More safe API to manage running fibers and event loops

src/commonMain/kotlin/ru/landgrafhomyak/multitasking_0/threads/EventLoopClearer.kt

@@ -0,0 +1,11 @@
+package ru.landgrafhomyak.multitasking_0.threads
+
+import ru.landgrafhomyak.multitasking_0.WrongCallerThreadException
+import ru.landgrafhomyak.multitasking_0.fibers.Fiber
+
+/**
+ * @see ThreadLocalMethods.setEventLoop
+ */
+public interface EventLoopClearer {
+	public fun clearEventLoop()
+}

src/commonMain/kotlin/ru/landgrafhomyak/multitasking_0/threads/FiberExiter.kt

@@ -0,0 +1,19 @@
+package ru.landgrafhomyak.multitasking_0.threads
+
+import ru.landgrafhomyak.multitasking_0.WrongCallerThreadException
+import ru.landgrafhomyak.multitasking_0.fibers.Fiber
+
+/**
+ * @see ThreadLocalMethods.enterFiber
+ */
+public interface FiberExiter {
+	public val callerFiber: Fiber?
+	/**
+	 * Informs thread that execution flow was returned from [fiber][Fiber].
+	 *
+	 * @throws IllegalStateException if [fiberToExit] doesn't match [current running fiber][ThreadLocalMethods.runningFiber]
+	 * or this fiber isn't on top of fibers stack.
+	 * @throws WrongCallerThreadException if called on thread different that caller of [Thread.current].
+	 */
+	public fun exitFiber()
+}

src/commonMain/kotlin/ru/landgrafhomyak/multitasking_0/threads/ThreadLocalMethods.kt

@@ -29,30 +29,13 @@ public expect sealed interface ThreadLocalMethods {
 	 * Informs thread that execution flow was switched to [fiber][Fiber].
 	 *
 	 * @param fiberToEnter descriptor of fiber that is [going to run][Fiber.resume].
-	 * @param privateToken secret reference that should be used to call [exitFiber()][ThreadLocalMethods.exitFiber].
+	 * @return Callback object to rollback value of [Thread.current.runningFiber][ThreadLocalMethods.runningFiber]
-	 * Need to avoid clearing [information about running fiber][ThreadLocalMethods.runningFiber]
+	 * to state before this call.
-	 * by anyone except implementation of this fiber.
-	 * @return [fiber][Fiber] in which this function was called or `null` if it was called in thread.
 	 *
 	 * @throws WrongCallerThreadException if called on thread different that caller of [Thread.current].
 	 */
-	public fun enterFiber(fiberToEnter: Fiber, privateToken: Any): Fiber?
+	public fun enterFiber(fiberToEnter: Fiber): FiberExiter
-
-	/**
-	 * Informs thread that execution flow was returned from [fiber][Fiber].
-	 *
-	 * @param fiberToExit descriptor of fiber that is [going to return execution flow][Fiber.yield].
-	 * @param privateToken secret reference that was passed to [enterFiber()][ThreadLocalMethods.exitFiber].
-	 * Used to check that this function called by same caller as [enterFiber()][ThreadLocalMethods.exitFiber].
-	 * @param fiberToRestore return value of corresponding [enterFiber()][ThreadLocalMethods.exitFiber] call.
-	 *
-	 * @throws IllegalStateException if [fiberToExit] or [fiberToRestore] doesn't match.
-	 * @throws IllegalArgumentException if [privateToken] doesn't match.
-	 * @throws WrongCallerThreadException if called on thread different that caller of [Thread.current].
-	 */
-	public fun exitFiber(fiberToExit: Fiber, privateToken: Any, fiberToRestore: Fiber?)
 
 	public val runningEventLoop: SingleThreadEventLoop?
-	public fun setEventLoop(eventLoop: SingleThreadEventLoop, privateToken: Any)
+	public fun setEventLoop(eventLoop: SingleThreadEventLoop): EventLoopClearer
-	public fun clearEventLoop(eventLoop: SingleThreadEventLoop, privateToken: Any)
 }

src/commonMain/kotlin/ru/landgrafhomyak/multitasking_0/threads/_FibersStackNode.kt

@@ -1,21 +0,0 @@
-package ru.landgrafhomyak.multitasking_0.threads
-
-import kotlin.jvm.JvmField
-import ru.landgrafhomyak.multitasking_0.fibers.Fiber
-
-internal class _FibersStackNode(
-	@JvmField
-	val caller: _FibersStackNode?,
-	@JvmField
-	val fiber: Fiber,
-	@JvmField
-	val privateToken: Any,
-) {
-	fun assertExit(fiberToExit: Fiber, privateToken: Any, fiberToRestore: Fiber?) {
-		if (this.fiber !== fiberToExit || this.caller?.fiber !== fiberToRestore)
-			throw IllegalStateException("fiberToExit or fiberToRestore doesn't match")
-
-		if (this.privateToken !== privateToken)
-			throw IllegalArgumentException("privateToken doesn't match")
-	}
-}

src/jvmMain/kotlin/ru/landgrafhomyak/multitasking_0/impl/java_virtual_threads/JavaVirtualThreadFiber.kt

@@ -1,4 +1,4 @@
-package ru.landgrafhomyak.multitasking_0.threads.impl.java_virtual_threads
+package ru.landgrafhomyak.multitasking_0.impl.java_virtual_threads
 
 import java.lang.Object as jObject
 import java.lang.Thread as jThread
@@ -9,6 +9,7 @@ import ru.landgrafhomyak.multitasking_0.fibers.Fiber
 import ru.landgrafhomyak.multitasking_0.fibers.FiberRoutine
 import ru.landgrafhomyak.multitasking_0.WrongCallerThreadException
 import ru.landgrafhomyak.multitasking_0.fibers.FiberInterruptedException
+import ru.landgrafhomyak.multitasking_0.threads.FiberExiter
 import ru.landgrafhomyak.multitasking_0.threads.Thread as wThread
 
 public class JavaVirtualThreadFiber : Fiber {
@@ -19,7 +20,7 @@ public class JavaVirtualThreadFiber : Fiber {
 	private var _uncaughtException: Throwable?
 	override val name: String
 	private var _resumedOnThread: wThread?
-	private var _resumedOnFiber: Fiber?
+	private var _fiberExiter: FiberExiter?
 	private var _interruptionData: InterruptionData?
 
 	public constructor(name: String, routine: FiberRoutine) {
@@ -29,7 +30,7 @@ public class JavaVirtualThreadFiber : Fiber {
 		this._state = Fiber.State.CREATED
 		this._uncaughtException = null
 		this._resumedOnThread = null
-		this._resumedOnFiber = null
+		this._fiberExiter = null
 		this._interruptionData = null
 
 		this._syncLock.withLock {
@@ -84,7 +85,7 @@ public class JavaVirtualThreadFiber : Fiber {
 		get() = this._syncLock.withLock {
 			if (this._state == Fiber.State.DESTROYED)
 				throw IllegalStateException("Fiber destroyed")
-			return@withLock this._resumedOnFiber
+			return@withLock this._fiberExiter?.callerFiber
 		}
 
 	override fun yield() {
@@ -103,7 +104,8 @@ public class JavaVirtualThreadFiber : Fiber {
 				Fiber.State.DESTROYED -> throw IllegalStateException("Fiber destroyed")
 			}
 
-
+			this._fiberExiter!!.exitFiber()
+			this._fiberExiter = null
 			wThread._tl_currentThread.set(null)
 			this._syncCond.signal()
 			this._syncCond.await()
@@ -137,18 +139,15 @@ public class JavaVirtualThreadFiber : Fiber {
 				Fiber.State.DESTROYED -> throw IllegalStateException("Fiber destroyed")
 			}
 
-			val token = jObject()
 			val currentThread = wThread.current
 			this._resumedOnThread = currentThread.get()
-			this._resumedOnFiber = currentThread.enterFiber(this, token)
+			this._fiberExiter = currentThread.enterFiber(this)
 			this._interruptionData = id
 
 			this._syncCond.signal()
 			this._syncCond.await()
 
-			currentThread.exitFiber(this, token, this.resumedOnFiber)
 			this._resumedOnThread = null
-			this._resumedOnFiber = null
 		}
 	}
 

src/jvmMain/kotlin/ru/landgrafhomyak/multitasking_0/threads/Thread.kt

@@ -1,5 +1,6 @@
 package ru.landgrafhomyak.multitasking_0.threads
 
+import java.util.concurrent.atomic.AtomicBoolean
 import java.util.concurrent.locks.ReentrantLock
 import kotlin.concurrent.withLock
 import java.lang.Thread as jThread
@@ -159,7 +160,33 @@ public actual sealed class Thread {
 			return this@Thread
 		}
 
-		private var _fibersStack: _FibersStackNode? = null
+		private inner class FibersStackNode(
+			@JvmField
+			val caller: FibersStackNode?,
+			@JvmField
+			val fiber: Fiber,
+		) : FiberExiter {
+			private val _isClosed = AtomicBoolean(false)
+			override val callerFiber: Fiber?
+				get() {
+					if (this._isClosed.get()) throw IllegalStateException("Fiber already exited and value in this property isn't actual")
+					return this.caller?.fiber
+				}
+
+			override fun exitFiber() {
+				if (this._isClosed.compareAndExchange(false, true))
+					throw IllegalStateException("Fiber already exited")
+
+				if (this@ThreadLocalMethodsImpl._fibersStack !== this) {
+					this._isClosed.set(false)
+					throw IllegalStateException("Fiber being exited isn't on top of fibers stack")
+				}
+
+				this@ThreadLocalMethodsImpl._fibersStack = this.caller
+			}
+		}
+
+		private var _fibersStack: FibersStackNode? = null
 
 		override val runningFiber: Fiber?
 			get() {
@@ -167,27 +194,14 @@ public actual sealed class Thread {
 				return this._fibersStack?.fiber
 			}
 
-		override fun enterFiber(fiberToEnter: Fiber, privateToken: Any): Fiber? {
+		override fun enterFiber(fiberToEnter: Fiber): FiberExiter {
 			this._assertThread()
-			val caller = this._fibersStack
+			val node = this.FibersStackNode(this._fibersStack, fiberToEnter)
-			this._fibersStack = _FibersStackNode(caller, fiberToEnter, privateToken)
+			this._fibersStack = node
-			return caller?.fiber
+			return node
-		}
-
-		override fun exitFiber(fiberToExit: Fiber, privateToken: Any, fiberToRestore: Fiber?) {
-			this._assertThread()
-
-			val top = this._fibersStack
-			if (top == null)
-				throw IllegalStateException("There is no running fiber to exit")
-
-			top.assertExit(fiberToExit, privateToken, fiberToRestore)
-
-			this._fibersStack = top.caller
 		}
 
 		private var _runningEventLoop: SingleThreadEventLoop? = null
-		private var _runningEventLoopToken: Any? = null
 
 		override val runningEventLoop: SingleThreadEventLoop?
 			get() {
@@ -196,23 +210,25 @@ public actual sealed class Thread {
 			}
 
 
-		override fun setEventLoop(eventLoop: SingleThreadEventLoop, privateToken: Any) {
+		private inner class EventLoopClearerImpl(
+
+		) : EventLoopClearer {
+			private val _isClosed = AtomicBoolean(false)
+
+			override fun clearEventLoop() {
+				if (this._isClosed.compareAndExchange(false, true))
+					throw IllegalStateException("Event loop already cleared")
+
+				this@ThreadLocalMethodsImpl._runningEventLoop = null
+			}
+		}
+
+		override fun setEventLoop(eventLoop: SingleThreadEventLoop): EventLoopClearer {
 			this._assertThread()
 			if (this._runningEventLoop != null)
 				throw IllegalStateException("There is already a running event loop here")
 			this._runningEventLoop = eventLoop
-			this._runningEventLoopToken = privateToken
+			return this.EventLoopClearerImpl()
-		}
-
-		override fun clearEventLoop(eventLoop: SingleThreadEventLoop, privateToken: Any) {
-			this._assertThread()
-			if (this._runningEventLoop !== eventLoop)
-				throw IllegalStateException("Currently another event loop is running")
-			if (this._runningEventLoopToken !== privateToken)
-				throw IllegalArgumentException("privateToken doesn't match")
-
-			this._runningEventLoop = null
-			this._runningEventLoopToken = null
 		}
 	}
 }

src/jvmMain/kotlin/ru/landgrafhomyak/multitasking_0/threads/ThreadLocalMethods.kt

@@ -7,10 +7,8 @@ public actual sealed interface ThreadLocalMethods {
 	public actual fun get(): Thread
 
 	public actual val runningFiber: Fiber?
-	public actual fun enterFiber(fiberToEnter: Fiber, privateToken: Any): Fiber?
+	public actual fun enterFiber(fiberToEnter: Fiber): FiberExiter
-	public actual fun exitFiber(fiberToExit: Fiber, privateToken: Any, fiberToRestore: Fiber?)
 
 	public actual val runningEventLoop: SingleThreadEventLoop?
-	public actual fun setEventLoop(eventLoop: SingleThreadEventLoop, privateToken: Any)
+	public actual fun setEventLoop(eventLoop: SingleThreadEventLoop): EventLoopClearer
-	public actual fun clearEventLoop(eventLoop: SingleThreadEventLoop, privateToken: Any)
 }