Fix structured concurrency

uranos-api/src/main/kotlin/space/uranos/net/Session.kt

@@ -6,7 +6,10 @@
 package space.uranos.net
 
 import io.netty.buffer.ByteBuf
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.SupervisorJob
 import space.uranos.Position
+import space.uranos.Uranos
 import space.uranos.chat.TextComponent
 import space.uranos.event.EventBusWrapper
 import space.uranos.net.packet.OutgoingPacket
@@ -16,21 +19,20 @@ import space.uranos.player.Player
 import space.uranos.world.World
 import java.net.InetAddress
 import java.util.*
-import kotlin.coroutines.CoroutineContext
 
 abstract class Session {
     val events by lazy { EventBusWrapper<Session>(this) }
 
+    /**
+     * A coroutine scope that is cancelled when the session disconnected.
+     */
+    val scope = CoroutineScope(SupervisorJob() + Uranos.dispatcher)
+
     /**
      * The IP address of this session
      */
     abstract val address: InetAddress
 
-    /**
-     * Unconfined [CoroutineContext] which is cancelled when the session is disconnected.
-     */
-    abstract val coroutineContext: CoroutineContext
-
     /**
      * The brand name the client optionally sent during the login procedure.
      * [ClientBrandReceivedEvent][space.uranos.net.event.ClientBrandReceivedEvent] is emitted when this value changes.
@@ -48,7 +50,6 @@ abstract class Session {
      * The player corresponding to this session.
      */
     val player: Player? get() = (state as? State.Playing)?.player
-//    val player: Player? get() = (state as? State.WithPlayer)?.player
 
     /**
      * The current state of this session.

uranos-api/src/main/kotlin/space/uranos/player/Player.kt

@@ -11,10 +11,9 @@ import space.uranos.net.Session
 import space.uranos.world.Chunk
 import space.uranos.world.VoxelLocation
 import java.util.*
-import kotlin.coroutines.CoroutineContext
 
 interface Player {
-    val coroutineContext: CoroutineContext get() = session.coroutineContext
+    val scope get() = session.scope
 
     /**
      * The session of this player.

uranos-api/src/main/kotlin/space/uranos/server/Server.kt

@@ -5,7 +5,9 @@
 
 package space.uranos.server
 
-import space.uranos.CalledFromWrongThread
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.SupervisorJob
 import space.uranos.Registry
 import space.uranos.Scheduler
 import space.uranos.command.Command
@@ -18,25 +20,26 @@ import space.uranos.net.Session
 import space.uranos.player.Player
 import space.uranos.plugin.PluginManager
 import space.uranos.recipe.Recipe
+import space.uranos.util.newSingleThreadDispatcher
 import space.uranos.world.BiomeRegistry
 import space.uranos.world.Dimension
 import java.io.File
 import java.util.*
 import java.util.concurrent.atomic.AtomicInteger
-import kotlin.coroutines.CoroutineContext
 
 abstract class Server {
     abstract val eventBus: EventBus
     abstract val eventHandlerPositions: EventHandlerPositionManager
 
-    protected abstract val serverThread: Thread
+    /**
+     * A coroutine dispatcher that is confined to the server thread.
+     */
+    val dispatcher: CoroutineDispatcher = newSingleThreadDispatcher("Server")
 
     /**
-     * [CoroutineContext] confined to the server thread.
-     *
-     * Is cancelled when the server is shutting down.
+     * A coroutine scope that is cancelled when the server is shutdown.
      */
-    abstract val coroutineContext: CoroutineContext
+    val scope = CoroutineScope(SupervisorJob() + dispatcher)
 
     /**
      * All sessions connected to the server.
@@ -68,13 +71,6 @@ abstract class Server {
      */
     abstract fun shutdown()
 
-    /**
-     * Throws [CalledFromWrongThread] when called from a thread which is not the server thread.
-     */
-    fun ensureServerThread(errorMessage: String) {
-        if (Thread.currentThread() != serverThread) throw CalledFromWrongThread(errorMessage)
-    }
-
     /**
      * Set of all existing [Entity] instances.
      *

uranos-api/src/main/kotlin/space/uranos/util/runInServerThread.kt

@@ -8,4 +8,4 @@ package space.uranos.util
 import kotlinx.coroutines.withContext
 import space.uranos.Uranos
 
-suspend fun <T> runInServerThread(block: suspend () -> T): T = withContext(Uranos.coroutineContext) { block() }
+suspend fun <T> runInServerThread(block: suspend () -> T): T = withContext(Uranos.dispatcher) { block() }

uranos-api/src/main/kotlin/space/uranos/world/Chunk.kt

@@ -5,10 +5,10 @@
 
 package space.uranos.world
 
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.SupervisorJob
 import space.uranos.Uranos
 import space.uranos.player.Player
-import space.uranos.util.supervisorChild
-import kotlin.coroutines.CoroutineContext
 import kotlin.math.floor
 
 abstract class Chunk(
@@ -40,11 +40,9 @@ abstract class Chunk(
     }
 
     /**
-     * [CoroutineContext] confined to the world thread.
-     *
-     * Is cancelled when the chunk is unloaded.
+     * A coroutine scope confined to the world's dispatcher that is cancelled when the chunk is unloaded.
      */
-    val coroutineContext: CoroutineContext = world.coroutineContext.supervisorChild(identifier)
+    val scope = CoroutineScope(SupervisorJob() + world.dispatcher)
 
     /**
      * A list of all players who have locked this chunk.

uranos-api/src/main/kotlin/space/uranos/world/World.kt

@@ -5,33 +5,31 @@
 
 package space.uranos.world
 
-import kotlinx.coroutines.cancel
-import kotlinx.coroutines.coroutineScope
-import kotlinx.coroutines.launch
-import kotlinx.coroutines.withContext
-import space.uranos.Uranos
+import kotlinx.coroutines.*
 import space.uranos.Vector
 import space.uranos.entity.Entity
 import space.uranos.util.newSingleThreadDispatcher
-import space.uranos.util.supervisorChild
 import space.uranos.util.untilPossiblyLower
 import java.util.*
 import java.util.concurrent.CopyOnWriteArraySet
-import kotlin.coroutines.CoroutineContext
 
 /**
  * A Minecraft world.
  */
 abstract class World(val uuid: UUID) {
     private val identifier = "World($uuid)"
-    private val threadExecutor = newSingleThreadDispatcher(identifier)
+
+    private val internalDispatcher = newSingleThreadDispatcher(identifier)
 
     /**
-     * [CoroutineContext] confined to the world thread.
-     *
-     * Is cancelled when the world is unloaded.
+     * A coroutine dispatcher that is confined to the server thread.
      */
-    val coroutineContext: CoroutineContext = Uranos.coroutineContext.supervisorChild(identifier) + threadExecutor
+    val dispatcher: CoroutineDispatcher = internalDispatcher
+
+    /**
+     * A coroutine scope confined to [dispatcher] that is cancelled when the world is destroyed.
+     */
+    val scope = CoroutineScope(SupervisorJob() + dispatcher)
 
     abstract val dimension: Dimension
     abstract val loadedChunks: Map<Chunk.Key, Chunk>
@@ -104,14 +102,14 @@ abstract class World(val uuid: UUID) {
         }
     }
 
-    suspend fun destroy() = withContext(coroutineContext) {
+    suspend fun destroy() {
         // TODO: Move or kick players
-        coroutineContext.cancel()
+        scope.cancel()
 
         coroutineScope {
             loadedChunks.values.forEach { launch { (it as? Chunk.Unloadable)?.unload() } }
         }
 
-        threadExecutor.close()
+        internalDispatcher.close()
     }
 }

uranos-server/src/main/kotlin/space/uranos/UranosServer.kt

@@ -8,9 +8,6 @@ package space.uranos
 import com.sksamuel.hoplite.ConfigFilePropertySource
 import com.sksamuel.hoplite.ConfigLoader
 import com.sksamuel.hoplite.ConfigSource
-import kotlinx.coroutines.CoroutineName
-import kotlinx.coroutines.SupervisorJob
-import kotlinx.coroutines.asCoroutineDispatcher
 import kotlinx.coroutines.runBlocking
 import space.uranos.command.Command
 import space.uranos.config.UranosConfig
@@ -26,13 +23,11 @@ import space.uranos.recipe.Recipe
 import space.uranos.server.Server
 import space.uranos.util.EncryptionUtils
 import space.uranos.util.msToTicks
+import space.uranos.util.runInServerThread
 import space.uranos.world.BiomeRegistry
 import space.uranos.world.Dimension
 import java.io.File
 import java.security.KeyPair
-import java.util.concurrent.ExecutorService
-import java.util.concurrent.Executors
-import kotlin.coroutines.CoroutineContext
 import kotlin.system.exitProcess
 
 // TODO: Consider using DI because this improves testability
@@ -50,13 +45,6 @@ class UranosServer internal constructor() : Server() {
 
     val x509EncodedPublicKey: ByteArray = EncryptionUtils.generateX509Key(keyPair.public).encoded
 
-    override lateinit var serverThread: Thread
-    private val scheduledExecutorService: ExecutorService =
-        Executors.newSingleThreadExecutor { r -> Thread(r, "Server").also { serverThread = it } }
-
-    override val coroutineContext: CoroutineContext =
-        CoroutineName("Server") + SupervisorJob() + scheduledExecutorService.asCoroutineDispatcher()
-
     override val sessions by socketServer::sessions
     override val players get() = sessions.mapNotNull { it.player as UranosPlayer? }
 
@@ -124,14 +112,16 @@ class UranosServer internal constructor() : Server() {
 
     private fun startTicking() {
         scheduler.executeRepeating(1, 0) {
-            players.forEach { it.container.tick() }
+            runInServerThread {
+                players.forEach { it.container.tick() }
 
-            entities.forEach {
-                @Suppress("DEPRECATION_ERROR")
-                it.tick()
+                entities.forEach {
+                    @Suppress("DEPRECATION_ERROR")
+                    it.tick()
+                }
+
+                sessions.forEach { it.packetsAdapter.tick() }
             }
-
-            sessions.forEach { it.packetsAdapter.tick() }
         }
     }
 

uranos-server/src/main/kotlin/space/uranos/net/PacketsAdapter.kt

@@ -9,7 +9,6 @@ import io.netty.buffer.ByteBuf
 import io.netty.util.ReferenceCountUtil
 import kotlinx.coroutines.channels.Channel
 import kotlinx.coroutines.launch
-import kotlinx.coroutines.withContext
 import space.uranos.event.ifNotCancelled
 import space.uranos.net.MinecraftProtocolDataTypes.readVarInt
 import space.uranos.net.event.PacketReceivedEvent
@@ -22,7 +21,7 @@ import space.uranos.util.awaitSuspending
 class PacketsAdapter(val session: UranosSession) {
     private val packetsForNextTick = ArrayList<OutgoingPacket>()
 
-    suspend fun tick() = withContext(session.coroutineContext) {
+    suspend fun tick() {
         packetsForNextTick.forEach { send(it) }
         packetsForNextTick.clear()
     }
@@ -44,14 +43,14 @@ class PacketsAdapter(val session: UranosSession) {
         }
     }
 
-    suspend fun sendNextTick(packet: OutgoingPacket) = withContext(session.coroutineContext) {
+    fun sendNextTick(packet: OutgoingPacket) {
         if (packet is Mergeable) {
             for (i in packetsForNextTick.indices.reversed()) {
                 val merged = packet.mergeWith(packetsForNextTick[i])
 
                 if (merged != null) {
                     packetsForNextTick[i] = merged
-                    return@withContext
+                    return
                 }
             }
         }
@@ -59,7 +58,7 @@ class PacketsAdapter(val session: UranosSession) {
         packetsForNextTick.add(packet)
     }
 
-    suspend fun send(packet: OutgoingPacket): Unit = withContext(session.coroutineContext) {
+    suspend fun send(packet: OutgoingPacket) {
         if (session.server.config.logging.shouldLog(packet)) session.logger.trace { "Sending packet: $packet" }
 
         session.server.eventBus.emit(PacketSendEvent(session, packet)).ifNotCancelled {

uranos-server/src/main/kotlin/space/uranos/net/UranosSession.kt

@@ -23,11 +23,9 @@ import space.uranos.net.packet.play.PlayProtocol
 import space.uranos.net.packet.play.PlayerInfoPacket
 import space.uranos.net.packet.status.StatusProtocol
 import space.uranos.server.event.SessionInitializedEvent
-import space.uranos.util.supervisorChild
 import java.net.InetAddress
 import java.net.InetSocketAddress
 import javax.crypto.SecretKey
-import kotlin.coroutines.CoroutineContext
 import kotlin.properties.Delegates
 
 class UranosSession(val channel: io.netty.channel.Channel, val server: UranosServer) : Session() {
@@ -36,9 +34,6 @@ class UranosSession(val channel: io.netty.channel.Channel, val server: UranosSer
     private val identifier = "UranosSession(${address.hostAddress})"
     val logger = Logger(identifier)
 
-    override val coroutineContext: CoroutineContext = server.coroutineContext.supervisorChild(identifier)
-    val scope = CoroutineScope(coroutineContext)
-
     override var brand: String? = null
 
     override var ping: Int = -1
@@ -75,9 +70,7 @@ class UranosSession(val channel: io.netty.channel.Channel, val server: UranosSer
     val packetsAdapter = PacketsAdapter(this)
 
     override suspend fun send(packet: OutgoingPacket) = packetsAdapter.send(packet)
-    override fun sendNextTick(packet: OutgoingPacket) {
-        scope.launch { packetsAdapter.sendNextTick(packet) }
-    }
+    override fun sendNextTick(packet: OutgoingPacket) = packetsAdapter.sendNextTick(packet)
 
     override suspend fun sendPluginMessage(channel: String, data: ByteBuf) {
         if (this.currentProtocol != PlayProtocol) throw IllegalStateException("The session is not using the PLAY protocol")