| /** |
| * 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; |
| } |
| } |