Merge pull request #2093 from adriaanm/ticket-6961

SI-6961 no structural sharing in list serialization

3 files changed, 9 insertions, 106 deletions

diff --git a/src/library/scala/collection/immutable/List.scala b/src/library/scala/collection/immutable/List.scala
index 55ac3995e9..9765e7c52f 100644
--- a/src/library/scala/collection/immutable/List.scala
+++ b/src/library/scala/collection/immutable/List.scala
@@ -55,6 +55,12 @@ import java.io._
  *  val shorter =  mainList.tail  // costs nothing as it uses the same 2::1::Nil instances as mainList
  *  }}}
  *
+ *  @note The functional list is characterized by persistence and structural sharing, thus offering considerable
+ *        performance and space consumption benefits in some scenarios if used correctly.
+ *        However, note that objects having multiple references into the same functional list (that is,
+ *        objects that rely on structural sharing), will be serialized and deserialized with multiple lists, one for
+ *        each reference to it. I.e. structural sharing is lost after serialization/deserialization.
+ *
  *  @author  Martin Odersky and others
  *  @version 2.8
  *  @since   1.0
@@ -352,25 +358,8 @@ final case class ::[B](private var hd: B, private[scala] var tl: List[B]) extend
   override def tail : List[B] = tl
   override def isEmpty: Boolean = false
 
-  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) {
+    val firstObject = in.readObject()
     hd = firstObject.asInstanceOf[B]
     assert(hd != ListSerializeEnd)
     var current: ::[B] = this
@@ -378,14 +367,14 @@ final case class ::[B](private var hd: B, private[scala] var tl: List[B]) extend
       case ListSerializeEnd =>
         current.tl = Nil
         return
-      case a : Any =>
+      case a =>
         val list : ::[B] = new ::(a.asInstanceOf[B], Nil)
         current.tl = list
         current = list
     }
   }
 
-  private def oldWriteObject(out: ObjectOutputStream) {
+  private def writeObject(out: ObjectOutputStream) {
     var xs: List[B] = this
     while (!xs.isEmpty) { out.writeObject(xs.head); xs = xs.tail }
     out.writeObject(ListSerializeEnd)
@@ -654,10 +643,6 @@ object List extends SeqFactory[List] {
 }
 
 /** Only used for list serialization */
-@SerialVersionUID(0L - 8287891243975527522L)
-private[scala] case object ListSerializeStart
-
-/** Only used for list serialization */
 @SerialVersionUID(0L - 8476791151975527571L)
 private[scala] case object ListSerializeEnd
 
diff --git a/test/files/run/t5374.check b/test/files/run/t5374.check
deleted file mode 100644
index 6be88d77ec..0000000000
--- a/test/files/run/t5374.check
+++ /dev/null
@@ -1,6 +0,0 @@
-ListBuffer(1, 2, 3, 1)
-ListBuffer(1, 2, 3, 1)
-ListBuffer()
-List(1, 2, 3, 4, 5)
-List(1, 2, 3)
-ok
\ No newline at end of file
diff --git a/test/files/run/t5374.scala b/test/files/run/t5374.scala
deleted file mode 100644
index 9b1671e795..0000000000
--- a/test/files/run/t5374.scala
+++ /dev/null
@@ -1,76 +0,0 @@
-
-
-
-import collection.mutable.ListBuffer
-import java.io._
-
-
-
-object Test {
-  
-  def main(args: Array[String]) {
-    ticketExample()
-    emptyListBuffer()
-    list()
-    legacyList()
-    objectWithMultipleLists()
-  }
-  
-  def inAndOut[T <: AnyRef](obj: T): T = {
-    val baos = new ByteArrayOutputStream
-    val oos = new ObjectOutputStream(baos)
-    oos.writeObject( obj )
-    val bais = new ByteArrayInputStream( baos.toByteArray )
-    val ois = new ObjectInputStream(bais)
-    ois.readObject.asInstanceOf[T]
-  }
-  
-  def ticketExample() {
-    val lb = inAndOut(ListBuffer(1, 2, 3))
-    val lb2 = ListBuffer[Int]() ++= lb
-    
-    lb2 ++= List(1)
-    lb ++= List(1)
-    println(lb)
-    println(lb2)
-  }
-  
-  def emptyListBuffer() {
-    val lb = inAndOut(ListBuffer[Int]())
-    
-    println(lb)
-  }
-  
-  def list() {
-    val l = inAndOut(List(1, 2, 3, 4, 5))
-    
-    println(l)
-  }
-  
-  // this byte array corresponds to what List(1, 2, 3) used to be serialized to prior to this fix
-  val listBytes = Array[Byte](-84, -19, 0, 5, 115, 114, 0, 39, 115, 99, 97, 108, 97, 46, 99, 111, 108, 108, 101, 99, 116, 105, 111, 110, 46, 105, 109, 109, 117, 116, 97, 98, 108, 101, 46, 36, 99, 111, 108, 111, 110, 36, 99, 111, 108, 111, 110, -118, 92, 99, 91, -10, -40, -7, 109, 3, 0, 2, 76, 0, 43, 115, 99, 97, 108, 97, 36, 99, 111, 108, 108, 101, 99, 116, 105, 111, 110, 36, 105, 109, 109, 117, 116, 97, 98, 108, 101, 36, 36, 99, 111, 108, 111, 110, 36, 99, 111, 108, 111, 110, 36, 36, 104, 100, 116, 0, 18, 76, 106, 97, 118, 97, 47, 108, 97, 110, 103, 47, 79, 98, 106, 101, 99, 116, 59, 76, 0, 2, 116, 108, 116, 0, 33, 76, 115, 99, 97, 108, 97, 47, 99, 111, 108, 108, 101, 99, 116, 105, 111, 110, 47, 105, 109, 109, 117, 116, 97, 98, 108, 101, 47, 76, 105, 115, 116, 59, 120, 112, 115, 114, 0, 17, 106, 97, 118, 97, 46, 108, 97, 110, 103, 46, 73, 110, 116, 101, 103, 101, 114, 18, -30, -96, -92, -9, -127, -121, 56, 2, 0, 1, 73, 0, 5, 118, 97, 108, 117, 101, 120, 114, 0, 16, 106, 97, 118, 97, 46, 108, 97, 110, 103, 46, 78, 117, 109, 98, 101, 114, -122, -84, -107, 29, 11, -108, -32, -117, 2, 0, 0, 120, 112, 0, 0, 0, 1, 115, 113, 0, 126, 0, 4, 0, 0, 0, 2, 115, 113, 0, 126, 0, 4, 0, 0, 0, 3, 115, 114, 0, 44, 115, 99, 97, 108, 97, 46, 99, 111, 108, 108, 101, 99, 116, 105, 111, 110, 46, 105, 109, 109, 117, 116, 97, 98, 108, 101, 46, 76, 105, 115, 116, 83, 101, 114, 105, 97, 108, 105, 122, 101, 69, 110, 100, 36, -118, 92, 99, 91, -9, 83, 11, 109, 2, 0, 0, 120, 112, 120)
-  
-  def legacyList() {
-    val bais = new ByteArrayInputStream(listBytes)
-    val ois = new ObjectInputStream(bais)
-    val l = ois.readObject()
-    
-    println(l)
-  }
-  
-  class Foo extends Serializable {
-    val head = List(1, 2, 3)
-    val last = head.tail.tail
-    def structuralSharing: Boolean = head.tail.tail eq last
-    
-    assert(structuralSharing)
-  }
-  
-  def objectWithMultipleLists() {
-    val foo = inAndOut(new Foo)
-    
-    if (foo.structuralSharing) println("ok")
-    else println("no structural sharing")
-  }
-  
-}