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package com.salesforce.hbase.index.covered.data;
import java.io.IOException;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import org.apache.hadoop.hbase.KeyValue;
import com.salesforce.hbase.index.ValueGetter;
import com.salesforce.hbase.index.covered.update.ColumnReference;
import com.salesforce.hbase.index.scanner.Scanner;
import com.salesforce.hbase.index.util.ImmutableBytesPtr;
/**
* {@link ValueGetter} that uses lazy initialization to get the value for the given
* {@link ColumnReference}. Once stored, the mapping for that reference is retained.
*/
public class LazyValueGetter implements ValueGetter {
private Scanner scan;
private volatile Map<ColumnReference, ImmutableBytesPtr> values;
private byte[] row;
/**
* Back the getter with a {@link Scanner} to actually access the local data.
* @param scan backing scanner
* @param currentRow row key for the row to seek in the scanner
*/
public LazyValueGetter(Scanner scan, byte[] currentRow) {
this.scan = scan;
this.row = currentRow;
}
@Override
public ImmutableBytesPtr getLatestValue(ColumnReference ref) throws IOException {
// ensure we have a backing map
if (values == null) {
synchronized (this) {
values = Collections.synchronizedMap(new HashMap<ColumnReference, ImmutableBytesPtr>());
}
}
// check the value in the map
ImmutableBytesPtr value = values.get(ref);
if (value == null) {
value = get(ref);
values.put(ref, value);
}
return value;
}
/**
* @param ref
* @return the first value on the scanner for the given column
*/
private ImmutableBytesPtr get(ColumnReference ref) throws IOException {
KeyValue first = ref.getFirstKeyValueForRow(row);
if (!scan.seek(first)) {
return null;
}
// there is a next value - we only care about the current value, so we can just snag that
KeyValue next = scan.next();
if (ref.matches(next)) {
return new ImmutableBytesPtr(next.getBuffer(), next.getValueOffset(), next.getValueLength());
}
return null;
}
}