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Serialization of Store data in worker thread is now opt-in

· 2 min read
Erik Montnemery

The Store class from homeassistant/helpers/storage.py accepts a new constructor argument serialize_in_event_loop

If serialize_in_event_loop is True (the default):

  • The data_func passed to Store.async_delay_save is called from the event loop
  • Data produced by data_func passed to Store.async_delay_save is serialized to JSON in the event loop
  • Data passed to Store.async_save is serialized to JSON in the event loop

If serialize_in_event_loop is False:

  • The data_func passed to Store.async_delay_save is called from a separate thread, which means it must be thread safe and must not access the hass object
  • Data produced by data_func passed to Store.async_delay_save is serialized to JSON in a separate thread, which means it must be thread safe
  • Data passed to Store.async_save is serialized to JSON in a separate thread, which means it must be thread safe

The behavior has changed; data_func passed to Store.async_delay_save was previously always called from a separate thread and data produced by it or data passed to Store.async_save was previously always serialized by a separate thread.

The reason for the change is that it was not documented that data_func would be called by a thread other than the event loop or that JSON serialization would happen in a thread other than the event loop, and the data_func and data produced by it or passed to Store.async_save was generally not thread safe.

For more details, see core PR 157158 and core PR 157263.