chore: Proper test virtual thread dispatcher and update doc.

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

@@ -34,7 +34,7 @@ object VirtualThreadPoolDispatcherSpec {
 
     override def receive = {
       case "ping" =>
-        sender() ! "All fine"
+        sender() ! Thread.currentThread().getName
     }
   }
 
@@ -43,14 +43,16 @@ object VirtualThreadPoolDispatcherSpec {
 class VirtualThreadPoolDispatcherSpec extends PekkoSpec(VirtualThreadPoolDispatcherSpec.config) with ImplicitSender {
   import VirtualThreadPoolDispatcherSpec._
 
-  val Iterations = 1000
-
   "VirtualThreadPool support" must {
 
     "handle simple dispatch" in {
       val innocentActor = system.actorOf(Props(new InnocentActor).withDispatcher("virtual-thread-dispatcher"))
-      innocentActor ! "ping"
-      expectMsg("All fine")
+      for (_ <- 1 to 1000) {
+        innocentActor ! "ping"
+        expectMsgPF() { case name: String =>
+          name should include("VirtualThreadPoolDispatcherSpec-virtual-thread-dispatcher-virtual-thread-")
+        }
+      }
     }
 
   }

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

@@ -417,7 +417,7 @@ final class VirtualThreadExecutorConfigurator(config: Config, prerequisites: Dis
     val tf: ThreadFactory = threadFactory match {
       case MonitorableThreadFactory(name, _, contextClassLoader, exceptionHandler, _) =>
         new ThreadFactory {
-          private val vtFactory = newVirtualThreadFactory(name)
+          private val vtFactory = newVirtualThreadFactory(name + "-" + id)
 
           override def newThread(r: Runnable): Thread = {
             val vt = vtFactory.newThread(r)
@@ -426,7 +426,7 @@ final class VirtualThreadExecutorConfigurator(config: Config, prerequisites: Dis
             vt
           }
         }
-      case _ => VirtualThreadSupport.newVirtualThreadFactory(prerequisites.settings.name);
+      case _ => VirtualThreadSupport.newVirtualThreadFactory(prerequisites.settings.name + "-" + id);
     }
     new ExecutorServiceFactory {
       import VirtualThreadSupport._

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

@@ -68,6 +68,7 @@ private[dispatch] object VirtualThreadSupport {
       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)
     }
   }

docs/src/main/paradox/dispatchers.md

@@ -42,6 +42,8 @@ allocated by the ForkJoinPool. It is a setting specifically talking about the nu
 threads the pool keep running in order to reduce the latency of handling a new incoming task.
 You can read more about parallelism in the JDK's [ForkJoinPool documentation](https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ForkJoinPool.html).
 
+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.
+
 @@@
 
 Another example that uses the "thread-pool-executor":

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

@@ -127,6 +127,8 @@ allocated by the ForkJoinPool. It is a setting specifically talking about the nu
 threads the pool will keep running in order to reduce the latency of handling a new incoming task.
 You can read more about parallelism in the JDK's [ForkJoinPool documentation](https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ForkJoinPool.html).
 
+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.
+
 @@@
 
 @@@ note

project/PekkoBuild.scala

@@ -290,6 +290,7 @@ object PekkoBuild {
         UsefulTask("testQuick",
           "Runs all the tests. When run multiple times will only run previously failing tests (shell mode only)"),
         UsefulTask("testOnly *.AnySpec", "Only run a selected test"),
+        UsefulTask("TestJdk9 / testOnly *.AnySpec", "Only run a Jdk9+ selected test"),
         UsefulTask("testQuick *.AnySpec",
           "Only run a selected test. When run multiple times will only run previously failing tests (shell mode only)"),
         UsefulTask("testQuickUntilPassed", "Runs all tests in a continuous loop until all tests pass"),