[GitHub] [flink] AHeise commented on a change in pull request #11177: [FLINK-16219][runtime] Made AsyncWaitOperator chainable to non-sources.

[GitBox <gi...@apache.org>]

AHeise commented on a change in pull request #11177: [FLINK-16219][runtime] Made AsyncWaitOperator chainable to non-sources.
URL: https://github.com/apache/flink/pull/11177#discussion_r384318641
 
 

 ##########
 File path: flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/ChainingStrategy.java
 ##########
 @@ -38,16 +38,46 @@
 	 * <p>To optimize performance, it is generally a good practice to allow maximal
 	 * chaining and increase operator parallelism.
 	 */
-	ALWAYS,
+	ALWAYS {
+		@Override
+		public boolean canBeChainedTo(StreamOperatorFactory<?> headOperator) {
+			return true;
+		}
+	},
 
 	/**
 	 * The operator will not be chained to the preceding or succeeding operators.
 	 */
-	NEVER,
+	NEVER {
+		@Override
+		public boolean canBeChainedTo(StreamOperatorFactory<?> headOperator) {
+			return false;
+		}
+	},
 
 	/**
 	 * The operator will not be chained to the predecessor, but successors may chain to this
 	 * operator.
 	 */
-	HEAD
+	HEAD {
+		@Override
+		public boolean canBeChainedTo(StreamOperatorFactory<?> headOperator) {
+			return false;
+		}
+	},
+
+	/**
+	 * Operators will be eagerly chained whenever possible, except after legacy sources.
+	 *
+	 * <p>Operators that will not properly when processInput is called from another thread, must use this strategy
+	 * instead of {@link #ALWAYS}.
+	 */
+	HEAD_AFTER_LEGACY_SOURCE {
+		@Override
+		public boolean canBeChainedTo(StreamOperatorFactory<?> headOperator) {
+			return !headOperator.isStreamSource();
+		}
+	};
+
+	public abstract boolean canBeChainedTo(StreamOperatorFactory<?> headOperator);
 
 Review comment:
   It was not. Good catch.

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