Moved ChannelAtomicCancelStressTest to newFixedThreadPoolContext

Hopefully, this is going to make this test less flaky (more stable)
due to more predictably scheduling of two stressed tasks onto two
different core and, at the time, increases quality of the test
by stressing multi-threaded channel operation more.

Author: elizarov

kotlinx-coroutines-core/jvm/test/channels/ChannelAtomicCancelStressTest.kt

@@ -24,9 +24,12 @@ class ChannelAtomicCancelStressTest(private val kind: TestChannelKind) : TestBas
         fun params(): Collection<Array<Any>> = TestChannelKind.values().map { arrayOf<Any>(it) }
     }
 
-    private val TEST_DURATION = 3000L * stressTestMultiplier
+    private val TEST_DURATION = 1000L * stressTestMultiplier
 
-    val channel = kind.create()
+    private val dispatcher = newFixedThreadPoolContext(2, "ChannelAtomicCancelStressTest")
+    private val scope = CoroutineScope(dispatcher)
+
+    private val channel = kind.create()
     private val senderDone = Channel<Boolean>(1)
     private val receiverDone = Channel<Boolean>(1)
 
@@ -44,6 +47,11 @@ class ChannelAtomicCancelStressTest(private val kind: TestChannelKind) : TestBas
     lateinit var sender: Job
     lateinit var receiver: Job
 
+    @After
+    fun tearDown() {
+        dispatcher.close()
+    }
+
     fun fail(e: Throwable) = failed.compareAndSet(null, e)
 
     private inline fun cancellable(done: Channel<Boolean>, block: () -> Unit) {
@@ -95,7 +103,7 @@ class ChannelAtomicCancelStressTest(private val kind: TestChannelKind) : TestBas
     }
 
     private fun launchSender() {
-        sender = GlobalScope.launch(start = CoroutineStart.ATOMIC) {
+        sender = scope.launch(start = CoroutineStart.ATOMIC) {
             val rnd = Random()
             cancellable(senderDone) {
                 var counter = 0
@@ -120,7 +128,7 @@ class ChannelAtomicCancelStressTest(private val kind: TestChannelKind) : TestBas
     }
 
     private fun launchReceiver() {
-        receiver = GlobalScope.launch(start = CoroutineStart.ATOMIC) {
+        receiver = scope.launch(start = CoroutineStart.ATOMIC) {
             val rnd = Random()
             cancellable(receiverDone) {
                 while (true) {