Github user aljoscha commented on a diff in the pull request:
https://github.com/apache/flink/pull/5230#discussion_r166337949
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/state/KeyedStateBackend.java
---
@@ -38,6 +38,37 @@
*/
void setCurrentKey(K newKey);
+ /**
+ * Returns a safe version of the current key (see {@link
#setCurrentKey(Object)}).
+ *
+ * <p>"Safe" means that the user can interact with it without
jeopardizing correctness.
+ * This implies that:
+ * <ol>
+ * <li>for the {@code MemoryStateBackend} and the {@code
FsStateBackend} we
+ * return a <b>copy</b> of the actual key, while
+ * <li>for the {@code RocksDBStateBackend} we return the key
itself, as returned
+ * by the backend.
+ * </ol>
+ *
+ * <p>The copy is created using the {@link TypeSerializer#copy(Object)
copy()} method
+ * of the key {@link TypeSerializer}. Consequently, the correctness of
the method assumes
+ * a correct {@code copy()} method.
+ *
+ */
+ K getCurrentKeySafe();
+
+ /**
+ * Applies the provided {@link KeyedStateFunction} to the state with
the provided
+ * {@link StateDescriptor} of all the currently active keys.
+ *
+ * @param stateDescriptor the descriptor of the state to which the
+ * function is going to be applied.
+ * @param function the function to be applied to the keyed state.
+ */
+ <S extends State, T> void applyToAllKeys(
--- End diff --
I think this method needs to take the namespace. The current implementation
in `AbstractKeyedStateBackend` always iterates over `VoidNamespace` implicitly,
which can be a bit surprising.
---
