Add eager workflow start sample

.gitignore

@@ -15,3 +15,4 @@ vendor/
 # Executables produced by temporal-go-samples repo
 bin/
 .fossa.yml
+*~

README.md

@@ -140,6 +140,8 @@ Each sample demonstrates one feature of the SDK, together with tests.
 - [**Update**](./update): Demonstrates how to create a workflow that reacts
   to workflow update requests.
 
+- [**Eager Workflow Start**](./eager-workflow-start): Demonstrates how to start a workflow in eager mode, an experimental latency optimization.
+
 ### Dynamic Workflow logic examples
 
 These samples demonstrate some common control flow patterns using Temporal's Go SDK API.

eager-workflow-start/README.md

@@ -0,0 +1,10 @@
+### Steps to run this sample:
+1) Run a [Temporal service](https://github.com/temporalio/samples-go/tree/main/#how-to-use) with eager workflow start enabled by a dynamic config value.
+```
+temporal server start-dev --dynamic-config-value system.enableEagerWorkflowStart=true
+```
+2) Run the following command to start the combined worker and example
+```
+go run eager-workflow-start/main.go
+```
+

eager-workflow-start/main.go

@@ -0,0 +1,59 @@
+package main
+
+import (
+	"context"
+	"log"
+
+	"github.com/pborman/uuid"
+	"go.temporal.io/sdk/client"
+	"go.temporal.io/sdk/worker"
+
+	"github.com/temporalio/samples-go/helloworld"
+)
+
+const taskQueueName = "eager_wf_start"
+
+func main() {
+	// 1. Create the shared client.
+	c, err := client.Dial(client.Options{})
+	if err != nil {
+		log.Fatalln("Unable to create client", err)
+	}
+	defer c.Close()
+
+	// 2. Start the worker in a non-blocking manner before the workflow.
+	workerOptions := worker.Options{
+		OnFatalError: func(err error) { log.Fatalln("Worker error", err) },
+	}
+	w := worker.New(c, taskQueueName, workerOptions)
+	w.RegisterWorkflow(helloworld.Workflow)
+	w.RegisterActivity(helloworld.Activity)
+	err = w.Start()
+	if err != nil {
+		log.Fatalln("Unable to start worker", err)
+	}
+	defer w.Stop()
+
+	workflowOptions := client.StartWorkflowOptions{
+		ID:        "eager_wf" + uuid.New(),
+		TaskQueue: taskQueueName,
+
+		// 3. Set this flag to true to enable EWS.
+		EnableEagerStart: true,
+	}
+
+	// 4. Reuse the client connection.
+	we, err := c.ExecuteWorkflow(context.Background(), workflowOptions,
+		helloworld.Workflow, "Temporal")
+	if err != nil {
+		log.Fatalln("Unable to execute workflow", err)
+	}
+
+	// 5. Wait for workflow completion.
+	var result string
+	err = we.Get(context.Background(), &result)
+	if err != nil {
+		log.Fatalln("Unable to get workflow result", err)
+	}
+	log.Println("Workflow result:", result)
+}