H5: General Library Functions

The C Interfaces:

H5open H5close

H5get_libversion H5check_version

H5set_free_list_limits H5garbage_collect H5dont_atexit

Alphabetical Listing

H5check_version H5close H5dont_atexit

H5garbage_collect H5get_libversion H5open

H5set_free_list_limits

The FORTRAN90 Interfaces:
In general, each FORTRAN90 subroutine performs exactly the same task as the corresponding C function. The links below go to the C function descriptions, which serve as general descriptions for both. A button, under Non-C API(s) at the end of the C function description, opens an external browser window displaying the FORTRAN90-specific information. You will probably want to adjust the size and location of this external window so that both browser windows are visible and to facilitate moving easily between them.

h5open_f h5close_f

h5get_libversion_f h5check_version_f

h5set_free_list_limits_f h5garbage_collect_f h5dont_atexit_f

Name: H5open

Signature:

herr_t H5open(void)

Purpose:

Initializes the HDF5 library.

Description:

H5open initialize the library. This function is normally called automatically, but if you find that an HDF5 library function is failing inexplicably, try calling this function first.

Parameters:

None.

Returns:

Returns a non-negative value if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5close

Signature:

herr_t H5close(void)

Purpose:

Flushes all data to disk, closes file identifiers, and cleans up memory.

Description:

H5close flushes all data to disk, closes all file identifiers, and cleans up all memory used by the library. This function is generally called when the application calls exit, but may be called earlier in event of an emergency shutdown or out of desire to free all resources used by the HDF5 library.

Parameters:

None.

Returns:

Returns a non-negative value if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5set_free_list_limits

Signature:

herr_t H5set_free_list_limits(int reg_global_lim, int reg_list_lim, int arr_global_lim, int arr_list_lim, int blk_global_lim, int blk_list_lim )

Purpose:

Sets free-list size limits.

Description:

H5set_free_list_limits sets size limits on all types of free lists. The HDF5 library uses free lists internally to manage memory. There are three types of free lists:

• Regular free lists manage a single data structure.
• Array free lists manage arrays of a data structure.
• Block free lists manage blocks of bytes.

Alternate phrasing?:

• Regular free lists manage data structures containing atomic data.
• Array free lists manage data structures containing array data.
• Block free lists manage blocks of bytes.

These are global limits, but each limit applies only to free lists of the specified type. Therefore, if an application sets a 1Mb limit on each of the global lists, up to 3Mb of total storage might be allocated, 1Mb for each of the regular, array, and block type lists.

Using a value of -1 for a limit means that no limit is set for the specified type of free list.

Parameters:

int reg_global_lim

IN: The limit on all regular free list memory used

int reg_list_lim

IN: The limit on memory used in each regular free list

int arr_global_lim

IN: The limit on all array free list memory used

int arr_list_lim

IN: The limit on memory used in each array free list

int blk_global_lim

IN: The limit on all block free list memory used

int blk_list_lim

IN: The limit on memory used in each block free list

Returns:

Returns a non-negative value if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5garbage_collect

Signature:

herr_t H5garbage_collect(void)

Purpose:

Garbage collects on all free-lists of all types.

Description:

H5garbage_collect walks through all the garbage collection routines of the library, freeing any unused memory.

It is not required that H5garbage_collect be called at any particular time; it is only necessary in certain situations where the application has performed actions that cause the library to allocate many objects. The application should call H5garbage_collect if it eventually releases those objects and wants to reduce the memory used by the library from the peak usage required.

The library automatically garbage collects all the free lists when the application ends.

Parameters:

None.

Returns:

Returns a non-negative value if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5dont_atexit

Signature:

herr_t H5dont_atexit(void)

Purpose:

Instructs library not to install atexit cleanup routine.

Description:

H5dont_atexit indicates to the library that an atexit() cleanup routine should not be installed. The major purpose for this is in situations where the library is dynamically linked into an application and is un-linked from the application before exit() gets called. In those situations, a routine installed with atexit() would jump to a routine which was no longer in memory, causing errors.

In order to be effective, this routine must be called before any other HDF function calls, and must be called each time the library is loaded/linked into the application (the first time and after it's been un-loaded).

Parameters:

None.

Returns:

Returns a non-negative value if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5get_libversion

Signature:

herr_t H5get_libversion(unsigned *majnum, unsigned *minnum, unsigned *relnum )

Purpose:

Returns the HDF library release number.

Description:

H5get_libversion retrieves the major, minor, and release numbers of the version of the HDF library which is linked to the application.

Parameters:

unsigned *majnum

OUT: The major version of the library.

unsigned *minnum

OUT: The minor version of the library.

unsigned *relnum

OUT: The release number of the library.

Returns:

Returns a non-negative value if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5check_version

Signature:

herr_t H5check_version(unsigned majnum, unsigned minnum, unsigned relnum )

Purpose:

Verifies that library versions are consistent.

Description:

H5check_version verifies that the arguments provided with the function call match the version numbers compiled into the library.

H5check_version serves two slightly differing purposes.

First, the function is intended to be called by the user to verify that the version of the header files compiled into an application matches the version of the HDF5 library being used. One may look at the H5check definition in the file H5public.h as an example.

Due to the risks of data corruption or segmentation faults, H5check_version causes the application to abort if the version numbers do not match. The abort is achieved by means of a call to the standard C function abort().

Note that H5check_version verifies only the major and minor version numbers and the release number; it does not verify the sub-release value as that should be an empty string for any official release. This means that any two incompatible library versions must have different {major,minor,release} numbers. (Notice the reverse is not necessarily true.)

Secondarily, H5check_version verifies that the library version identifiers H5_VERS_MAJOR, H5_VERS_MINOR, H5_VERS_RELEASE, H5_VERS_SUBRELEASE, and H5_VERS_INFO are consistent. This is designed to catch source code inconsistencies, but does not generate the fatal error as in the first stage because this inconsistency does not cause errors in the data files. If this check reveals inconsistencies, the library issues a warning but the function does not fail.

Parameters:

unsigned majnum

IN: The major version of the library.

unsigned minnum

IN: The minor version of the library.

unsigned relnum

IN: The release number of the library.

Returns:

Returns a non-negative value if successful. Upon failure, this function causes the application to abort.

Non-C API(s):