Run Worker processes - Java SDK

How to run Worker Processes

The Worker Process is where Workflow Functions and Activity Functions are executed.

• Each Worker Entity in the Worker Process must register the exact Workflow Types and Activity Types it may execute.
• Each Worker Entity must also associate itself with exactly one Task Queue.
• Each Worker Entity polling the same Task Queue must be registered with the same Workflow Types and Activity Types.

A Worker Entity is the component within a Worker Process that listens to a specific Task Queue.

Although multiple Worker Entities can be in a single Worker Process, a single Worker Entity Worker Process may be perfectly sufficient. For more information, see the Worker tuning guide.

A Worker Entity contains a Workflow Worker and/or an Activity Worker, which makes progress on Workflow Executions and Activity Executions, respectively.

Use the newWorker method on an instance of a WorkerFactory to create a new Worker in Java.

A single Worker Entity can contain many Worker Objects. Call the start() method on the instance of the WorkerFactory to start all the Workers created in this process.

// ...
import io.temporal.client.WorkflowClient;
import io.temporal.serviceclient.WorkflowServiceStubs;
import io.temporal.worker.Worker;
import io.temporal.worker.WorkerFactory;

public class YourWorker {

  public static void main(String[] args) {

    WorkflowServiceStubs service = WorkflowServiceStubs.newLocalServiceStubs();
    WorkflowClient client = WorkflowClient.newInstance(service);
    WorkerFactory factory = WorkerFactory.newInstance(client);
    Worker yourWorker = factory.newWorker("your_task_queue");

    // Register Workflow
    // and/or register Activities

    factory.start();
  }
}

After creating the Worker entity, register all Workflow Types and all Activity Types that the Worker can execute. A Worker can be registered with just Workflows, just Activities, or both.

Operation guides:

• How to tune Workers

How to register types

All Workers listening to the same Task Queue name must be registered to handle the exact same Workflows Types and Activity Types.

If a Worker polls a Task for a Workflow Type or Activity Type it does not know about, it fails that Task. However, the failure of the Task does not cause the associated Workflow Execution to fail.

Use worker.registerWorkflowImplementationTypes to register Workflow Type and worker.registerActivitiesImplementations to register Activity implementation with Workers.

For Workflows, the Workflow Type is registered with a Worker. A Workflow Type can be registered only once per Worker entity. If you define multiple Workflow implementations of the same type, you get an exception at the time of registration.

For Activities, Activity implementation instances are registered with a Worker because they are stateless and thread-safe. You can pass any number of dependencies in the Activity implementation constructor, such as the database connections, services, etc.

The following example shows how to register a Workflow and an Activity with a Worker.

Worker worker = workerFactory.newWorker("your_task_queue");
...
// Register Workflow
worker.registerWorkflowImplementationTypes(GreetingWorkflowImpl.class);
// Register Activity
worker.registerActivitiesImplementations(new GreetingActivitiesImpl());

When you register a single instance of an Activity, you can have multiple instances of Workflow Executions calling the same Activity. Activity code must be thread-safe because the same instance of the Activity code is run for every Workflow Execution that calls it.

For DynamicWorkflow, only one Workflow implementation that extends DynamicWorkflow can be registered with a Worker. The following example shows how to register the DynamicWorkflow and DynamicActivity implementation with a Worker.

  public static void main(String[] arg) {

    WorkflowServiceStubs service = WorkflowServiceStubs.newInstance();
    WorkflowClient client = WorkflowClient.newInstance(service);
    WorkerFactory factory = WorkerFactory.newInstance(client);
    Worker worker = factory.newWorker(TASK_QUEUE);

    /* Register the Dynamic Workflow implementation with the Worker. Workflow implementations
    ** must be known to the Worker at runtime to dispatch Workflow Tasks.
    */
    worker.registerWorkflowImplementationTypes(DynamicGreetingWorkflowImpl.class);

    // Start all the Workers that are in this process.
    factory.start();

    /* Create the Workflow stub. Note that the Workflow Type is not explicitly registered with the Worker. */
    WorkflowOptions workflowOptions =
        WorkflowOptions.newBuilder().setTaskQueue(TASK_QUEUE).setWorkflowId(WORKFLOW_ID).build();
    WorkflowStub workflow = client.newUntypedWorkflowStub("DynamicWF", workflowOptions);
    /**
     * Register Dynamic Activity implementation with the Worker. Since Activities are stateless
     * and thread-safe, we need to register a shared instance.
    */
    worker.registerActivitiesImplementations(new DynamicGreetingActivityImpl());

    /* Start Workflow Execution and immmediately send Signal. Pass in the Workflow args and Signal args. */
    workflow.signalWithStart("greetingSignal", new Object[] {"John"}, new Object[] {"Hello"});

    // Wait for the Workflow to finish getting the results.
    String result = workflow.getResult(String.class);

    System.out.println(result);

    System.exit(0);
  }
}

You can register multiple type-specific Workflow implementations alongside a single DynamicWorkflow implementation. You can register only one Activity instance that implements DynamicActivity with a Worker.