Activity heartbeating and selective cancelation example.

In this example workflow starts a single activity that can be canceled. Activity execution has three stages :s1, :s2 and :s3. Each activity stage takes some time to execute. Activity execution can be canceled in stages :s1 and :s3 but not in stage :s2. Activity heartbeating provides a detailed history of activity stage execution, which can be considered activity mini-metrics in the Temporal web UI. Consecutive heartbeats sent to the Temporal server are echoed to the terminal.

Workflow execution can be started with start/1 which takes a cancellation stage number as an argument. To skip activity cancelation step, cancelation stage number should be any integer greater than 3.

Example run output for activity cancelation request in stage 2 (HB heartbeats echoed every second):

Elixir

iex(1)> ActivityHeartbeat.start(2)
HB: %{cancel_requested: false, current_stage: :s1, s1: 1}
HB: %{cancel_requested: false, current_stage: :s1, s1: 2}
HB: %{cancel_requested: false, current_stage: :s1, s1: 3}
HB: %{cancel_requested: false, current_stage: :s2, s1: 3, s2: 1}
HB: %{cancel_requested: false, current_stage: :s2, s1: 3, s2: 2}
HB: %{cancel_requested: false, current_stage: :s2, s1: 3, s2: 3}
HB: %{cancel_requested: false, current_stage: :s2, s1: 3, s2: 4}
cancelation: Ignore cancelation in stage s2.
HB: %{cancel_requested: true, current_stage: :s2, s1: 3, s2: 5}
cancelation: Ignore cancelation in stage s2.
HB: %{cancel_requested: true, current_stage: :s3, s1: 3, s2: 5, s3: 1}
cancelation: Cleanup and cancelation in stage s3.
{%{
   started: true,
   request_id: ~c"cluster_1-Elixir.ActivityHeartbeat.Workflow-f7a69412-2537-468e-9a54-12372f2de997",
   workflow_execution: %{
     workflow_id: ~c"Elixir.ActivityHeartbeat.Workflow/f920b769-0446-416c-951a-327931d52e49",
     run_id: "019a91ea-c4d3-7e97-b74a-4f0f81de4441"
   }
 },
 {:completed,
  %{
    result: ["stage s3 cancelation"],
    workflow_task_completed_event_id: 16,
    new_execution_run_id: ""
  }}}

Sample source: lib/activity_heartbeat

Erlang

1> activity_heartbeat:start(2).
HB: #{cancel_requested => false,current_stage => s1,s1 => 1}
HB: #{cancel_requested => false,current_stage => s1,s1 => 2}
HB: #{cancel_requested => false,current_stage => s1,s1 => 3}
HB: #{cancel_requested => false,current_stage => s2,s1 => 3,s2 => 1}
HB: #{cancel_requested => false,current_stage => s2,s1 => 3,s2 => 2}
HB: #{cancel_requested => false,current_stage => s2,s1 => 3,s2 => 3}
HB: #{cancel_requested => false,current_stage => s2,s1 => 3,s2 => 4}
cancelation: Ignore cancelation in stage s2.
HB: #{cancel_requested => true,current_stage => s2,s1 => 3,s2 => 5}
cancelation: Ignore cancelation in stage s2.
HB: #{cancel_requested => true,current_stage => s3,s1 => 3,s2 => 5,s3 => 1}
cancelation: Cleanup and cancelation in stage s3.
{#{started => true,
   request_id =>
       "cluster_1-activity_heartbeat_workflow-88914644-d406-4c9c-9e76-3521d3720539",
   workflow_execution =>
       #{workflow_id =>
             "activity_heartbeat_workflow/d02fa362-9bea-4508-896c-b1ae9d86e56a",
         run_id => <<"019a1fc0-6924-726a-a456-f9999fc9acfb">>}},
 {completed,#{result => ["stage s3 cancelation"],
              workflow_task_completed_event_id => 16,
              new_execution_run_id => <<>>}}}

Sample source: src/activity_heartbeat

REMAINDER: Activity can only be canceled if it has a :heartbeat_timeout option set, otherwise workflow execution will fail.