Interrupt a Workflow Execution - Java SDK

You can interrupt a Workflow Execution in one of the following ways:

• Cancel: Canceling a Workflow provides a graceful way to stop Workflow Execution.
• Terminate: Terminating a Workflow forcefully stops Workflow Execution.

Terminating a Workflow forcefully stops Workflow Execution. This action resembles killing a process.

• The system records a WorkflowExecutionTerminated event in the Workflow History.
• The termination forcefully and immediately stops the Workflow Execution.
• The Workflow code gets no chance to handle termination.
• A Workflow Task doesn't get scheduled.

In most cases, canceling is preferable because it allows the Workflow to finish gracefully. Terminate only if the Workflow is stuck and cannot be canceled normally.

Cancel a Workflow Execution

Canceling a Workflow provides a graceful way to stop Workflow Execution. This action resembles sending a SIGTERM to a process.

• The system records a WorkflowExecutionCancelRequested event in the Workflow History.
• A Workflow Task gets scheduled to process the cancelation.
• The Workflow code can handle the cancelation and execute any cleanup logic.
• The system doesn't forcefully stop the Workflow.

To cancel a Workflow Execution in Java, use the cancel() function on the WorkflowStub.

WorkflowStub workflowStub = WorkflowStub.fromTyped(workflow);
workflowStub.cancel();

Cancellation scopes in Java

In the Java SDK, Workflows are represented internally by a tree of cancellation scopes, each with cancellation behaviors you can specify. By default, everything runs in the "root" scope.

Scopes are created using the Workflow.newCancellationScope constructor

Cancellations are applied to cancellation scopes, which can encompass an entire Workflow or just part of one. Scopes can be nested, and cancellation propagates from outer scopes to inner ones. A Workflow's method runs in the outermost scope. Cancellations are handled by catching CanceledFailures thrown by cancelable operations.

You can also use the following APIs:

• CancellationScope.current(): Get the current scope.
• scope.cancel(): Cancel all operations inside a scope.
• scope.getCancellationRequest(): A promise that resolves when a scope cancellation is requested, such as when Workflow code calls cancel() or the entire Workflow is cancelled by an external client.

When a CancellationScope is cancelled, it propagates cancellation in any child scopes and of any cancelable operations created within it, such as the following:

• Activities
• Timers (created with the sleep function)
• Child Workflows
• Nexus Operations

Cancel an Activity from a Workflow

Canceling an Activity from within a Workflow requires that the Activity Execution sends Heartbeats and sets a Heartbeat Timeout. If the Heartbeat is not invoked, the Activity cannot receive a cancellation request. When any non-immediate Activity is executed, the Activity Execution should send Heartbeats and set a Heartbeat Timeout to ensure that the server knows it is still working.

When an Activity is canceled, an error is raised in the Activity at the next available opportunity. If cleanup logic needs to be performed, it can be done in a finally clause or inside a caught cancel error. However, for the Activity to appear canceled the exception needs to be re-raised.

note

Unlike regular Activities, Local Activities currently do not support cancellation.

To cancel an Activity from a Workflow Execution, call the cancel() method on the CancellationScope that the activity was started in.

public class GreetingWorkflowImpl implements GreetingWorkflow {
    @Override
    public String getGreeting(String name) {
      List<Promise<String>> results = new ArrayList<>(greetings.length);

      /*
       * Create our CancellationScope. Within this scope we call the workflow activity
       * composeGreeting method asynchronously for each of our defined greetings in different
       * languages.
       */
      CancellationScope scope =
          Workflow.newCancellationScope(
              () -> {
                for (String greeting : greetings) {
                  results.add(Async.function(activities::composeGreeting, greeting, name));
                }
              });

      /*
       * Execute all activities within the CancellationScope. Note that this execution is
       * non-blocking as the code inside our cancellation scope is also non-blocking.
       */
      scope.run();

      // We use "anyOf" here to wait for one of the activity invocations to return
      String result = Promise.anyOf(results).get();

      // Trigger cancellation of all uncompleted activity invocations within the cancellation scope
      scope.cancel();

      /*
       *  Wait for all activities to perform cleanup if needed.
       *  For the sake of the example we ignore cancellations and
       *  get all the results so that we can print them in the end.
       *
       *  Note that we cannot use "allOf" here as that fails on any Promise failures
       */
      for (Promise<String> activityResult : results) {
        try {
          activityResult.get();
        } catch (ActivityFailure e) {
          if (!(e.getCause() instanceof CanceledFailure)) {
            throw e;
          }
        }
      }
      return result;
    }
}

Terminate a Workflow Execution

Terminating a Workflow forcefully stops Workflow Execution. This action resembles killing a process.

• The system records a WorkflowExecutionTerminated event in the Workflow History.
• The termination forcefully and immediately stops the Workflow Execution.
• The Workflow code gets no chance to handle termination.
• A Workflow Task doesn't get scheduled.

To terminate a Workflow Execution in Java, use the terminate() function on the WorkflowStub.

WorkflowStub untyped = WorkflowStub.fromTyped(myWorkflowStub);
untyped.terminate("Sample reason");