Multithreaded support in select expression

Fixes #1764

kotlinx-coroutines-core/api/kotlinx-coroutines-core.api

@@ -1073,8 +1073,8 @@ public final class kotlinx/coroutines/selects/SelectBuilderImpl : kotlinx/corout
 	public fun resumeSelectWithException (Ljava/lang/Throwable;)V
 	public fun resumeWith (Ljava/lang/Object;)V
 	public fun toString ()Ljava/lang/String;
-	public fun trySelect ()Z
-	public fun trySelectOther (Lkotlinx/coroutines/internal/LockFreeLinkedListNode$PrepareOp;)Ljava/lang/Object;
+	public fun trySelect (Lkotlin/jvm/functions/Function0;)Z
+	public fun trySelectOther (Lkotlinx/coroutines/internal/LockFreeLinkedListNode$PrepareOp;Lkotlin/jvm/functions/Function0;)Ljava/lang/Object;
 }
 
 public abstract interface class kotlinx/coroutines/selects/SelectClause0 {
@@ -1095,8 +1095,12 @@ public abstract interface class kotlinx/coroutines/selects/SelectInstance {
 	public abstract fun isSelected ()Z
 	public abstract fun performAtomicTrySelect (Lkotlinx/coroutines/internal/AtomicDesc;)Ljava/lang/Object;
 	public abstract fun resumeSelectWithException (Ljava/lang/Throwable;)V
-	public abstract fun trySelect ()Z
-	public abstract fun trySelectOther (Lkotlinx/coroutines/internal/LockFreeLinkedListNode$PrepareOp;)Ljava/lang/Object;
+	public abstract fun trySelect (Lkotlin/jvm/functions/Function0;)Z
+	public abstract fun trySelectOther (Lkotlinx/coroutines/internal/LockFreeLinkedListNode$PrepareOp;Lkotlin/jvm/functions/Function0;)Ljava/lang/Object;
+}
+
+public final class kotlinx/coroutines/selects/SelectInstance$DefaultImpls {
+	public static synthetic fun trySelect$default (Lkotlinx/coroutines/selects/SelectInstance;Lkotlin/jvm/functions/Function0;ILjava/lang/Object;)Z
 }
 
 public final class kotlinx/coroutines/selects/SelectKt {

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

@@ -138,6 +138,6 @@ public abstract class AbstractCoroutine<in T>(
      */
     public fun <R> start(start: CoroutineStart, receiver: R, block: suspend R.() -> T) {
         initParentJob()
-        startCoroutine(start, this, receiver, block)
+        startCoroutine(start, receiver, this, block)
     }
 }

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

@@ -174,13 +174,13 @@ public suspend inline operator fun <T> CoroutineDispatcher.invoke(
 
 internal fun <T, R> startCoroutineImpl(
     start: CoroutineStart,
-    coroutine: AbstractCoroutine<T>,
     receiver: R,
+    completion: Continuation<T>,
     block: suspend R.() -> T
 ) = when (start) {
-    CoroutineStart.DEFAULT -> block.startCoroutineCancellable(receiver, coroutine)
-    CoroutineStart.ATOMIC -> block.startCoroutine(receiver, coroutine)
-    CoroutineStart.UNDISPATCHED -> block.startCoroutineUndispatched(receiver, coroutine)
+    CoroutineStart.DEFAULT -> block.startCoroutineCancellable(receiver, completion)
+    CoroutineStart.ATOMIC -> block.startCoroutine(receiver, completion)
+    CoroutineStart.UNDISPATCHED -> block.startCoroutineUndispatched(receiver, completion)
     CoroutineStart.LAZY -> Unit // will start lazily
 }
 
@@ -189,8 +189,8 @@ internal fun <T, R> startCoroutineImpl(
 // todo: impl a separate startCoroutineCancellable as a fast-path for startCoroutine(DEFAULT, ...)
 internal expect fun <T, R> startCoroutine(
     start: CoroutineStart,
-    coroutine: AbstractCoroutine<T>,
     receiver: R,
+    completion: Continuation<T>,
     block: suspend R.() -> T
 )
 

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

@@ -382,7 +382,10 @@ internal abstract class AbstractSendChannel<E> : SendChannel<E> {
                         select.disposeOnSelect(node)
                         return
                     }
-                    enqueueResult is Closed<*> -> throw recoverStackTrace(helpCloseAndGetSendException(enqueueResult))
+                    enqueueResult is Closed<*> -> {
+                        node.dispose()
+                        throw recoverStackTrace(helpCloseAndGetSendException(enqueueResult))
+                    }
                     enqueueResult === ENQUEUE_FAILED -> {} // try to offer
                     enqueueResult is Receive<*> -> {} // try to offer
                     else -> error("enqueueSend returned $enqueueResult ")
@@ -448,16 +451,18 @@ internal abstract class AbstractSendChannel<E> : SendChannel<E> {
         override val pollResult: Any?,
         @JvmField val channel: AbstractSendChannel<E>,
         @JvmField val select: SelectInstance<R>,
-        @JvmField val block: suspend (SendChannel<E>) -> R
+        block: suspend (SendChannel<E>) -> R
     ) : Send(), DisposableHandle {
+        @JvmField val block: suspend (SendChannel<E>) -> R = block.asShareable()
+
         override fun tryResumeSend(otherOp: PrepareOp?): Symbol? =
-            select.trySelectOther(otherOp) as Symbol? // must return symbol
+            select.trySelectOther(otherOp, onSelect = block::shareableWillBeUsed) as Symbol? // must return symbol
 
-        override fun completeResumeSend() {
-            block.startCoroutine(receiver = channel, completion = select.completion)
-        }
+        override fun completeResumeSend() =
+            startCoroutine(CoroutineStart.ATOMIC, channel, select.completion, block)
 
         override fun dispose() { // invoked on select completion
+            block.shareableDispose(useIt = false)
             remove()
         }
 
@@ -773,7 +778,11 @@ internal abstract class AbstractChannel<E> : AbstractSendChannel<E>(), Channel<E
     ): Boolean {
         val node = ReceiveSelect(this, select, block, receiveMode)
         val result = enqueueReceive(node)
-        if (result) select.disposeOnSelect(node)
+        if (result) {
+            select.disposeOnSelect(node)
+        } else {
+            node.dispose()
+        }
         return result
     }
 
@@ -871,41 +880,53 @@ internal abstract class AbstractChannel<E> : AbstractSendChannel<E>(), Channel<E
     }
 
     private class ReceiveElement<in E>(
-        @JvmField val cont: CancellableContinuation<Any?>,
+        cont: CancellableContinuation<Any?>,
         @JvmField val receiveMode: Int
     ) : Receive<E>() {
+        private val _cont = atomic<CancellableContinuation<Any?>?>(cont)
+        private fun useCont() = _cont.getAndSet(null)
+
         fun resumeValue(value: E): Any? = when (receiveMode) {
             RECEIVE_RESULT -> ValueOrClosed.value(value)
             else -> value
         }
 
         @Suppress("IMPLICIT_CAST_TO_ANY")
         override fun tryResumeReceive(value: E, otherOp: PrepareOp?): Symbol? {
-            val token = cont.tryResume(resumeValue(value), otherOp?.desc) ?: return null
+            val token = _cont.value?.tryResume(resumeValue(value), otherOp?.desc) ?: run {
+                _cont.value = null
+                return null
+            }
             assert { token === RESUME_TOKEN } // the only other possible result
             // We can call finishPrepare only after successful tryResume, so that only good affected node is saved
             otherOp?.finishPrepare()
             return RESUME_TOKEN
         }
 
-        override fun completeResumeReceive(value: E) = cont.completeResume(RESUME_TOKEN)
+        override fun completeResumeReceive(value: E)  { useCont()?.completeResume(RESUME_TOKEN) }
 
         override fun resumeReceiveClosed(closed: Closed<*>) {
             when {
-                receiveMode == RECEIVE_NULL_ON_CLOSE && closed.closeCause == null -> cont.resume(null)
-                receiveMode == RECEIVE_RESULT -> cont.resume(closed.toResult<Any>())
-                else -> cont.resumeWithException(closed.receiveException)
+                receiveMode == RECEIVE_NULL_ON_CLOSE && closed.closeCause == null -> useCont()?.resume(null)
+                receiveMode == RECEIVE_RESULT -> useCont()?.resume(closed.toResult<Any>())
+                else -> useCont()?.resumeWithException(closed.receiveException)
             }
         }
         override fun toString(): String = "ReceiveElement@$hexAddress[receiveMode=$receiveMode]"
     }
 
     private class ReceiveHasNext<E>(
         @JvmField val iterator: Itr<E>,
-        @JvmField val cont: CancellableContinuation<Boolean>
+        cont: CancellableContinuation<Boolean>
     ) : Receive<E>() {
+        private val _cont = atomic<CancellableContinuation<Boolean>?>(cont)
+        private fun useCont() = _cont.getAndSet(null)
+
         override fun tryResumeReceive(value: E, otherOp: PrepareOp?): Symbol? {
-            val token = cont.tryResume(true, otherOp?.desc) ?: return null
+            val token = _cont.value?.tryResume(true, otherOp?.desc) ?: run{
+                _cont.value = null
+                return null
+            }
             assert { token === RESUME_TOKEN } // the only other possible result
             // We can call finishPrepare only after successful tryResume, so that only good affected node is saved
             otherOp?.finishPrepare()
@@ -918,51 +939,61 @@ internal abstract class AbstractChannel<E> : AbstractSendChannel<E>(), Channel<E
                but completeResumeReceive is called once so we set iterator result here.
              */
             iterator.result = value
-            cont.completeResume(RESUME_TOKEN)
+            useCont()?.completeResume(RESUME_TOKEN)
         }
 
         override fun resumeReceiveClosed(closed: Closed<*>) {
             val token = if (closed.closeCause == null) {
-                cont.tryResume(false)
+                _cont.value?.tryResume(false)
             } else {
-                cont.tryResumeWithException(recoverStackTrace(closed.receiveException, cont))
+                _cont.value?.let { cont ->
+                    cont.tryResumeWithException(recoverStackTrace(closed.receiveException, cont))
+                }
             }
             if (token != null) {
                 iterator.result = closed
-                cont.completeResume(token)
+                _cont.value?.completeResume(token)
             }
+            _cont.value = null
         }
         override fun toString(): String = "ReceiveHasNext@$hexAddress"
     }
 
     private class ReceiveSelect<R, E>(
         @JvmField val channel: AbstractChannel<E>,
         @JvmField val select: SelectInstance<R>,
-        @JvmField val block: suspend (Any?) -> R,
+        block: suspend (Any?) -> R,
         @JvmField val receiveMode: Int
     ) : Receive<E>(), DisposableHandle {
+        @JvmField val block: suspend (Any?) -> R = block.asShareable() // captured variables in this block need screening
+
         override fun tryResumeReceive(value: E, otherOp: PrepareOp?): Symbol? =
-            select.trySelectOther(otherOp) as Symbol?
+            select.trySelectOther(otherOp, onSelect = block::shareableWillBeUsed) as Symbol?
 
         @Suppress("UNCHECKED_CAST")
         override fun completeResumeReceive(value: E) {
-            block.startCoroutine(if (receiveMode == RECEIVE_RESULT) ValueOrClosed.value(value) else value, select.completion)
+            startCoroutine(CoroutineStart.ATOMIC, if (receiveMode == RECEIVE_RESULT) ValueOrClosed.value(value) else value, select.completion, block)
         }
 
         override fun resumeReceiveClosed(closed: Closed<*>) {
-            if (!select.trySelect()) return
+            if (!select.trySelect(onSelect = block::shareableWillBeUsed)) return
             when (receiveMode) {
-                RECEIVE_THROWS_ON_CLOSE -> select.resumeSelectWithException(closed.receiveException)
-                RECEIVE_RESULT -> block.startCoroutine(ValueOrClosed.closed<R>(closed.closeCause), select.completion)
+                RECEIVE_THROWS_ON_CLOSE -> {
+                    block.shareableDispose(useIt = true)
+                    select.resumeSelectWithException(closed.receiveException)
+                }
+                RECEIVE_RESULT -> startCoroutine(CoroutineStart.ATOMIC, ValueOrClosed.closed<R>(closed.closeCause), select.completion, block)
                 RECEIVE_NULL_ON_CLOSE -> if (closed.closeCause == null) {
-                    block.startCoroutine(null, select.completion)
+                    startCoroutine(CoroutineStart.ATOMIC, null, select.completion, block)
                 } else {
+                    block.shareableDispose(useIt = true)
                     select.resumeSelectWithException(closed.receiveException)
                 }
             }
         }
 
         override fun dispose() { // invoked on select completion
+            block.shareableDispose(useIt = false)
             if (remove())
                 channel.onReceiveDequeued() // notify cancellation of receive
         }
@@ -1031,17 +1062,23 @@ internal interface ReceiveOrClosed<in E> {
 @Suppress("UNCHECKED_CAST")
 internal class SendElement(
     override val pollResult: Any?,
-    @JvmField val cont: CancellableContinuation<Unit>
+    cont: CancellableContinuation<Unit>
 ) : Send() {
+    private val _cont = atomic<CancellableContinuation<Unit>?>(cont)
+    private fun useCont() = _cont.getAndSet(null)
+
     override fun tryResumeSend(otherOp: PrepareOp?): Symbol? {
-        val token = cont.tryResume(Unit, otherOp?.desc) ?: return null
+        val token = _cont.value?.tryResume(Unit, otherOp?.desc) ?: run {
+            _cont.value = null
+            return null
+        }
         assert { token === RESUME_TOKEN } // the only other possible result
         // We can call finishPrepare only after successful tryResume, so that only good affected node is saved
         otherOp?.finishPrepare() // finish preparations
         return RESUME_TOKEN
     }
-    override fun completeResumeSend() = cont.completeResume(RESUME_TOKEN)
-    override fun resumeSendClosed(closed: Closed<*>) = cont.resumeWithException(closed.sendException)
+    override fun completeResumeSend() { useCont()?.completeResume(RESUME_TOKEN) }
+    override fun resumeSendClosed(closed: Closed<*>) { useCont()?.resumeWithException(closed.sendException) }
     override fun toString(): String = "SendElement@$hexAddress($pollResult)"
 }
 

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

@@ -17,8 +17,15 @@ internal expect fun <T> Continuation<T>.asLocalOrNull() : Continuation<T>?
 internal expect fun <T> Continuation<T>.asLocalOrNullIfNotUsed() : Continuation<T>?
 internal expect fun <T> Continuation<T>.useLocal() : Continuation<T>
 internal expect fun <T> Continuation<T>.shareableInterceptedResumeCancellableWith(result: Result<T>)
+internal expect fun <T> Continuation<T>.shareableInterceptedResumeWith(result: Result<T>)
+internal expect fun <T> Continuation<T>.shareableDispose()
 internal expect fun disposeContinuation(cont: () -> Continuation<*>)
 internal expect fun <T> CancellableContinuationImpl<T>.shareableResume(delegate: Continuation<T>, useMode: Int)
+
+internal expect fun <T, R> (suspend (T) -> R).asShareable(): suspend (T) -> R
+internal expect fun <T, R> (suspend (T) -> R).shareableDispose(useIt: Boolean)
+internal expect fun <T, R> (suspend (T) -> R).shareableWillBeUsed()
+
 internal expect fun isReuseSupportedInPlatform(): Boolean
 internal expect fun <T> ArrayList<T>.addOrUpdate(element: T, update: (ArrayList<T>) -> Unit)
 internal expect fun <T> ArrayList<T>.addOrUpdate(index: Int, element: T, update: (ArrayList<T>) -> Unit)