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package spark.serializer
import java.nio.ByteBuffer
import java.io.{EOFException, InputStream, OutputStream}
import it.unimi.dsi.fastutil.io.FastByteArrayOutputStream
import spark.util.ByteBufferInputStream
/**
* A serializer. Because some serialization libraries are not thread safe, this class is used to
* create [[spark.serializer.SerializerInstance]] objects that do the actual serialization and are
* guaranteed to only be called from one thread at a time.
*/
trait Serializer {
def newInstance(): SerializerInstance
}
/**
* An instance of a serializer, for use by one thread at a time.
*/
trait SerializerInstance {
def serialize[T](t: T): ByteBuffer
def deserialize[T](bytes: ByteBuffer): T
def deserialize[T](bytes: ByteBuffer, loader: ClassLoader): T
def serializeStream(s: OutputStream): SerializationStream
def deserializeStream(s: InputStream): DeserializationStream
def serializeMany[T](iterator: Iterator[T]): ByteBuffer = {
// Default implementation uses serializeStream
val stream = new FastByteArrayOutputStream()
serializeStream(stream).writeAll(iterator)
val buffer = ByteBuffer.allocate(stream.position.toInt)
buffer.put(stream.array, 0, stream.position.toInt)
buffer.flip()
buffer
}
def deserializeMany(buffer: ByteBuffer): Iterator[Any] = {
// Default implementation uses deserializeStream
buffer.rewind()
deserializeStream(new ByteBufferInputStream(buffer)).asIterator
}
}
/**
* A stream for writing serialized objects.
*/
trait SerializationStream {
def writeObject[T](t: T): SerializationStream
def flush(): Unit
def close(): Unit
def writeAll[T](iter: Iterator[T]): SerializationStream = {
while (iter.hasNext) {
writeObject(iter.next())
}
this
}
}
/**
* A stream for reading serialized objects.
*/
trait DeserializationStream {
def readObject[T](): T
def close(): Unit
/**
* Read the elements of this stream through an iterator. This can only be called once, as
* reading each element will consume data from the input source.
*/
def asIterator: Iterator[Any] = new Iterator[Any] {
var gotNext = false
var finished = false
var nextValue: Any = null
private def getNext() {
try {
nextValue = readObject[Any]()
} catch {
case eof: EOFException =>
finished = true
}
gotNext = true
}
override def hasNext: Boolean = {
if (!gotNext) {
getNext()
}
if (finished) {
close()
}
!finished
}
override def next(): Any = {
if (!gotNext) {
getNext()
}
if (finished) {
throw new NoSuchElementException("End of stream")
}
gotNext = false
nextValue
}
}
}
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