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SecondaryPageCursorReadDataAdapter.java
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SecondaryPageCursorReadDataAdapter.java
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/*
* Copyright (c) 2002-2016 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.kernel.impl.store.format.highlimit;
import java.io.IOException;
import org.neo4j.io.pagecache.PageCursor;
import org.neo4j.io.pagecache.PagedFile;
import org.neo4j.kernel.impl.store.format.highlimit.Reference.DataAdapter;
import org.neo4j.kernel.impl.util.Bits;
/**
* {@link DataAdapter} able to acquire a secondary {@link PageCursor} on potentially a different page
* for continuing reading contents belonging to the primary record.
*/
class SecondaryPageCursorReadDataAdapter implements DataAdapter<PageCursor>, SecondaryPageCursorControl
{
private final PageCursor primaryCursor;
private final int primaryInitialOffset;
private final int primaryEndOffset;
private final PageCursor secondaryCursor;
private final int secondaryOffset;
private boolean switched;
private byte secondaryHeaderByte;
SecondaryPageCursorReadDataAdapter( PageCursor cursor, PagedFile storeFile,
long secondaryPageId, int secondaryOffset, int primaryEndOffset, int pfFlags ) throws IOException
{
this.primaryCursor = cursor;
this.primaryEndOffset = primaryEndOffset;
this.primaryInitialOffset = cursor.getOffset();
this.secondaryCursor = storeFile.io( secondaryPageId, pfFlags );
this.secondaryCursor.next();
this.secondaryOffset = secondaryOffset;
}
@Override
public byte get( PageCursor primaryCursor /*same as the one we have*/ )
{
if ( primaryCursor.getOffset() == primaryEndOffset )
{
// We've come to the end of the primary cursor, use the secondary cursor instead
if ( !switched )
{
// Just read out the header, get it out of the way. Verification of the header byte happens in #close()
// because it is the only place where we surely read the consistent value
secondaryHeaderByte = secondaryCursor.getByte();
switched = true;
}
return secondaryCursor.getByte();
}
// There's still data to be read from the primary cursor
return primaryCursor.getByte();
}
@Override
public void put( byte oneByte, PageCursor primaryCursor )
{
throw new UnsupportedOperationException();
}
@Override
public void reposition()
{
primaryCursor.setOffset( primaryInitialOffset );
secondaryCursor.setOffset( secondaryOffset );
switched = false;
}
@Override
public boolean shouldRetry() throws IOException
{
// Don't check shouldRetry on primary here since that will happen in the outer loop
// and will guard both units.
return secondaryCursor.shouldRetry();
}
@Override
public void close()
{
secondaryCursor.close();
assert (secondaryHeaderByte & BaseHighLimitRecordFormat.HEADER_BIT_RECORD_UNIT) != 0 : illegalHeader();
assert (secondaryHeaderByte & BaseHighLimitRecordFormat.HEADER_BIT_FIRST_RECORD_UNIT) == 0 : illegalHeader();
}
private String illegalHeader()
{
return "Read illegal secondary record unit header: " + Bits.numberToString( secondaryHeaderByte, Byte.BYTES );
}
}