetching, building and testing HDF5
        VOL connectors during the library build process and documented
        the feature under doc/cmake-vols-fetchcontent.md

      * Implemented the HDF5_TEST_API_INSTALL option that enables
        installation of the HDF5 API tests on the system

    - Added new CMake options for building and running HDF5 API tests
      (Experimental)

      HDF5 API tests are an experimental feature, primarily targeted
      toward HDF5 VOL connector authors, that is currently being developed.
      These tests exercise the HDF5 API and are being integrated back
      into the HDF5 library from the HDF5 VOL tests repository
      (https://github.com/HDFGroup/vol-tests). To support this feature,
      the following new options have been added to CMake:

        * HDF5_TEST_API: ON/OFF (Default: OFF)

          Controls whether the HDF5 API tests will be built. These tests
          will only be run during testing of HDF5 if the HDF5_TEST_SERIAL
          (for serial tests) and HDF5_TEST_PARALLEL (for parallel tests)
          options are enabled.

        * HDF5_TEST_API_INSTALL: ON/OFF (Default: OFF)

          Controls whether the HDF5 API test executables will be installed
          on the system alongside the HDF5 library. This option is currently
          not functional.

        * HDF5_TEST_API_ENABLE_ASYNC: ON/OFF (Default: OFF)

          Controls whether the HDF5 Async API tests will be built. These
          tests will only be run if the VOL connector used supports Async
          operations.

        * HDF5_TEST_API_ENABLE_DRIVER: ON/OFF (Default: OFF)

          Controls whether to build the HDF5 API test driver program. This
          test driver program is useful for VOL connectors that use a
          client/server model where the server needs to be up and running
          before the VOL connector can function. This option is currently
          not functional.

        * HDF5_TEST_API_SERVER: String (Default: "")

          Used to specify a path to the server executable that the test
          driver program should execute.

    - Added support for CMake presets file.

      CMake supports two main files, CMakePresets.json and CMakeUserPresets.json,
      that allow users to specify common configure options and share them with others.
      HDF added a CMakePresets.json file of a typical configuration and support
      file, config/cmake-presets/hidden-presets.json. 
      Also added a section to INSTALL_CMake.txt with very basic explanation of the
      process to use CMakePresets.

    - Deprecated and removed old SZIP library in favor of LIBAEC library

      LIBAEC library has been used in HDF5 binaries as the szip library of choice
      for a few years. We are removing the options for using the old SZIP library.

      Also removed the config/cmake/FindSZIP.cmake file.

    - Enabled instrumentation of the library by default in CMake for parallel
      debug builds

      HDF5 can be configured to instrument portions of the parallel library to
      aid in debugging. Autotools builds of HDF5 turn this capability on by
      default for parallel debug builds and off by default for other build types.
      CMake has been updated to match this behavior.

    - Added new option to build libaec and zlib inline with CMake.

      Using the CMake FetchContent module, the external filters can populate
      content at configure time via any method supported by the ExternalProject
      module. Whereas ExternalProject_Add() downloads at build time, the
      FetchContent module makes content available immediately, allowing the
      configure step to use the content in commands like add_subdirectory(),
      include() or file() operations.

      The HDF options (and defaults) for using this are:
          BUILD_SZIP_WITH_FETCHCONTENT:BOOL=OFF
          LIBAEC_USE_LOCALCONTENT:BOOL=OFF
          BUILD_ZLIB_WITH_FETCHCONTENT:BOOL=OFF
          ZLIB_USE_LOCALCONTENT:BOOL=OFF

      The CMake variables to control the path and file names:
          LIBAEC_TGZ_ORIGPATH:STRING
          LIBAEC_TGZ_ORIGNAME:STRING
          ZLIB_TGZ_ORIGPATH:STRING
          ZLIB_TGZ_ORIGNAME:STRING

      See the CMakeFilters.cmake and config/cmake/cacheinit.cmake files for usage.

    - Added the CMake variable HDF5_ENABLE_ROS3_VFD to the HDF5 CMake config
      file hdf5-config.cmake. This allows to easily detect if the library
      has been built with or without read-only S3 functionality.

    Library:
    --------
    - Implemented optimized support for vector I/O in the Subfiling VFD

      Previously, the Subfiling VFD would handle vector I/O requests by
      breaking them down into individual I/O requests, one for each entry
      in the I/O vectors provided. This could result in poor I/O performance
      for features in HDF5 that utilize vector I/O, such as parallel I/O
      to filtered datasets. The Subfiling VFD now properly handles vector
      I/O requests in their entirety, resulting in fewer I/O calls, improved
      vector I/O performance and improved vector I/O memory efficiency.
    
    - Added a simple cache to the read-only S3 (ros3) VFD

      The read-only S3 VFD now caches the first N bytes of a file stored
      in S3 to avoid a lot of small I/O operations when opening files.
      This cache is per-file and created when the file is opened.

      N is currently 16 MiB or the size of the file, whichever is smaller.

      Addresses GitHub issue #3381

    - Added new API function H5Pget_actual_selection_io_mode()

      This function allows the user to determine if the library performed
      selection I/O, vector I/O, or scalar (legacy) I/O during the last HDF5
      operation performed with the provided DXPL.

    - Added support for in-place type conversion in most cases

      In-place type conversion allows the library to perform type conversion
      without an intermediate type conversion buffer.  This can improve
      performance by allowing I/O in a single operation over the entire
      selection instead of being limited by the size of the intermediate buffer.
      Implemented for I/O on contiguous and chunked datasets when the selection
      is contiguous in memory and when the memory datatype is not smaller than
      the file datatype.

    - Changed selection I/O to be on by default when using the MPIO file driver

    - Added support for selection I/O in the MPIO file driver

      Previously, only vector I/O operations were supported.  Support for
      selection I/O should improve performance and reduce memory uses in some
      cases.

    - Changed the error handling for a not found path in the find plugin process.

      While attempting to load a plugin the HDF5 library will fail if one of the
      directories in the plugin paths does not exist, even if there are more paths
      to check. Instead of exiting the function with an error, just logged the error
      and continue processing the list of paths to check.

    - Implemented support for temporary security credentials for the Read-Only
      S3 (ROS3) file driver.

      When using temporary security credentials, one also needs to specify a
      session/security token next to the access key id and secret access key.
      This token can be specified by the new API function H5Pset_fapl_ros3_token().
      The API function H5Pget_fapl_ros3_token() can be used to retrieve
      the currently set token.

    - Added a Subfiling VFD configuration file prefix environment variable

      The Subfiling VFD now checks for values set in a new environment
      variable "H5FD_SUBFILING_CONFIG_FILE_PREFIX" to determine if the
      application has specified a pathname prefix to apply to the file
      path for its configuration file. For example, this can be useful
      for cases where the application wishes to write subfiles to a
      machine's node-local storage while placing the subfiling configuration
      file on a file system readable by all machine nodes.

    - Added H5Pset_selection_io(), H5Pget_selection_io(), and
      H5Pget_no_selection_io_cause() API functions to manage the selection I/O
      feature.  This can be used to enable collective I/O with type conversion,
      or it can be used with custom VFDs that support vector or selection I/O.

    - Added H5Pset_modify_write_buf() and H5Pget_modify_write_buf() API
      functions to allow the library to modify the contents of write buffers, in
      order to avoid malloc/memcpy.  Currently only used for type conversion
      with selection I/O.


    Parallel Library:
    -----------------
    - Added optimized support for the parallel compression feature when
      using the multi-dataset I/O API routines collectively

      Previously, calling H5Dwrite_multi/H5Dread_multi collectively in parallel
      with a list containing one or more filtered datasets would cause HDF5 to
      break out of the optimized multi-dataset I/O mode and instead perform I/O
      by looping over each dataset in the I/O request. The library has now been
      updated to perform I/O in a more optimized manner in this case by first
      performing I/O on all the filtered datasets at once and then performing
      I/O on all the unfiltered datasets at once.

    - Changed H5Pset_evict_on_close so that it can be called with a parallel
      build of HDF5

      Previously, H5Pset_evict_on_close would always fail when called from a
      parallel build of HDF5, stating that the feature is not supported with
      parallel HDF5. This failure would occur even if a parallel build of HDF5
      was used with a serial HDF5 application. H5Pset_evict_on_close can now
      be called regardless of the library build type and the library will
      instead fail during H5Fcreate/H5Fopen if the "evict on close" property
      has been set to true and the file is being opened for parallel access
      with more than 1 MPI process.


    Fortran Library:
    ----------------

    - Added Fortran H5E APIs:
      h5eregister_class_f, h5eunregister_class_f, h5ecreate_msg_f, h5eclose_msg_f
      h5eget_msg_f, h5epush_f, h5eget_num_f, h5ewalk_f, h5eget_class_name_f,
      h5eappend_stack_f, h5eget_current_stack_f, h5eset_current_stack_f, h5ecreate_stack_f,
      h5eclose_stack_f, h5epop_f, h5eprint_f (C h5eprint v2 signature)

    - Added API support for Fortran MPI_F08 module definitions:
      Adds support for MPI's MPI_F08 module datatypes: type(MPI_COMM) and type(MPI_INFO) for HDF5 APIs:
      H5PSET_FAPL_MPIO_F, H5PGET_FAPL_MPIO_F, H5PSET_MPI_PARAMS_F, H5PGET_MPI_PARAMS_F
      Ref. #3951

    - Added Fortran APIs:
      H5FGET_INTENT_F, H5SSEL_ITER_CREATE_F, H5SSEL_ITER_GET_SEQ_LIST_F,
      H5SSEL_ITER_CLOSE_F, H5S_mp_H5SSEL_ITER_RESET_F

    - Added Fortran Parameters:
      H5S_SEL_ITER_GET_SEQ_LIST_SORTED_F, H5S_SEL_ITER_SHARE_WITH_DATASPACE_F

    - Added Fortran Parameters:
      H5S_BLOCK_F and H5S_PLIST_F

    - The configuration definitions file, H5config_f.inc, is now installed
      and the HDF5 version number has been added to it.

    - Added Fortran APIs:
      h5fdelete_f

    - Added Fortran APIs:
      h5vlnative_addr_to_token_f and h5vlnative_token_to_address_f

    - Fixed an uninitialized error return value for hdferr
      to return the error state of the h5aopen_by_idx_f API.

    - Added h5pget_vol_cap_flags_f and related Fortran VOL
      capability definitions.

    - Fortran async APIs H5A, H5D, H5ES, H5G, H5F, H5L and H5O were added.

    - Added Fortran APIs:
      h5pset_selection_io_f, h5pget_selection_io_f,
      h5pget_actual_selection_io_mode_f,
      h5pset_modify_write_buf_f, h5pget_modify_write_buf_f

    - Added Fortran APIs:
      h5get_free_list_sizes_f, h5dwrite_chunk_f, h5dread_chunk_f,
      h5fget_info_f, h5lvisit_f, h5lvisit_by_name_f,
      h5pget_no_selection_io_cause_f, h5pget_mpio_no_collective_cause_f,
      h5sselect_shape_same_f, h5sselect_intersect_block_f,
      h5pget_file_space_page_size_f, h5pset_file_space_page_size_f,
      h5pget_file_space_strategy_f, h5pset_file_space_strategy_f

    - Removed "-commons" linking option on Darwin, as COMMON and EQUIVALENCE
      are no longer used in the Fortran source.

      Fixes GitHub issue #3571

    C++ Library:
    ------------
    -


    Java Library:
    -------------
    -


    Tools:
    ------
    -


    High-Level APIs:
    ----------------
    - Added Fortran HL API: h5doappend_f


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


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


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


Support for new platforms, languages and compilers
==================================================
    -
    
Bug Fixes since HDF5-1.14.0 release
===================================
    Library
    -------
    - Fixed asserts raised by large values of H5Pset_est_link_info() parameters

      If large values for est_num_entries and/or est_name_len were passed
      to H5Pset_est_link_info(), the library would attempt to create an
      object header NIL message to reserve enough space to hold the links in
      compact form (i.e., concatenated), which could exceed allowable object
      header message size limits and trip asserts in the library.

      This bug only occurred when using the HDF5 1.8 file format or later and
      required the product of the two values to be ~64k more than the size
      of any links written to the group, which would cause the library to
      write out a too-large NIL spacer message to reserve the space for the
      unwritten links.

      The library now inspects the phase change values to see if the dataset
      is likely to be compact and checks the size to ensure any NIL spacer
      messages won't be larger than the library allows.

      Fixes GitHub #1632

    - Fixed a bug where H5Tset_fields does not account for any offset
      set for a floating-point datatype when determining if values set
      for spos, epos, esize, mpos and msize make sense for the datatype

      Previously, H5Tset_fields did not take datatype offsets into account
      when determining if the values set make sense for the datatype.
      This would cause the function to fail when the precision for a
      datatype is correctly set such that the offset bits are not included.
      This has now been fixed.

    - Fixed H5Fget_access_plist so that it returns the file locking
      settings for a file

      When H5Fget_access_plist (and the internal H5F_get_access_plist)
      is called on a file, the returned File Access Property List has
      the library's default file locking settings rather than any
      settings set for the file. This causes two problems:

        - Opening an HDF5 file through an external link using H5Gopen,
          H5Dopen, etc. with H5P_DEFAULT for the Dataset/Group/etc.
          Access Property List will cause the external file to be opened
          with the library's default file locking settings rather than
          inheriting them from the parent file. This can be surprising
          when a file is opened with file locking disabled, but its
          external files are opened with file locking enabled.

        - An application cannot make use of the H5Pset_elink_fapl
          function to match file locking settings between an external
          file and its parent file without knowing the correct setting
          ahead of time, as calling H5Fget_access_plist on the parent
          file will not return the correct settings.

      This has been fixed by copying a file's file locking settings
      into the newly-created File Access Property List in H5F_get_access_plist.

      This fix partially addresses GitHub issue #4011

    - Memory usage growth issue

      Starting with the HDF5 1.12.1 release, an issue (GitHub issue #1256)
      was observed where running a simple program that has a loop of opening
      a file, reading from an object with a variable-length datatype and
      then closing the file would result in the process fairly quickly
      running out of memory. Upon further investigation, it was determined
      that this memory was being kept around in the library's datatype
      conversion pathway cache that is used to speed up datatype conversions
      which are repeatedly used within an HDF5 application's lifecycle. For
      conversions involving variable-length or reference datatypes, each of
      these cached pathway entries keeps a reference to its associated file
      for later use. Since the file was being closed and reopened on each
      loop iteration, and since the library compares for equality between
      instances of opened files (rather than equality of the actual files)
      when determining if it can reuse a cached conversion pathway, it was
      determining that no cached conversion pathways could be reused and was
      creating a new cache entry on each loop iteration during I/O. This
      would lead to constant growth of that cache and the memory it consumed,
      as well as constant growth of the memory consumed by each cached entry
      for the reference to its associated file.

      To fix this issue, the library now removes any cached datatype
      conversion path entries for variable-length or reference datatypes
      associated with a particular file when that file is closed.

      Fixes GitHub #1256

    - Suppressed floating-point exceptions in H5T init code

      The floating-point datatype initialization code in H5Tinit_float.c
      could raise FE_INVALID exceptions while munging bits and performing
      comparisons that might involve NaN. This was not a problem when the
      initialization code was executed in H5detect at compile time (prior
      to 1.14.3), but now that the code is executed at library startup
      (1.14.3+), these exceptions can be caught by user code, as is the
      default in the NAG Fortran compiler.

      Starting in 1.14.4, we now suppress floating-point exceptions while
      initializing the floating-point types and clear FE_INVALID before
      restoring the original environment.

      Fixes GitHub #3831

    - Fixed a file handle leak in the core VFD

      When opening a file with the core VFD and a file image, if the file
      already exists, the file check would leak the POSIX file handle.

      Fixes GitHub issue #635

    - Fixed some issues with chunk index metadata not getting read
      collectively when collective metadata reads are enabled

      When looking up dataset chunks during I/O, the parallel library
      temporarily disables collective metadata reads since it's generally
      unlikely that the application will read the same chunks from all
      MPI ranks. Leaving collective metadata reads enabled during
      chunk lookups can lead to hangs or other bad behavior depending
      on the chunk indexing structure used for the dataset in question.
      However, due to the way that dataset chunk index metadata was
      previously loaded in a deferred manner, this could mean that
      the metadata for the main chunk index structure or its
      accompanying pieces of metadata (e.g., fixed array data blocks)
      could end up being read independently if these chunk lookup
      operations are the first chunk index-related operation that
      occurs on a dataset. This behavior is generally observed when
      opening a dataset for which the metadata isn't in the metadata
      cache yet and then immediately performing I/O on that dataset.
      This behavior is not generally observed when creating a dataset
      and then performing I/O on it, as the relevant metadata will
      usually be in the metadata cache as a side effect of creating
      the chunk index structures during dataset creation. 

      This issue has been fixed by adding callbacks to the different
      chunk indexing structure classes that allow more explicit control
      over when chunk index metadata gets loaded. When collective
      metadata reads are enabled, the necessary index metadata will now
      get loaded collectively by all MPI ranks at the start of dataset
      I/O to ensure that the ranks don't unintentionally read this
      metadata independently further on. These changes fix collective
      loading of the main chunk index structure, as well as v2 B-tree
      root nodes, extensible array index blocks and fixed array data
      blocks. There are still pieces of metadata that cannot currently
      be loaded collectively, however, such as extensible array data
      blocks, data block pages and super blocks, as well as fixed array
      data block pages. These pieces of metadata are not necessarily
      read in by all MPI ranks since this depends on which chunks the
      ranks have selected in the dataset. Therefore, reading of these
      pieces of metadata remains an independent operation.

    - Fixed potential hangs in parallel library during collective I/O with
      independent metadata writes

      When performing collective parallel writes to a dataset where metadata
      writes are requested as (or left as the default setting of) independent,
      hangs could potentially occur during metadata cache sync points. This
      was due to incorrect management of the internal state tracking whether
      an I/O operation should be collective or not, causing the library to
      attempt collective writes of metadata when they were meant to be
      independent writes. During the metadata cache sync points, if the number
      of cache entries being flushed was a multiple of the number of MPI ranks
      in the MPI communicator used to access the HDF5 file, an equal amount of
      collective MPI I/O calls were made and the dataset write call would be
      successful. However, when the number of cache entries being flushed was
      NOT a multiple of the number of MPI ranks, the ranks with more entries
      than others would get stuck in an MPI_File_set_view call, while other
      ranks would get stuck in a post-write MPI_Barrier call. This issue has
      been fixed by correctly switching to independent I/O temporarily when
      writing metadata independently during collective dataset I/O.

    - Dropped support for MPI-2

      The MPI-2 supporting artifacts have been removed due to the cessation
      of MPI-2 maintenance and testing since version HDF5 1.12.

    - Fixed a bug with the way the Subfiling VFD assigns I/O concentrators

      During a file open operation, the Subfiling VFD determines the topology
      of the application and uses that to select a subset of MPI ranks that
      I/O will be forwarded to, called I/O concentrators. The code for this
      had previously assumed that the parallel job launcher application (e.g.,
      mpirun, srun, etc.) would distribute MPI ranks sequentially among a node
      until all processors on that node have been assigned before going on to
      the next node. When the launcher application mapped MPI ranks to nodes
      in a different fashion, such as round-robin, this could cause the Subfiling
      VFD to incorrectly map MPI ranks as I/O concentrators, leading to missing
      subfiles.

    - Fixed performance regression with some compound type conversions

      In-place type conversion was introduced for most use cases in 1.14.2.
      While being able to use the read buffer for type conversion potentially
      improves performance by performing the entire I/O at once, it also
      disables the optimized compound type conversion used when the destination
      is a subset of the source. Disabled in-place type conversion when using
      this optimized conversion and there is no benefit in terms of the I/O
      size.

    - Fixed an assertion in a previous fix for CVE-2016-4332

      An assert could fail when processing corrupt files that have invalid
      shared message flags (as in CVE-2016-4332).

      The assert statement in question has been replaced with pointer checks
      that don't raise errors. Since the function is in cleanup code, we do
      our best to close and free things, even when presented with partially
      initialized structs.

      Fixes CVE-2016-4332 and HDFFV-9950 (confirmed via the cve_hdf5 repo)

    - Fixed a file space allocation bug in the parallel library for chunked
      datasets

      With the addition of support for incremental file space allocation for
      chunked datasets with filters applied to them that are created/accessed
      in parallel, a bug was introduced to the library's parallel file space
      allocation code. This could cause file space to not be allocated correctly
      for datasets without filters applied to them that are created with serial
      file access and later opened with parallel file access. In turn, this could
      cause parallel writes to those datasets to place incorrect data in the file.

    - Fixed an assertion failure in Parallel HDF5 when a file can't be created
      due to an invalid library version bounds setting

      An assertion failure could occur in H5MF_settle_raw_data_fsm when a file
      can't be created with Parallel HDF5 due to specifying the use of a paged,
      persistent file free space manager
      (H5Pset_file_space_strategy(..., H5F_FSPACE_STRATEGY_PAGE, 1, ...)) with
      an invalid library version bounds combination
      (H5Pset_libver_bounds(..., H5F_LIBVER_EARLIEST, H5F_LIBVER_V18)). This
      has now been fixed.

    - Fixed bugs in selection I/O

      Previously, the library could fail in some cases when performing selection
      I/O with type conversion.

    - Fixed CVE-2018-13867

      A corrupt file containing an invalid local heap datablock address
      could trigger an assert failure when the metadata cache attempted
      to load the datablock from storage.

      The local heap now verifies that the datablock address is valid
      when the local heap header information is parsed.

    - Fixed CVE-2018-11202

      A malformed file could result in chunk index memory leaks. Under most
      conditions (i.e., when the --enable-using-memchecker option is NOT
      used), this would result in a small memory leak and and infinite loop
      and abort when shutting down the library. The infinite loop would be
      due to the "free list" package not being able to clear its resources
      so the library couldn't shut down. When the "using a memory checker"
      option is used, the free lists are disabled so there is just a memory
      leak with no abort on library shutdown.

      The chunk index resources are now correctly cleaned up when reading
      misparsed files and valgrind confirms no memory leaks.

    - Fixed an issue where an assert statement was converted to an
      incorrect error check statement

      An assert statement in the library dealing with undefined dataset data
      fill values was converted to an improper error check that would always
      trigger when a dataset's fill value was set to NULL (undefined). This
      has now been fixed.

    - Fixed an assertion failure when attempting to use the Subfiling IOC
      VFD directly

      The Subfiling feature makes use of two Virtual File Drivers, the
      Subfiling VFD and the IOC (I/O Concentrator) VFD. The two VFDs are
      intended to be stacked together such that the Subfiling VFD sits
      "on top" of the IOC VFD and routes I/O requests through it; using the
      IOC VFD alone is currently unsupported. The IOC VFD has been fixed so
      that an error message is displayed in this situation rather than causing
      an assertion failure.

    - Fixed a potential bug when copying empty enum datatypes

      Copying an empty enum datatype (including implicitly, as when an enum
      is a part of a compound datatype) would fail in an assert in debug
      mode and could fail in release mode depending on how the platform
      handles undefined behavior regarding size 0 memory allocations and
      using memcpy with a NULL src pointer.

      The library is now more careful about using memory operations when
      copying empty enum datatypes and will not error or raise an assert.

    - Added an AAPL check to H5Acreate

      A check was added to H5Acreate to ensure that a failure is correctly
      returned when an invalid Attribute Access Property List is passed
      in to the function. The HDF5 API tests were failing for certain
      build types due to this condition not being checked previously.

    - Fixed a bug in H5Ocopy that could generate invalid HDF5 files

      H5Ocopy was missing a check to determine whether the new object's
      object header version is greater than version 1. Without this check,
      copying of objects with object headers that are smaller than a
      certain size would cause H5Ocopy to create an object header for the
      new object that has a gap in the header data. According to the
      HDF5 File Format Specification, this is not allowed for version
      1 of the object header format.

      Fixes GitHub issue #2653

    - Fixed H5Pget_vol_cap_flags and H5Pget_vol_id to accept H5P_DEFAULT

      H5Pget_vol_cap_flags and H5Pget_vol_id were updated to correctly
      accept H5P_DEFAULT for the 'plist_id' FAPL parameter. Previously,
      they would fail if provided with H5P_DEFAULT as the FAPL.

    - Fixed ROS3 VFD anonymous credential usage with h5dump and h5ls

      ROS3 VFD anonymous credential functionality became broken in h5dump
      and h5ls in the HDF5 1.14.0 release with the added support for VFD
      plugins, which changed the way that the tools handled setting of
      credential information that the VFD uses. The tools could be
      provided the command-line option of "--s3-cred=(,,)" as a workaround
      for anonymous credential usage, but the documentation for this
      option stated that anonymous credentials could be used by simply
      omitting the option. The latter functionality has been restored.

      Fixes GitHub issue #2406

    - Fixed memory leaks when processing malformed object header continuation messages

      Malformed object header continuation messages can result in a too-small
      buffer being passed to the decode function, which could lead to reading
      past the end of the buffer. Additionally, errors in processing these
      malformed messages can lead to allocated memory not being cleaned up.

      This fix adds bounds checking and cleanup code to the object header
      continuation message processing.

      Fixes GitHub issue #2604

    - Fixed memory leaks, aborts, and overflows in H5O EFL decode

      The external file list code could call assert(), read past buffer
      boundaries, and not properly clean up resources when parsing malformed
      external data files messages.

      This fix cleans up allocated memory, adds buffer bounds checks, and
      converts asserts to HDF5 error checking.

      Fixes GitHub issue #2605

    - Fixed potential heap buffer overflow in decoding of link info message

      Detections of buffer overflow were added for decoding version, index
      flags, link creation order value, and the next three addresses.  The
      checkings will remove the potential invalid read of any of these
      values that could be triggered by a malformed file.

      Fixes GitHub issue #2603

    - Memory leak

      Memory leak was detected when running h5dump with "pov".  The memory was allocated
      via H5FL__malloc() in hdf5/src/H5FL.c

      The fuzzed file "pov" was an HDF5 file containing an illegal continuation message.
      When deserializing the object header chunks for the file, memory is allocated for the
      array of continuation messages (cont_msg_info->msgs) in continuation message info struct.
      As error is encountered in loading the illegal message, the memory allocated for
      cont_msg_info->msgs needs to be freed.

      Fixes GitHub issue #2599

    - Fixed memory leaks that could occur when reading a dataset from a
      malformed file

      When attempting to read layout, pline, and efl information for a
      dataset, memory leaks could occur if attempting to read pline/efl
      information threw an error, which is due to the memory that was 
      allocated for pline and efl not being properly cleaned up on error.  

      Fixes GitHub issue #2602

    - Fixed potential heap buffer overrun in group info header decoding from malformed file

      H5O__ginfo_decode could sometimes read past allocated memory when parsing a
      group info message from the header of a malformed file.
  
      It now checks buffer size before each read to properly throw an error in these cases.
  
      Fixes GitHub issue #2601
      
    - Fixed potential buffer overrun issues in some object header decode routines

      Several checks were added to H5O__layout_decode and H5O__sdspace_decode to
      ensure that memory buffers don't get overrun when decoding buffers read from
      a (possibly corrupted) HDF5 file.

    - Fixed a heap buffer overflow that occurs when reading from
      a dataset with a compact layout within a malformed HDF5 file

      During opening of a dataset that has a compact layout, the
      library allocates a buffer that stores the dataset's raw data.
      The dataset's object header that gets written to the file
      contains information about how large of a buffer the library
      should allocate. If this object header is malformed such that
      it causes the library to allocate a buffer that is too small
      to hold the dataset's raw data, future I/O to the dataset can
      result in heap buffer overflows. To fix this issue, an extra
      check is now performed for compact datasets to ensure that
      the size of the allocated buffer matches the expected size
      of the dataset's raw data (as calculated from the dataset's
      dataspace and datatype information). If the two sizes do not
      match, opening of the dataset will fail.

      Fixes GitHub issue #2606

    - Fixed a memory corruption issue that can occur when reading
      from a dataset using a hyperslab selection in the file
      dataspace and a point selection in the memory dataspace

      When reading from a dataset using a hyperslab selection in
      the dataset's file dataspace and a point selection in the
      dataset's memory dataspace where the file dataspace's "rank"
      is greater than the memory dataspace's "rank", memory corruption
      could occur due to an incorrect number of selection points
      being copied when projecting the point selection onto the
      hyperslab selection's dataspace.

    - Fixed issues in the Subfiling VFD when using the SELECT_IOC_EVERY_NTH_RANK
      or SELECT_IOC_TOTAL I/O concentrator selection strategies

      Multiple bugs involving these I/O concentrator selection strategies
      were fixed, including:

        * A bug that caused the selection strategy to be altered when
          criteria for the strategy was specified in the
          H5FD_SUBFILING_IOC_SELECTION_CRITERIA environment variable as
          a single value, rather than in the old and undocumented
          'integer:integer' format
        * Two bugs which caused a request for 'N' I/O concentrators to
          result in 'N - 1' I/O concentrators being assigned, which also
          lead to issues if only 1 I/O concentrator was requested

      Also added a regression test for these two I/O concentrator selection
      strategies to prevent future issues. 

    - Fix CVE-2021-37501 / GHSA-rfgw-5vq3-wrjf

      Check for overflow when calculating on-disk attribute data size.

      A bogus hdf5 file may contain dataspace messages with sizes
      which lead to the on-disk data sizes to exceed what is addressable.
      When calculating the size, make sure, the multiplication does not
      overflow.
      The test case was crafted in a way that the overflow caused the
      size to be 0.

      Fixes GitHub #2458

    - Fixed an issue with collective metadata writes of global heap data

      New test failures in parallel netCDF started occurring with debug
      builds of HDF5 due to an assertion failure and this was reported in
      GitHub issue #2433. The assertion failure began happening after the
      collective metadata write pathway in the library was updated to use
      vector I/O so that parallel-enabled HDF5 Virtual File Drivers (other
      than the existing MPI I/O VFD) can support collective metadata writes.

      The assertion failure was fixed by updating collective metadata writes
      to treat global heap metadata as raw data, as done elsewhere in the
      library. 

      Fixes GitHub issue #2433

    - Fixed buffer overflow error in image decoding function.

      The error occurred in the function for decoding address from the specified
      buffer, which is called many times from the function responsible for image
      decoding. The length of the buffer is known in the image decoding function,
      but no checks are produced, so the buffer overflow can occur in many places,
      including callee functions for address decoding. 

      The error was fixed by inserting corresponding checks for buffer overflow.

      Fixes GitHub issue #2432

    - Reading a H5std_string (std::string) via a C++ DataSet previously
      truncated the string at the first null byte as if reading a C string.
      Fixed length datasets are now read into H5std_string as a fixed length
      string of the appropriate size. Variable length datasets will still be
      truncated at the first null byte.

      Fixes Github issue #3034

    - Fixed write buffer overflow in H5O__alloc_chunk

      The overflow was found by OSS-Fuzz https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=58658

    Java Library
    ------------
    - Fixed switch case 'L' block missing a break statement.

      The HDF5Array.arrayify method is missing a break statement in the case 'L': section
      which causes it to fall through and throw an HDF5JavaException when attempting to
      read an Array[Array[Long]].

      The error was fixed by inserting a break statement at the end of the case 'L': sections.

      Fixes GitHub issue #3056


    Configuration
    -------------
    - Changed default of 'Error on HDF5 doxygen warnings' DOXYGEN_WARN_AS_ERROR option.

      The default setting of DOXYGEN_WARN_AS_ERROR to 'FAIL_ON_WARNINGS' has been changed
      to 'NO'. It was decided that the setting was too aggressive and should be a user choice.
      The github actions and scripts have been updated to reflect this.

        * HDF5_ENABLE_DOXY_WARNINGS: ON/OFF (Default: OFF)
        * --enable-doxygen-errors: enable/disable (Default: disable)

    - Removed an Autotools configure hack that causes problems on MacOS

      A sed line in configure.ac was added in the past to paper over some
      problems with older versions of the Autotools that would add incorrect
      linker flags. This hack is not needed with recent versions of the
      Autotools and the sed line errors on MacOS (though this was a silent
      error that didn't break the build) so the hack has been removed.

      Fixes GitHub issue #3843

    - Fixed an issue where the h5tools_test_utils test program was being
      installed on the system for Autotools builds of HDF5

      The h5tools_test_utils test program was mistakenly added to bin_PROGRAMS
      in its Makefile.am configuration file, causing the executable to be
      installed on the system. The executable is now added to noinst_PROGRAMS
      instead and will no longer be installed on the system for Autotools builds
      of HDF5. The CMake configuration code already avoids installing the
      executable on the system.

    - Fixed a configuration issue that prevented building of the Subfiling VFD on macOS

      Checks were added to the CMake and Autotools code to verify that CLOCK_MONOTONIC_COARSE,
      PTHREAD_MUTEX_ADAPTIVE_NP and pthread_condattr_setclock() are available before attempting
      to use them in Subfiling VFD-related utility code. Without these checks, attempting
      to build the Subfiling VFD on macOS would fail.

    - Fixes the ordering of INCLUDES when building with CMake

      Include directories in the source or build tree should come before other
      directories to prioritize headers in the sources over installed ones.

      Fixes GitHub #1027

    - The accum test now passes on macOS 12+ (Monterey) w/ CMake

      Due to changes in the way macOS handles LD_LIBRARY_PATH, the accum test
      started failing on macOS 12+ when building with CMake. CMake has been
      updated to set DYLD_LIBRARY_PATH on macOS and the test now passes.

      Fixes GitHub #2994, #2261, and #1289

    - Changed the default settings used by CMake for the GZIP filter

      The default for the option HDF5_ENABLE_Z_LIB_SUPPORT was OFF. Now the default is ON.
      This was done to match the defaults used by the autotools configure.ac.
      In addition, the CMake message level for not finding a suitable filter library was
      changed from FATAL_ERROR (which would halt the build process) to WARNING (which
      will print a message to stderr). Associated files and documentation were changed to match.

      In addition, the default settings in the config/cmake/cacheinit.cmake file were changed to
      allow CMake to disable building the filters if the tgz file could not be found. The option
      to allow CMake to download the file from the original Github location requires setting
      the ZLIB_USE_LOCALCONTENT option to OFF for gzip. And setting the LIBAEC_USE_LOCALCONTENT
      option to OFF for libaec (szip).

      Fixes GitHub issue #2926

    - Fixed syntax of generator expressions used by CMake

      Add quotes around the generator expression should allow CMake to
      correctly parse the expression. Generator expressions are typically
      parsed after command arguments. If a generator expression contains
      spaces, new lines, semicolons or other characters that may be
      interpreted as command argument separators, the whole expression
      should be surrounded by quotes when passed to a command. Failure to
      do so may result in the expression being split and it may no longer
      be recognized as a generator expression.

      Fixes GitHub issue #2906

    - Fixed improper include of Subfiling VFD build directory

      With the release of the Subfiling Virtual File Driver feature, compiler
      flags were added to the Autotools build's CPPFLAGS and AM_CPPFLAGS
      variables to always include the Subfiling VFD source code directory,
      regardless of whether the VFD is enabled and built or not. These flags
      are needed because the header files for the VFD contain macros that are
      assumed to always be available, such as H5FD_SUBFILING_NAME, so the
      header files are unconditionally included in the HDF5 library. However,
      these flags are only needed when building HDF5, so they belong in the
      H5_CPPFLAGS variable instead. Inclusion in the CPPFLAGS and AM_CPPFLAGS
      variables would export these flags to the h5cc and h5c++ wrapper scripts,
      as well as the libhdf5.settings file, which would break builds of software
      that use HDF5 and try to use or parse information out of these files after
      deleting temporary HDF5 build directories.

      Fixes GitHub issue #2621

    - Correct the CMake generated pkg-config file

      The pkg-config file generated by CMake had the order and placement of the
      libraries wrong. Also added support for debug library names.

      Changed the order of Libs.private libraries so that dependencies come after
      dependents. Did not move the compression libraries into Requires.private
      because there was not a way to determine if the compression libraries had
      supported pkconfig files. Still recommend that the CMake config file method
      be used for building projects with CMake.

      Fixes GitHub issues #1546 and #2259

    - Force lowercase Fortran module file names

      The Cray Fortran compiler  uses  uppercase Fortran module file names, which
      caused CMake installs to fail. A compiler option was added to use lowercase
      instead.


    Tools
    -----

    - Renamed h5fuse.sh to h5fuse

      Addresses Discussion #3791


    - Fixed an issue with unmatched MPI messages in ph5diff

      The "manager" MPI rank in ph5diff was unintentionally sending "program end"
      messages to its workers twice, leading to an error from MPICH similar to the
      following:

      Abort(810645519) on node 1 (rank 1 in comm 0): Fatal error in internal_Finalize: Other MPI error, error stack:
      internal_Finalize(50)...........: MPI_Finalize failed
      MPII_Finalize(394)..............:
      MPIR_Comm_delete_internal(1224).: Communicator (handle=44000000) being freed has 1 unmatched message(s)
      MPIR_Comm_release_always(1250)..:
      MPIR_finalize_builtin_comms(154):

    - Fixed an issue in h5repack for variable-length typed datasets

      When repacking datasets into a new file, h5repack tries to determine whether
      it can use H5Ocopy to copy each dataset into the new file, or if it needs to
      manually re-create the dataset, then read data from the old dataset and write
      it to the new dataset. H5repack was previously using H5Ocopy for datasets with
      variable-length datatypes, but this can be problematic if the global heap
      addresses involved do not match exactly between the old and new files. These
      addresses could change for a variety of reasons, such as the command-line options
      provided to h5repack, how h5repack allocate space in the repacked file, etc.      
      Since H5Ocopy does not currently perform any translation when these addresses
      change, datasets that were repacked with H5Ocopy could become unreadable in the
      new file. H5repack has been fixed to repack variable-length typed datasets without
      using H5Ocopy to ensure that the new datasets always have the correct global heap
      addresses.
    
    - Names of objects with square brackets will have trouble without the
      special argument, --no-compact-subset, on the h5dump command line.

      h5diff did not have this option and now it has been added.

      Fixes GitHub issue #2682

    - In the tools traverse function - an error in either visit call
      will bypass the cleanup of the local data variables.

      Replaced the H5TOOLS_GOTO_ERROR with just H5TOOLS_ERROR.

      Fixes GitHub issue #2598


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


    Fortran API
    -----------
    - Fixed: HDF5 fails to compile with -Werror=lto-type-mismatch

      Removed the use of the offending C stub wrapper.

      Fixes GitHub issue #3987


    High-Level Library
    ------------------
    - Fixed a memory leak in H5LTopen_file_image with H5LT_FILE_IMAGE_DONT_COPY flag

      When the H5LT_FILE_IMAGE_DONT_COPY flag is passed to H5LTopen_file_image, the
      internally-allocated udata structure gets leaked as the core file driver doesn't
      have a way to determine when or if it needs to call the "udata_free" callback.
      This has been fixed by freeing the udata structure when the "image_free" callback
      gets made during file close, where the file is holding the last reference to the
      udata structure.

      Fixes GitHub issue #827


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


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


    F90 APIs
    --------
    -


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


    Testing
    -------
    - Disabled running of MPI Atomicity tests for OpenMPI major versions < 5

      Support for MPI atomicity operations is not implemented for major
      versions of OpenMPI less than version 5. This would cause the MPI
      atomicity tests for parallel HDF5 to sporadically fail when run
      with OpenMPI. Testphdf5 now checks if OpenMPI is being used and will
      skip running the atomicity tests if the major version of OpenMPI is
      < 5.

    - Fixed a testing failure in testphdf5 on Cray machines

      On some Cray machines, what appears to be a bug in Cray MPICH was causing
      calls to H5Fis_accessible to create a 0-byte file with strange Unix
      permissions. This was causing an H5Fdelete file deletion test in the
      testphdf5 program to fail due to a just-deleted HDF5 file appearing to
      still be accessible on the file system. The issue in Cray MPICH has been
      worked around for the time being by resetting the MPI_Info object on the
      File Access Property List used to MPI_INFO_NULL before passing it to the
      H5Fis_accessible call.

    - A bug was fixed in the HDF5 API test random datatype generation code

      A bug in the random datatype generation code could cause test failures
      when trying to generate an enumeration datatype that has duplicated
      name/value pairs in it. This has now been fixed.

    - A bug was fixed in the HDF5 API test VOL connector registration checking code

      The HDF5 API test code checks to see if the VOL connector specified by the
      HDF5_VOL_CONNECTOR environment variable (if any) is registered with the library
      before attempting to run tests with it so that testing can be skipped and an
      error can be returned when a VOL connector fails to register successfully.
      Previously, this code didn't account for VOL connectors that specify extra
      configuration information in the HDF5_VOL_CONNECTOR environment variable and
      would incorrectly report that the specified VOL connector isn't registered
      due to including the configuration information as part of the VOL connector
      name being checked for registration status. This has now been fixed.

   - Fixed Fortran 2003 test with gfortran-v13, optimization levels O2,O3

     Fixes failing Fortran 2003 test with gfortran, optimization level O2,O3
     with -fdefault-real-16. Fixes GH #2928.


Platforms Tested
===================

    - HDF5 supports the latest macOS versions, including the current and two
      preceding releases. As new major macOS versions become available, HDF5
      will discontinue  support for the  oldest  version and add  the latest
      version to its list of compatible systems, along with the previous two
      releases.

    Linux 5.16.14-200.fc35           GNU gcc (GCC) 11.2.1 20220127 (Red Hat 11.2.1-9)
    #1 SMP x86_64  GNU/Linux         GNU Fortran (GCC) 11.2.1 20220127 (Red Hat 11.2.1-9)
    Fedora35                         clang version 13.0.0 (Fedora 13.0.0-3.fc35)
                                     (cmake and autotools)

    Linux 5.19.0-1027-aws            GNU gcc (GCC) 11.3.0-1ubuntu1
    #36-Ubuntu SMP x86_64 GNU/Linux  GNU Fortran (GCC) 11.3.0-1ubuntu1
    Ubuntu 22.04                     Intel oneAPI DPC++/C++ Compiler, IFX 2023.1.0
                                     Ubuntu clang version 14.0.0-1ubuntu1
                                     (cmake and autotools)

    Linux 5.15.0-1037-aws            GNU gcc (GCC) 9.4.0-1ubuntu1
    #36-Ubuntu SMP x86_64 GNU/Linux  GNU Fortran (GCC) 9.4.0-1ubuntu1
    Ubuntu 20.04                     Intel oneAPI DPC++/C++ Compiler, IFX 2023.1.0
                                     Ubuntu clang version 10.0.0-4ubuntu1
                                     (cmake and autotools)

    Linux 5.14.21-cray_shasta_c      cray-mpich/8.1.25
    #1 SMP x86_64 GNU/Linux            cce 15.0.1
    (perlmutter)                       GCC 12.2.0
                                       intel-oneapi/2023.1.0
                                       nvidia/22.7
                                     (cmake)

    Linux 5.14.21-cray_shasta_c      cray-mpich/8.1.23
    #1 SMP x86_64 GNU/Linux              cce 15.0.1
    (crusher)                            GCC 12.2.0
                                     (cmake)

    Linux-4.14.0-115.21.2            spectrum-mpi/rolling-release
    #1 SMP ppc64le GNU/Linux             clang 12.0.1, 14.0.5
    (lassen)                             GCC 8.3.1
                                         XL 16.1.1.2, 2021,09.22, 2022.08.05
                                     (cmake)

    Linux-4.12.14-197.99-default     cray-mpich/7.7.14
    #1 SMP x86_64 GNU/Linux              cce 12.0.3
    (theta)                              GCC 11.2.0
                                         llvm 9.0
                                         Intel 19.1.2

    Linux 3.10.0-1160.36.2.el7.ppc64 gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-39)
    #1 SMP ppc64be GNU/Linux         g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-39)
    Power8 (echidna)                 GNU Fortran (GCC) 4.8.5 20150623 (Red Hat 4.8.5-39)
                                     IBM XL C for Linux, V13.1
                                     IBM XL Fortran for Linux, V15.1

    Linux 3.10.0-1160.24.1.el7       GNU C (gcc), Fortran (gfortran), C++ (g++)
    #1 SMP x86_64 GNU/Linux          compilers:
    Centos7                              Version 4.8.5 20150623 (Red Hat 4.8.5-4)
    (jelly/kituo/moohan)                 Version 4.9.3, Version 5.3.0, Version 6.3.0,
                                         Version 7.2.0, Version 8.3.0, Version 9.1.0
                                         Version 10.2.0
                                     Intel(R) C (icc), C++ (icpc), Fortran (icc)
                                     compilers:
                                         Version 17.0.0.098 Build 20160721
                                     GNU C (gcc) and C++ (g++) 4.8.5 compilers
                                         with NAG Fortran Compiler Release 6.1(Tozai)
                                     Intel(R) C (icc) and C++ (icpc) 17.0.0.098 compilers
                                         with NAG Fortran Compiler Release 6.1(Tozai)
                                     MPICH 3.3 compiled with GCC 7.2.0
                                     MPICH 4.0.3 compiled with GCC 7.2.0
                                     OpenMPI 3.1.3 compiled with GCC 7.2.0
                                     OpenMPI 4.1.2 compiled with GCC 9.1.0
                                     PGI C, Fortran, C++ for 64-bit target on
                                     x86_64;
                                         Version 19.10-0
                                     NVIDIA C, Fortran, C++ for 64-bit target on
                                     x86_64;
                                         Version 22.5-0
                                     (autotools and cmake)

    Linux-3.10.0-1160.0.0.1chaos     openmpi-4.1.2
    #1 SMP x86_64 GNU/Linux              clang 6.0.0, 11.0.1
    (quartz)                             GCC 7.3.0, 8.1.0
                                         Intel 19.0.4, 2022.2, oneapi.2022.2

    macOS Apple M1 11.6              Apple clang version 12.0.5 (clang-1205.0.22.11)
    Darwin 20.6.0 arm64              gfortran GNU Fortran (Homebrew GCC 11.2.0) 11.1.0
    (macmini-m1)                     Intel icc/icpc/ifort version 2021.3.0 202106092021.3.0 20210609

    macOS Big Sur 11.3.1             Apple clang version 12.0.5 (clang-1205.0.22.9)
    Darwin 20.4.0 x86_64             gfortran GNU Fortran (Homebrew GCC 10.2.0_3) 10.2.0
    (bigsur-1)                       Intel icc/icpc/ifort version 2021.2.0 20210228

    macOS High Sierra 10.13.6        Apple LLVM version 10.0.0 (clang-1000.10.44.4)
    64-bit                           gfortran GNU Fortran (GCC) 6.3.0
    (bear)                           Intel icc/icpc/ifort version 19.0.4.233 20190416

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

    Linux 2.6.32-573.22.1.el6        GNU C (gcc), Fortran (gfortran), C++ (g++)
    #1 SMP x86_64 GNU/Linux          compilers:
    Centos6                              Version 4.4.7 20120313
    (platypus)                           Version 4.9.3, 5.3.0, 6.2.0
                                     MPICH 3.1.4 compiled with GCC 4.9.3
                                     PGI C, Fortran, C++ for 64-bit target on
                                     x86_64;
                                         Version 19.10-0

    Windows 10 x64                  Visual Studio 2019 w/ clang 12.0.0
                                        with MSVC-like command-line (C/C++ only - cmake)
                                    Visual Studio 2019 w/ Intel (C/C++ only - cmake)
                                    Visual Studio 2022 w/ clang 15.0.1
                                        with MSVC-like command-line (C/C++ only - cmake)
                                    Visual Studio 2022 w/ Intel C/C++/Fortran oneAPI 2023 (cmake)
                                    Visual Studio 2019 w/ MSMPI 10.1 (C only - cmake)


Known Problems
==============

    When HDF5 is compiled with NVHPC versions 23.5 - 23.9 (additional versions may
    also be applicable) and with -O2 (or higher) and -DNDEBUG, test failures occur
    in the following tests:

        H5PLUGIN-filter_plugin
        H5TEST-flush2
        H5TEST-testhdf5-base
        MPI_TEST_t_filters_parallel

    Since these tests pass with an optimization level of -O1 (and -O0) and it is
    currently unclear whether the test failures are due to issues in HDF5 or issues
    in the 'nvc' compiler, the maximum optimization level for NVHPC has been set
    to -O1 until the test failures can be resolved. Note that even at -O1 optimization
    level, there still appears to be a sporadic test failure in the Java JUnit tests
    that has occasionally been seen in JUnit-TestH5Pfapl and JUnit-TestH5D. It is also
    unclear whether this is an issue in HDF5 or with the 'nvc' compiler. Finally, note
    that NVHPC 23.9 will fail to compile the test/tselect.c test file with a compiler
    error of 'use of undefined value' when the optimization level is -O2 or higher.
    Nvidia is aware of this issue and has suggested lowering the optimization level to
    -O1 for the time being:
    https://forums.developer.nvidia.com/t/hdf5-no-longer-compiles-with-nv-23-9/269045.

    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.

    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.

    The subsetting option in ph5diff currently will fail and should be avoided.
    The subsetting option works correctly in serial h5diff.

    Flang Fortran compilation will fail (last check version 17) due to not yet
    implemented: (1) derived type argument passed by value (H5VLff.F90),
    and (2) support for REAL with KIND = 2 in intrinsic SPACING used in testing.

    Several tests currently fail on certain platforms:
        MPI_TEST-t_bigio fails with spectrum-mpi on ppc64le platforms.

        MPI_TEST-t_subfiling_vfd and MPI_TEST_EXAMPLES-ph5_subfiling fail with
        cray-mpich on theta and with XL compilers on ppc64le platforms.

        MPI_TEST_testphdf5_tldsc fails with cray-mpich 7.7 on cori and theta.

    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.

The issues with the gif tool are:
    HDFFV-10592 CVE-2018-17433
    HDFFV-10593 CVE-2018-17436
    HDFFV-11048 CVE-2020-10809
These CVE issues have not yet been addressed and are avoided by not building
the gif tool by default. Enable building the High-Level tools with these options:
    autotools:   --enable-hlgiftools
    cmake:       HDF5_BUILD_HL_GIF_TOOLS=ON