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 temporal_sdk_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 RespondActivityTaskCompleted 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