Do not report exceptions raised in CoroutineDispatcher.dispatch as in…

…ternal errors (#4181)

Co-authored-by: Dmitry Khalanskiy <[email protected]>
Co-authored-by: Vsevolod Tolstopyatov <[email protected]>

Fixes #4091

integration-testing/src/jvmCoreTest/kotlin/ListAllCoroutineThrowableSubclassesTest.kt

@@ -26,6 +26,7 @@ class ListAllCoroutineThrowableSubclassesTest {
         "kotlinx.coroutines.internal.DiagnosticCoroutineContextException",
         "kotlinx.coroutines.internal.ExceptionSuccessfullyProcessed",
         "kotlinx.coroutines.CoroutinesInternalError",
+        "kotlinx.coroutines.DispatchException",
         "kotlinx.coroutines.channels.ClosedSendChannelException",
         "kotlinx.coroutines.channels.ClosedReceiveChannelException",
         "kotlinx.coroutines.flow.internal.ChildCancelledException",

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

@@ -225,7 +225,7 @@ public abstract class CoroutineDispatcher :
      * @suppress **This an internal API and should not be used from general code.**
      */
     @InternalCoroutinesApi
-    public open fun dispatchYield(context: CoroutineContext, block: Runnable): Unit = dispatch(context, block)
+    public open fun dispatchYield(context: CoroutineContext, block: Runnable): Unit = safeDispatch(context, block)
 
     /**
      * Returns a continuation that wraps the provided [continuation], thus intercepting all resumptions.

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

@@ -16,18 +16,19 @@ import kotlin.coroutines.*
  */
 @InternalCoroutinesApi
 public fun handleCoroutineException(context: CoroutineContext, exception: Throwable) {
+    val reportException = if (exception is DispatchException) exception.cause else exception
     // Invoke an exception handler from the context if present
     try {
         context[CoroutineExceptionHandler]?.let {
-            it.handleException(context, exception)
+            it.handleException(context, reportException)
             return
         }
     } catch (t: Throwable) {
-        handleUncaughtCoroutineException(context, handlerException(exception, t))
+        handleUncaughtCoroutineException(context, handlerException(reportException, t))
         return
     }
     // If a handler is not present in the context or an exception was thrown, fallback to the global handler
-    handleUncaughtCoroutineException(context, exception)
+    handleUncaughtCoroutineException(context, reportException)
 }
 
 internal fun handlerException(originalException: Throwable, thrownException: Throwable): Throwable {

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

@@ -26,7 +26,7 @@ public suspend fun yield(): Unit = suspendCoroutineUninterceptedOrReturn sc@ { u
     val context = uCont.context
     context.ensureActive()
     val cont = uCont.intercepted() as? DispatchedContinuation<Unit> ?: return@sc Unit
-    if (cont.dispatcher.isDispatchNeeded(context)) {
+    if (cont.dispatcher.safeIsDispatchNeeded(context)) {
         // this is a regular dispatcher -- do simple dispatchYield
         cont.dispatchYield(context, Unit)
     } else {

kotlinx-coroutines-core/common/src/internal/DispatchedContinuation.kt

@@ -187,10 +187,10 @@ internal class DispatchedContinuation<in T>(
 
     override fun resumeWith(result: Result<T>) {
         val state = result.toState()
-        if (dispatcher.isDispatchNeeded(context)) {
+        if (dispatcher.safeIsDispatchNeeded(context)) {
             _state = state
             resumeMode = MODE_ATOMIC
-            dispatcher.dispatch(context, this)
+            dispatcher.safeDispatch(context, this)
         } else {
             executeUnconfined(state, MODE_ATOMIC) {
                 withCoroutineContext(context, countOrElement) {
@@ -205,10 +205,10 @@ internal class DispatchedContinuation<in T>(
     @Suppress("NOTHING_TO_INLINE")
     internal inline fun resumeCancellableWith(result: Result<T>) {
         val state = result.toState()
-        if (dispatcher.isDispatchNeeded(context)) {
+        if (dispatcher.safeIsDispatchNeeded(context)) {
             _state = state
             resumeMode = MODE_CANCELLABLE
-            dispatcher.dispatch(context, this)
+            dispatcher.safeDispatch(context, this)
         } else {
             executeUnconfined(state, MODE_CANCELLABLE) {
                 if (!resumeCancelled(state)) {
@@ -249,6 +249,22 @@ internal class DispatchedContinuation<in T>(
         "DispatchedContinuation[$dispatcher, ${continuation.toDebugString()}]"
 }
 
+internal fun CoroutineDispatcher.safeDispatch(context: CoroutineContext, runnable: Runnable) {
+    try {
+        dispatch(context, runnable)
+    } catch (e: Throwable) {
+        throw DispatchException(e, this, context)
+    }
+}
+
+internal fun CoroutineDispatcher.safeIsDispatchNeeded(context: CoroutineContext): Boolean {
+    try {
+        return isDispatchNeeded(context)
+    } catch (e: Throwable) {
+        throw DispatchException(e, this, context)
+    }
+}
+
 /**
  * It is not inline to save bytecode (it is pretty big and used in many places)
  * and we leave it public so that its name is not mangled in use stack traces if it shows there.

kotlinx-coroutines-core/common/src/internal/DispatchedTask.kt

@@ -76,7 +76,6 @@ internal abstract class DispatchedTask<in T> internal constructor(
 
     final override fun run() {
         assert { resumeMode != MODE_UNINITIALIZED } // should have been set before dispatching
-        var fatalException: Throwable? = null
         try {
             val delegate = delegate as DispatchedContinuation<T>
             val continuation = delegate.continuation
@@ -102,11 +101,10 @@ internal abstract class DispatchedTask<in T> internal constructor(
                     }
                 }
             }
+        } catch (e: DispatchException) {
+            handleCoroutineException(delegate.context, e.cause)
         } catch (e: Throwable) {
-            // This instead of runCatching to have nicer stacktrace and debug experience
-            fatalException = e
-        } finally {
-            fatalException?.let { handleFatalException(it) }
+            handleFatalException(e)
         }
     }
 
@@ -143,8 +141,8 @@ internal fun <T> DispatchedTask<T>.dispatch(mode: Int) {
         // dispatch directly using this instance's Runnable implementation
         val dispatcher = delegate.dispatcher
         val context = delegate.context
-        if (dispatcher.isDispatchNeeded(context)) {
-            dispatcher.dispatch(context, this)
+        if (dispatcher.safeIsDispatchNeeded(context)) {
+            dispatcher.safeDispatch(context, this)
         } else {
             resumeUnconfined()
         }
@@ -205,3 +203,17 @@ internal inline fun DispatchedTask<*>.runUnconfinedEventLoop(
 internal inline fun Continuation<*>.resumeWithStackTrace(exception: Throwable) {
     resumeWith(Result.failure(recoverStackTrace(exception, this)))
 }
+
+/**
+ * This exception holds an exception raised in [CoroutineDispatcher.dispatch] method.
+ * When dispatcher methods fail unexpectedly, it is likely a user-induced programmatic bug,
+ * such as calling `executor.close()` prematurely. To avoid reporting such exceptions as fatal errors,
+ * we handle them with a separate code path. See also #4091.
+ *
+ * @see safeDispatch
+ */
+internal class DispatchException(
+    override val cause: Throwable,
+    dispatcher: CoroutineDispatcher,
+    context: CoroutineContext,
+) : Exception("Coroutine dispatcher $dispatcher threw an exception, context = $context", cause)

kotlinx-coroutines-core/common/src/internal/LimitedDispatcher.kt

@@ -42,7 +42,7 @@ internal class LimitedDispatcher(
 
     override fun dispatch(context: CoroutineContext, block: Runnable) {
         dispatchInternal(block) { worker ->
-            dispatcher.dispatch(this, worker)
+            dispatcher.safeDispatch(this, worker)
         }
     }
 
@@ -116,10 +116,10 @@ internal class LimitedDispatcher(
                 }
                 currentTask = obtainTaskOrDeallocateWorker() ?: return
                 // 16 is our out-of-thin-air constant to emulate fairness. Used in JS dispatchers as well
-                if (++fairnessCounter >= 16 && dispatcher.isDispatchNeeded(this@LimitedDispatcher)) {
+                if (++fairnessCounter >= 16 && dispatcher.safeIsDispatchNeeded(this@LimitedDispatcher)) {
                     // Do "yield" to let other views execute their runnable as well
                     // Note that we do not decrement 'runningWorkers' as we are still committed to our part of work
-                    dispatcher.dispatch(this@LimitedDispatcher, this)
+                    dispatcher.safeDispatch(this@LimitedDispatcher, this)
                     return
                 }
             }

kotlinx-coroutines-core/common/src/intrinsics/Cancellable.kt

@@ -58,6 +58,7 @@ private fun dispatcherFailure(completion: Continuation<*>, e: Throwable) {
      * 2) Rethrow the exception immediately, so it will crash the caller (e.g. when the coroutine had
      *    no parent or it was async/produce over MainScope).
      */
-    completion.resumeWith(Result.failure(e))
-    throw e
+    val reportException = if (e is DispatchException) e.cause else e
+    completion.resumeWith(Result.failure(reportException))
+    throw reportException
 }

kotlinx-coroutines-core/common/src/intrinsics/Undispatched.kt

@@ -20,7 +20,8 @@ internal fun <R, T> (suspend (R) -> T).startCoroutineUndispatched(receiver: R, c
             startCoroutineUninterceptedOrReturn(receiver, actualCompletion)
         }
     } catch (e: Throwable) {
-        actualCompletion.resumeWithException(e)
+        val reportException = if (e is DispatchException) e.cause else e
+        actualCompletion.resumeWithException(reportException)
         return
     }
     if (value !== COROUTINE_SUSPENDED) {

kotlinx-coroutines-core/jvm/src/Executors.kt

@@ -105,8 +105,8 @@ public fun CoroutineDispatcher.asExecutor(): Executor =
 
 private class DispatcherExecutor(@JvmField val dispatcher: CoroutineDispatcher) : Executor {
     override fun execute(block: Runnable) {
-        if (dispatcher.isDispatchNeeded(EmptyCoroutineContext)) {
-            dispatcher.dispatch(EmptyCoroutineContext, block)
+        if (dispatcher.safeIsDispatchNeeded(EmptyCoroutineContext)) {
+            dispatcher.safeDispatch(EmptyCoroutineContext, block)
         } else {
             block.run()
         }

kotlinx-coroutines-core/jvm/test/ExecutorsTest.kt

@@ -119,4 +119,106 @@ class ExecutorsTest : TestBase() {
         dispatcher.close()
         check(executorService.isShutdown)
     }
+
+    @Test
+    fun testEarlyExecutorShutdown() {
+        runTestExceptionInDispatch(6, { it is RejectedExecutionException }) {
+            expect(1)
+            val dispatcher = newSingleThreadContext("Ctx")
+            launch(dispatcher) {
+                withContext(Dispatchers.Default) {
+                    expect(2)
+                    delay(100)
+                    expect(4)
+                }
+            }
+
+            delay(50)
+            expect(3)
+
+            dispatcher.close()
+        }
+    }
+
+    @Test
+    fun testExceptionInDispatch() {
+        runTestExceptionInDispatch(5, { it is TestException }) {
+            val dispatcher = object : CoroutineDispatcher() {
+                private var closed = false
+                override fun dispatch(context: CoroutineContext, block: Runnable) {
+                    if (closed) throw TestException()
+                    Dispatchers.Default.dispatch(context, block)
+                }
+
+                fun close() {
+                    closed = true
+                }
+            }
+            launch(dispatcher) {
+                withContext(Dispatchers.Default) {
+                    expect(1)
+                    delay(100)
+                    expect(3)
+                }
+            }
+
+            delay(50)
+            expect(2)
+            dispatcher.close()
+        }
+    }
+
+    @Test
+    fun testExceptionInIsDispatchNeeded() {
+        val dispatcher = object : CoroutineDispatcher() {
+            override fun isDispatchNeeded(context: CoroutineContext): Boolean {
+                expect(2)
+                throw TestException()
+            }
+            override fun dispatch(context: CoroutineContext, block: Runnable) = expectUnreached()
+        }
+        try {
+            runBlocking {
+                expect(1)
+                try {
+                    launch(dispatcher) {
+                        expectUnreached()
+                    }
+                    expectUnreached()
+                } catch (_: TestException) {
+                    expect(3)
+                }
+
+            }
+        } catch (_: TestException) {
+            finish(4)
+        }
+    }
+
+    private fun runTestExceptionInDispatch(
+        totalSteps: Int,
+        isExpectedException: (Throwable) -> Boolean,
+        block: suspend CoroutineScope.() -> Unit,
+    ) {
+        var mainThread: Thread? = null
+        val exceptionHandler = CoroutineExceptionHandler { _, e ->
+            if (isExpectedException(e)) {
+                expect(totalSteps - 1)
+                mainThread!!.run {
+                    interrupt()
+                    unpark(this)
+                }
+            } else {
+                expectUnreached()
+            }
+        }
+        try {
+            runBlocking(exceptionHandler) {
+                block()
+                mainThread = Thread.currentThread()
+            }
+        } catch (_: InterruptedException) {
+            finish(totalSteps)
+        }
+    }
 }