Make Random implementations serializable (KT-25571)

Make Random.Default, XorWowRandom, and wrapper classes for JDK Random implement Serializable interface.

Co-authored-by: Ilya Gorbunov <ilya.gorbunov@jetbrains.com>

libraries/stdlib/jvm/src/kotlin/random/PlatformRandom.kt

@@ -5,8 +5,8 @@
 
 package kotlin.random
 
-import kotlin.UnsupportedOperationException
-import kotlin.internal.*
+import kotlin.internal.IMPLEMENTATIONS
+import kotlin.internal.InlineOnly
 
 /**
  * Creates a [java.util.Random][java.util.Random] instance that uses the specified Kotlin [Random] generator as a randomness source.
@@ -49,15 +49,18 @@ internal abstract class AbstractPlatformRandom : Random() {
 
 internal class FallbackThreadLocalRandom : AbstractPlatformRandom() {
     private val implStorage = object : ThreadLocal<java.util.Random>() {
-        override fun initialValue(): java.util.Random {
-            return java.util.Random()
-        }
+        override fun initialValue(): java.util.Random = java.util.Random()
     }
+
     override val impl: java.util.Random
         get() = implStorage.get()
 }
 
-private class PlatformRandom(override val impl: java.util.Random) : AbstractPlatformRandom()
+private class PlatformRandom(override val impl: java.util.Random) : AbstractPlatformRandom(), Serializable {
+    private companion object {
+        private const val serialVersionUID: Long = 0L
+    }
+}
 
 private class KotlinRandom(val impl: Random) : java.util.Random() {
     override fun next(bits: Int): Int = impl.nextBits(bits)
@@ -73,6 +76,7 @@ private class KotlinRandom(val impl: Random) : java.util.Random() {
     }
 
     private var seedInitialized: Boolean = false
+
     override fun setSeed(seed: Long) {
         if (!seedInitialized) {
             // ignore seed value from constructor
@@ -81,4 +85,8 @@ private class KotlinRandom(val impl: Random) : java.util.Random() {
             throw UnsupportedOperationException("Setting seed is not supported.")
         }
     }
+
+    private companion object {
+        private const val serialVersionUID: Long = 0L
+    }
 }

libraries/stdlib/jvm/test/random/RandomSerializationTest.kt

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package random
+
+import test.io.deserializeFromHex
+import test.io.serializeAndDeserialize
+import kotlin.random.Random
+import kotlin.random.asJavaRandom
+import kotlin.random.asKotlinRandom
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertSame
+import kotlin.test.assertTrue
+
+class RandomSerializationTest {
+    @Test
+    fun defaultIsSerializable() {
+        val instance = Random
+        discardSomeValues(instance)
+        assertSame(instance, serializeAndDeserialize(instance))
+    }
+
+    private fun discardSomeValues(instance: Random) {
+        instance.nextInt()
+        instance.nextDouble()
+        instance.nextLong()
+        instance.nextBytes(64)
+    }
+
+    private fun testRandomsHaveSameState(first: Random, second: Random) {
+        assertEquals(first.nextInt(), second.nextInt())
+        assertEquals(first.nextDouble(), second.nextDouble())
+        assertEquals(first.nextLong(), second.nextLong())
+        assertTrue(first.nextBytes(64).contentEquals(second.nextBytes(64)))
+    }
+
+    @Test
+    fun deserializeDefault() = assertSame(
+        expected = Random,
+        actual = deserializeFromHex("ac ed 00 05 73 72 00 22 6b 6f 74 6c 69 6e 2e 72 61 6e 64 6f 6d 2e 52 61 6e 64 6f 6d 24 44 65 66 61 75 6c 74 24 44 75 6d 6d 79 00 00 00 00 00 00 00 00 02 00 00 78 70"),
+    )
+
+    @Test
+    fun deserializeXorWow() {
+        val instance = Random(0)
+
+        val deserialized =
+            deserializeFromHex<Random>("ac ed 00 05 73 72 00 1a 6b 6f 74 6c 69 6e 2e 72 61 6e 64 6f 6d 2e 58 6f 72 57 6f 77 52 61 6e 64 6f 6d 00 00 00 00 00 00 00 00 02 00 06 49 00 06 61 64 64 65 6e 64 49 00 01 76 49 00 01 77 49 00 01 78 49 00 01 79 49 00 01 7a 78 70 01 61 f1 40 23 9d 3d b3 c9 07 82 1d 6a 67 48 b0 e3 f9 bd 0c b6 5b de 32")
+
+        testRandomsHaveSameState(instance, deserialized)
+    }
+
+    @Test
+    fun xorwowIsSerializable() {
+        val instance = Random(0)
+        discardSomeValues(instance)
+        val deserialized = serializeAndDeserialize(instance)
+        testRandomsHaveSameState(instance, deserialized)
+    }
+
+    @Test
+    fun wrapperOfKotlinRandomIsSerializable() {
+        val java = Random(0).asJavaRandom()
+        java.nextInt()
+        java.nextDouble()
+        java.nextLong()
+        java.nextBytes(ByteArray(64) { 0 })
+        val deserialized = serializeAndDeserialize(java)
+        testRandomsHaveSameState(java.asKotlinRandom(), deserialized.asKotlinRandom())
+    }
+
+    @Test
+    fun wrapperOfJavaRandomIsSerializable() {
+        val kotlin = java.util.Random(0).asKotlinRandom()
+        discardSomeValues(kotlin)
+        val deserialized = serializeAndDeserialize(kotlin)
+        testRandomsHaveSameState(kotlin, deserialized)
+    }
+}