feat: Add support for switching scheduler

actor-tests/src/test/scala-jdk21-only/org/apache/pekko/dispatch/ForkJoinPoolVirtualThreadSpec.scala

@@ -0,0 +1,69 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.pekko.dispatch
+
+import com.typesafe.config.ConfigFactory
+
+import org.apache.pekko
+import pekko.actor.{ Actor, Props }
+import pekko.testkit.{ ImplicitSender, PekkoSpec }
+import pekko.util.JavaVersion
+
+object ForkJoinPoolVirtualThreadSpec {
+  val config = ConfigFactory.parseString("""
+      |custom {
+      |  task-dispatcher {
+      |    mailbox-type = "org.apache.pekko.dispatch.SingleConsumerOnlyUnboundedMailbox"
+      |    throughput = 5
+      |    fork-join-executor {
+      |      parallelism-factor = 2
+      |      parallelism-max = 2
+      |      parallelism-min = 2
+      |      virtualize = on
+      |    }
+      |  }
+      |}
+    """.stripMargin)
+
+  class ThreadNameActor extends Actor {
+
+    override def receive = {
+      case "ping" =>
+        sender() ! Thread.currentThread().getName
+    }
+  }
+
+}
+
+class ForkJoinPoolVirtualThreadSpec extends PekkoSpec(ForkJoinPoolVirtualThreadSpec.config) with ImplicitSender {
+  import ForkJoinPoolVirtualThreadSpec._
+
+  "PekkoForkJoinPool" must {
+
+    "support virtualization with Virtual Thread" in {
+      val actor = system.actorOf(Props(new ThreadNameActor).withDispatcher("custom.task-dispatcher"))
+      for (_ <- 1 to 1000) {
+        actor ! "ping"
+        expectMsgPF() { case name: String =>
+          name should include("ForkJoinPoolVirtualThreadSpec-custom.task-dispatcher-virtual-thread-")
+        }
+      }
+    }
+
+  }
+}

actor/src/main/resources/reference.conf

@@ -487,6 +487,19 @@ pekko {
         # This config is new in Pekko v1.1.0 and only has an effect if you are running with JDK 9 and above.
         # Read the documentation on `java.util.concurrent.ForkJoinPool` to find out more. Default in hex is 0x7fff.
         maximum-pool-size = 32767
+
+        # This config is new in Pekko v1.2.0 and only has an effect if you are running with JDK 21 and above,
+        # When set to `on` but underlying runtime does not support virtual threads, an Exception will throw.
+        # Virtualize this dispatcher as a virtual-thread-executor
+        # Valid values are: `on`, `off`
+        #
+        # NOTE: THIS IS AN ADVANCED OPTION, USE WITH CAUTION.
+        # REQUIREMENTS:
+        # 1. JDK 21+
+        # 2. add options to the JVM:
+        #   --add-opens=java.base/jdk.internal.misc=ALL-UNNAMED
+        #   --add-opens=java.base/java.lang=ALL-UNNAMED
+        virtualize = off
       }
 
       # This will be used if you have set "executor = "thread-pool-executor""

actor/src/main/scala/org/apache/pekko/dispatch/AbstractDispatcher.scala

@@ -453,7 +453,7 @@ final class VirtualThreadExecutorConfigurator(config: Config, prerequisites: Dis
           }
         }
         new VirtualizedExecutorService(
-          tf,
+          tf, // the virtual thread factory
           pool, // the default scheduler of virtual thread
           loadMetricsProvider,
           cascadeShutdown = false // we don't want to cascade shutdown the default virtual thread scheduler

actor/src/main/scala/org/apache/pekko/dispatch/ForkJoinExecutorConfigurator.scala

@@ -14,13 +14,14 @@
 package org.apache.pekko.dispatch
 
 import com.typesafe.config.Config
+import org.apache.pekko
+import pekko.dispatch.VirtualThreadSupport.newVirtualThreadFactory
+import pekko.util.JavaVersion
 
 import java.lang.invoke.{ MethodHandle, MethodHandles, MethodType }
-import java.util.concurrent.{ ExecutorService, ForkJoinPool, ForkJoinTask, ThreadFactory }
+import java.util.concurrent.{ Executor, ExecutorService, ForkJoinPool, ForkJoinTask, ThreadFactory }
 import scala.util.Try
 
-import org.apache.pekko.util.JavaVersion
-
 object ForkJoinExecutorConfigurator {
 
   /**
@@ -86,15 +87,28 @@ class ForkJoinExecutorConfigurator(config: Config, prerequisites: DispatcherPrer
   }
 
   class ForkJoinExecutorServiceFactory(
+      val id: String,
       val threadFactory: ForkJoinPool.ForkJoinWorkerThreadFactory,
       val parallelism: Int,
       val asyncMode: Boolean,
-      val maxPoolSize: Int)
+      val maxPoolSize: Int,
+      val virtualize: Boolean)
       extends ExecutorServiceFactory {
+    def this(threadFactory: ForkJoinPool.ForkJoinWorkerThreadFactory,
+        parallelism: Int,
+        asyncMode: Boolean,
+        maxPoolSize: Int,
+        virtualize: Boolean) =
+      this(null, threadFactory, parallelism, asyncMode, maxPoolSize, virtualize)
 
     def this(threadFactory: ForkJoinPool.ForkJoinWorkerThreadFactory,
         parallelism: Int,
-        asyncMode: Boolean) = this(threadFactory, parallelism, asyncMode, ForkJoinPoolConstants.MaxCap)
+        asyncMode: Boolean) = this(threadFactory, parallelism, asyncMode, ForkJoinPoolConstants.MaxCap, false)
+
+    def this(threadFactory: ForkJoinPool.ForkJoinWorkerThreadFactory,
+        parallelism: Int,
+        asyncMode: Boolean,
+        maxPoolSize: Int) = this(threadFactory, parallelism, asyncMode, maxPoolSize, false)
 
     private def pekkoJdk9ForkJoinPoolClassOpt: Option[Class[_]] =
       Try(Class.forName("org.apache.pekko.dispatch.PekkoJdk9ForkJoinPool")).toOption
@@ -116,12 +130,50 @@ class ForkJoinExecutorConfigurator(config: Config, prerequisites: DispatcherPrer
     def this(threadFactory: ForkJoinPool.ForkJoinWorkerThreadFactory, parallelism: Int) =
       this(threadFactory, parallelism, asyncMode = true)
 
-    def createExecutorService: ExecutorService = pekkoJdk9ForkJoinPoolHandleOpt match {
-      case Some(handle) =>
-        handle.invoke(parallelism, threadFactory, maxPoolSize,
-          MonitorableThreadFactory.doNothing, asyncMode).asInstanceOf[ExecutorService]
-      case _ =>
-        new PekkoForkJoinPool(parallelism, threadFactory, MonitorableThreadFactory.doNothing, asyncMode)
+    def createExecutorService: ExecutorService = {
+      val tf = if (virtualize && JavaVersion.majorVersion >= 21) {
+        threadFactory match {
+          // we need to use the thread factory to create carrier thread
+          case m: MonitorableThreadFactory => new MonitorableCarrierThreadFactory(m.name)
+          case _                           => threadFactory
+        }
+      } else threadFactory
+
+      val pool = pekkoJdk9ForkJoinPoolHandleOpt match {
+        case Some(handle) =>
+          // carrier Thread only exists in JDK 17+
+          handle.invoke(parallelism, tf, maxPoolSize, MonitorableThreadFactory.doNothing, asyncMode)
+            .asInstanceOf[ExecutorService with LoadMetrics]
+        case _ =>
+          new PekkoForkJoinPool(parallelism, tf, MonitorableThreadFactory.doNothing, asyncMode)
+      }
+
+      if (virtualize && JavaVersion.majorVersion >= 21) {
+        // when virtualized, we need enhanced thread factory
+        val factory: ThreadFactory = threadFactory match {
+          case MonitorableThreadFactory(name, _, contextClassLoader, exceptionHandler, _) =>
+            new ThreadFactory {
+              private val vtFactory = newVirtualThreadFactory(name, pool) // use the pool as the scheduler
+
+              override def newThread(r: Runnable): Thread = {
+                val vt = vtFactory.newThread(r)
+                vt.setUncaughtExceptionHandler(exceptionHandler)
+                contextClassLoader.foreach(vt.setContextClassLoader)
+                vt
+              }
+            }
+          case _ => newVirtualThreadFactory(prerequisites.settings.name, pool); // use the pool as the scheduler
+        }
+        // wrap the pool with virtualized executor service
+        new VirtualizedExecutorService(
+          factory, // the virtual thread factory
+          pool, // the underlying pool
+          (_: Executor) => pool.atFullThrottle(), // the load metrics provider, we use the pool itself
+          cascadeShutdown = true // cascade shutdown
+        )
+      } else {
+        pool
+      }
     }
   }
 
@@ -143,12 +195,14 @@ class ForkJoinExecutorConfigurator(config: Config, prerequisites: DispatcherPrer
     }
 
     new ForkJoinExecutorServiceFactory(
+      id,
       validate(tf),
       ThreadPoolConfig.scaledPoolSize(
         config.getInt("parallelism-min"),
         config.getDouble("parallelism-factor"),
         config.getInt("parallelism-max")),
       asyncMode,
-      config.getInt("maximum-pool-size"))
+      config.getInt("maximum-pool-size"),
+      config.getBoolean("virtualize"))
   }
 }

actor/src/main/scala/org/apache/pekko/dispatch/ThreadPoolBuilder.scala

@@ -235,6 +235,18 @@ final case class MonitorableThreadFactory(
   }
 }
 
+class MonitorableCarrierThreadFactory(name: String)
+    extends ForkJoinPool.ForkJoinWorkerThreadFactory {
+  private val counter = new AtomicLong(0L)
+
+  def newThread(pool: ForkJoinPool): ForkJoinWorkerThread = {
+    val thread = VirtualThreadSupport.CarrierThreadFactory.newThread(pool)
+    // Name of the threads for the ForkJoinPool are not customizable. Change it here.
+    thread.setName(name + "-" + "CarrierThread" + "-" + counter.incrementAndGet())
+    thread
+  }
+}
+
 /**
  * As the name says
  */

actor/src/main/scala/org/apache/pekko/dispatch/VirtualThreadSupport.scala

@@ -17,11 +17,12 @@
 
 package org.apache.pekko.dispatch
 
-import org.apache.pekko.annotation.InternalApi
-import org.apache.pekko.util.JavaVersion
+import org.apache.pekko
+import pekko.annotation.InternalApi
+import pekko.util.JavaVersion
 
 import java.lang.invoke.{ MethodHandles, MethodType }
-import java.util.concurrent.{ ExecutorService, ForkJoinPool, ThreadFactory }
+import java.util.concurrent.{ ExecutorService, ForkJoinPool, ForkJoinWorkerThread, ThreadFactory }
 import scala.util.control.NonFatal
 
 @InternalApi
@@ -34,8 +35,26 @@ private[dispatch] object VirtualThreadSupport {
   val isSupported: Boolean = JavaVersion.majorVersion >= 21
 
   /**
-   * Create a virtual thread factory with a executor, the executor will be used as the scheduler of
-   * virtual thread.
+   * Create a newThreadPerTaskExecutor with the specified thread factory.
+   */
+  def newThreadPerTaskExecutor(threadFactory: ThreadFactory): ExecutorService = {
+    require(threadFactory != null, "threadFactory should not be null.")
+    try {
+      val executorsClazz = ClassLoader.getSystemClassLoader.loadClass("java.util.concurrent.Executors")
+      val newThreadPerTaskExecutorMethod = lookup.findStatic(
+        executorsClazz,
+        "newThreadPerTaskExecutor",
+        MethodType.methodType(classOf[ExecutorService], classOf[ThreadFactory]))
+      newThreadPerTaskExecutorMethod.invoke(threadFactory).asInstanceOf[ExecutorService]
+    } catch {
+      case NonFatal(e) =>
+        // --add-opens java.base/java.lang=ALL-UNNAMED
+        throw new UnsupportedOperationException("Failed to create newThreadPerTaskExecutor.", e)
+    }
+  }
+
+  /**
+   * Create a virtual thread factory with the default Virtual Thread executor.
    */
   def newVirtualThreadFactory(prefix: String): ThreadFactory = {
     require(isSupported, "Virtual thread is not supported.")
@@ -57,19 +76,38 @@ private[dispatch] object VirtualThreadSupport {
     }
   }
 
-  def newThreadPerTaskExecutor(threadFactory: ThreadFactory): ExecutorService = {
-    require(threadFactory != null, "threadFactory should not be null.")
+  /**
+   * Create a virtual thread factory with the specified executor as the scheduler of virtual thread.
+   */
+  def newVirtualThreadFactory(prefix: String, executor: ExecutorService): ThreadFactory =
     try {
-      val executorsClazz = ClassLoader.getSystemClassLoader.loadClass("java.util.concurrent.Executors")
-      val newThreadPerTaskExecutorMethod = lookup.findStatic(
-        executorsClazz,
-        "newThreadPerTaskExecutor",
-        MethodType.methodType(classOf[ExecutorService], classOf[ThreadFactory]))
-      newThreadPerTaskExecutorMethod.invoke(threadFactory).asInstanceOf[ExecutorService]
+      val builderClass = ClassLoader.getSystemClassLoader.loadClass("java.lang.Thread$Builder")
+      val ofVirtualClass = ClassLoader.getSystemClassLoader.loadClass("java.lang.Thread$Builder$OfVirtual")
+      val ofVirtualMethod = classOf[Thread].getDeclaredMethod("ofVirtual")
+      var builder = ofVirtualMethod.invoke(null)
+      if (executor != null) {
+        val clazz = builder.getClass
+        val field = clazz.getDeclaredField("scheduler")
+        field.setAccessible(true)
+        field.set(builder, executor)
+      }
+      val nameMethod = ofVirtualClass.getDeclaredMethod("name", classOf[String], classOf[Long])
+      val factoryMethod = builderClass.getDeclaredMethod("factory")
+      val zero = java.lang.Long.valueOf(0L)
+      builder = nameMethod.invoke(builder, prefix + "-virtual-thread-", zero)
+      factoryMethod.invoke(builder).asInstanceOf[ThreadFactory]
     } catch {
       case NonFatal(e) =>
         // --add-opens java.base/java.lang=ALL-UNNAMED
-        throw new UnsupportedOperationException("Failed to create newThreadPerTaskExecutor.", e)
+        throw new UnsupportedOperationException("Failed to create virtual thread factory", e)
+    }
+
+  object CarrierThreadFactory extends ForkJoinPool.ForkJoinWorkerThreadFactory {
+    private val clazz = ClassLoader.getSystemClassLoader.loadClass("jdk.internal.misc.CarrierThread")
+    // TODO lookup.findClass is only available in Java 9
+    private val constructor = clazz.getDeclaredConstructor(classOf[ForkJoinPool])
+    override def newThread(pool: ForkJoinPool): ForkJoinWorkerThread = {
+      constructor.newInstance(pool).asInstanceOf[ForkJoinWorkerThread]
     }
   }
 
@@ -79,7 +117,7 @@ private[dispatch] object VirtualThreadSupport {
   def getVirtualThreadDefaultScheduler: ForkJoinPool =
     try {
       require(isSupported, "Virtual thread is not supported.")
-      val clazz = Class.forName("java.lang.VirtualThread")
+      val clazz = ClassLoader.getSystemClassLoader.loadClass("java.lang.VirtualThread")
       val fieldName = "DEFAULT_SCHEDULER"
       val field = clazz.getDeclaredField(fieldName)
       field.setAccessible(true)

actor/src/main/scala/org/apache/pekko/dispatch/VirtualizedExecutorService.scala

@@ -39,13 +39,6 @@ final class VirtualizedExecutorService(
   require(vtFactory != null, "Virtual thread factory must not be null")
   require(loadMetricsProvider != null, "Load metrics provider must not be null")
 
-  def this(prefix: String,
-      underlying: ExecutorService,
-      loadMetricsProvider: Executor => Boolean,
-      cascadeShutdown: Boolean) = {
-    this(VirtualThreadSupport.newVirtualThreadFactory(prefix), underlying, loadMetricsProvider, cascadeShutdown)
-  }
-
   private val executor = VirtualThreadSupport.newThreadPerTaskExecutor(vtFactory)
 
   override def atFullThrottle(): Boolean = loadMetricsProvider(this)

docs/src/main/paradox/dispatchers.md

@@ -44,6 +44,17 @@ You can read more about parallelism in the JDK's [ForkJoinPool documentation](ht
 
 When Running on Java 9+, you can use `maximum-pool-size` to set the upper bound on the total number of threads allocated by the ForkJoinPool.
 
+**Experimental**: When Running on Java 21+, you can use `virtualize=on` to enable the virtual threads feature.
+When using virtual threads, all virtual threads will use the same `unparker`, so you may want to 
+increase the number of `jdk.unparker.maxPoolSize`. 
+
+NOTE: THIS IS AN ADVANCED OPTION, USE WITH CAUTION.
+REQUIREMENTS:
+
+1. JDK 21+
+2. add options to the JVM:
+ - --add-opens=java.base/jdk.internal.misc=ALL-UNNAMED
+ - --add-opens=java.base/java.lang=ALL-UNNAMED
 @@@
 
 Another example that uses the "thread-pool-executor":

docs/src/main/paradox/typed/dispatchers.md

@@ -129,6 +129,18 @@ You can read more about parallelism in the JDK's [ForkJoinPool documentation](ht
 
 When Running on Java 9+, you can use `maximum-pool-size` to set the upper bound on the total number of threads allocated by the ForkJoinPool.
 
+**Experimental**: When Running on Java 21+, you can use `virtualize=on` to enable the virtual threads feature.
+When using virtual threads, all virtual threads will use the same `unparker`, so you may want to
+increase the number of `jdk.unparker.maxPoolSize`.
+
+NOTE: THIS IS AN ADVANCED OPTION, USE WITH CAUTION.
+REQUIREMENTS:
+
+1. JDK 21+
+2. add options to the JVM:
+ - --add-opens=java.base/jdk.internal.misc=ALL-UNNAMED
+ - --add-opens=java.base/java.lang=ALL-UNNAMED
+
 @@@
 
 @@@ note