README.md

Exercise #1: Sending an External Signal

During this exercise, you will:

• Define and handle a Signal
• Retrieve a handle on the Workflow to Signal
• Send an external Signal
• Use a Temporal Client to submit execution requests for both Workflows

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

1. This exercise contains one Client that runs two different Workflows — PizzaWorkflow and FulfillOrderWorkflow. Both Workflows are defined in workflow.go. PizzaWorkflow is designed not to complete its final activity — SendBill — until it receives a Signal from FulfillOrderWorkflow. You'll start by defining that Signal. Edit workflow.go. Near the top of the file, after the import() block and before your Workflow definitions, create a type of struct{} named FulfillOrderSignal that contains a single bool named Fulfilled.
2. Next, directly below that, create a var named signal that is an instance of FulfillOrderSignal with Fulfilled: true. This is the Signal that FulfillOrderWorkflow will send to PizzaWorkflow.
3. Save the file.

Part B: Handling the Signal

1. Next, you need to enable your PizzaWorkflow to receive a Signal from FulfillOrderWorkflow. After var confirmation OrderConfirmation, define a Signal Channel, and use signalChan.Receive() to block the Workflow until it receives a Signal, after which it can proceed with the logic contained in if signal.Fulfilled == true{}. Begin by adding a call to workflow.GetSignalChannel(ctx, "fulfill-order-signal") and assign it to a variable like signalChan.
2. After that, add signalChan.Receive(ctx, &signal) on the following line.
3. Save the file.

Part C: Signaling your Workflow

1. Near the bottom of workflow.go, within FulfillOrderWorkflow, you will notice that it runs two Activities — MakePizzas and DeliverPizzas. After those Activities complete successfuly, the next step should be to send a Signal to the PizzaWorkflow that it is time to bill the customer and complete the Workflow. To do this, you need call workflow.SignalExternalWorkflow().
2. Add this call to the end of FulfillOrderWorkflow. SignalExternalWorkflow needs, as arguments, the ctx Workflow context, Workflow ID (which should be pizza-workflow-order-Z1238), an optional Run ID (which you can omit by providing "" as the next argument), and the name of the Signal,fulfill-order-signal. For SignalExternalWorkflow calls to block and return properly in Go, you also need to append .Get(ctx, [return-value-pointer]) to a SignalExternalWorkflow call, though [return-value-pointer] can be nil here.
3. Save and close the file.

Part D: Making your Client start both Workflows

1. Finally, open start/main.go for editing. Currently, this Client only starts the PizzaWorkflow. Directly after the c.ExecuteWorkflow() call for the PizzaWorkflow, add another call that starts the FulfillOrderWorkflow. You can use the call that starts the PizzaWorkflow and the signalFulfilledOptions block as a reference. Don't forget to capture the Workflow Execution and any errors in different variables.
2. Save and close the file.

Part E: Running both Workflows

At this point, you can run your Workflows.

1. In one terminal, navigate to the worker subdirectory and run go run main.go.

2. In another terminal, navigate to the start subdirectory and run go run main.go. You should receive output from both Workflows having started and returning the expected result:

   2024/04/12 10:41:11 Started workflow WorkflowID pizza-workflow-order-Z1238 RunID d41177c4-ffe6-4f51-a884-7fefb3e13cff
   2024/04/12 10:41:11 Started workflow WorkflowID signal-fulfilled-order-Z1238 RunID 9d5168e9-1c58-41c3-aca2-ea8182dff11d
   2024/04/12 10:41:11 Workflow result: {
     "OrderNumber": "Z1238",
     "Status": "SUCCESS",
     "ConfirmationNumber": "AB9923",
     "BillingTimestamp": 1712943671,
     "Amount": 2700
   }
   

3. If you look at the terminal running your Worker, you should see logging from each individual step run by both Workflows, including the Signal being sent and all the related activities:

   ...
   2024/04/12 10:41:11 INFO  Starting delivery Namespace default TaskQueue pizza-tasks WorkerID 35880@ted.local@ ActivityID 11 ActivityType DeliverPizzas Attempt 1 WorkflowType FulfillOrderWorkflow WorkflowID signal-fulfilled-order-Z1238 RunID 9d5168e9-1c58-41c3-aca2-ea8182dff11d Z1238 to {701 Mission Street Apartment 9C San Francisco CA 94103}
   2024/04/12 10:41:11 INFO  Z1238 Namespace default TaskQueue pizza-tasks WorkerID 35880@ted.local@ ActivityID 11 ActivityType DeliverPizzas Attempt 1 WorkflowType FulfillOrderWorkflow WorkflowID signal-fulfilled-order-Z1238 RunID 9d5168e9-1c58-41c3-aca2-ea8182dff11d delivered.
   ...
   

This is the end of the exercise.