Mutable marker sample.

This sample workflow implementation performs the following steps:

1. Start and await the :first_activity activity.
2. Record the mutable OS env marker from the :mutable_marker OS environment variable.
3. Start the :second_activity long-running activity, whose input depends on the mutable recorded marker value from step 2.

To demonstrate the mutable marker functionality we simulate three worker node restarts using a timer and TemporalSdk.Workflow.terminate_executor/0. After the workflow executor is forcefully terminated, workflow task timeouts which can be ignored in this context. This triggers workflow execution retry replaying existing workflow history events. During workflow replay :first_activity and :mutable_marker results are fetched from the history. If the count of mutable marker mutations is less than the mutation limit, the SDK executes the function that evaluates the :mutable_marker value during replay. If the current marker value differs from the value recorded in the workflow events history, the SDK resets the workflow execution to the task-finish event that immediately precedes the mutable marker. The Temporal server then starts a new, reset workflow execution. After each mutation of the marker and workflow reset, the :second_activity is started with new, mutated input.

During sample runs, the Temporal server returns "workflow execution already completed" errors when handling "RespondActivityTaskCompleted" gRPC requests for :second_activity. These errors occur because SDK activity executors for :second_activity are unaware of parent workflow resets and still attempt to dispatch respond_activity_task_completed to workflow executions that have already been closed.

Example run (error messages are omitted):

Elixir

iex(1)> MutableMarker.run()
:ok
Mutable Marker - mutations count: 0, marker value: 49.
Mutable Marker - mutations count: 1, marker value: 51.

14:29:59.482 [error] [reason: %{grpc_response_headers:
...
Mutable Marker - mutations count: 2, marker value: 53.
Mutable Marker - mutations count: 3, marker value: 55.

Sample source: lib/mutable_marker

Erlang

1> mutable_marker:run().
ok
Mutable Marker - mutations count: 0, marker value: 49.
Mutable Marker - mutations count: 1, marker value: 51.
=ERROR REPORT==== 20-Mar-2026::13:54:11.521082 ===
    reason: #{grpc_response_headers =>
...
Mutable Marker - mutations count: 2, marker value: 53.
Mutable Marker - mutations count: 3, marker value: 55.

Sample source: src/mutable_marker