Fix memory bug induced by frozen lazy. (#2018)

backend.native/tests/build.gradle

@@ -713,6 +713,11 @@ task lazy1(type: RunKonanTest) {
     source = "runtime/workers/lazy1.kt"
 }
 
+task lazy2(type: RunStandaloneKonanTest) {
+    goldValue = "123\nOK\n"
+    source = "runtime/workers/lazy2.kt"
+}
+
 task enumIdentity(type: RunKonanTest) {
     disabled = (project.testTarget == 'wasm32') // Workers need pthreads.
     goldValue = "true\n"

backend.native/tests/runtime/workers/lazy2.kt

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the LICENSE file.
+ */
+import kotlin.test.*
+
+object Foo {
+    val bar = Bar()
+}
+
+class Bar {
+    val f by lazy {
+        foo()
+    }
+
+    fun foo() = 123
+}
+
+fun printAll() {
+    println(Foo.bar.f)
+}
+
+// This test is extracted from the real problem found in kotlinx.serialization, where zeroing out
+// initializer field in frozen lazy object led to the crash, induced by breaking frozen objects'
+// invariant (initializer end up in the same container as the lazy object itself, so it was destroyed
+// earlier than it should when reference counter was decremented).
+fun main(args: Array<String>) {
+    printAll()
+    kotlin.native.internal.GC.collect()
+    println("OK")
+}

runtime/src/main/kotlin/kotlin/native/concurrent/Lazy.kt

@@ -36,8 +36,9 @@ internal class FreezeAwareLazyImpl<out T>(initializer: () -> T) : Lazy<T> {
                     if (!ensureAcyclicAndSet(this, 0, result)) {
                         throw InvalidMutabilityException("Setting cyclic data via lazy in $this: $result")
                     }
-                    // Clear initializer_ reference.
+                    // Do not clear initializer_ reference, as it may break freezing invariants and zero out
-                    ensureAcyclicAndSet(this, 1, null)
+                    // still valid object. It seems to be safe only in case when `this` is not reachable from
+                    // initializer.
                     @Suppress("UNCHECKED_CAST")
                     return result as T
                 }