Merge pull request #77 from uber/async-child

Add example to start child workflow in async style

Author: abhishekj720

src/main/java/com/uber/cadence/samples/spring/workflows/impl/ParentWorkflowImpl.java

@@ -17,9 +17,12 @@
 
 package com.uber.cadence.samples.spring.workflows.impl;
 
+import com.uber.cadence.WorkflowExecution;
 import com.uber.cadence.samples.spring.models.SampleMessage;
 import com.uber.cadence.samples.spring.workflows.ChildWorkflow;
 import com.uber.cadence.samples.spring.workflows.ParentWorkflow;
+import com.uber.cadence.workflow.Async;
+import com.uber.cadence.workflow.Promise;
 import com.uber.cadence.workflow.Workflow;
 
 public class ParentWorkflowImpl implements ParentWorkflow {
@@ -29,4 +32,20 @@ public String getGreetingInParent(SampleMessage sampleMessage) {
     ChildWorkflow childWorkflow = Workflow.newChildWorkflowStub(ChildWorkflow.class);
     return childWorkflow.greetInChild(sampleMessage.GetMessage());
   }
+
+  // This example allows parent workflow returns first and leave child workflow keep running.
+  private String runChildWorkflowAsync(SampleMessage sampleMessage) {
+    ChildWorkflow childWorkflow = Workflow.newChildWorkflowStub(ChildWorkflow.class);
+    // non-blocking call that starts the child workflow
+    Async.function(childWorkflow::greetInChild, sampleMessage.GetMessage());
+
+    // Directly invoking child workflow method is a blocking call. It will block the thread
+    // until child workflow completes. In this example, parent workflow will immediately
+    // and keep child workflow running.
+    Promise<WorkflowExecution> childWorkflowPromise = Workflow.getWorkflowExecution(childWorkflow);
+    // block until child workflow started, otherwise parent workflow may completes first
+    // before child workflow even starts.
+    childWorkflowPromise.get();
+    return "child can keep running, parent return first";
+  }
 }