Github user paul-rogers commented on a diff in the pull request:
https://github.com/apache/drill/pull/921#discussion_r150976659
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/server/DrillbitStateManager.java
---
@@ -0,0 +1,80 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.drill.exec.server;
+/*
+ State manager to manage the state of drillbit.
+ */
+public class DrillbitStateManager {
+
+
+ public DrillbitStateManager(DrillbitState currentState) {
+ this.currentState = currentState;
+ }
+
+ public enum DrillbitState {
+ STARTUP, ONLINE, GRACE, DRAINING, OFFLINE, SHUTDOWN
+ }
+
+ public DrillbitState getState() {
+ return currentState;
+ }
+
+ private DrillbitState currentState;
+ public void setState(DrillbitState state) {
+ switch (state) {
+ case ONLINE:
+ if (currentState == DrillbitState.STARTUP) {
+ currentState = state;
+ } else {
+ throw new IllegalStateException("Cannot set drillbit to" + state
+ "from" + currentState);
--- End diff --
To avoid redundant code and to catch new states:
```
setState(State newState) {
currentState = transitionTo(newState);
}
State transitionTo(State newState) {
switch (newState) {
case ONLINE:
if (currentState == DrillbitState.STARTUP) {
return newState;
}
break;
...
default:
break;
}
throw new IllegalStateException("Cannot set drillbit to" + state + "from"
+ currentState);
```
An alternative is to switch on current state to say, essentially "if we are
in state X, we allow transition to states Y and Z." But, that may be overkill
here.
---
