Improve WorkerBoundReference exceptions and add valueOrNull (#4115)

2020-04-23 18:31:43 +03:00
parent 1b6dac76d5
commit 5b75a009db
9 changed files with 241 additions and 756 deletions
@@ -885,11 +885,6 @@ task worker_bound_reference0(type: KonanLocalTest) {
    source = "runtime/concurrent/worker_bound_reference0.kt"
 }

-task worker_bound_reference1(type: KonanLocalTest) {
-    enabled = (project.testTarget != 'wasm32') // Workers need pthreads.
-    source = "runtime/concurrent/worker_bound_reference1.kt"
-}
-
 task worker0(type: KonanLocalTest) {
    enabled = (project.testTarget != 'wasm32') // Workers need pthreads.
    goldValue = "Got Input processed\nOK\n"
@@ -10,6 +10,7 @@ import kotlin.test.*
 import kotlin.native.concurrent.*
 import kotlin.native.internal.GC
 import kotlin.native.ref.WeakReference
+import kotlin.text.Regex

 class A(var a: Int)

@@ -18,6 +19,7 @@ val global1: WorkerBoundReference<A> = WorkerBoundReference(A(3))
@Test
 fun testGlobal() {
    assertEquals(3, global1.value.a)
+    assertEquals(3, global1.valueOrNull?.a)

    val worker = Worker.start()
    val future = worker.execute(TransferMode.SAFE, {}) {
@@ -26,6 +28,7 @@ fun testGlobal() {

    val value = future.result
    assertEquals(3, value.value.a)
+    assertEquals(3, value.valueOrNull?.a)
    worker.requestTermination().result
 }

@@ -41,6 +44,7 @@ fun testGlobalDenyAccessOnWorker() {
        assertFailsWith<IncorrectDereferenceException> {
            local.value
        }
+        assertEquals(null, local.valueOrNull)
        Unit
    }

@@ -53,6 +57,7 @@ val global3: WorkerBoundReference<A> = WorkerBoundReference(A(3).freeze())
@Test
 fun testGlobalAccessOnWorkerFrozenInitially() {
    assertEquals(3, global3.value.a)
+    assertEquals(3, global3.valueOrNull?.a)

    val worker = Worker.start()
    val future = worker.execute(TransferMode.SAFE, {}) {
@@ -131,6 +136,7 @@ fun testGlobalModification() {

    val value = future.result
    assertEquals(4, value.value.a)
+    assertEquals(4, value.valueOrNull?.a)
    worker.requestTermination().result
 }

@@ -138,6 +144,7 @@ fun testGlobalModification() {
 fun testLocal() {
    val local = WorkerBoundReference(A(3))
    assertEquals(3, local.value.a)
+    assertEquals(3, local.valueOrNull?.a)

    val worker = Worker.start()
    val future = worker.execute(TransferMode.SAFE, { local }) { local ->
@@ -146,6 +153,7 @@ fun testLocal() {

    val value = future.result
    assertEquals(3, value.value.a)
+    assertEquals(3, value.valueOrNull?.a)
    worker.requestTermination().result
 }

@@ -159,6 +167,7 @@ fun testLocalDenyAccessOnWorker() {
        assertFailsWith<IncorrectDereferenceException> {
            local.value
        }
+        assertEquals(null, local.valueOrNull)
        Unit
    }

@@ -170,6 +179,7 @@ fun testLocalDenyAccessOnWorker() {
 fun testLocalAccessOnWorkerFrozenInitially() {
    val local = WorkerBoundReference(A(3).freeze())
    assertEquals(3, local.value.a)
+    assertEquals(3, local.valueOrNull?.a)

    val worker = Worker.start()
    val future = worker.execute(TransferMode.SAFE, { local }) { local ->
@@ -235,6 +245,7 @@ fun testLocalDenyAccessOnMainThread() {
    assertFailsWith<IncorrectDereferenceException> {
        value.value
    }
+    assertEquals(null, value.valueOrNull)

    worker.requestTermination().result
 }
@@ -261,6 +272,7 @@ fun testLocalModification() {

    val value = future.result
    assertEquals(4, value.value.a)
+    assertEquals(4, value.valueOrNull?.a)
    worker.requestTermination().result
 }

@@ -421,6 +433,110 @@ fun doesNotCollectCrossThreadCyclicGarbage() {
    worker.requestTermination().result
 }

+class C1 {
+    lateinit var c2: AtomicReference<WorkerBoundReference<C2>?>
+
+    fun dispose() {
+        c2.value = null
+    }
+}
+
+data class C2(val c1: AtomicReference<WorkerBoundReference<C1>>)
+
+fun createCyclicGarbageWithAtomics(): Triple<AtomicReference<WorkerBoundReference<C1>?>, WeakReference<C1>, WeakReference<C2>> {
+    val ref1 = WorkerBoundReference(C1())
+    val ref1Weak = WeakReference(ref1.value)
+
+    val ref2 = WorkerBoundReference(C2(AtomicReference(ref1)))
+    val ref2Weak = WeakReference(ref2.value)
+
+    ref1.value.c2 = AtomicReference(ref2)
+
+    return Triple(AtomicReference(ref1), ref1Weak, ref2Weak)
+}
+
+fun dispose(refOwner: AtomicReference<WorkerBoundReference<C1>?>) {
+    refOwner.value!!.value.dispose()
+    refOwner.value = null
+}
+
+@Test
+fun doesNotCollectCyclicGarbageWithAtomics() {
+    val (ref1Owner, ref1Weak, ref2Weak) = createCyclicGarbageWithAtomics()
+
+    ref1Owner.value = null
+    GC.collect()
+
+    // If these asserts fail, that means AtomicReference<WorkerBoundReference> managed to clean up cyclic garbage all by itself.
+    assertNotNull(ref1Weak.value)
+    assertNotNull(ref2Weak.value)
+}
+
+@Test
+fun collectCyclicGarbageWithAtomics() {
+    val (ref1Owner, ref1Weak, ref2Weak) = createCyclicGarbageWithAtomics()
+
+    dispose(ref1Owner)
+    GC.collect()
+
+    assertNull(ref1Weak.value)
+    assertNull(ref2Weak.value)
+}
+
+fun createCrossThreadCyclicGarbageWithAtomics(
+        worker: Worker
+): Triple<AtomicReference<WorkerBoundReference<C1>?>, WeakReference<C1>, WeakReference<C2>> {
+    val ref1 = WorkerBoundReference(C1())
+    val ref1Weak = WeakReference(ref1.value)
+
+    val future = worker.execute(TransferMode.SAFE, { ref1 }) { ref1 ->
+        val ref2 = WorkerBoundReference(C2(AtomicReference(ref1)))
+        Pair(ref2, WeakReference(ref2.value))
+    }
+    val (ref2, ref2Weak) = future.result
+
+    ref1.value.c2 = AtomicReference(ref2)
+
+    return Triple(AtomicReference(ref1), ref1Weak, ref2Weak)
+}
+
+@Test
+fun doesNotCollectCrossThreadCyclicGarbageWithAtomics() {
+    val worker = Worker.start()
+
+    val (ref1Owner, ref1Weak, ref2Weak) = createCrossThreadCyclicGarbageWithAtomics(worker)
+
+    ref1Owner.value = null
+    GC.collect()
+    worker.execute(TransferMode.SAFE, {}) { GC.collect() }.result
+
+    // If these asserts fail, that means AtomicReference<WorkerBoundReference> managed to clean up cyclic garbage all by itself.
+    assertNotNull(ref1Weak.value)
+    assertNotNull(ref2Weak.value)
+
+    worker.requestTermination().result
+}
+
+@Test
+fun collectCrossThreadCyclicGarbageWithAtomics() {
+    val worker = Worker.start()
+
+    val (ref1Owner, ref1Weak, ref2Weak) = createCrossThreadCyclicGarbageWithAtomics(worker)
+
+    dispose(ref1Owner)
+    // This marks C2 as gone on the main thread
+    GC.collect()
+    // This cleans up all the references from the worker thread and destroys C2, but C1 is still alive.
+    worker.execute(TransferMode.SAFE, {}) { GC.collect() }.result
+    // And this finally destroys C1
+    GC.collect()
+
+    assertNull(ref1Weak.value)
+    assertNull(ref2Weak.value)
+
+    worker.requestTermination().result
+}
+
@Test
 fun concurrentAccess() {
    val workerCount = 10
@@ -453,3 +569,22 @@ fun concurrentAccess() {
        worker.requestTermination().result
    }
 }
+
+@Test
+fun testExceptionMessage() {
+    val worker = Worker.start()
+    val future = worker.execute(TransferMode.SAFE, {}) {
+        WorkerBoundReference(A(3))
+    }
+    val value = future.result
+
+    val ownerName = worker.name
+    val messagePattern = Regex("illegal attempt to access non-shared runtime\\.concurrent\\.worker_bound_reference0\\.A@[a-f0-9]+ bound to `$ownerName` from `${Worker.current.name}`")
+
+    val exception = assertFailsWith<IncorrectDereferenceException> {
+        value.value
+    }
+    assertTrue(messagePattern matches exception.message!!)
+
+    worker.requestTermination().result
+}
@@ -1,684 +0,0 @@
-/*
- * Copyright 2010-2020 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.
- */
-
-package runtime.concurrent.worker_bound_reference1
-
-import kotlin.test.*
-
-import kotlin.native.concurrent.*
-import kotlin.native.internal.GC
-import kotlin.native.ref.WeakReference
-
-class A(var a: Int)
-
-val global1: DisposableWorkerBoundReference<A> = DisposableWorkerBoundReference(A(3))
-
-@Test
-fun testGlobal() {
-    assertEquals(3, global1.value.a)
-
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, {}) {
-        global1
-    }
-
-    val value = future.result
-    assertEquals(3, value.value.a)
-    worker.requestTermination().result
-}
-
-val global2: DisposableWorkerBoundReference<A> = DisposableWorkerBoundReference(A(3))
-
-@Test
-fun testGlobalDenyAccessOnWorker() {
-    assertEquals(3, global2.value.a)
-
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, {}) {
-        val local = global2
-        assertFailsWith<IncorrectDereferenceException> {
-            local.value
-        }
-        Unit
-    }
-
-    future.result
-    worker.requestTermination().result
-}
-
-val global3: DisposableWorkerBoundReference<A> = DisposableWorkerBoundReference(A(3).freeze())
-
-@Test
-fun testGlobalAccessOnWorkerFrozenInitially() {
-    assertEquals(3, global3.value.a)
-
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, {}) {
-        global3.value.a
-    }
-
-    val value = future.result
-    assertEquals(3, value)
-    worker.requestTermination().result
-}
-
-val global4: DisposableWorkerBoundReference<A> = DisposableWorkerBoundReference(A(3))
-
-@Test
-fun testGlobalAccessOnWorkerFrozenBeforePassing() {
-    assertEquals(3, global4.value.a)
-    global4.value.freeze()
-
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, {}) {
-        global4.value.a
-    }
-
-    val value = future.result
-    assertEquals(3, value)
-    worker.requestTermination().result
-}
-
-val global5: DisposableWorkerBoundReference<A> = DisposableWorkerBoundReference(A(3))
-
-@Test
-fun testGlobalAccessOnWorkerFrozenBeforeAccess() {
-    val semaphore: AtomicInt = AtomicInt(0)
-
-    assertEquals(3, global5.value.a)
-
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, { semaphore }) { semaphore ->
-        semaphore.increment()
-        while (semaphore.value < 2) {
-        }
-
-        global5.value.a
-    }
-
-    while (semaphore.value < 1) {
-    }
-    global5.value.freeze()
-    semaphore.increment()
-
-    val value = future.result
-    assertEquals(3, value)
-    worker.requestTermination().result
-}
-
-val global6: DisposableWorkerBoundReference<A> = DisposableWorkerBoundReference(A(3))
-
-@Test
-fun testGlobalModification() {
-    val semaphore: AtomicInt = AtomicInt(0)
-
-    assertEquals(3, global6.value.a)
-
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, { semaphore }) { semaphore ->
-        semaphore.increment()
-        while (semaphore.value < 2) {
-        }
-        global6
-    }
-
-    while (semaphore.value < 1) {
-    }
-    global6.value.a = 4
-    semaphore.increment()
-
-    val value = future.result
-    assertEquals(4, value.value.a)
-    worker.requestTermination().result
-}
-
-val global7: DisposableWorkerBoundReference<A> = DisposableWorkerBoundReference(A(3))
-
-@Test
-fun testGlobalDispose() {
-    assertEquals(3, global7.value.a)
-
-    global7.dispose()
-    global7.dispose()
-}
-
-val global8: DisposableWorkerBoundReference<A> = DisposableWorkerBoundReference(A(3))
-
-@Test
-fun testGlobalAccessAfterDispose() {
-    assertEquals(3, global8.value.a)
-
-    global8.dispose()
-    assertFailsWith<IllegalStateException> {
-        global8.value.a
-    }
-}
-
-@Test
-fun testLocal() {
-    val local = DisposableWorkerBoundReference(A(3))
-    assertEquals(3, local.value.a)
-
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, { local }) { local ->
-        local
-    }
-
-    val value = future.result
-    assertEquals(3, value.value.a)
-    worker.requestTermination().result
-}
-
-@Test
-fun testLocalDenyAccessOnWorker() {
-    val local = DisposableWorkerBoundReference(A(3))
-    assertEquals(3, local.value.a)
-
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, { local }) { local ->
-        assertFailsWith<IncorrectDereferenceException> {
-            local.value
-        }
-        Unit
-    }
-
-    future.result
-    worker.requestTermination().result
-}
-
-@Test
-fun testLocalAccessOnWorkerFrozenInitially() {
-    val local = DisposableWorkerBoundReference(A(3).freeze())
-    assertEquals(3, local.value.a)
-
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, { local }) { local ->
-        local.value.a
-    }
-
-    val value = future.result
-    assertEquals(3, value)
-    worker.requestTermination().result
-}
-
-@Test
-fun testLocalAccessOnWorkerFrozenBeforePassing() {
-    val local = DisposableWorkerBoundReference(A(3))
-    assertEquals(3, local.value.a)
-    local.value.freeze()
-
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, { local }) { local ->
-        local.value.a
-    }
-
-    val value = future.result
-    assertEquals(3, value)
-    worker.requestTermination().result
-}
-
-@Test
-fun testLocalAccessOnWorkerFrozenBeforeAccess() {
-    val semaphore: AtomicInt = AtomicInt(0)
-
-    val local = DisposableWorkerBoundReference(A(3))
-    assertEquals(3, local.value.a)
-
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, { Pair(local, semaphore) }) { (local, semaphore) ->
-        semaphore.increment()
-        while (semaphore.value < 2) {
-        }
-
-        local.value.a
-    }
-
-    while (semaphore.value < 1) {
-    }
-    local.value.freeze()
-    semaphore.increment()
-
-    val value = future.result
-    assertEquals(3, value)
-    worker.requestTermination().result
-}
-
-@Test
-fun testLocalDenyAccessOnMainThread() {
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, {}) {
-        DisposableWorkerBoundReference(A(3))
-    }
-
-    val value = future.result
-    assertFailsWith<IncorrectDereferenceException> {
-        value.value
-    }
-
-    worker.requestTermination().result
-}
-
-@Test
-fun testLocalModification() {
-    val semaphore: AtomicInt = AtomicInt(0)
-
-    val local = DisposableWorkerBoundReference(A(3))
-    assertEquals(3, local.value.a)
-
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, { Pair(local, semaphore) }) { (local, semaphore) ->
-        semaphore.increment()
-        while (semaphore.value < 2) {
-        }
-        local
-    }
-
-    while (semaphore.value < 1) {
-    }
-    local.value.a = 4
-    semaphore.increment()
-
-    val value = future.result
-    assertEquals(4, value.value.a)
-    worker.requestTermination().result
-}
-
-@Test
-fun testLocalDispose() {
-    val local = DisposableWorkerBoundReference(A(3))
-    assertEquals(3, local.value.a)
-
-    local.dispose()
-    local.dispose()
-}
-
-@Test
-fun testLocalAccessAfterDispose() {
-    val local = DisposableWorkerBoundReference(A(3))
-    assertEquals(3, local.value.a)
-
-    local.dispose()
-    assertFailsWith<IllegalStateException> {
-        local.value.a
-    }
-}
-
-fun getOwnerAndWeaks(initial: Int): Triple<AtomicReference<DisposableWorkerBoundReference<A>?>, WeakReference<DisposableWorkerBoundReference<A>>, WeakReference<A>> {
-    val ref = DisposableWorkerBoundReference(A(initial))
-    val refOwner: AtomicReference<DisposableWorkerBoundReference<A>?> = AtomicReference(ref)
-    val refWeak = WeakReference(ref)
-    val refValueWeak = WeakReference(ref.value)
-
-    return Triple(refOwner, refWeak, refValueWeak)
-}
-
-fun <T : Any> callDispose(ref: AtomicReference<DisposableWorkerBoundReference<T>?>) {
-    ref.value!!.dispose()
-}
-
-@Test
-fun testCollect() {
-    val (refOwner, refWeak, refValueWeak) = getOwnerAndWeaks(3)
-
-    refOwner.value = null
-    GC.collect()
-
-    // Last reference to DisposableWorkerBoundReference is gone, so it and it's referent are destroyed.
-    assertNull(refWeak.value)
-    assertNull(refValueWeak.value)
-}
-
-@Test
-fun testDisposeAndCollect() {
-    val (refOwner, refWeak, refValueWeak) = getOwnerAndWeaks(3)
-
-    callDispose(refOwner)
-    GC.collect()
-
-    // refOwner still contains a reference to DisposableWorkerBoundReference. But it's referent is
-    // destroyed because of explicit dispose call.
-    assertNotNull(refWeak.value)
-    assertNull(refValueWeak.value)
-}
-
-fun collectInWorker(worker: Worker, semaphore: AtomicInt): Pair<WeakReference<A>, Future<Unit>> {
-    val (refOwner, _, refValueWeak) = getOwnerAndWeaks(3)
-
-    val future = worker.execute(TransferMode.SAFE, { Pair(refOwner, semaphore) }) { (refOwner, semaphore) ->
-        semaphore.increment()
-        while (semaphore.value < 2) {
-        }
-
-        refOwner.value = null
-        GC.collect()
-    }
-
-    while (semaphore.value < 1) {
-    }
-    // At this point worker is spinning on semaphore. refOwner still contains reference to
-    // DisposableWorkerBoundReference, so referent is kept alive.
-    GC.collect()
-    assertNotNull(refValueWeak.value)
-
-    return Pair(refValueWeak, future)
-}
-
-@Test
-fun testCollectInWorker() {
-    val semaphore: AtomicInt = AtomicInt(0)
-
-    val worker = Worker.start()
-
-    val (refValueWeak, future) = collectInWorker(worker, semaphore)
-    semaphore.increment()
-    future.result
-
-    // At this point DisposableWorkerBoundReference no longer has a reference, so it's referent is destroyed.
-    // DisposableWorkerBoundReference, so referent is kept alive.
-    GC.collect()
-    assertNull(refValueWeak.value)
-
-    worker.requestTermination().result
-}
-
-fun doNotCollectInWorker(worker: Worker, semaphore: AtomicInt): Future<DisposableWorkerBoundReference<A>> {
-    val ref = DisposableWorkerBoundReference(A(3))
-
-    return worker.execute(TransferMode.SAFE, { Pair(ref, semaphore) }) { (ref, semaphore) ->
-        semaphore.increment()
-        while (semaphore.value < 2) {
-        }
-
-        GC.collect()
-        ref
-    }
-}
-
-@Test
-fun testDoNotCollectInWorker() {
-    val semaphore: AtomicInt = AtomicInt(0)
-
-    val worker = Worker.start()
-
-    val future = doNotCollectInWorker(worker, semaphore)
-    while (semaphore.value < 1) {
-    }
-    GC.collect()
-    semaphore.increment()
-
-    val value = future.result
-    assertEquals(3, value.value.a)
-    worker.requestTermination().result
-}
-
-fun disposeInWorker(worker: Worker, semaphore: AtomicInt): Triple<WeakReference<DisposableWorkerBoundReference<A>>, WeakReference<A>, Future<AtomicReference<DisposableWorkerBoundReference<A>?>>> {
-    val (refOwner, refWeak, refValueWeak) = getOwnerAndWeaks(3)
-
-    val future = worker.execute(TransferMode.SAFE, { Pair(refOwner, semaphore) }) { (refOwner, semaphore) ->
-        semaphore.increment()
-        while (semaphore.value < 2) {
-        }
-
-        callDispose(refOwner)
-        GC.collect()
-        refOwner
-    }
-
-    while (semaphore.value < 1) {
-    }
-    // At this point worker is spinning on semaphore. refOwner still contains reference to
-    // DisposableWorkerBoundReference, so referent is kept alive.
-    GC.collect()
-    assertNotNull(refValueWeak.value)
-
-    return Triple(refWeak, refValueWeak, future)
-}
-
-@Test
-fun testDisposeInWorker() {
-    val semaphore: AtomicInt = AtomicInt(0)
-
-    val worker = Worker.start()
-
-    val (refWeak, refValueWeak, future) = disposeInWorker(worker, semaphore)
-    semaphore.increment()
-    val refOwner = future.result
-
-    // At this point refOwner still has a reference, but it's explicitly disposed,
-    // so referent is destroyed.
-    GC.collect()
-    assertNotNull(refWeak.value)
-    assertNull(refValueWeak.value)
-
-    worker.requestTermination().result
-}
-
-@Test
-fun testDisposeOnMainThreadAndAccessInWorker() {
-    val ref = DisposableWorkerBoundReference(A(3))
-    assertEquals(3, ref.value.a)
-
-    ref.dispose()
-
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, { ref }) { ref ->
-        var result = 0
-        assertFailsWith<IllegalStateException> {
-            result = ref.value.a
-        }
-        result
-    }
-
-    val value = future.result
-    assertEquals(0, value)
-    worker.requestTermination().result
-}
-
-@Test
-fun testDisposeInWorkerAndAccessOnMainThread() {
-    val ref = DisposableWorkerBoundReference(A(3))
-    assertEquals(3, ref.value.a)
-
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, { ref }) { ref ->
-        ref.dispose()
-    }
-
-    future.result
-    assertFailsWith<IllegalStateException> {
-        ref.value.a
-    }
-    worker.requestTermination().result
-}
-
-class B1 {
-    lateinit var b2: DisposableWorkerBoundReference<B2>
-}
-
-data class B2(val b1: DisposableWorkerBoundReference<B1>)
-
-fun createCyclicGarbage(): Triple<AtomicReference<DisposableWorkerBoundReference<B1>?>, WeakReference<B1>, WeakReference<B2>> {
-    val ref1 = DisposableWorkerBoundReference(B1())
-    val ref1Owner: AtomicReference<DisposableWorkerBoundReference<B1>?> = AtomicReference(ref1)
-    val ref1Weak = WeakReference(ref1.value)
-
-    val ref2 = DisposableWorkerBoundReference(B2(ref1))
-    val ref2Weak = WeakReference(ref2.value)
-
-    ref1.value.b2 = ref2
-
-    return Triple(ref1Owner, ref1Weak, ref2Weak)
-}
-
-@Test
-fun doesNotCollectCyclicGarbage() {
-    val (ref1Owner, ref1Weak, ref2Weak) = createCyclicGarbage()
-
-    ref1Owner.value = null
-    GC.collect()
-
-    // If these asserts fail, that means DisposableWorkerBoundReference managed to clean up cyclic garbage all by itself.
-    assertNotNull(ref1Weak.value)
-    assertNotNull(ref2Weak.value)
-}
-
-@Test
-fun collectCyclicGarbageWithExplicitDispose() {
-    val (ref1Owner, ref1Weak, ref2Weak) = createCyclicGarbage()
-
-    callDispose(ref1Owner)
-    GC.collect()
-
-    assertNull(ref1Weak.value)
-    assertNull(ref2Weak.value)
-}
-
-fun createCrossThreadCyclicGarbage(
-        worker: Worker
-): Triple<AtomicReference<DisposableWorkerBoundReference<B1>?>, WeakReference<B1>, WeakReference<B2>> {
-    val ref1 = DisposableWorkerBoundReference(B1())
-    val ref1Owner: AtomicReference<DisposableWorkerBoundReference<B1>?> = AtomicReference(ref1)
-    val ref1Weak = WeakReference(ref1.value)
-
-    val future = worker.execute(TransferMode.SAFE, { ref1 }) { ref1 ->
-        val ref2 = DisposableWorkerBoundReference(B2(ref1))
-        Pair(ref2, WeakReference(ref2.value))
-    }
-    val (ref2, ref2Weak) = future.result
-
-    ref1.value.b2 = ref2
-
-    return Triple(ref1Owner, ref1Weak, ref2Weak)
-}
-
-@Test
-fun doesNotCollectCrossThreadCyclicGarbage() {
-    val worker = Worker.start()
-
-    val (ref1Owner, ref1Weak, ref2Weak) = createCrossThreadCyclicGarbage(worker)
-
-    ref1Owner.value = null
-    GC.collect()
-    worker.execute(TransferMode.SAFE, {}) { GC.collect() }.result
-
-    // If these asserts fail, that means DisposableWorkerBoundReference managed to clean up cyclic garbage all by itself.
-    assertNotNull(ref1Weak.value)
-    assertNotNull(ref2Weak.value)
-
-    worker.requestTermination().result
-}
-
-@Test
-fun collectCrossThreadCyclicGarbageWithExplicitDispose() {
-    val worker = Worker.start()
-
-    val (ref1Owner, ref1Weak, ref2Weak) = createCrossThreadCyclicGarbage(worker)
-
-    callDispose(ref1Owner)
-    GC.collect()
-    worker.execute(TransferMode.SAFE, {}) { GC.collect() }.result
-
-    assertNull(ref1Weak.value)
-    assertNull(ref2Weak.value)
-
-    worker.requestTermination().result
-}
-
-@Test
-fun concurrentAccess() {
-    val workerCount = 10
-    val workerUnlocker = AtomicInt(0)
-
-    val ref = DisposableWorkerBoundReference(A(3))
-    assertEquals(3, ref.value.a)
-
-    val workers = Array(workerCount) {
-        Worker.start()
-    }
-    val futures = Array(workers.size) {
-        workers[it].execute(TransferMode.SAFE, { Pair(ref, workerUnlocker) }) { (ref, workerUnlocker) ->
-            while (workerUnlocker.value < 1) {
-            }
-
-            assertFailsWith<IncorrectDereferenceException> {
-                ref.value
-            }
-            Unit
-        }
-    }
-    workerUnlocker.increment()
-
-    for (future in futures) {
-        future.result
-    }
-
-    for (worker in workers) {
-        worker.requestTermination().result
-    }
-}
-
-@Test
-fun concurrentDispose() {
-    val workerCount = 10
-    val workerUnlocker = AtomicInt(0)
-
-    val ref = DisposableWorkerBoundReference(A(3))
-    assertEquals(3, ref.value.a)
-
-    val workers = Array(workerCount) {
-        Worker.start()
-    }
-    val futures = Array(workers.size) {
-        workers[it].execute(TransferMode.SAFE, { Pair(ref, workerUnlocker) }) { (ref, workerUnlocker) ->
-            while (workerUnlocker.value < 1) {
-            }
-
-            ref.dispose()
-        }
-    }
-    workerUnlocker.increment()
-
-    for (future in futures) {
-        future.result
-    }
-
-    assertFailsWith<IllegalStateException> {
-        ref.value.a
-    }
-
-    for (worker in workers) {
-        worker.requestTermination().result
-    }
-}
-
-@Test
-fun concurrentDisposeAndAccess() {
-    val workerUnlocker = AtomicInt(0)
-
-    val ref = DisposableWorkerBoundReference(A(3))
-    assertEquals(3, ref.value.a)
-
-    val worker = Worker.start()
-    val future = worker.execute(TransferMode.SAFE, { Pair(ref, workerUnlocker) }) { (ref, workerUnlocker) ->
-        while (workerUnlocker.value < 1) {
-        }
-
-        ref.dispose()
-    }
-    workerUnlocker.increment()
-
-    var result = 0
-    // This is a race, but it should either get value successfully or get IllegalStateException.
-    // Any other kind of failure is unacceptable.
-    try {
-        result = ref.value.a
-    } catch (e: IllegalStateException) {
-        result = 3
-    }
-    assertEquals(3, result)
-
-    future.result
-    worker.requestTermination().result
-}
@@ -7,6 +7,33 @@
 #include "MemoryPrivate.hpp"
 #include "MemorySharedRefs.hpp"
 #include "Runtime.h"
+#include "Types.h"
+
+extern "C" {
+// Returns a string describing object at `address` of type `typeInfo`.
+OBJ_GETTER(DescribeObjectForDebugging, KConstNativePtr typeInfo, KConstNativePtr address);
+}  // extern "C"
+
+namespace {
+
+inline bool isForeignRefAccessible(ObjHeader* object, ForeignRefContext context) {
+  if (!Kotlin_hasRuntime()) {
+    // So the object is either unowned or shared.
+    // In the former case initialized runtime is required to throw exceptions
+    // in the latter case -- to provide proper execution context for caller.
+    Kotlin_initRuntimeIfNeeded();
+  }
+
+  return IsForeignRefAccessible(object, context);
+}
+
+RUNTIME_NORETURN inline void throwIllegalSharingException(ObjHeader* object) {
+  // TODO: add some info about the context.
+  // Note: retrieving 'type_info()' is supposed to be correct even for unowned object.
+  ThrowIllegalObjectSharingException(object->type_info(), object);
+}
+
+}  // namespace

 void KRefSharedHolder::initLocal(ObjHeader* obj) {
  RuntimeAssert(obj != nullptr, "must not be null");
@@ -21,24 +48,18 @@ void KRefSharedHolder::init(ObjHeader* obj) {
 }

 ObjHeader* KRefSharedHolder::ref() const {
-  ensureRefAccessible();
-  AdoptReferenceFromSharedVariable(obj_);
-  return obj_;
+  if (auto* result = refOrNull())
+    return result;
+
+  throwIllegalSharingException(obj_);
 }

-static inline void ensureForeignRefAccessible(ObjHeader* object, ForeignRefContext context) {
-  if (!Kotlin_hasRuntime()) {
-    // So the object is either unowned or shared.
-    // In the former case initialized runtime is required to throw the exception below,
-    // in the latter case -- to provide proper execution context for caller.
-    Kotlin_initRuntimeIfNeeded();
-  }
-
-  if (!IsForeignRefAccessible(object, context)) {
-    // TODO: add some info about the context.
-    // Note: retrieving 'type_info()' is supposed to be correct even for unowned object.
-    ThrowIllegalObjectSharingException(object->type_info(), object);
+ObjHeader* KRefSharedHolder::refOrNull() const {
+  if (!isRefAccessible()) {
+    return nullptr;
  }
+  AdoptReferenceFromSharedVariable(obj_);
+  return obj_;
 }

 void KRefSharedHolder::dispose() const {
@@ -50,8 +71,13 @@ void KRefSharedHolder::dispose() const {
  DeinitForeignRef(obj_, context_);
 }

-void KRefSharedHolder::ensureRefAccessible() const {
-  ensureForeignRefAccessible(obj_, context_);
+OBJ_GETTER0(KRefSharedHolder::describe) const {
+  // Note: retrieving 'type_info()' is supposed to be correct even for unowned object.
+  RETURN_RESULT_OF(DescribeObjectForDebugging, obj_->type_info(), obj_);
+}
+
+bool KRefSharedHolder::isRefAccessible() const {
+  return isForeignRefAccessible(obj_, context_);
 }

 void BackRefFromAssociatedObject::initAndAddRef(ObjHeader* obj) {
@@ -106,7 +132,9 @@ ObjHeader* BackRefFromAssociatedObject::ref() const {
 }

 void BackRefFromAssociatedObject::ensureRefAccessible() const {
-  ensureForeignRefAccessible(obj_, context_);
+  if (!isForeignRefAccessible(obj_, context_)) {
+    throwIllegalSharingException(obj_);
+  }
 }

 extern "C" {
@@ -125,4 +153,4 @@ RUNTIME_NOTHROW void KRefSharedHolder_dispose(const KRefSharedHolder* holder) {
 ObjHeader* KRefSharedHolder_ref(const KRefSharedHolder* holder) {
  return holder->ref();
 }
-} // extern "C"
+} // extern "C"
@@ -6,6 +6,8 @@
 #ifndef RUNTIME_MEMORYSHAREDREFS_HPP
 #define RUNTIME_MEMORYSHAREDREFS_HPP

+#include <type_traits>
+
 #include "Memory.h"

 class KRefSharedHolder {
@@ -15,16 +17,22 @@ class KRefSharedHolder {
  void init(ObjHeader* obj);

  ObjHeader* ref() const;
+  ObjHeader* refOrNull() const;

  void dispose() const;

+  OBJ_GETTER0(describe) const;
+
 private:
  ObjHeader* obj_;
  ForeignRefContext context_;

-  void ensureRefAccessible() const;
+  bool isRefAccessible() const;
 };

+static_assert(std::is_trivially_destructible<KRefSharedHolder>::value,
+    "KRefSharedHolder destructor is not guaranteed to be called.");
+
 class BackRefFromAssociatedObject {
 public:
  void initAndAddRef(ObjHeader* obj);
@@ -49,4 +57,7 @@ class BackRefFromAssociatedObject {
  void ensureRefAccessible() const;
 };

+static_assert(std::is_trivially_destructible<BackRefFromAssociatedObject>::value,
+    "BackRefFromAssociatedObject destructor is not guaranteed to be called.");
+
 #endif // RUNTIME_MEMORYSHAREDREFS_HPP
@@ -38,7 +38,11 @@ KNativePtr Kotlin_WorkerBoundReference_create(KRef value) {
 }

 OBJ_GETTER(Kotlin_WorkerBoundReference_deref, KNativePtr holder) {
-  RETURN_OBJ(reinterpret_cast<KRefSharedHolder*>(holder)->ref());
+  RETURN_OBJ(reinterpret_cast<KRefSharedHolder*>(holder)->refOrNull());
+}
+
+OBJ_GETTER(Kotlin_WorkerBoundReference_describe, KNativePtr holder) {
+  RETURN_RESULT_OF0(reinterpret_cast<KRefSharedHolder*>(holder)->describe);
 }

 }
@@ -5,7 +5,9 @@

 package kotlin.native.concurrent

+import kotlin.native.internal.DescribeObjectForDebugging
 import kotlin.native.internal.ExportForCppRuntime
+import kotlin.native.internal.debugDescription
 import kotlin.native.identityHashCode
 import kotlin.reflect.KClass
 import kotlinx.cinterop.*
@@ -92,17 +94,9 @@ internal fun ThrowInvalidMutabilityException(where: Any): Nothing {

@ExportForCppRuntime
 internal fun ThrowIllegalObjectSharingException(typeInfo: NativePtr, address: NativePtr) {
-    val kClass = kotlin.native.internal.KClassImpl<Any>(typeInfo)
-    val description = debugDescription(kClass, address.toLong().toInt())
+    val description = DescribeObjectForDebugging(typeInfo, address)
    throw IncorrectDereferenceException("illegal attempt to access non-shared $description from other thread")
 }

-private fun debugDescription(kClass: KClass<*>, identity: Int): String {
-    val className = kClass.qualifiedName ?: kClass.simpleName ?: "<object>"
-    val unsignedIdentity = identity.toLong() and 0xffffffffL
-    val identityStr = unsignedIdentity.toString(16)
-    return "$className@$identityStr"
-}
-
@SymbolName("Kotlin_AtomicReference_checkIfFrozen")
 external internal fun checkIfFrozen(ref: Any?)
@@ -11,16 +11,20 @@ import kotlin.native.internal.*
 external private fun createWorkerBoundReference(value: Any): NativePtr

@SymbolName("Kotlin_WorkerBoundReference_deref")
-external private fun derefWorkerBoundReference(ref: NativePtr): Any
+external private fun derefWorkerBoundReference(ref: NativePtr): Any?
+
+@SymbolName("Kotlin_WorkerBoundReference_describe")
+external private fun describeWorkerBoundReference(ref: NativePtr): String

 /**
- * A frozen shared reference to a Kotlin object
+ * A frozen shared reference to a Kotlin object.
 *
 * Can be safely passed between workers, but [value] can only be accessed on the worker [WorkerBoundReference] was created on,
- * unless the referred object is frozen too
+ * unless the referred object is frozen too.
 *
- * Note: Garbage collector currently cannot free any reference cycles with [WorkerBoundReference] or [DisposableWorkerBoundReference] in them.
- * Consider using [DisposableWorkerBoundReference] to manually resolve cycles with explicit calls to [DisposableWorkerBoundReference.dispose]
+ * Note: Garbage collector currently cannot free any reference cycles with [WorkerBoundReference] in them.
+ * To resolve such cycles consider using [AtomicReference<WorkerBoundReference?>] which can be explicitly
+ * nulled out.
 */
@Frozen
@NoReorderFields
@@ -28,44 +32,21 @@ external private fun derefWorkerBoundReference(ref: NativePtr): Any
 public class WorkerBoundReference<out T : Any>(value: T) {

    private val ptr = createWorkerBoundReference(value)
+    private val ownerName = Worker.current.name
+
+    private val valueDescription
+        get() = describeWorkerBoundReference(ptr)

    /**
     * The referenced value.
-     * @throws IncorrectDereferenceException if referred object is not frozen and current worker is different from the one created [this]
+     * @throws IncorrectDereferenceException if referred object is not frozen and current worker is different from the one created [this].
     */
    val value: T
-        get() = @Suppress("UNCHECKED_CAST") (derefWorkerBoundReference(ptr) as T)
-}
-
-/**
- * A frozen shared reference to a Kotlin object
- *
- * Can be safely passed between workers, but [value] can only be accessed on the worker [DisposableWorkerBoundReference] was created on,
- * unless the referred object is frozen too
- * Garbage collector currently cannot free any reference cycles with [WorkerBoundReference] or [DisposableWorkerBoundReference] in them.
- * Call [dispose] manually to resolve cycles
- *
- * Note: This class has more expensive [value] getter than [WorkerBoundReference]. If you don't have reference
- * cycles with [WorkerBoundReference] or [DisposableWorkerBoundReference], consider using [WorkerBoundReference]
- */
-@Frozen
-public class DisposableWorkerBoundReference<out T : Any>(value: T) {
-
-    private val ref: AtomicReference<WorkerBoundReference<T>?> = AtomicReference(WorkerBoundReference(value))
+        get() = valueOrNull ?: throw IncorrectDereferenceException("illegal attempt to access non-shared $valueDescription bound to `$ownerName` from `${Worker.current.name}`")

    /**
-     * Free the reference. Any call to [DisposableWorkerBoundReference.value] after that will
-     * fail with [IllegalStateException]
+     * The referenced value or null if referred object is not frozen and current worker is different from the one created [this].
     */
-    fun dispose() {
-        ref.value = null
-    }
-
-    /**
-     * The referenced value.
-     * @throws IncorrectDereferenceException if referred object is not frozen and current worker is different from the one created [this]
-     * @throws IllegalStateException if [DisposableWorkerBoundReference.dispose] was called on this reference.
-     */
-    val value: T
-        get() = ref.value?.value ?: throw IllegalStateException("illegal attempt to dereference disposed $this")
+    val valueOrNull: T?
+        get() = @Suppress("UNCHECKED_CAST") (derefWorkerBoundReference(ptr) as T?)
 }
@@ -0,0 +1,21 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the LICENSE file.
+ */
+
+package kotlin.native.internal
+
+import kotlin.reflect.KClass
+
+@ExportForCppRuntime
+internal fun DescribeObjectForDebugging(typeInfo: NativePtr, address: NativePtr): String {
+    val kClass = kotlin.native.internal.KClassImpl<Any>(typeInfo)
+    return debugDescription(kClass, address.toLong().toInt())
+}
+
+internal fun debugDescription(kClass: KClass<*>, identity: Int): String {
+    val className = kClass.qualifiedName ?: kClass.simpleName ?: "<object>"
+    val unsignedIdentity = identity.toLong() and 0xffffffffL
+    val identityStr = unsignedIdentity.toString(16)
+    return "$className@$identityStr"
+}