HDDS-302. Fix javadoc and add implementation details in ContainerStateMachine. Contributed by Shashikant Banerjee.

hadoop-hdds/client/src/main/java/org/apache/hadoop/hdds/scm/XceiverClientRatis.java

@@ -19,6 +19,7 @@
 package org.apache.hadoop.hdds.scm;
 
 import com.google.common.base.Preconditions;
+import org.apache.hadoop.hdds.HddsUtils;
 import org.apache.ratis.shaded.com.google.protobuf
     .InvalidProtocolBufferException;
 import org.apache.hadoop.conf.Configuration;
@@ -183,34 +184,9 @@ private RaftClient getClient() {
     return Objects.requireNonNull(client.get(), "client is null");
   }
 
-  private boolean isReadOnly(ContainerCommandRequestProto proto) {
-    switch (proto.getCmdType()) {
-    case ReadContainer:
-    case ReadChunk:
-    case ListKey:
-    case GetKey:
-    case GetSmallFile:
-    case ListContainer:
-    case ListChunk:
-      return true;
-    case CloseContainer:
-    case WriteChunk:
-    case UpdateContainer:
-    case CompactChunk:
-    case CreateContainer:
-    case DeleteChunk:
-    case DeleteContainer:
-    case DeleteKey:
-    case PutKey:
-    case PutSmallFile:
-    default:
-      return false;
-    }
-  }
-
   private RaftClientReply sendRequest(ContainerCommandRequestProto request)
       throws IOException {
-    boolean isReadOnlyRequest = isReadOnly(request);
+    boolean isReadOnlyRequest = HddsUtils.isReadOnly(request);
     ByteString byteString = request.toByteString();
     LOG.debug("sendCommand {} {}", isReadOnlyRequest, request);
     final RaftClientReply reply =  isReadOnlyRequest ?
@@ -222,7 +198,7 @@ private RaftClientReply sendRequest(ContainerCommandRequestProto request)
 
   private CompletableFuture<RaftClientReply> sendRequestAsync(
       ContainerCommandRequestProto request) throws IOException {
-    boolean isReadOnlyRequest = isReadOnly(request);
+    boolean isReadOnlyRequest = HddsUtils.isReadOnly(request);
     ByteString byteString = request.toByteString();
     LOG.debug("sendCommandAsync {} {}", isReadOnlyRequest, request);
     return isReadOnlyRequest ? getClient().sendReadOnlyAsync(() -> byteString) :

hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/HddsUtils.java

@@ -24,6 +24,7 @@
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.CommonConfigurationKeys;
 import org.apache.hadoop.fs.CommonConfigurationKeysPublic;
+import org.apache.hadoop.hdds.protocol.datanode.proto.ContainerProtos;
 import org.apache.hadoop.hdds.scm.ScmConfigKeys;
 import org.apache.hadoop.net.DNS;
 import org.apache.hadoop.net.NetUtils;
@@ -315,4 +316,36 @@ public static String getHostName(Configuration conf)
     return name;
   }
 
+  /**
+   * Checks if the container command is read only or not.
+   * @param proto ContainerCommand Request proto
+   * @return True if its readOnly , false otherwise.
+   */
+  public static boolean isReadOnly(
+      ContainerProtos.ContainerCommandRequestProto proto) {
+    switch (proto.getCmdType()) {
+    case ReadContainer:
+    case ReadChunk:
+    case ListKey:
+    case GetKey:
+    case GetSmallFile:
+    case ListContainer:
+    case ListChunk:
+    case GetCommittedBlockLength:
+      return true;
+    case CloseContainer:
+    case WriteChunk:
+    case UpdateContainer:
+    case CompactChunk:
+    case CreateContainer:
+    case DeleteChunk:
+    case DeleteContainer:
+    case DeleteKey:
+    case PutKey:
+    case PutSmallFile:
+    default:
+      return false;
+    }
+  }
+
 }

hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/transport/server/ratis/ContainerStateMachine.java

@@ -57,7 +57,7 @@
  * requests.
  *
  * Read only requests are classified in
- * {@link org.apache.hadoop.hdds.scm.XceiverClientRatis#isReadOnly}
+ * {@link org.apache.hadoop.hdds.HddsUtils#isReadOnly}
  * and these readonly requests are replied from the {@link #query(Message)}.
  *
  * The write requests can be divided into requests with user data
@@ -84,6 +84,11 @@
  * 2) Write chunk commit operation is executed after write chunk state machine
  * operation. This will ensure that commit operation is sync'd with the state
  * machine operation.
+ *
+ * Synchronization between {@link #writeStateMachineData} and
+ * {@link #applyTransaction} need to be enforced in the StateMachine
+ * implementation. For example, synchronization between writeChunk and
+ * createContainer in {@link ContainerStateMachine}.
  * */
 public class ContainerStateMachine extends BaseStateMachine {
   static final Logger LOG = LoggerFactory.getLogger(
@@ -213,6 +218,10 @@ private CompletableFuture<Message> handleCreateContainer(
     return CompletableFuture.completedFuture(() -> ByteString.EMPTY);
   }
 
+  /*
+   * writeStateMachineData calls are not synchronized with each other
+   * and also with applyTransaction.
+   */
   @Override
   public CompletableFuture<Message> writeStateMachineData(LogEntryProto entry) {
     try {
@@ -244,6 +253,9 @@ public CompletableFuture<Message> query(Message request) {
     }
   }
 
+  /*
+   * ApplyTransaction calls in Ratis are sequential.
+   */
   @Override
   public CompletableFuture<Message> applyTransaction(TransactionContext trx) {
     try {