Re: [PR] RATIS-1979. Allow StateMachine.read to return a ReferentCountedObject [ratis]

["duongkame (via GitHub)" <gi...@apache.org>]

duongkame commented on code in PR #1062:
URL: https://github.com/apache/ratis/pull/1062#discussion_r1546878670


##########
ratis-server-api/src/main/java/org/apache/ratis/server/raftlog/RaftLog.java:
##########
@@ -188,17 +188,41 @@ default long getNextIndex() {
   interface EntryWithData {
     /** @return the index of this entry. */
     default long getIndex() {
+      ReferenceCountedObject<LogEntryProto> ref = null;
       try {
-        return getEntry(TimeDuration.ONE_MINUTE).getIndex();
+        ref = getEntryWithRetainedData(TimeDuration.ONE_MINUTE);
+        return ref.get().getIndex();
       } catch (Exception e) {
         throw new IllegalStateException("Failed to getIndex", e);
+      } finally {
+        if (ref != null) {
+          ref.release();
+        }
       }
     }
 
     /** @return the serialized size including both log entry and state machine data. */
     int getSerializedSize();
 
-    /** @return the {@link LogEntryProto} containing both the log entry and the state machine data. */
-    LogEntryProto getEntry(TimeDuration timeout) throws RaftLogIOException, TimeoutException;
+    /**
+     * @return the {@link LogEntryProto} containing both the log entry and the state machine data.
+     * @deprecated
+     */
+    default LogEntryProto getEntry(TimeDuration timeout) throws RaftLogIOException, TimeoutException {
+      throw new UnsupportedOperationException();
+    }
+
+    /**
+     * @return a {@link ReferenceCountedObject} wrapping {@link LogEntryProto} containing both the log entry
+     * and the state machine data.
+     * The state machine data are retained (by the state machine) and this is represented by the wrapping
+     * {@link ReferenceCountedObject}. The caller must call {@link ReferenceCountedObject#release()}} after use.
+     */
+    default ReferenceCountedObject<LogEntryProto> getEntryWithRetainedData(TimeDuration timeout)

Review Comment:
   Agree, I was concerned about the same thing but couldn't find a good way to wrap the ref of the LogEntry and the one in the future. 



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