org.apache.hadoop.fs.PositionedReadable 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.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.
*
* Warning: Not all filesystems satisfy the thread-safety requirement.
* @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.
*
* Warning: Not all filesystems satisfy the thread-safety requirement.
* @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.
*
* Warning: Not all filesystems satisfy the thread-safety requirement.
* @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;
}