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Deserialization of ListBuffer results in a non-mutable structure prone to throwing NoSuchElementException #5374

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scabug opened this issue Jan 13, 2012 · 4 comments
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@scabug scabug commented Jan 13, 2012

Something is amiss with deserialization of ListBuffer, as shown here:

import collection.mutable.ListBuffer
import java.io._
val baos = new ByteArrayOutputStream
val oos = new ObjectOutputStream(baos)
oos.writeObject( ListBuffer(1,2,3) )
val bais = new ByteArrayInputStream( baos.toByteArray )
val ois = new ObjectInputStream(bais)
val lb = ois.readObject.asInstanceOf[ListBuffer[Int]]
val lb2 = ListBuffer[Int]() ++= lb
lb2 ++= List(1)  // All okay
lb ++= List(1)  // Throws an exception for me

Not sure whether this is related to other deserialization bugs (e.g. #SI-5262).

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@scabug scabug commented Jan 13, 2012

Imported From: https://issues.scala-lang.org/browse/SI-5374?orig=1
Reporter: @Ichoran
Affected Versions: 2.9.1
See #5262

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@scabug scabug commented Jan 15, 2012

Jed Wesley-Smith (jedws) said (edited on Jan 15, 2012 7:09:23 AM UTC):
From what I can tell the last0 field isn't being deserialized correctly. As the :: has custom deserialization (see ::.readResolve) when the ListBuffer is deserialized it holds the old last0 reference, but it needs to be updated to the correct one in start chain. This hypotheses is supported by the fact that length is indeed increased as expected.

OT but interesting, the code above does indeed throw an exception in the REPL, but not when compiled by SBT.

Also, verified that prepending does work.

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@scabug scabug commented Jan 15, 2012

Jed Wesley-Smith (jedws) said:
Originally a StackOverflow question

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@scabug scabug commented Jan 23, 2012

@axel22 said:
This is indeed due to list serialization. With the current implementation there, any object that is serialized and which has multiple fields with references into the same list will be inaccurately deserialized. While we could patch list buffers to fix this, a better solution would be to change the way lists are serialized, and avoid surprising behaviour in the future.

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