| /** |
| * 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.fs; |
| |
| import java.io.*; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| |
| /** |
| * Stream that permits positional reading. |
| * |
| * Implementations are required to implement thread-safe operations; this may |
| * be supported by concurrent access to the data, or by using a synchronization |
| * mechanism to serialize access. |
| * |
| * Not all implementations meet this requirement. Those that do not cannot |
| * be used as a backing store for some applications, such as Apache HBase. |
| * |
| * Independent of whether or not they are thread safe, some implementations |
| * may make the intermediate state of the system, specifically the position |
| * obtained in {@code Seekable.getPos()} visible. |
| */ |
| @InterfaceAudience.Public |
| @InterfaceStability.Evolving |
| public interface PositionedReadable { |
| /** |
| * Read up to the specified number of bytes, from a given |
| * position within a file, and return the number of bytes read. This does not |
| * change the current offset of a file, and is thread-safe. |
| * |
| * <i>Warning: Not all filesystems satisfy the thread-safety requirement.</i> |
| * @param position position within file |
| * @param buffer destination buffer |
| * @param offset offset in the buffer |
| * @param length number of bytes to read |
| * @return actual number of bytes read; -1 means "none" |
| * @throws IOException IO problems. |
| */ |
| int read(long position, byte[] buffer, int offset, int length) |
| throws IOException; |
| |
| /** |
| * Read the specified number of bytes, from a given |
| * position within a file. This does not |
| * change the current offset of a file, and is thread-safe. |
| * |
| * <i>Warning: Not all filesystems satisfy the thread-safety requirement.</i> |
| * @param position position within file |
| * @param buffer destination buffer |
| * @param offset offset in the buffer |
| * @param length number of bytes to read |
| * @throws IOException IO problems. |
| * @throws EOFException the end of the data was reached before |
| * the read operation completed |
| */ |
| void readFully(long position, byte[] buffer, int offset, int length) |
| throws IOException; |
| |
| /** |
| * Read number of bytes equal to the length of the buffer, from a given |
| * position within a file. This does not |
| * change the current offset of a file, and is thread-safe. |
| * |
| * <i>Warning: Not all filesystems satisfy the thread-safety requirement.</i> |
| * @param position position within file |
| * @param buffer destination buffer |
| * @throws IOException IO problems. |
| * @throws EOFException the end of the data was reached before |
| * the read operation completed |
| */ |
| void readFully(long position, byte[] buffer) throws IOException; |
| } |