add errgroup sample

errgroup/README.md

@@ -0,0 +1,24 @@
+This sample demonstrates how to use `errgroup` pattern to synchronise
+cancellation of workflow coroutines.
+
+
+This sample only uses workflow code and uses `testsuite` in the `main` function
+instead of using `worker` and `starter` to simplify the code.
+
+To run this sample, simply do:
+
+```
+go run errgroup.go
+```
+
+And output should be:
+
+```
+2022/05/10 09:44:41 DEBUG RequestCancelTimer TimerID 1
+2022/05/10 09:44:41 DEBUG RequestCancelTimer TimerID 2
+2022/05/10 09:44:41 DEBUG RequestCancelTimer TimerID 3
+ctx error canceled
+ctx error canceled
+ctx error canceled
+2022/05/10 09:44:41 result: expected error received: foo error
+```

errgroup/errgroup.go

@@ -0,0 +1,91 @@
+package main
+
+import (
+	"errors"
+	"log"
+	"time"
+
+	"go.temporal.io/sdk/testsuite"
+	"go.temporal.io/sdk/workflow"
+)
+
+func Workflow(ctx workflow.Context) (string, error) {
+	g, cc := WithContext(ctx)
+
+	for i := 0; i < 3; i++ {
+		g.Go(cc, func(ctx workflow.Context) error {
+			workflow.Sleep(ctx, 3*time.Second)
+			if ctx.Err() != nil {
+				println("ctx error", ctx.Err().Error())
+			} else {
+				panic("shouldn't be here")
+			}
+			return nil
+		})
+	}
+	g.Go(cc, func(ctx workflow.Context) error {
+		return errors.New("foo error")
+	})
+
+	err := g.Wait(cc)
+	if err == nil {
+		return "", errors.New("expected error")
+	}
+	return "expected error received: " + err.Error(), nil
+}
+
+func main() {
+	s := &testsuite.WorkflowTestSuite{}
+	env := s.NewTestWorkflowEnvironment()
+
+	env.ExecuteWorkflow(Workflow)
+	err := env.GetWorkflowError()
+	if err != nil {
+		log.Fatalf("[ERROR] not expecting workflow error: %v", err)
+	}
+	var result interface{}
+	err = env.GetWorkflowResult(&result)
+	if err != nil {
+		log.Fatalf("[ERROR] failed to get workflow result: %v", err)
+	}
+	log.Printf("result: %v", result)
+}
+
+// adapted from https://cs.opensource.google/go/x/sync/+/036812b2:errgroup/errgroup.go
+type ErrGroup struct {
+	wg     workflow.WaitGroup
+	cancel func()
+	err    error
+}
+
+func WithContext(ctx workflow.Context) (*ErrGroup, workflow.Context) {
+	cc, cancel := workflow.WithCancel(ctx)
+	eg := &ErrGroup{
+		cancel: cancel,
+		wg:     workflow.NewWaitGroup(ctx),
+	}
+	return eg, cc
+}
+
+func (g *ErrGroup) Wait(ctx workflow.Context) error {
+	g.wg.Wait(ctx)
+	if g.cancel != nil {
+		g.cancel()
+	}
+	return g.err
+}
+
+func (g *ErrGroup) Go(ctx workflow.Context, f func(workflow.Context) error) {
+	g.wg.Add(1)
+	workflow.Go(ctx, func(ctx workflow.Context) {
+		defer g.wg.Done()
+		if err := f(ctx); err != nil {
+			if g.err == nil {
+				g.err = err
+			}
+			if g.cancel != nil {
+				g.cancel()
+			}
+		}
+	})
+}