spark FileBasedWriteAheadLogRandomReader 源码
spark FileBasedWriteAheadLogRandomReader 代码
文件路径：/streaming/src/main/scala/org/apache/spark/streaming/util/FileBasedWriteAheadLogRandomReader.scala
/*
* 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.spark.streaming.util
import java.io.Closeable
import java.nio.ByteBuffer
import org.apache.hadoop.conf.Configuration
/**
* A random access reader for reading write ahead log files written using
* [[org.apache.spark.streaming.util.FileBasedWriteAheadLogWriter]]. Given the file segment info,
* this reads the record (ByteBuffer) from the log file.
*/
private[streaming] class FileBasedWriteAheadLogRandomReader(path: String, conf: Configuration)
extends Closeable {
private val instream = HdfsUtils.getInputStream(path, conf)
private var closed = (instream == null) // the file may be deleted as we're opening the stream
def read(segment: FileBasedWriteAheadLogSegment): ByteBuffer = synchronized {
assertOpen()
instream.seek(segment.offset)
val nextLength = instream.readInt()
HdfsUtils.checkState(nextLength == segment.length,
s"Expected message length to be ${segment.length}, but was $nextLength")
val buffer = new Array[Byte](nextLength)
instream.readFully(buffer)
ByteBuffer.wrap(buffer)
}
override def close(): Unit = synchronized {
closed = true
instream.close()
}
private def assertOpen(): Unit = {
HdfsUtils.checkState(!closed, "Stream is closed. Create a new Reader to read from the file.")
}
}
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