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Exercise #2: Sending a Signal from a Client

During this exercise, you will:

  • Define and handle a Signal
  • Retrieve a handle on the Workflow to Signal
  • Use a Temporal Client to send the Signal

Make your changes to the code in the practice subdirectory (look for TODO comments that will guide you to where you should make changes to the code). If you need a hint or want to verify your changes, look at the complete version in the solution subdirectory.

Part A: Defining a Signal

In this part of the exercise, you will define your Signal.

  1. Edit the workflow.go file.
  2. Between the import and Workflow() blocks, define a new Signal type struct named FulfillOrderSignal. It should contain a single variable, a bool, named Fulfilled.
  3. Save the file.

Part B: Handling the Signal

You will now handle the Signal you defined in part A, and let the Workflow know what to do when it encounters the FulfillOrderSignal.

  1. In workflow.go, locate the signalChan.Receive() call. This will block the Workflow until a Signal is received.
  2. Wrap the ExecuteActivity() call and the logger.Info() call in a test for if signal.Fulfilled == true.
  3. Save the file.

Part C: Import the Signal type into your Signal Client

In this part of the exercise, you will create another Temporal client that sends a Signal. signalclient/main.go currently contains a near-empty Temporal client -- it looks like a Starter or a Worker, but it does not register any Workflows or do anything. You will use this client to send a Signal.

  1. Edit the signalclient/main.go file.
  2. Within the main() block, use the FullfillOrderSignal struct type from the signals module (i.e., the workflow.go file in the parent directory) to create an instance of FulfillOrderSignal that contains Fulfilled: true.
  3. Save the file.

Part D: Signaling Your Workflow

Now you will add the SignalWorkflow() call itself.

  1. Continue editing the signalclient/main.go file.
  2. Within the main() block, after you create an instance of FulfillOrderSignal, call SignalWorkflow() to send a Signal to your running Workflow. It needs, as arguments, context.Background(), your workflow ID, your run ID (which can be an empty string), the name of the signal, and the signal instance. It should assign its result to err so that it can be checked in the next line.
  3. Save the file.

Part E: Start Your Workflow

At this point, you can run your Workflow. It should run normally but wait to receive a Signal.

  1. In one terminal, navigate to the worker subdirectory and run go run main.go.
  2. In another terminal, navigate to the starter subdirectory and run go run main.go. You should receive some logging from your Worker along these lines:
2024/03/14 08:48:10 INFO  No logger configured for temporal client. Created default one.
2024/03/14 08:48:10 INFO  Started Worker Namespace default TaskQueue signals WorkerID 43388@Omelas@
2024/03/14 08:48:21 INFO  Signal workflow started Namespace default TaskQueue signals WorkerID 43388@Omelas@ WorkflowType Workflow WorkflowID signals RunID 905330da-9c0f-490e-bd48-c6a9e8840f7a Attempt 1 input Plain text input
  1. Your Workflow will not return as you added a blocking Signal call. In the next step, you will Signal your workflow.

Part F: Send Your Signal

  1. In a third terminal, navigate to the signalclient subdirectory and run go run main.go. It will send a Signal to your Workflow. This should cause your Workflow to return, and the Signal workflow completed call to be logged in the terminal running your Worker:
2024/03/14 08:48:37 INFO  Signal workflow completed. Namespace default TaskQueue signals WorkerID 43388@Omelas@ WorkflowType Workflow WorkflowID signals RunID 905330da-9c0f-490e-bd48-c6a9e8840f7a Attempt 1 result Received Plain text input
  1. You have successfully sent a Signal from a Temporal Client to a running Workflow.

This is the end of the exercise.