Fixed unlimited channel select onSend on closed channel

It was hanging not being able to properly see that the channel was
already closed at that send attempt should fail.

Author: elizarov

kotlinx-coroutines-core/common/src/channels/AbstractChannel.kt

@@ -112,9 +112,10 @@ internal abstract class AbstractSendChannel<E> : SendChannel<E> {
         queue: LockFreeLinkedListHead,
         element: E
     ) : AddLastDesc<SendBuffered<E>>(queue, SendBuffered(element)) {
-        override fun failure(affected: LockFreeLinkedListNode, next: Any): Any? {
-            if (affected is ReceiveOrClosed<*>) return OFFER_FAILED
-            return null
+        override fun failure(affected: LockFreeLinkedListNode, next: Any): Any? = when (affected) {
+            is Closed<*> -> affected
+            is ReceiveOrClosed<*> -> OFFER_FAILED
+            else -> null
         }
     }
 
@@ -332,10 +333,10 @@ internal abstract class AbstractSendChannel<E> : SendChannel<E> {
     ) : RemoveFirstDesc<ReceiveOrClosed<E>>(queue) {
         @JvmField var resumeToken: Any? = null
 
-        override fun failure(affected: LockFreeLinkedListNode, next: Any): Any? {
-            if (affected !is ReceiveOrClosed<*>) return OFFER_FAILED
-            if (affected is Closed<*>) return affected
-            return null
+        override fun failure(affected: LockFreeLinkedListNode, next: Any): Any? = when (affected) {
+            is Closed<*> -> affected
+            !is ReceiveOrClosed<*> -> OFFER_FAILED
+            else -> null
         }
 
         override fun validatePrepared(node: ReceiveOrClosed<E>): Boolean {
@@ -633,10 +634,10 @@ internal abstract class AbstractChannel<E> : AbstractSendChannel<E>(), Channel<E
         @JvmField var resumeToken: Any? = null
         @JvmField var pollResult: E? = null
 
-        override fun failure(affected: LockFreeLinkedListNode, next: Any): Any? {
-            if (affected is Closed<*>) return affected
-            if (affected !is Send) return POLL_FAILED
-            return null
+        override fun failure(affected: LockFreeLinkedListNode, next: Any): Any? = when (affected) {
+            is Closed<*> -> affected
+            !is Send -> POLL_FAILED
+            else -> null
         }
 
         @Suppress("UNCHECKED_CAST")

kotlinx-coroutines-core/common/test/selects/SelectLinkedListChannelTest.kt

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2016-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.coroutines.selects
+
+import kotlinx.coroutines.*
+import kotlinx.coroutines.channels.*
+import kotlin.test.*
+
+class SelectLinkedListChannelTest : TestBase() {
+    @Test
+    fun testSelectSendWhenClosed() = runTest {
+        expect(1)
+        val c = Channel<Int>(Channel.UNLIMITED)
+        c.send(1) // enqueue buffered element
+        c.close() // then close
+        assertFailsWith<ClosedSendChannelException> {
+            // select sender should fail
+            expect(2)
+            select {
+                c.onSend(2) {
+                    expectUnreached()
+                }
+            }
+        }
+        finish(3)
+    }
+}

kotlinx-coroutines-core/common/test/selects/SelectRendezvousChannelTest.kt

@@ -403,6 +403,29 @@ class SelectRendezvousChannelTest : TestBase() {
         finish(10)
     }
 
+    @Test
+    fun testSelectSendWhenClosed() = runTest {
+        expect(1)
+        val c = Channel<Int>(Channel.RENDEZVOUS)
+        val sender = launch(start = CoroutineStart.UNDISPATCHED) {
+            expect(2)
+            c.send(1) // enqueue sender
+            expectUnreached()
+        }
+        c.close() // then close
+        assertFailsWith<ClosedSendChannelException> {
+            // select sender should fail
+            expect(3)
+            select {
+                c.onSend(2) {
+                    expectUnreached()
+                }
+            }
+        }
+        sender.cancel()
+        finish(4)
+    }
+
     // only for debugging
     internal fun <R> SelectBuilder<R>.default(block: suspend () -> R) {
         this as SelectBuilderImpl // type assertion