List serialization/deserialization can overflow the stack in 2.10

Chris Marshall

unread,

Jan 11, 2013, 4:36:32 AM1/11/13

to scala-i...@googlegroups.com

This is a big problem:

object ListSer extends App {

val largeList = (1 to 1000000).toList

val oos = new ObjectOutputStream(new FileOutputStream("C:/tmp/largeList.ser"))
oos.writeObject(largeList)
oos.flush()
oos.close()

val ois = new ObjectInputStream(new FileInputStream("C:/tmp/largeList.ser"))
val read = ois.readObject().asInstanceOf[List[Int]]
println(read.size)

}

Running the above program will overflow the stack in 2.10; it works fine in 2.9 - I'm sure you guys are working on emergency fixes - this looks like something which has to be included. I've reported it here: https://issues.scala-lang.org/browse/SI-6961

Chris

Eugene Burmako

unread,

Jan 11, 2013, 4:39:36 AM1/11/13

to <scala-internals@googlegroups.com>

Could you please also provide a stacktrace?

Chris Marshall

unread,

Jan 11, 2013, 4:40:18 AM1/11/13

to scala-i...@googlegroups.com

The only workaround I can find is increasing the stack size - if anyone has any other suggestions, please can you let me know. The issue is that the old serialization code in List has been changed (because of https://issues.scala-lang.org/browse/SI-5374), from this:

private def writeObject(out: ObjectOutputStream) {
var xs: List[B] = this
while (!xs.isEmpty) { out.writeObject(xs.head); xs = xs.tail }
out.writeObject(ListSerializeEnd)
}

private def readObject(in: ObjectInputStream) {
hd = in.readObject.asInstanceOf[B]
assert(hd != ListSerializeEnd)
var current: ::[B] = this
while (true) in.readObject match {
case ListSerializeEnd =>
current.tl = Nil
return
case a : Any =>
val list : ::[B] = new ::(a.asInstanceOf[B], Nil)
current.tl = list
current = list
}
}

to this:

private def writeObject(out: ObjectOutputStream) {

out.writeObject(ListSerializeStart) // needed to differentiate with the legacy `::` serialization

out.writeObject(this.hd)

out.writeObject(this.tl)

}

private def readObject(in: ObjectInputStream) {

val obj = in.readObject()

if (obj == ListSerializeStart) {

this.hd = in.readObject().asInstanceOf[B]

this.tl = in.readObject().asInstanceOf[List[B]]

} else oldReadObject(in, obj)

}

/* The oldReadObject method exists here for compatibility reasons.

* :: objects used to be serialized by serializing all the elements to

* the output stream directly, but this was broken (see SI-5374).

*/

private def oldReadObject(in: ObjectInputStream, firstObject: AnyRef) {

hd = firstObject.asInstanceOf[B]

assert(hd != ListSerializeEnd)

var current: ::[B] = this

while (true) in.readObject match {

case ListSerializeEnd =>

current.tl = Nil

return

case a : Any =>

val list : ::[B] = new ::(a.asInstanceOf[B], Nil)

current.tl = list

current = list

}

private def oldWriteObject(out: ObjectOutputStream) {

var xs: List[B] = this

while (!xs.isEmpty) { out.writeObject(xs.head); xs = xs.tail }

out.writeObject(ListSerializeEnd)

}

Chris

From: oxbow...@hotmail.com
To: scala-i...@googlegroups.com
Subject: [scala-internals] List serialization/deserialization can overflow the stack in 2.10
Date: Fri, 11 Jan 2013 09:36:32 +0000

Chris Marshall

unread,

Jan 11, 2013, 4:42:59 AM1/11/13

to scala-i...@googlegroups.com

Sorry - thought it was obvious:

at scala.collection.immutable.$colon$colon.readObject(List.scala:362)

at sun.reflect.GeneratedMethodAccessor16.invoke(Unknown Source)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

at java.lang.reflect.Method.invoke(Method.java:601)

at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1004)

at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1866)

at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1771)

at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1347)

at java.io.ObjectInputStream.readObject(ObjectInputStream.java:369)