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| HDF5 Last Updated on 2026-07-28 The HDF5 Field Guide

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Event Set Interface (H5ES)

## Detailed Description

Event Set Interface.

Todo
  Add the event set life cycle.

This interface can only be used with the HDF5 VOL connectors that enable the asynchronous feature in HDF5. The native HDF5 library has only synchronous operations.

HDF5 VOL connectors with support for asynchronous operations:

- ASYNC
- DAOS

Example:
  fid = H5Fopen(..);
  gid = H5Gopen(fid, ..); //Starts when H5Fopen completes
  did = H5Dopen(gid, ..); //Starts when H5Gopen completes
  es_id = H5EScreate(); // Create event set for tracking async operations
  status = H5Dwrite_async(did, .., es_id); //Asynchronous, starts when H5Dopen completes,
  // may run concurrently with other H5Dwrite_async
  // in event set.
  status = H5Dwrite_async(did, .., es_id); //Asynchronous, starts when H5Dopen completes,
  // may run concurrently with other H5Dwrite_async
  // in event set....
  <other user code>
  ...
  H5ESwait(es_id); // Wait for operations in event set to complete, buffers
  // used for H5Dwrite_async must only be changed after wait
  // returns.
  H5Dopen
  #define H5Dopen
  Definition H5version.h:1219
  H5Dwrite_async
  herr_t H5Dwrite_async(hid_t dset_id, hid_t mem_type_id, hid_t mem_space_id, hid_t file_space_id, hid_t dxpl_id, const void *buf, hid_t es_id)
  H5EScreate
  hid_t H5EScreate(void)
  Creates an event set.
  H5Fopen
  hid_t H5Fopen(const char *filename, unsigned flags, hid_t fapl_id)
  Opens an existing HDF5 file.
  H5Gopen
  #define H5Gopen
  Definition H5version.h:1335

## Functions
herr_t | H5EScancel (hid_t es_id, size_t *num_not_canceled, bool *err_occurred)
| Attempt to cancel operations in an event set.
herr_t | H5ESclose (hid_t es_id)
| Terminates access to an event set.
hid_t | H5EScreate (void)
| Creates an event set.
herr_t | H5ESfree_err_info (size_t num_err_info, H5ES_err_info_t err_info[])
| Convenience routine to free an array of H5ES_err_info_t structs.
herr_t | H5ESget_count (hid_t es_id, size_t *count)
| Retrieves number of events in an event set.
herr_t | H5ESget_err_count (hid_t es_id, size_t *num_errs)
| Retrieves the number of failed operations.
herr_t | H5ESget_err_info (hid_t es_id, size_t num_err_info, H5ES_err_info_t err_info[], size_t *err_cleared)
| Retrieves information about failed operations.
herr_t | H5ESget_err_status (hid_t es_id, bool *err_occurred)
| Checks for failed operations.
herr_t | H5ESget_op_counter (hid_t es_id, uint64_t *counter)
| Retrieves the accumulative operation counter for an event set.
herr_t | H5ESregister_complete_func (hid_t es_id, H5ES_event_complete_func_t func, void *ctx)
| Registers a callback to invoke when an operation completes within an event set.
herr_t | H5ESregister_insert_func (hid_t es_id, H5ES_event_insert_func_t func, void *ctx)
| Registers a callback to invoke when a new operation is inserted into an event set.
herr_t | H5ESwait (hid_t es_id, uint64_t timeout, size_t *num_in_progress, bool *err_occurred)
| Waits for operations in event set to complete.

## Function Documentation

## ◆ H5EScancel()

herr_t H5EScancel | ( | hid_t | es_id,
|  | size_t * | num_not_canceled,
|  | bool * | err_occurred )

Attempt to cancel operations in an event set.

Parameters

  [in] | es_id | Event set identifier
  [out] | num_not_canceled | The number of events not canceled
  [out] | err_occurred | Status indicating if error is present in the event set

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

H5EScancel() attempts to cancel operations in an event set specified by `es_id`. H5ES_NONE is a valid value for `es_id`, but functions as a no-op.

Since
  1.14.0

## ◆ H5ESclose()

herr_t H5ESclose | ( | hid_t | es_id | ) |

Terminates access to an event set.

Parameters

  [in] | es_id | Event set identifier

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

H5ESclose() terminates access to an event set specified by `es_id`.

Since
  1.14.0

## ◆ H5EScreate()

hid_t H5EScreate | ( | void |  | ) |

Creates an event set.

Returns
  Returns a event set identifier if successful; otherwise returns H5I_INVALID_HID.

H5EScreate() creates a new event set and returns a corresponding event set identifier.

Since
  1.14.0

## ◆ H5ESfree_err_info()

herr_t H5ESfree_err_info | ( | size_t | num_err_info,
|  | H5ES_err_info_t | err_info[] )

Convenience routine to free an array of H5ES_err_info_t structs.

Parameters

  [in] | num_err_info | The number of elements in `err_info` array
  [in] | err_info | Array of structures

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

Since
  1.14.0

## ◆ H5ESget_count()

herr_t H5ESget_count | ( | hid_t | es_id,
|  | size_t * | count )

Retrieves number of events in an event set.

Parameters

  [in] | es_id | Event set identifier
  [out] | count | The number of events in the event set

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

H5ESget_count() retrieves number of events in an event set specified by `es_id`.

Since
  1.14.0

## ◆ H5ESget_err_count()

herr_t H5ESget_err_count | ( | hid_t | es_id,
|  | size_t * | num_errs )

Retrieves the number of failed operations.

Parameters

  [in] | es_id | Event set identifier
  [out] | num_errs | Number of errors

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

H5ESget_err_count() retrieves the number of failed operations in an event set specified by `es_id`.

The function does not wait for active operations to complete, so count may not include all failures.

Since
  1.14.0

## ◆ H5ESget_err_info()

herr_t H5ESget_err_info | ( | hid_t | es_id,
|  | size_t | num_err_info,
|  | H5ES_err_info_t | err_info[],
|  | size_t * | err_cleared )

Retrieves information about failed operations.

Parameters

  [in] | es_id | Event set identifier
  [in] | num_err_info | The number of elements in `err_info` array
  [out] | err_info | Array of structures
  [out] | err_cleared | Number of cleared errors

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

H5ESget_err_info() retrieves information about failed operations in an event set specified by `es_id`. The strings retrieved for each error info must be released by calling H5free_memory().

Below is the description of the H5ES_err_info_t structure:

typedef struct H5ES_err_info_t {
/* API call info */
char *api_name;
char *api_args;
/* Application info */
char *app_file_name;
char *app_func_name;
unsigned app_line_num;
/* Operation info */
uint64_t op_ins_count;
uint64_t op_ins_ts;
uint64_t op_exec_ts;
uint64_t op_exec_time;
/* Error info */
hid_t err_stack_id;
} H5ES_err_info_t;

(Click on a enumerator, field, or type for more information.)

Since
  1.14.0

## ◆ H5ESget_err_status()

herr_t H5ESget_err_status | ( | hid_t | es_id,
|  | bool * | err_occurred )

Checks for failed operations.

Parameters

  [in] | es_id | Event set identifier
  [out] | err_occurred | Status indicating if error is present in the event set

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

H5ESget_err_status() checks if event set specified by es_id has failed operations.

Since
  1.14.0

## ◆ H5ESget_op_counter()

herr_t H5ESget_op_counter | ( | hid_t | es_id,
|  | uint64_t * | counter )

Retrieves the accumulative operation counter for an event set.

Parameters

  [in] | es_id | Event set identifier
  [out] | counter | The accumulative counter value for an event set

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

H5ESget_op_counter() retrieves the current accumulative count of event set operations since the event set creation of `es_id`.

Note
  This is designed for wrapper libraries mainly, to use as a mechanism for matching operations inserted into the event set with possible errors that occur.

Since
  1.14.0

## ◆ H5ESregister_complete_func()

herr_t H5ESregister_complete_func | ( | hid_t | es_id,
|  | H5ES_event_complete_func_t | func,
|  | void * | ctx )

Registers a callback to invoke when an operation completes within an event set.

Parameters

  [in] | es_id | Event set identifier
  [in] | func | The completion function to register
  [in] | ctx | User-specified information (context) to pass to `func`

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

Only one complete callback can be registered for each event set. Registering a new callback will replace the existing one. H5ES_NONE is a valid value for 'es_id', but functions as a no-op

Since
  1.14.0

## ◆ H5ESregister_insert_func()

herr_t H5ESregister_insert_func | ( | hid_t | es_id,
|  | H5ES_event_insert_func_t | func,
|  | void * | ctx )

Registers a callback to invoke when a new operation is inserted into an event set.

Parameters

  [in] | es_id | Event set identifier
  [in] | func | The insert function to register
  [in] | ctx | User-specified information (context) to pass to `func`

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

Only one insert callback can be registered for each event set. Registering a new callback will replace the existing one. H5ES_NONE is a valid value for 'es_id', but functions as a no-op

Since
  1.14.0

## ◆ H5ESwait()

herr_t H5ESwait | ( | hid_t | es_id,
|  | uint64_t | timeout,
|  | size_t * | num_in_progress,
|  | bool * | err_occurred )

Waits for operations in event set to complete.

Parameters

  [in] | es_id | Event set identifier
  [in] | timeout | Total time in nanoseconds to wait for all operations in the event set to complete
  [out] | num_in_progress | The number of operations still in progress
  [out] | err_occurred | Flag if an operation in the event set failed

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

H5ESwait() waits for operations in an event set `es_id` to wait with `timeout`.

Timeout value is in nanoseconds, and is for the H5ESwait() call and not for each individual operation in the event set. For example, if "10" is passed as a timeout value and the event set waited 4 nanoseconds for the first operation to complete, the remaining operations would be allowed to wait for at most 6 nanoseconds more, i.e., the timeout value used across all operations in the event set until it reaches 0, then any remaining operations are only checked for completion, not waited on.

This call will stop waiting on operations and will return immediately if an operation fails. If a failure occurs, the value returned for the number of operations in progress may be inaccurate.

Since
  1.14.0