org.apache.hadoop.hdfs.ReplicaAccessor 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;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import java.io.IOException;
import java.nio.ByteBuffer;
/**
* The public API for ReplicaAccessor objects.
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public abstract class ReplicaAccessor {
/**
* Read bytes from the replica.
*
* @param pos The position in the replica to start reading at.
* Must not be negative.
* @param buf The byte array to read into.
* @param off The offset within buf to start reading into.
* @param len The maximum length to read.
*
* @return The number of bytes read. If the read extends past the end
* of the replica, a short read count will be returned. We
* will should return -1 if EOF is reached and no bytes
* can be returned. We will never return a short read
* count unless EOF is reached.
*/
public abstract int read(long pos, byte[] buf, int off, int len)
throws IOException;
/**
* Read bytes from the replica.
*
* @param pos The position in the replica to start reading at.
* Must not be negative.
* @param buf The byte buffer to read into. The amount to read will be
* dictated by the remaining bytes between the current
* position and the limit. The ByteBuffer may or may not be
* direct.
*
* @return The number of bytes read. If the read extends past the end
* of the replica, a short read count will be returned. We
* should return -1 if EOF is reached and no bytes can be
* returned. We will never return a short read count unless
* EOF is reached.
*/
public abstract int read(long pos, ByteBuffer buf) throws IOException;
/**
* Release the resources associated with the ReplicaAccessor.
*
* It is recommended that implementations never throw an IOException. The
* method is declared as throwing IOException in order to remain compatible
* with java.io.Closeable. If an exception is thrown, the ReplicaAccessor
* must still be closed when the function returns in order to prevent a
* resource leak.
*/
public abstract void close() throws IOException;
/**
* Return true if bytes read via this accessor should count towards the
* local byte count statistics.
*/
public abstract boolean isLocal();
/**
* Return true if bytes read via this accessor should count towards the
* short-circuit byte count statistics.
*/
public abstract boolean isShortCircuit();
/**
* Return the network distance between local machine and the remote machine.
*/
public int getNetworkDistance() {
return isLocal() ? 0 : Integer.MAX_VALUE;
}
}