Add cancel sample (#82)

This workflow provides an example on how to cancel an workflow and execute subsequent activities upon a cancelled context.

Author: chopincode

new_samples/README.md

@@ -101,3 +101,27 @@ cadence --env development \
   --et 60 \
   --input '{}'
 ```
+
+### Cancel workflow
+This workflow includes multiple activities and each will respond to the workflow `cancel` action differently.
+To start the workflow first, simply run
+
+```bash
+cadence --env development \
+  --domain cadence-samples \
+  workflow start \
+  --workflow_type cadence_samples.CancelWorkflow \
+  --tl cadence-samples-worker \
+  --et 60 \
+  --input '{}'
+```
+
+You should have a workflow ID output in the terminal. Then to cancel the workflow, run
+```bash
+cadence --env development \
+  --domain cadence-samples \
+  workflow cancel \
+  --workflow_id <YOUR_WORKFLOW_ID>
+```
+
+Inspect the behavior of the activities in the console. 

new_samples/worker/worker.go

@@ -55,6 +55,12 @@ func StartWorker() {
 	w.RegisterWorkflowWithOptions(workflows.ParallelBranchPickFirstWorkflow, workflow.RegisterOptions{Name: "cadence_samples.ParallelBranchPickFirstWorkflow"})
 	w.RegisterActivityWithOptions(workflows.ParallelActivity, activity.RegisterOptions{Name: "cadence_samples.ParallelActivity"})
 
+	// Cancel workflow registration
+	w.RegisterWorkflowWithOptions(workflows.CancelWorkflow, workflow.RegisterOptions{Name: "cadence_samples.CancelWorkflow"})
+	w.RegisterActivityWithOptions(workflows.ActivityToBeSkipped, activity.RegisterOptions{Name: "cadence_samples.ActivityToBeSkipped"})
+	w.RegisterActivityWithOptions(workflows.ActivityToBeCanceled, activity.RegisterOptions{Name: "cadence_samples.ActivityToBeCanceled"})
+	w.RegisterActivityWithOptions(workflows.CleanupActivity, activity.RegisterOptions{Name: "cadence_samples.CleanupActivity"})
+
 	err := w.Start()
 	if err != nil {
 		panic("Failed to start worker: " + err.Error())

new_samples/workflows/cancel_workflow.go

@@ -0,0 +1,84 @@
+package workflows
+
+import (
+	"context"
+	"fmt"
+	"go.uber.org/cadence"
+	"go.uber.org/cadence/activity"
+	"go.uber.org/cadence/workflow"
+	"go.uber.org/zap"
+	"time"
+)
+
+func CancelWorkflow(ctx workflow.Context) (retError error) {
+	ao := workflow.ActivityOptions{
+		ScheduleToStartTimeout: time.Minute,
+		StartToCloseTimeout:    time.Minute * 30,
+		HeartbeatTimeout:       time.Second * 5,
+		WaitForCancellation:    true,
+	}
+	ctx = workflow.WithActivityOptions(ctx, ao)
+	logger := workflow.GetLogger(ctx)
+	logger.Info("cancel workflow started")
+
+	defer func() {
+		if cadence.IsCanceledError(retError) {
+			// When workflow is canceled, it has to get a new disconnected context to execute any activities
+			newCtx, _ := workflow.NewDisconnectedContext(ctx)
+			err := workflow.ExecuteActivity(newCtx, CleanupActivity).Get(ctx, nil)
+			if err != nil {
+				logger.Error("Cleanup activity failed", zap.Error(err))
+				retError = err
+				return
+			}
+			retError = nil
+			logger.Info("Workflow completed.")
+		}
+	}()
+
+	var result string
+	err := workflow.ExecuteActivity(ctx, ActivityToBeCanceled).Get(ctx, &result)
+	if err != nil && !cadence.IsCanceledError(err) {
+		logger.Error("Error from activityToBeCanceled", zap.Error(err))
+		return err
+	}
+	logger.Info(fmt.Sprintf("activityToBeCanceled returns %v, %v", result, err))
+
+	// Execute activity using a canceled ctx,
+	// activity won't be scheduled and a cancelled error will be returned
+	err = workflow.ExecuteActivity(ctx, ActivityToBeSkipped).Get(ctx, nil)
+	if err != nil && !cadence.IsCanceledError(err) {
+		logger.Error("Error from activityToBeSkipped", zap.Error(err))
+	}
+
+	return err
+}
+
+func ActivityToBeCanceled(ctx context.Context) (string, error) {
+	logger := activity.GetLogger(ctx)
+	logger.Info("activity started, to cancel workflow, use CLI: 'cadence --do samples-domain wf cancel -w <WorkflowID>' to cancel")
+	for {
+		select {
+		case <-time.After(1 * time.Second):
+			logger.Info("heart beating...")
+			activity.RecordHeartbeat(ctx, "")
+		case <-ctx.Done():
+			logger.Info("context is cancelled")
+			// returned canceled error here so that in workflow history we can see ActivityTaskCanceled event
+			// or if not cancelled, return timeout error
+			return "I am canceled by Done", ctx.Err()
+		}
+	}
+}
+
+func CleanupActivity(ctx context.Context) error {
+	logger := activity.GetLogger(ctx)
+	logger.Info("cleanupActivity started")
+	return nil
+}
+
+func ActivityToBeSkipped(ctx context.Context) error {
+	logger := activity.GetLogger(ctx)
+	logger.Info("this activity will be skipped due to cancellation")
+	return nil
+}