org.apache.hadoop.fs.FSOutputSummer 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 org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.util.DataChecksum;
import java.io.IOException;
import java.io.OutputStream;
import java.util.zip.Checksum;
/**
* This is a generic output stream for generating checksums for
* data before it is written to the underlying stream
*/
@InterfaceAudience.LimitedPrivate({"HDFS"})
@InterfaceStability.Unstable
abstract public class FSOutputSummer extends OutputStream {
// data checksum
private final DataChecksum sum;
// internal buffer for storing data before it is checksumed
private byte buf[];
// internal buffer for storing checksum
private byte checksum[];
// The number of valid bytes in the buffer.
private int count;
// We want this value to be a multiple of 3 because the native code checksums
// 3 chunks simultaneously. The chosen value of 9 strikes a balance between
// limiting the number of JNI calls and flushing to the underlying stream
// relatively frequently.
private static final int BUFFER_NUM_CHUNKS = 9;
protected FSOutputSummer(DataChecksum sum) {
this.sum = sum;
this.buf = new byte[sum.getBytesPerChecksum() * BUFFER_NUM_CHUNKS];
this.checksum = new byte[getChecksumSize() * BUFFER_NUM_CHUNKS];
this.count = 0;
}
/* write the data chunk in b staring at offset with
* a length of len > 0, and its checksum
*/
protected abstract void writeChunk(byte[] b, int bOffset, int bLen,
byte[] checksum, int checksumOffset, int checksumLen) throws IOException;
/**
* Check if the implementing OutputStream is closed and should no longer
* accept writes. Implementations should do nothing if this stream is not
* closed, and should throw an {@link IOException} if it is closed.
*
* @throws IOException if this stream is already closed.
*/
protected abstract void checkClosed() throws IOException;
/** Write one byte */
@Override
public synchronized void write(int b) throws IOException {
buf[count++] = (byte)b;
if(count == buf.length) {
flushBuffer();
}
}
/**
* Writes len bytes from the specified byte array
* starting at offset off and generate a checksum for
* each data chunk.
*
* This method stores bytes from the given array into this
* stream's buffer before it gets checksumed. The buffer gets checksumed
* and flushed to the underlying output stream when all data
* in a checksum chunk are in the buffer. If the buffer is empty and
* requested length is at least as large as the size of next checksum chunk
* size, this method will checksum and write the chunk directly
* to the underlying output stream. Thus it avoids uneccessary data copy.
*
* @param b the data.
* @param off the start offset in the data.
* @param len the number of bytes to write.
* @exception IOException if an I/O error occurs.
*/
@Override
public synchronized void write(byte b[], int off, int len)
throws IOException {
checkClosed();
if (off < 0 || len < 0 || off > b.length - len) {
throw new ArrayIndexOutOfBoundsException();
}
for (int n=0;n=buf.length) {
// local buffer is empty and user buffer size >= local buffer size, so
// simply checksum the user buffer and send it directly to the underlying
// stream
final int length = buf.length;
writeChecksumChunks(b, off, length);
return length;
}
// copy user data to local buffer
int bytesToCopy = buf.length-count;
bytesToCopy = (len>> 24) & 0xFF);
bytes[1] = (byte) ((integer >>> 16) & 0xFF);
bytes[2] = (byte) ((integer >>> 8) & 0xFF);
bytes[3] = (byte) ((integer >>> 0) & 0xFF);
return bytes;
}
return bytes;
}
/**
* Resets existing buffer with a new one of the specified size.
*/
protected synchronized void setChecksumBufSize(int size) {
this.buf = new byte[size];
this.checksum = new byte[sum.getChecksumSize(size)];
this.count = 0;
}
protected synchronized void resetChecksumBufSize() {
setChecksumBufSize(sum.getBytesPerChecksum() * BUFFER_NUM_CHUNKS);
}
}