001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hbase.client;
019
020import java.util.Optional;
021import org.apache.yetus.audience.InterfaceAudience;
022
023/**
024 * This is the low level API for asynchronous scan.
025 * <p>
026 * All results that match the given scan object will be passed to this class by calling
027 * {@link #onNext(Result[], ScanController)}. {@link #onComplete()} means the scan is finished, and
028 * {@link #onError(Throwable)} means we hit an unrecoverable error and the scan is terminated.
029 * {@link #onHeartbeat(ScanController)} means the RS is still working but we can not get a valid
030 * result to call {@link #onNext(Result[], ScanController)}. This is usually because the matched
031 * results are too sparse, for example, a filter which almost filters out everything is specified.
032 * <p>
033 * Notice that, all the methods here will be called directly in the thread which we send request to
034 * HBase service. So if you want the asynchronous scanner fetch data from HBase in background while
035 * you process the returned data, you need to move the processing work to another thread to make the
036 * {@link #onNext(Result[], ScanController)} call return immediately. And please do NOT do any time
037 * consuming tasks in these methods unless you know what you are doing.
038 * @since 2.0.0
039 */
040@InterfaceAudience.Public
041public interface AdvancedScanResultConsumer extends ScanResultConsumerBase {
042
043  /**
044   * Used to resume a scan.
045   */
046  @InterfaceAudience.Public
047  interface ScanResumer {
048
049    /**
050     * Resume the scan. You are free to call it multiple time but only the first call will take
051     * effect.
052     */
053    void resume();
054  }
055
056  /**
057   * Used to suspend or stop a scan, or get a scan cursor if available.
058   * <p>
059   * Notice that, you should only call the {@link #suspend()} or {@link #terminate()} inside onNext
060   * or onHeartbeat method. A IllegalStateException will be thrown if you call them at other places.
061   * <p>
062   * You can only call one of the {@link #suspend()} and {@link #terminate()} methods(of course you
063   * are free to not call them both), and the methods are not reentrant. An IllegalStateException
064   * will be thrown if you have already called one of the methods.
065   */
066  @InterfaceAudience.Public
067  interface ScanController {
068
069    /**
070     * Suspend the scan.
071     * <p>
072     * This means we will stop fetching data in background, i.e., will not call onNext any more
073     * before you resume the scan.
074     * @return A resumer used to resume the scan later.
075     */
076    ScanResumer suspend();
077
078    /**
079     * Terminate the scan.
080     * <p>
081     * This is useful when you have got enough results and want to stop the scan in onNext method,
082     * or you want to stop the scan in onHeartbeat method because it has spent too many time.
083     */
084    void terminate();
085
086    /**
087     * Get the scan cursor if available.
088     * @return The scan cursor.
089     */
090    Optional<Cursor> cursor();
091  }
092
093  /**
094   * Indicate that we have receive some data.
095   * @param results    the data fetched from HBase service.
096   * @param controller used to suspend or terminate the scan. Notice that the {@code controller}
097   *                   instance is only valid within scope of onNext method. You can only call its
098   *                   method in onNext, do NOT store it and call it later outside onNext.
099   */
100  void onNext(Result[] results, ScanController controller);
101
102  /**
103   * Indicate that there is a heartbeat message but we have not cumulated enough cells to call
104   * {@link #onNext(Result[], ScanController)}.
105   * <p>
106   * Note that this method will always be called when RS returns something to us but we do not have
107   * enough cells to call {@link #onNext(Result[], ScanController)}. Sometimes it may not be a
108   * 'heartbeat' message for RS, for example, we have a large row with many cells and size limit is
109   * exceeded before sending all the cells for this row. For RS it does send some data to us and the
110   * time limit has not been reached, but we can not return the data to client so here we call this
111   * method to tell client we have already received something.
112   * <p>
113   * This method give you a chance to terminate a slow scan operation.
114   * @param controller used to suspend or terminate the scan. Notice that the {@code controller}
115   *                   instance is only valid within the scope of onHeartbeat method. You can only
116   *                   call its method in onHeartbeat, do NOT store it and call it later outside
117   *                   onHeartbeat.
118   */
119  default void onHeartbeat(ScanController controller) {
120  }
121}