Support of new K/N memory model

* Dispatchers.Default backed by pool of workers on Linux and by global_queue on iOS-like
* Implementation of Dispatchers.Main that uses main queue on iOS and default dispatcher on other platforms (#2858)
* Introduced newSingleThreadDispatcher and newFixedThreadPoolDispatcher
* Use proper reentrant locking and CoW arrays on new memory model, make TestBase _almost_ race-free
* More thread-safety in Native counterpart and one more test from native-mt
* Source-set sharing for tests shared between JVM and K/N
* Wrap Obj-C interop into autorelease pool to avoid memory leaks

build.gradle

@@ -139,6 +139,7 @@ allprojects {
          */
         google()
         mavenCentral()
+        maven { url "https://maven.pkg.jetbrains.space/kotlin/p/kotlin/dev" }
     }
 }
 
@@ -169,6 +170,10 @@ configure(subprojects.findAll { !sourceless.contains(it.name) }) {
         // Remove null assertions to get smaller bytecode on Android
         kotlinOptions.freeCompilerArgs += ["-Xno-param-assertions", "-Xno-receiver-assertions", "-Xno-call-assertions"]
     }
+
+    tasks.withType(org.jetbrains.kotlin.gradle.tasks.AbstractKotlinNativeCompile) {
+        kotlinOptions.freeCompilerArgs += ["-memory-model", "experimental"]
+    }
 }
 
 if (build_snapshot_train) {

gradle.properties

@@ -57,3 +57,4 @@ org.gradle.jvmargs=-Xmx4g
 
 kotlin.mpp.enableCompatibilityMetadataVariant=true
 kotlin.mpp.stability.nowarn=true
+kotlin.native.cacheKind=none

kotlinx-coroutines-core/build.gradle

@@ -91,9 +91,11 @@ kotlin {
             binaries {
                 // Test for memory leaks using a special entry point that does not exit but returns from main
                 binaries.getTest("DEBUG").freeCompilerArgs += ["-e", "kotlinx.coroutines.mainNoExit"]
+                binaries.getTest("DEBUG").optimized = true
                 // Configure a separate test where code runs in background
                 test("background", [org.jetbrains.kotlin.gradle.plugin.mpp.NativeBuildType.DEBUG]) {
                     freeCompilerArgs += ["-e", "kotlinx.coroutines.mainBackground"]
+                    optimized = true
                 }
             }
             testRuns {

kotlinx-coroutines-core/common/src/CoroutineDispatcher.kt

@@ -59,6 +59,7 @@ public abstract class CoroutineDispatcher :
      * This method should generally be exception-safe. An exception thrown from this method
      * may leave the coroutines that use this dispatcher in the inconsistent and hard to debug state.
      */
+    @ExperimentalCoroutinesApi
     public open fun isDispatchNeeded(context: CoroutineContext): Boolean = true
 
     /**

kotlinx-coroutines-core/common/src/EventLoop.common.kt

@@ -271,7 +271,7 @@ internal abstract class EventLoopImplBase: EventLoopImplPlatform(), Delay {
         // then process one event from queue
         val task = dequeue()
         if (task != null) {
-            task.run()
+            platformAutoreleasePool { task.run() }
             return 0
         }
         return nextTime
@@ -526,3 +526,13 @@ internal expect object DefaultExecutor {
     public fun enqueue(task: Runnable)
 }
 
+/**
+ * Used by Darwin targets to wrap a [Runnable.run] call in an Objective-C Autorelease Pool. It is a no-op on JVM, JS and
+ * non-Darwin native targets.
+ *
+ * Coroutines on Darwin targets can call into the Objective-C world, where a callee may push a to-be-returned object to
+ * the Autorelease Pool, so as to avoid a premature ARC release before it reaches the caller. This means the pool must
+ * be eventually drained to avoid leaks. Since Kotlin Coroutines does not use [NSRunLoop], which provides automatic
+ * pool management, it must manage the pool creation and pool drainage manually.
+ */
+internal expect inline fun platformAutoreleasePool(crossinline block: () -> Unit)

kotlinx-coroutines-core/common/test/EmptyContext.kt

@@ -7,10 +7,6 @@ package kotlinx.coroutines
 import kotlinx.coroutines.intrinsics.*
 import kotlin.coroutines.*
 
-suspend fun <T> withEmptyContext(block: suspend () -> T): T {
-    val baseline = Result.failure<T>(IllegalStateException("Block was suspended"))
-    var result: Result<T> = baseline
-    block.startCoroutineUnintercepted(Continuation(EmptyCoroutineContext) { result = it })
-    while (result == baseline) yield()
-    return result.getOrThrow()
+suspend fun <T> withEmptyContext(block: suspend () -> T): T = suspendCoroutine { cont ->
+    block.startCoroutineUnintercepted(Continuation(EmptyCoroutineContext) { cont.resumeWith(it) })
 }

kotlinx-coroutines-core/common/test/TestBase.common.kt

@@ -12,6 +12,7 @@ import kotlin.test.*
 
 public expect val isStressTest: Boolean
 public expect val stressTestMultiplier: Int
+public expect val stressTestMultiplierSqrt: Int
 
 /**
  * The result of a multiplatform asynchronous test.
@@ -20,6 +21,10 @@ public expect val stressTestMultiplier: Int
 @Suppress("NO_ACTUAL_FOR_EXPECT")
 public expect class TestResult
 
+public expect val isNative: Boolean
+// "Speedup" native stress tests
+public val stressTestNativeDivisor = if (isNative) 10 else 1
+
 public expect open class TestBase constructor() {
     /*
      * In common tests we emulate parameterized tests

kotlinx-coroutines-core/common/test/flow/FlowInvariantsTest.kt

@@ -235,7 +235,7 @@ class FlowInvariantsTest : TestBase() {
             }
             expectUnreached()
         } catch (e: IllegalStateException) {
-            assertTrue(e.message!!.contains("Flow invariant is violated"))
+            assertTrue(e.message!!.contains("Flow invariant is violated"), "But had: ${e.message}")
             finish(2)
         }
     }

kotlinx-coroutines-core/concurrent/src/Builders.concurrent.kt

@@ -0,0 +1,14 @@
+/*
+ * Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.coroutines
+
+import kotlin.coroutines.*
+
+/**
+ * Runs a new coroutine and **blocks** the current thread until its completion.
+ * This function should not be used from a coroutine. It is designed to bridge regular blocking code
+ * to libraries that are written in suspending style, to be used in `main` functions and in tests.
+ */
+public expect fun <T> runBlocking(context: CoroutineContext = EmptyCoroutineContext, block: suspend CoroutineScope.() -> T): T

kotlinx-coroutines-core/concurrent/src/MultithreadedDispatchers.common.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.coroutines
+
+@ExperimentalCoroutinesApi
+public expect fun newSingleThreadContext(name: String): MultithreadedDispatcher
+
+@ExperimentalCoroutinesApi
+public expect fun newFixedThreadPoolContext(nThreads: Int, name: String): MultithreadedDispatcher
+
+/**
+ * A coroutine dispatcher that is confined to a single thread.
+ */
+@ExperimentalCoroutinesApi
+public expect abstract class MultithreadedDispatcher : CoroutineDispatcher {
+
+    /**
+     * Closes this coroutine dispatcher and shuts down its thread.
+     */
+    public abstract fun close()
+}

kotlinx-coroutines-core/jvm/src/internal/LockFreeLinkedList.kt → kotlinx-coroutines-core/concurrent/src/internal/LockFreeLinkedList.kt

@@ -7,6 +7,7 @@ package kotlinx.coroutines.internal
 
 import kotlinx.atomicfu.*
 import kotlinx.coroutines.*
+import kotlin.jvm.*
 
 private typealias Node = LockFreeLinkedListNode
 
@@ -616,7 +617,7 @@ public actual open class LockFreeLinkedListNode {
         assert { next === this._next.value }
     }
 
-    override fun toString(): String = "${this::class.java.simpleName}@${Integer.toHexString(System.identityHashCode(this))}"
+    override fun toString(): String = "${this::classSimpleName}@${this.hexAddress}"
 }
 
 private class Removed(@JvmField val ref: Node) {

kotlinx-coroutines-core/concurrent/test/AbstractDispatcherConcurrencyTest.kt

@@ -0,0 +1,54 @@
+package kotlinx.coroutines
+
+import kotlinx.coroutines.channels.*
+import kotlin.test.*
+
+/*
+ * Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+abstract class AbstractDispatcherConcurrencyTest : TestBase() {
+
+   public abstract val dispatcher: CoroutineDispatcher
+
+    @Test
+    fun testLaunchAndJoin() {
+        expect(1)
+        var capturedMutableState = 0
+        val job = GlobalScope.launch(dispatcher) {
+            ++capturedMutableState
+            expect(2)
+        }
+        runBlocking { job.join() }
+        assertEquals(1, capturedMutableState)
+        finish(3)
+    }
+
+    @Test
+    fun testDispatcherIsActuallyMultithreaded() {
+        val channel = Channel<Int>()
+        GlobalScope.launch(dispatcher) {
+            channel.send(42)
+        }
+
+        var result = ChannelResult.failure<Int>()
+        while (!result.isSuccess) {
+            result = channel.tryReceive()
+            // Block the thread, wait
+        }
+        // Delivery was successful, let's check it
+        assertEquals(42, result.getOrThrow())
+    }
+
+    @Test
+    fun testDelayInDefaultDispatcher() {
+        expect(1)
+        val job = GlobalScope.launch(dispatcher) {
+            expect(2)
+            delay(100)
+            expect(3)
+        }
+        runBlocking { job.join() }
+        finish(4)
+    }
+}

kotlinx-coroutines-core/jvm/test/AtomicCancellationTest.kt → kotlinx-coroutines-core/concurrent/test/AtomicCancellationTest.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ * Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
  */
 
 package kotlinx.coroutines
@@ -142,4 +142,4 @@ class AtomicCancellationTest : TestBase() {
         yield() // to jobToJoin & canceller
         expect(6)
     }
-}
+}

kotlinx-coroutines-core/concurrent/test/ConcurrentExceptionsStressTest.kt

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2016-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.coroutines
+
+import kotlinx.coroutines.exceptions.*
+import kotlin.test.*
+
+class ConcurrentExceptionsStressTest : TestBase() {
+    private val nWorkers = 4
+    private val nRepeat = 1000 * stressTestMultiplier
+
+    private val workers = Array(nWorkers) { index ->
+        newSingleThreadContext("JobExceptionsStressTest-$index")
+    }
+
+    @AfterTest
+    fun tearDown() {
+        workers.forEach {
+            it.close()
+        }
+    }
+
+    @Test
+    fun testStress() = runTest {
+        repeat(nRepeat) {
+            testOnce()
+        }
+    }
+
+    @Suppress("SuspendFunctionOnCoroutineScope") // workaround native inline fun stacktraces
+    private suspend fun CoroutineScope.testOnce() {
+        val deferred = async(NonCancellable) {
+            repeat(nWorkers) { index ->
+                // Always launch a coroutine even if parent job was already cancelled (atomic start)
+                launch(workers[index], start = CoroutineStart.ATOMIC) {
+                    randomWait()
+                    throw StressException(index)
+                }
+            }
+        }
+        deferred.join()
+        assertTrue(deferred.isCancelled)
+        val completionException = deferred.getCompletionExceptionOrNull()
+        val cause = completionException as? StressException
+            ?: unexpectedException("completion", completionException)
+        val suppressed = cause.suppressed
+        val indices = listOf(cause.index) + suppressed.mapIndexed { index, e ->
+            (e as? StressException)?.index ?: unexpectedException("suppressed $index", e)
+        }
+        repeat(nWorkers) { index ->
+            assertTrue(index in indices, "Exception $index is missing: $indices")
+        }
+        assertEquals(nWorkers, indices.size, "Duplicated exceptions in list: $indices")
+    }
+
+    private fun unexpectedException(msg: String, e: Throwable?): Nothing {
+        e?.printStackTrace()
+        throw IllegalStateException("Unexpected $msg exception", e)
+    }
+
+    private class StressException(val index: Int) : SuppressSupportingThrowable()
+}
+

kotlinx-coroutines-core/concurrent/test/ConcurrentTestUtilities.common.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.coroutines.exceptions
+
+import kotlinx.coroutines.*
+
+internal expect open class SuppressSupportingThrowable() : Throwable
+expect val Throwable.suppressed: Array<Throwable>
+expect fun Throwable.printStackTrace()
+
+expect fun randomWait()
+
+expect fun currentThreadName(): String
+
+inline fun MultithreadedDispatcher.use(block: (MultithreadedDispatcher) -> Unit) {
+    try {
+        block(this)
+    } finally {
+        close()
+    }
+}

kotlinx-coroutines-core/concurrent/test/DefaultDispatcherConcurrencyTest.kt

@@ -0,0 +1,8 @@
+/*
+ * Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+package kotlinx.coroutines
+
+class DefaultDispatcherConcurrencyTest : AbstractDispatcherConcurrencyTest() {
+    override val dispatcher: CoroutineDispatcher = Dispatchers.Default
+}

kotlinx-coroutines-core/jvm/test/JobStructuredJoinStressTest.kt → kotlinx-coroutines-core/concurrent/test/JobStructuredJoinStressTest.kt

@@ -1,10 +1,9 @@
 /*
- * Copyright 2016-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ * Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
  */
 
-package kotlinx.coroutines
-
-import org.junit.*
+import kotlinx.coroutines.*
+import kotlin.test.*
 import kotlin.coroutines.*
 
 /**
@@ -61,4 +60,4 @@ class JobStructuredJoinStressTest : TestBase() {
         }
         finish(2 + nRepeats)
     }
-}
+}