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/*
* 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.hadoop.hbase.regionserver;
import com.google.errorprone.annotations.RestrictedApi;
import java.util.List;
import java.util.concurrent.atomic.AtomicBoolean;
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.nio.RefCnt;
import org.apache.yetus.audience.InterfaceAudience;
/**
* A MemStoreLAB implementation which wraps N MemStoreLABs. Its main duty is in proper managing the
* close of the individual MemStoreLAB. This is treated as an immutable one and so do not allow to
* add any more Cells into it. {@link #copyCellInto(Cell)} throws Exception
*/
@InterfaceAudience.Private
public class ImmutableMemStoreLAB implements MemStoreLAB {
private final RefCnt refCnt;
private final AtomicBoolean closed = new AtomicBoolean(false);
private final List mslabs;
public ImmutableMemStoreLAB(List mslabs) {
this.mslabs = mslabs;
this.refCnt = RefCnt.create(() -> {
closeMSLABs();
});
}
@Override
public Cell copyCellInto(Cell cell) {
throw new IllegalStateException("This is an Immutable MemStoreLAB.");
}
/**
* The process of merging assumes all cells are allocated on mslab. There is a rare case in which
* the first immutable segment, participating in a merge, is a CSLM. Since the CSLM hasn't been
* flattened yet, and there is no point in flattening it (since it is going to be merged), its big
* cells (for whom size > maxAlloc) must be copied into mslab. This method copies the passed cell
* into the first mslab in the mslabs list, returning either a new cell instance over the copied
* data, or null when this cell cannt be copied.
*/
@Override
public Cell forceCopyOfBigCellInto(Cell cell) {
MemStoreLAB mslab = this.mslabs.get(0);
return mslab.forceCopyOfBigCellInto(cell);
}
/*
* Returning a new pool chunk, without replacing current chunk, meaning MSLABImpl does not make
* the returned chunk as CurChunk. The space on this chunk will be allocated externally. The
* interface is only for external callers.
*/
@Override
public Chunk getNewExternalChunk(ChunkCreator.ChunkType chunkType) {
MemStoreLAB mslab = this.mslabs.get(0);
return mslab.getNewExternalChunk(chunkType);
}
/*
* Returning a new chunk, without replacing current chunk, meaning MSLABImpl does not make the
* returned chunk as CurChunk. The space on this chunk will be allocated externally. The interface
* is only for external callers.
*/
@Override
public Chunk getNewExternalChunk(int size) {
MemStoreLAB mslab = this.mslabs.get(0);
return mslab.getNewExternalChunk(size);
}
@Override
public void close() {
// 'refCnt' here tracks the scanners opened on segments which directly refer to this
// MSLAB. The individual MSLABs this refers also having its own 'refCnt'. The usage of
// the variable in close() and decScannerCount() is as as that in HeapMemstoreLAB. Here the
// close just delegates the call to the individual MSLABs. The actual return of the chunks to
// MSLABPool will happen within individual MSLABs only (which is at the leaf level).
// Say an ImmutableMemStoreLAB is created over 2 HeapMemStoreLABs at some point and at that time
// both of them were referred by ongoing scanners. So they have > 0 'refCnt'. Now over
// the new Segment some scanners come in and this MSLABs 'refCnt' also goes up and
// then come down on finish of scanners. Now a close() call comes to this Immutable MSLAB. As
// it's 'refCnt' is zero it will call close() on both of the Heap MSLABs. Say by that
// time the old scanners on one of the MSLAB got over where as on the other, still an old
// scanner is going on. The call close() on that MSLAB will not close it immediately but will
// just decrease it's 'refCnt' and it's 'refCnt' still > 0. Later once the old scan is
// over, the decScannerCount() call will do the actual close and return of the chunks.
if (!this.closed.compareAndSet(false, true)) {
return;
}
// When there are still on going scanners over this MSLAB, we will defer the close until all
// scanners finish. We will just decrease it's 'refCnt'. See #decScannerCount(). This will be
// called at end of every scan. When it's 'refCnt' reached 0, we will do the actual close then.
this.refCnt.release();
}
private void closeMSLABs() {
for (MemStoreLAB mslab : this.mslabs) {
mslab.close();
}
}
@Override
public void incScannerCount() {
this.refCnt.retain();
}
@Override
public void decScannerCount() {
this.refCnt.release();
}
@Override
public boolean isOnHeap() {
return !isOffHeap();
}
@Override
public boolean isOffHeap() {
return ChunkCreator.getInstance().isOffheap();
}
@RestrictedApi(explanation = "Should only be called in tests", link = "",
allowedOnPath = ".*/src/test/.*")
int getRefCntValue() {
return this.refCnt.refCnt();
}
@RestrictedApi(explanation = "Should only be called in tests", link = "",
allowedOnPath = ".*/src/test/.*")
boolean isClosed() {
return this.closed.get();
}
}