eejbyfeldt commented on PR #37206:
URL: https://github.com/apache/spark/pull/37206#issuecomment-1691166611
Hi @gowa, I don't think you issue you describe has the same root cause and I
think it more related to how serialization work. Consider the following code:
```
$ cat custom_serialization.scala
import java.io._
abstract class Acc extends Serializable {
private def readObject(in: ObjectInputStream): Unit = {
in.defaultReadObject()
println(s"readObject Acc ${toString()}")
}
}
class MyAcc extends Acc {
final private val myVar = Map()
override def toString: String = {
s"Class MyAcc(myVar=${myVar})"
}
}
object Test {
def main(args: Array[String]): Unit = {
val outputStream: ByteArrayOutputStream = new
ByteArrayOutputStream(1024 * 1024)
val objectStream: ObjectOutputStream = new
ObjectOutputStream(outputStream)
objectStream.writeObject(new MyAcc)
objectStream.close()
val input = new ObjectInputStream(new
ByteArrayInputStream(outputStream.toByteArray()))
val result = input.readObject()
println(result)
}
}
```
when executed it will print
```
$ scala custom_serialization.scala
readObject Acc Class MyAcc(myVar=null)
Class MyAcc(myVar=Map())
```
This code is similar to what we have in `AccumulatorV2` which also has a
custom `readObject` method
https://github.com/apache/spark/blob/v3.4.1/core/src/main/scala/org/apache/spark/util/AccumulatorV2.scala#L191
it from inside the method that the accumulator is registered and therefore
becomes accessible from the hearbeat thread. So there is a possibility that the
heartbeat thread might call `isZero` after AccummulatorV2.readObject called but
before the default deserialization of your custom class has not completed. This
hole setup of giving up references to objects that are not fully deserialized
is really nasty.
Here is a PR addressing/discussing the same bug from an accumulator in
spark: https://github.com/apache/spark/pull/31540
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: [email protected]
For queries about this service, please contact Infrastructure at:
[email protected]
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
