User-defined ID Types

Detailed Description

The Identifiers (H5I) module contains functions to define new identifier types. For convenience, handles of type hid_t can then be associated with the new identifier types and user objects.

New identifier types can be created by registering a new identifier type with the HDF5 library. Once a new identifier type has bee registered, it can be used to generate identifiers for user objects.

User-defined identifier types can be searched and iterated.

Like library-defined identifiers, user-defined identifiers and identifier types are reference counted, and the reference counts can be manipulated accordingly.

User-defined identifiers no longer in use should be deleted or reclaimed, and identifier types should be destroyed if they are no longer required.

Create	Read
herr_t free_func(void *obj) { printf("Calling free_func...\n"); H5free_memory(obj); return 0; } { __label__ fail_id, fail_obj, fail_register; H5I_type_t type; int *obj; hid_t obj_id; // register a new ID type if ((type = H5Iregister_type(128, 1024, &free_func)) < 0) { ret_val = EXIT_FAILURE; goto fail_register; } printf("New identifier type ID: %d\n", type); // create a new object if ((obj = H5allocate_memory(10 * sizeof(int), 0)) == NULL) { ret_val = EXIT_FAILURE; goto fail_obj; } // obtain an ID for the new object if ((obj_id = H5Iregister(type, obj)) == H5I_INVALID_HID) { ret_val = EXIT_FAILURE; goto fail_id; } printf("New object identifier: %ld\n", obj_id); fail_id: H5Iclear_type(type, 1); fail_obj: H5Idestroy_type(type); fail_register:; }	{ __label__ fail_query, fail_register; H5I_type_t type; hsize_t count; // register a new ID type if ((type = H5Iregister_type(128, 1024, NULL)) < 0) { ret_val = EXIT_FAILURE; goto fail_register; } printf("New FOO identifier type ID: %d\n", type); // return the number of identifiers of TYPE currently in use if (H5Inmembers(type, &count) < 0) { ret_val = EXIT_FAILURE; goto fail_query; } printf("%llu FOO identifiers in use\n", count); fail_query: H5Idestroy_type(type); fail_register:; }
Update	Delete
{ __label__ fail_id, fail_register; H5I_type_t type; int obj = 42; hid_t obj_id; // register a new ID type if ((type = H5Iregister_type(128, 1024, NULL)) < 0) { ret_val = EXIT_FAILURE; goto fail_register; } printf("New identifier type ID: %d\n", type); // obtain an ID for the new object if ((obj_id = H5Iregister(type, &obj)) == H5I_INVALID_HID) { ret_val = EXIT_FAILURE; goto fail_id; } printf("New object identifier: %ld\n", obj_id); // bump the reference count assert(H5Iinc_ref(obj_id) == 2); // force the deletion of all IDs regardless of reference count H5Iclear_type(type, 1); fail_id: H5Idestroy_type(type); fail_register:; }	{ __label__ fail_register; H5I_type_t type; // register a new ID type if ((type = H5Iregister_type(128, 1024, NULL)) < 0) { ret_val = EXIT_FAILURE; goto fail_register; } printf("New identifier type ID: %d\n", type); // decrementing the identifier type's ref. count to 0 triggers // the type to be destroyed assert(H5Idec_type_ref(type) == 0); fail_register:; }

Functions
hid_t	H5Iregister (H5I_type_t type, const void *object)
	Registers an object under a type and returns an ID for it.
void *	H5Iobject_verify (hid_t id, H5I_type_t type)
	Returns the object referenced by an ID.
void *	H5Iremove_verify (hid_t id, H5I_type_t type)
	Removes an ID from its type.
H5I_type_t	H5Iregister_type (size_t hash_size, unsigned reserved, H5I_free_t free_func)
	Creates and returns a new ID type.
herr_t	H5Iclear_type (H5I_type_t type, hbool_t force)
	Deletes all identifiers of the given type.
herr_t	H5Idestroy_type (H5I_type_t type)
	Removes an identifier type and all identifiers within that type.
int	H5Iinc_type_ref (H5I_type_t type)
	Increments the reference count on an ID type.
int	H5Idec_type_ref (H5I_type_t type)
	Decrements the reference count on an identifier type.
int	H5Iget_type_ref (H5I_type_t type)
	Retrieves the reference count on an ID type.
void *	H5Isearch (H5I_type_t type, H5I_search_func_t func, void *key)
	Finds the memory referred to by an ID within the given ID type such that some criterion is satisfied.
herr_t	H5Iiterate (H5I_type_t type, H5I_iterate_func_t op, void *op_data)
	Calls a callback for each member of the identifier type specified.
herr_t	H5Inmembers (H5I_type_t type, hsize_t *num_members)
	Returns the number of identifiers in a given identifier type.
htri_t	H5Itype_exists (H5I_type_t type)
	Determines whether an identifier type is registered.

Function Documentation

H5Iclear_type()

herr_t H5Iclear_type	(	H5I_type_t	type,
		hbool_t	force
	)

Deletes all identifiers of the given type.

Parameters

[in]	type	Identifier of identifier type which is to be cleared of identifiers
[in]	force	Whether or not to force deletion of all identifiers

Returns

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

H5Iclear_type() deletes all identifiers of the type identified by the argument type.

The identifier type's free function is first called on all of these identifiers to free their memory, then they are removed from the type.

If the force flag is set to false, only those identifiers whose reference counts are equal to 1 will be deleted, and all other identifiers will be entirely unchanged. If the force flag is true, all identifiers of this type will be deleted.

Since

1.8.0

H5Idec_type_ref()

int H5Idec_type_ref

(

H5I_type_t

type

)

Decrements the reference count on an identifier type.

Parameters

[in]

type

The identifier of the type whose reference count is to be decremented

Returns

Returns the current reference count on success, negative on failure.

H5Idec_type_ref() decrements the reference count on an identifier type. The reference count is used by the library to indicate when an identifier type can be destroyed. If the reference count reaches zero, this function will destroy it.

The type parameter is the identifier for the identifier type whose reference count is to be decremented. This identifier must have been created by a call to H5Iregister_type().

Since

1.8.0

H5Idestroy_type()

herr_t H5Idestroy_type

(

H5I_type_t

type

)

Removes an identifier type and all identifiers within that type.

Parameters

[in]

type

Identifier of identifier type which is to be destroyed

Returns

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

H5Idestroy_type deletes an entire identifier type type. All identifiers of this type are destroyed and no new identifiers of this type can be registered.

The type's free function is called on all of the identifiers which are deleted by this function, freeing their memory. In addition, all memory used by this type's hash table is freed.

Since the H5I_type_t values of destroyed identifier types are reused when new types are registered, it is a good idea to set the variable holding the value of the destroyed type to H5I_UNINIT.

Since

1.8.0

H5Iget_type_ref()

int H5Iget_type_ref

(

H5I_type_t

type

)

Retrieves the reference count on an ID type.

Parameters

[in]

type

The identifier of the type whose reference count is to be retrieved

Returns

Returns the current reference count on success, negative on failure.

H5Iget_type_ref() retrieves the reference count on an ID type. The reference count is used by the library to indicate when an ID type can be destroyed.

The type parameter is the identifier for the ID type whose reference count is to be retrieved. This identifier must have been created by a call to H5Iregister_type().

Since

1.8.0

H5Iinc_type_ref()

int H5Iinc_type_ref

(

H5I_type_t

type

)

Increments the reference count on an ID type.

Parameters

[in]

type

The identifier of the type whose reference count is to be incremented

Returns

Returns the current reference count on success, negative on failure.

H5Iinc_type_ref() increments the reference count on an ID type. The reference count is used by the library to indicate when an ID type can be destroyed.

The type parameter is the identifier for the ID type whose reference count is to be incremented. This identifier must have been created by a call to H5Iregister_type().

Since

1.8.0

H5Iiterate()

herr_t H5Iiterate	(	H5I_type_t	type,
		H5I_iterate_func_t	op,
		void *	op_data
	)

Calls a callback for each member of the identifier type specified.

Parameters

[in]	type	The identifier type
[in]	op	The callback function
[in,out]	op_data	The data for the callback function

Returns

The last value returned by op

H5Iiterate() calls the callback function op for each member of the identifier type type. The callback function type for op, H5I_iterate_func_t, is defined in H5Ipublic.h as:

typedef herr_t (*H5I_iterate_func_t)(hid_t id, void *udata);

op takes as parameters the identifier and a pass through of op_data, and returns an herr_t.

A positive return from op will cause the iteration to stop and H5Iiterate() will return the value returned by op. A negative return from op will cause the iteration to stop and H5Iiterate() will return failure. A zero return from op will allow iteration to continue, as long as there are other identifiers remaining in type.

Warning

Adding or removing members of the identifier type during iteration will lead to undefined behavior.

Attention

Leaving callback functions:
The callback function must return normally, even in the case of error. Returning with H5_ITER_ERROR, instead of leaving by means of exceptions, exit() function, etc... will allow the HDF5 library to manage its resources and maintain a consistent state. See C++ Developers using HDF5 C-API functions warning for detail.

Since

1.12.0

H5Inmembers()

herr_t H5Inmembers	(	H5I_type_t	type,
		hsize_t *	num_members
	)

Returns the number of identifiers in a given identifier type.

Parameters

[in]	type	The identifier type
[out]	num_members	Number of identifiers of the specified identifier type

Returns

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

H5Inmembers() returns the number of identifiers of the identifier type specified in type.

The number of identifiers is returned in num_members. If no identifiers of this type have been registered, the type does not exist, or it has been destroyed, num_members is returned with the value 0.

Since

1.8.0

H5Iobject_verify()

void * H5Iobject_verify	(	hid_t	id,
		H5I_type_t	type
	)

Returns the object referenced by an ID.

Parameters

[in]	id	ID to be dereferenced
[in]	type	The identifier type

Returns

Pointer to the object referenced by id on success, NULL on failure.

H5Iobject_verify() returns a pointer to the memory referenced by id after verifying that id is of type type. This function is analogous to dereferencing a pointer in C with type checking.

Note

H5Iobject_verify() does not change the ID it is called on in any way (as opposed to H5Iremove_verify(), which removes the ID from its type's hash table).

See also

H5Iregister()

Since

1.8.0

H5Iregister()

hid_t H5Iregister	(	H5I_type_t	type,
		const void *	object
	)

Registers an object under a type and returns an ID for it.

Parameters

[in]	type	The identifier of the type of the new ID
[in]	object	Pointer to object for which a new ID is created

Returns

Returns a object identifier if successful; otherwise returns H5I_INVALID_HID.

H5Iregister() creates and returns a new ID for an object.

The type parameter is the identifier for the ID type to which this new ID will belong. This identifier must have been created by a call to H5Iregister_type().

The object parameter is a pointer to the memory which the new ID will be a reference to. This pointer will be stored by the library and returned via a call to H5Iobject_verify().

Since

1.8.0

H5Iregister_type()

H5I_type_t H5Iregister_type	(	size_t	hash_size,
		unsigned	reserved,
		H5I_free_t	free_func
	)

Creates and returns a new ID type.

Parameters

[in]	hash_size	Minimum hash table size (in entries) used to store IDs for the new type (unused in 1.8.13 and later)
[in]	reserved	Number of reserved IDs for the new type
[in]	free_func	Function used to deallocate space for a single ID

Returns

Returns the type identifier on success, negative on failure.

H5Iregister_type() allocates space for a new ID type and returns an identifier for it.

The hash_size parameter indicates the minimum size of the hash table used to store IDs in the new type. This parameter is unused in 1.8.13 and later, when the implementation of ID storage changed.

The reserved parameter indicates the number of IDs in this new type to be reserved. Reserved IDs are valid IDs which are not associated with any storage within the library.

The free_func parameter is a function pointer to a function which returns an herr_t and accepts a void*. The purpose of this function is to deallocate memory for a single ID. It will be called by H5Iclear_type() and H5Idestroy_type() on each ID. This function is NOT called by H5Iremove_verify(). The void* will be the same pointer which was passed in to the H5Iregister() function. The free_func function should return 0 on success and -1 on failure.

Since

1.8.0

H5Iremove_verify()

void * H5Iremove_verify	(	hid_t	id,
		H5I_type_t	type
	)

Removes an ID from its type.

Parameters

[in]	id	The ID to be removed from its type
[in]	type	The identifier type

Returns

Returns a pointer to the memory referred to by id on success, NULL on failure.

H5Iremove_verify() first ensures that id belongs to type. If so, it removes id from its type and returns the pointer to the memory it referred to. This pointer is the same pointer that was placed in storage by H5Iregister(). If id does not belong to type, then NULL is returned.

The id parameter is the ID which is to be removed from its type.

The type parameter is the identifier for the ID type which id is supposed to belong to. This identifier must have been created by a call to H5Iregister_type().

Note

This function does NOT deallocate the memory that id refers to. The pointer returned by H5Iregister() must be deallocated by the user to avoid memory leaks.

Since

1.8.0

H5Isearch()

void * H5Isearch	(	H5I_type_t	type,
		H5I_search_func_t	func,
		void *	key
	)

Finds the memory referred to by an ID within the given ID type such that some criterion is satisfied.

Parameters

[in]	type	The identifier of the type to be searched
[in]	func	The function defining the search criteria
[in]	key	A key for the search function

Returns

Returns a pointer to the object which satisfies the search function on success, NULL on failure.

H5Isearch() searches through a given ID type to find an object that satisfies the criteria defined by func. If such an object is found, the pointer to the memory containing this object is returned. Otherwise, NULL is returned. To do this, func is called on every member of type type. The first member to satisfy func is returned.

The type parameter is the identifier for the ID type which is to be searched. This identifier must have been created by a call to H5Iregister_type().

The parameter func is a function pointer to a function which takes three parameters. The first parameter is a void* and will be a pointer to the object to be tested. This is the same object that was placed in storage using H5Iregister(). The second parameter is a hid_t and is the ID of the object to be tested. The last parameter is a void*. This is the key parameter and can be used however the user finds helpful, or it can be ignored if it is not needed. func returns 0 if the object it is testing does not pass its criteria. A non-zero value should be returned if the object does pass its criteria. H5I_search_func_t is defined in H5Ipublic.h and is shown below.

typedef int (*H5I_search_func_t)(void *obj, hid_t id, void *key);

The key parameter will be passed to the search function as a parameter. It can be used to further define the search at run-time.

Since

1.8.0

H5Itype_exists()

htri_t H5Itype_exists

(

H5I_type_t

type

)

Determines whether an identifier type is registered.

Parameters

[in]

type

Identifier type

Returns

Returns zero (false), a positive (true) or a negative (failure) value.

H5Itype_exists() determines whether the given identifier type, type, is registered with the library.

Since

1.8.0