Add supporting APIs for evacuation

helix-core/src/main/java/org/apache/helix/HelixAdmin.java

@@ -738,4 +738,15 @@ Map<String, Boolean> validateResourcesForWagedRebalance(String clusterName,
    */
   Map<String, Boolean> validateInstancesForWagedRebalance(String clusterName,
       List<String> instancesNames);
+
+  /**
+   * Return if instance operation 'Evacuate' is finished.
+   * Only return true if there is no current state on the instance and that instance is still alive.
+   * @param clusterName
+   * @param instancesNames
+   * @return
+   */
+  boolean isEvacuateFinished(String clusterName, String instancesNames);
+
+  boolean isPrepopulateReady(String clusterName, String instancesNames);
 }

helix-core/src/main/java/org/apache/helix/manager/zk/ZKHelixAdmin.java

@@ -47,6 +47,7 @@
 import org.apache.helix.HelixDataAccessor;
 import org.apache.helix.HelixDefinedState;
 import org.apache.helix.HelixException;
+import org.apache.helix.HelixProperty;
 import org.apache.helix.InstanceType;
 import org.apache.helix.PropertyKey;
 import org.apache.helix.PropertyPathBuilder;
@@ -406,7 +407,41 @@ public ZNRecord update(ZNRecord currentData) {
     }
   }
 
+
   @Override
+  public boolean isEvacuateFinished(String clusterName, String instanceName) {
+    HelixDataAccessor accessor =
+        new ZKHelixDataAccessor(clusterName, new ZkBaseDataAccessor<ZNRecord>(_zkClient));
+    PropertyKey.Builder keyBuilder = accessor.keyBuilder();
+
+    // check the instance is alive
+    LiveInstance liveInstance = accessor.getProperty(keyBuilder.liveInstance(instanceName));
+    if (liveInstance == null) {
+      logger.warn("instance {} in cluster {} is not alive.", instanceName, clusterName);
+      return false;
+    }
+
+    BaseDataAccessor<ZNRecord> baseAccessor = new ZkBaseDataAccessor<ZNRecord>(_zkClient);
+    String sessionId = liveInstance.getEphemeralOwner();
+
+    String path = PropertyPathBuilder.instanceCurrentState(clusterName, instanceName, sessionId);
+    List<String> currentStates = baseAccessor.getChildNames(path, 0);
+    if (currentStates == null) {
+      logger.warn("instance {} in cluster {} does not have live session.", instanceName,
+          clusterName);
+      return false;
+    }
+    return  currentStates.isEmpty();
+  }
+
+  @Override
+  public boolean isPrepopulateReady(String clusterName, String instanceName) {
+    return this.getInstanceConfig(clusterName, instanceName)
+        .getInstanceOperation()
+        .equals(InstanceConstants.InstanceOperation.EVACUATE.name());
+  }
+
+    @Override
   public void enableResource(final String clusterName, final String resourceName,
       final boolean enabled) {
     logger.info("{} resource {} in cluster {}.", enabled ? "Enable" : "Disable", resourceName,

helix-core/src/test/java/org/apache/helix/integration/rebalancer/TestInstanceOperation.java

@@ -11,6 +11,7 @@
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.stream.Collectors;
 import org.apache.helix.ConfigAccessor;
+import org.apache.helix.HelixAdmin;
 import org.apache.helix.HelixDataAccessor;
 import org.apache.helix.HelixRollbackException;
 import org.apache.helix.NotificationContext;
@@ -22,6 +23,7 @@
 import org.apache.helix.controller.rebalancer.waged.AssignmentMetadataStore;
 import org.apache.helix.integration.manager.ClusterControllerManager;
 import org.apache.helix.integration.manager.MockParticipantManager;
+import org.apache.helix.manager.zk.ZKHelixAdmin;
 import org.apache.helix.manager.zk.ZKHelixDataAccessor;
 import org.apache.helix.manager.zk.ZkBucketDataAccessor;
 import org.apache.helix.model.BuiltInStateModelDefinitions;
@@ -57,6 +59,8 @@ public class TestInstanceOperation extends ZkTestBase {
   private ZkHelixClusterVerifier _clusterVerifier;
   private ConfigAccessor _configAccessor;
   private long _stateModelDelay = 3L;
+
+  private HelixAdmin _admin;
   protected AssignmentMetadataStore _assignmentMetadataStore;
   HelixDataAccessor _dataAccessor;
 
@@ -91,6 +95,8 @@ public void beforeClass() throws Exception {
     createTestDBs(200);
 
     setUpWagedBaseline();
+
+    _admin = new ZKHelixAdmin(_gZkClient);
   }
 
   @Test
@@ -119,6 +125,9 @@ public void testEvacuate() throws Exception {
       Assert.assertFalse(newPAssignedParticipants.contains(instanceToEvacuate));
       Assert.assertTrue(newPAssignedParticipants.containsAll(currentActiveInstances));
     }
+
+    Assert.assertTrue(_admin.isEvacuateFinished(CLUSTER_NAME, instanceToEvacuate));
+    Assert.assertTrue(_admin.isPrepopulateReady(CLUSTER_NAME, instanceToEvacuate));
   }
 
   @Test(dependsOnMethods = "testEvacuate")
@@ -215,6 +224,7 @@ public void testEvacuateAndCancelBeforeBootstrapFinish() throws Exception {
       TestHelper.verify(
           () -> ((_dataAccessor.getChildNames(_dataAccessor.keyBuilder().messages(participant))).isEmpty()), 30000);
     }
+    Assert.assertFalse(_admin.isEvacuateFinished(CLUSTER_NAME, instanceToEvacuate));
 
     // sleep a bit so ST messages can start executing
     Thread.sleep(Math.abs(_stateModelDelay / 100));
@@ -261,6 +271,7 @@ public void testEvacuateAndCancelBeforeDropFinish() throws Exception {
     // message should be pending at the to evacuate participant
     TestHelper.verify(
         () -> ((_dataAccessor.getChildNames(_dataAccessor.keyBuilder().messages(instanceToEvacuate))).isEmpty()), 30000);
+    Assert.assertFalse(_admin.isEvacuateFinished(CLUSTER_NAME, instanceToEvacuate));
 
     // cancel evacuation
     _gSetupTool.getClusterManagementTool()
@@ -323,7 +334,7 @@ public void testMarkEvacuationAfterEMM() throws Exception {
       Assert.assertFalse(newPAssignedParticipants.contains(instanceToEvacuate));
       Assert.assertTrue(newPAssignedParticipants.containsAll(currentActiveInstances));
     }
-
+    Assert.assertTrue(_admin.isPrepopulateReady(CLUSTER_NAME, instanceToEvacuate));
   }
 
   @Test(dependsOnMethods = "testMarkEvacuationAfterEMM")

helix-core/src/test/java/org/apache/helix/mock/MockHelixAdmin.java

@@ -550,4 +550,14 @@ public Map<String, Boolean> validateInstancesForWagedRebalance(String clusterNam
       List<String> instancesNames) {
     return null;
   }
+
+  @Override
+  public boolean isEvacuateFinished(String clusterName, String instancesNames) {
+    return false;
+  }
+
+  @Override
+  public boolean isPrepopulateReady(String clusterName, String instancesNames) {
+    return false;
+  }
 }