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.regionserver;
019
020import com.google.errorprone.annotations.RestrictedApi;
021import java.util.List;
022import java.util.concurrent.atomic.AtomicBoolean;
023import org.apache.hadoop.hbase.Cell;
024import org.apache.hadoop.hbase.nio.RefCnt;
025import org.apache.yetus.audience.InterfaceAudience;
026
027/**
028 * A MemStoreLAB implementation which wraps N MemStoreLABs. Its main duty is in proper managing the
029 * close of the individual MemStoreLAB. This is treated as an immutable one and so do not allow to
030 * add any more Cells into it. {@link #copyCellInto(Cell)} throws Exception
031 */
032@InterfaceAudience.Private
033public class ImmutableMemStoreLAB implements MemStoreLAB {
034
035  private final RefCnt refCnt;
036  private final AtomicBoolean closed = new AtomicBoolean(false);
037
038  private final List<MemStoreLAB> mslabs;
039
040  public ImmutableMemStoreLAB(List<MemStoreLAB> mslabs) {
041    this.mslabs = mslabs;
042    this.refCnt = RefCnt.create(() -> {
043      closeMSLABs();
044    });
045  }
046
047  @Override
048  public Cell copyCellInto(Cell cell) {
049    throw new IllegalStateException("This is an Immutable MemStoreLAB.");
050  }
051
052  /**
053   * The process of merging assumes all cells are allocated on mslab. There is a rare case in which
054   * the first immutable segment, participating in a merge, is a CSLM. Since the CSLM hasn't been
055   * flattened yet, and there is no point in flattening it (since it is going to be merged), its big
056   * cells (for whom size > maxAlloc) must be copied into mslab. This method copies the passed cell
057   * into the first mslab in the mslabs list, returning either a new cell instance over the copied
058   * data, or null when this cell cannt be copied.
059   */
060  @Override
061  public Cell forceCopyOfBigCellInto(Cell cell) {
062    MemStoreLAB mslab = this.mslabs.get(0);
063    return mslab.forceCopyOfBigCellInto(cell);
064  }
065
066  /*
067   * Returning a new pool chunk, without replacing current chunk, meaning MSLABImpl does not make
068   * the returned chunk as CurChunk. The space on this chunk will be allocated externally. The
069   * interface is only for external callers.
070   */
071  @Override
072  public Chunk getNewExternalChunk(ChunkCreator.ChunkType chunkType) {
073    MemStoreLAB mslab = this.mslabs.get(0);
074    return mslab.getNewExternalChunk(chunkType);
075  }
076
077  /*
078   * Returning a new chunk, without replacing current chunk, meaning MSLABImpl does not make the
079   * returned chunk as CurChunk. The space on this chunk will be allocated externally. The interface
080   * is only for external callers.
081   */
082  @Override
083  public Chunk getNewExternalChunk(int size) {
084    MemStoreLAB mslab = this.mslabs.get(0);
085    return mslab.getNewExternalChunk(size);
086  }
087
088  @Override
089  public void close() {
090    // 'refCnt' here tracks the scanners opened on segments which directly refer to this
091    // MSLAB. The individual MSLABs this refers also having its own 'refCnt'. The usage of
092    // the variable in close() and decScannerCount() is as as that in HeapMemstoreLAB. Here the
093    // close just delegates the call to the individual MSLABs. The actual return of the chunks to
094    // MSLABPool will happen within individual MSLABs only (which is at the leaf level).
095    // Say an ImmutableMemStoreLAB is created over 2 HeapMemStoreLABs at some point and at that time
096    // both of them were referred by ongoing scanners. So they have > 0 'refCnt'. Now over
097    // the new Segment some scanners come in and this MSLABs 'refCnt' also goes up and
098    // then come down on finish of scanners. Now a close() call comes to this Immutable MSLAB. As
099    // it's 'refCnt' is zero it will call close() on both of the Heap MSLABs. Say by that
100    // time the old scanners on one of the MSLAB got over where as on the other, still an old
101    // scanner is going on. The call close() on that MSLAB will not close it immediately but will
102    // just decrease it's 'refCnt' and it's 'refCnt' still > 0. Later once the old scan is
103    // over, the decScannerCount() call will do the actual close and return of the chunks.
104    if (!this.closed.compareAndSet(false, true)) {
105      return;
106    }
107    // When there are still on going scanners over this MSLAB, we will defer the close until all
108    // scanners finish. We will just decrease it's 'refCnt'. See #decScannerCount(). This will be
109    // called at end of every scan. When it's 'refCnt' reached 0, we will do the actual close then.
110    this.refCnt.release();
111  }
112
113  private void closeMSLABs() {
114    for (MemStoreLAB mslab : this.mslabs) {
115      mslab.close();
116    }
117  }
118
119  @Override
120  public void incScannerCount() {
121    this.refCnt.retain();
122  }
123
124  @Override
125  public void decScannerCount() {
126    this.refCnt.release();
127  }
128
129  @Override
130  public boolean isOnHeap() {
131    return !isOffHeap();
132  }
133
134  @Override
135  public boolean isOffHeap() {
136    return ChunkCreator.getInstance().isOffheap();
137  }
138
139  @RestrictedApi(explanation = "Should only be called in tests", link = "",
140      allowedOnPath = ".*/src/test/.*")
141  int getRefCntValue() {
142    return this.refCnt.refCnt();
143  }
144
145  @RestrictedApi(explanation = "Should only be called in tests", link = "",
146      allowedOnPath = ".*/src/test/.*")
147  boolean isClosed() {
148    return this.closed.get();
149  }
150
151}