/*
 * 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.flink.connector.base.source.reader.fetcher;

import org.apache.flink.api.connector.source.SourceSplit;
import org.apache.flink.connector.base.source.reader.RecordsWithSplitIds;
import org.apache.flink.connector.base.source.reader.splitreader.SplitReader;
import org.apache.flink.connector.base.source.reader.synchronization.FutureCompletingBlockingQueue;

import java.util.List;
import java.util.function.Supplier;

/**
 * A Fetcher manager with a single fetcher and assign all the splits to it.
 */
public class SingleThreadFetcherManager<E, SplitT extends SourceSplit>
		extends SplitFetcherManager<E, SplitT> {

	public SingleThreadFetcherManager(
			FutureCompletingBlockingQueue<RecordsWithSplitIds<E>> elementsQueue,
			Supplier<SplitReader<E, SplitT>> splitReaderSupplier) {
		super(elementsQueue, splitReaderSupplier);
	}

	@Override
	public void addSplits(List<SplitT> splitsToAdd) {
		SplitFetcher<E, SplitT> fetcher = fetchers.get(0);
		if (fetcher == null) {
			fetcher = createSplitFetcher();
			// Add the splits to the fetchers.
			fetcher.addSplits(splitsToAdd);
			startFetcher(fetcher);
		} else {
			fetcher.addSplits(splitsToAdd);
		}
	}
}

@@ -996,16 +996,87 @@
 litIds;%0A
+import org.apache.flink.connector.base.source.reader.SourceReaderBase;%0A
 import o
@@ -1323,17 +1323,17 @@
 Fetcher 
-m
+M
 anager w
@@ -1354,162 +1354,997 @@
 etch
-er and assign all the splits to it.%0A */%0Apublic class SingleThreadFetcherManager%3CE, SplitT extends SourceSplit%3E%0A%09%09extends SplitFetcherManager%3CE, SplitT%3E %7B%0A
+ing thread (I/O thread) that handles all splits concurrently.%0A *%0A * %3Cp%3EThis pattern is, for example, useful for connectors like File Readers, Apache Kafka Readers, etc.%0A * In the example of Kafka, there is a single thread that reads all splits (topic partitions) via the%0A * same client. In the example of the file source, there is a single thread that reads the files%0A * after another.%0A */%0Apublic class SingleThreadFetcherManager%3CE, SplitT extends SourceSplit%3E%0A%09%09extends SplitFetcherManager%3CE, SplitT%3E %7B%0A%0A%09/**%0A%09 * Creates a new SplitFetcherManager with a single I/O threads.%0A%09 *%0A%09 * @param elementsQueue The queue that is used to hand over data from the I/O thread (the fetchers)%0A%09 *                      to the reader (which emits the records and book-keeps the state.%0A%09 *                      This must be the same queue instance that is also passed to the %7B@link SourceReaderBase%7D.%0A%09 * @param splitReaderSupplier The factory for the split reader that connects to the source system.%0A%09 */
 %0A%09pu

Improve JavaDocs for SingleThreadFetcherManager