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| HDF5 Last Updated on 2026-03-23 The HDF5 Field Guide

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HDF5 Event Set

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# The HDF5 Event Set Interface

## Introduction

HDF5 provides asynchronous APIs for the HDF5 VOL connectors that support asynchronous HDF5 operations using the HDF5 Event Set (H5ES) API. This allows I/O to proceed in the background while the application is performing other tasks.

To support AIO capabilities for the HDF5 VOL connectors, the AIO versions for the functions listed in the table below were added to HDF5 library version 1.14.0 and later. The async version of the function has “_async” suffix added to the function name. For example, the async version for H5Fcreate is H5Fcreate_async.

Interface | Functions
--- | ---
H5F | H5Fcreate, H5Fflush, H5Fopen, H5Fclose
H5G | H5Gcreate, H5Gget_info, H5Gget_info_by_idx, H5Gget_info_by_name, H5Gclose
H5D | H5Dcreate, H5Dopen, H5Dset_extent, H5Dwrite, H5Dread, H5Dget_space, H5Dclose
H5A | H5Acreate, H5Acreate_by_name, H5Aopen, H5Aopen_by_name, H5Aexists, H5Awrite, H5Aread, H5Aclose, H5Aopen_by_idx, H5Arename, H5Arename_by_name
H5L | H5Lcreate_hard, H5Lcreate_soft, H5Ldelete, H5Ldelete_by_idx, H5Lexists
H5O | H5Ocopy, H5Orefresh, H5Oflush, H5Oclose, H5Oopen, H5Oopen_by_idx
H5R | H5Ropen_attr, H5Ropen_object, H5Ropen_region
H5M | H5Mcreate, H5Mopen, H5Mput, H5Mget, H5Mclose
H5T | H5Tcommit, H5Topen, H5Tclose

Async versions of the functions have an extra parameter called the event set parameter or es_id. For example, compare the signatures of H5Dclose and H5Dclose_async:

herr_t H5Dclose(hid_t dset_id);
herr_t H5Dclose_async(hid_t dset_id, hid_t es_id);
hid_t
int64_t hid_t
Definition H5Ipublic.h:60
herr_t
int herr_t
Definition H5public.h:269
H5Dclose_async
herr_t H5Dclose_async(hid_t dset_id, hid_t es_id)
H5Dclose
herr_t H5Dclose(hid_t dset_id)
Closes the specified dataset.

An event set is an in-memory object that is created by an application and used to track many asynchronous operations with a single object. They function like a "bag" – holding request tokens from one or more asynchronous operations and provide a simple interface for inspecting the status of the entire set of operations.

See the Event Set Interface (H5ES) APIs that were added to the HDF5 library to manage event sets.

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