Add ChannelLFStressTest

It tests lock-freedom on send and receive operations on rendezvous
and conflated channels. The test is comprehensive enough to fail on
buffered channels (which are currently not lock-free) and will help us
ensuring that lock-freedom property is not lost while channels are
being improved and refactored.

Author: elizarov

gradle.properties

@@ -1,11 +1,15 @@
+#
+# Copyright 2016-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+#
+
 # Kotlin
 version=1.3.0-SNAPSHOT
 group=org.jetbrains.kotlinx
 kotlin_version=1.3.50
 
 # Dependencies
 junit_version=4.12
-atomicfu_version=0.12.10
+atomicfu_version=0.12.11
 html_version=0.6.8
 lincheck_version=2.0
 dokka_version=0.9.16-rdev-2-mpp-hacks

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

@@ -0,0 +1,110 @@
+/*
+ * Copyright 2016-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.coroutines.channels
+
+import kotlinx.atomicfu.*
+import kotlinx.coroutines.*
+import java.util.concurrent.atomic.AtomicLong
+import java.util.concurrent.atomic.AtomicLongArray
+import kotlin.math.*
+import kotlin.test.*
+
+/**
+ * Tests lock-freedom of send and receive operations on rendezvous and conflated channels.
+ * There is a single channel with two sender and two receiver threads.
+ * When one sender or receiver gets suspended at most one other operation is allowed to cease having progress
+ * (`allowSuspendedThreads = 1`).
+ *
+ * **Note**: In the current implementation buffered channels are not lock-free, so this test would fail
+ *           if channel is created with a buffer.
+ */
+class ChannelLFStressTest : TestBase() {
+    private val nSeconds = 5 * stressTestMultiplier
+    private val env = LockFreedomTestEnvironment("ChannelLFStressTest", allowSuspendedThreads = 1)
+    private lateinit var channel: Channel<Long>
+
+    private val sendIndex = AtomicLong()
+    private val receiveCount = AtomicLong()
+    private val duplicateCount = AtomicLong()
+
+    private val nCheckedSize = 10_000_000
+    private val nChecked = (nCheckedSize * Long.SIZE_BITS).toLong()
+    private val receivedBits = AtomicLongArray(nCheckedSize) // bit set of received values
+
+    @Test
+    fun testRendezvousLockFreedom() {
+        channel = Channel()
+        performLockFreedomTest()
+        // ensure that all sent were received
+        checkAllReceived()
+    }
+
+    @Test
+    fun testConflatedLockFreedom() {
+        // This test does not really verify that all sent elements were received
+        // and checks only LF property
+        channel = Channel(Channel.CONFLATED)
+        performLockFreedomTest()
+    }
+
+    private fun performLockFreedomTest() {
+        env.onCompletion { channel.close() }
+        repeat(2) { env.testThread { sender() } }
+        repeat(2) { env.testThread { receiver() } }
+        env.performTest(nSeconds) {
+            println("Sent: $sendIndex, Received: $receiveCount, dups: $duplicateCount")
+        }
+        // ensure no duplicates
+        assertEquals(0L, duplicateCount.get())
+    }
+
+    private fun checkAllReceived() {
+        for (i in 0 until min(sendIndex.get(), nChecked)) {
+            assertTrue(isReceived(i))
+        }
+    }
+
+    private suspend fun sender() {
+        val value = sendIndex.getAndIncrement()
+        try {
+            channel.send(value)
+        } catch (e: ClosedSendChannelException) {
+            check(env.isCompleted) // expected when test was completed
+            markReceived(value) // fake received (actually failed to send)
+        }
+    }
+
+    private suspend fun receiver() {
+        val value = try {
+            channel.receive()
+        } catch (e: ClosedReceiveChannelException) {
+            check(env.isCompleted) // expected when test was completed
+            return
+        }
+        receiveCount.incrementAndGet()
+        markReceived(value)
+    }
+
+    private fun markReceived(value: Long) {
+        if (value >= nChecked) return // too big
+        val index = (value / Long.SIZE_BITS).toInt()
+        val mask = 1L shl (value % Long.SIZE_BITS).toInt()
+        while (true) {
+            val bits = receivedBits.get(index)
+            if (bits and mask != 0L) {
+                duplicateCount.incrementAndGet()
+                break
+            }
+            if (receivedBits.compareAndSet(index, bits, bits or mask)) break
+        }
+    }
+
+    private fun isReceived(value: Long): Boolean {
+        val index = (value / Long.SIZE_BITS).toInt()
+        val mask = 1L shl (value % Long.SIZE_BITS).toInt()
+        val bits = receivedBits.get(index)
+        return bits and mask != 0L
+    }
+}