Demonstrates how to use awaitable events with the ActivityTaskStarted event.

Successfully completed regular activity awaitable transitions through the following states:

• cmd – the "command" state, set when the activity is started via the start_activity() command,
• scheduled – state after the Temporal server schedules activity and records the ActivityTaskScheduled event in the events history,
• started – state after SDK’s activity task worker successfully polls activity task and the ActivityTaskStarted event is recorded,
• completed – state after activity executor successfully completes activity execution and the ActivityTaskCompleted event is recorded.

See the :temporal_sdk_workflow module documentation for more information on awaitables.

Workflow used in this sample starts an echo_activity activity and sets its awaitable event to start. Awaiting such an activity will block until the activity transitions to at least the started state.

Activity is started on the "awaitable_event" task queue. Activity awaitable with event set to start is awaited with a 1-second timeout. If the activity worker polling "awaitable_event" task queue is unavailable and activity execution does not start within the timeout, a WARN message is logged. Finally, the activity awaitable event is set to the closed state, and awaiting an awaitable in a closed state follows as in the typical use cases.

Such a pattern can be useful, for example, when workflow logic requires prior knowledge of issues related to a given activity worker, without failing the activity through conventional activity timeouts.

Example run:

Elixir

iex(1)> AwaitableEvent.run(0)
Start activity worker.
INFO: Activity started within 1000 msec timeout.
Activity completed.
:ok
#
# Restart session here to terminate running activity worker
#
iex(1)> AwaitableEvent.run(2000)
WARN: Activity NOT started within 1000 msec timeout.
Start activity worker.
Activity completed.
:ok
iex(2)> AwaitableEvent.run(2000)
Activity worker already started.
INFO: Activity started within 1000 msec timeout.
Activity completed.
:ok

Sample source: lib/awaitable_event

Erlang

1> awaitable_event:run(0).
Start activity worker.
INFO: Activity started within 1000 msec timeout.
<<"Activity completed.">>
ok
%
% Restart session here to terminate running activity worker
%
1> awaitable_event:run(2000).
WARN: Activity NOT started within 1000 msec timeout.
Start activity worker.
<<"Activity completed.">>
ok
2> awaitable_event:run(2000).
Activity worker already started.
INFO: Activity started within 1000 msec timeout.
<<"Activity completed.">>
ok

Sample source: src/awaitable_event