org.apache.hadoop.hdfs.server.common.blockaliasmap.BlockAliasMap Maven / Gradle / Ivy
/**
* 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.hdfs.server.common.blockaliasmap;
import java.io.Closeable;
import java.io.IOException;
import java.util.Iterator;
import java.util.Optional;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.hdfs.protocol.Block;
import org.apache.hadoop.hdfs.server.common.BlockAlias;
/**
* An abstract class used to read and write block maps for provided blocks.
*/
@InterfaceAudience.Public
@InterfaceStability.Unstable
public abstract class BlockAliasMap {
/**
* ImmutableIterator is an Iterator that does not support the remove
* operation. This could inherit {@link java.util.Enumeration} but Iterator
* is supported by more APIs and Enumeration's javadoc even suggests using
* Iterator instead.
*/
public abstract class ImmutableIterator implements Iterator {
public void remove() {
throw new UnsupportedOperationException(
"Remove is not supported for provided storage");
}
}
/**
* An abstract class that is used to read {@link BlockAlias}es
* for provided blocks.
*/
public static abstract class Reader
implements Iterable, Closeable {
/**
* reader options.
*/
public interface Options { }
/**
* @param ident block to resolve
* @return BlockAlias corresponding to the provided block.
* @throws IOException
*/
public abstract Optional resolve(Block ident) throws IOException;
}
/**
* Returns a reader to the alias map.
* @param opts reader options
* @param blockPoolID block pool id to use
* @return {@link Reader} to the alias map. If a Reader for the blockPoolID
* cannot be created, this will return null.
* @throws IOException
*/
public abstract Reader getReader(Reader.Options opts, String blockPoolID)
throws IOException;
/**
* An abstract class used as a writer for the provided block map.
*/
public static abstract class Writer
implements Closeable {
/**
* writer options.
*/
public interface Options { }
public abstract void store(U token) throws IOException;
}
/**
* Returns the writer for the alias map.
* @param opts writer options.
* @param blockPoolID block pool id to use
* @return {@link Writer} to the alias map.
* @throws IOException
*/
public abstract Writer getWriter(Writer.Options opts, String blockPoolID)
throws IOException;
/**
* Refresh the alias map.
* @throws IOException
*/
public abstract void refresh() throws IOException;
public abstract void close() throws IOException;
}