From c701e387373fc624d9014d698e9e4a4384b25f39 Mon Sep 17 00:00:00 2001
From: Laird Nelson <laird.nelson@oracle.com>
Date: Thu, 29 Oct 2020 10:52:39 -0700
Subject: [PATCH] Initial stab at incorporating some Loom features into Helidon
 in a way that will work under JDK 11 or 16-loom-ea (#2417)

Signed-off-by: Laird Nelson <laird.nelson@oracle.com>
---
 .../server/ServerCdiExtension.java            | 29 +++++++++++++--
 pom.xml                                       | 29 +++++++++++++++
 .../jersey/AsyncExecutorProvider.java         | 36 +++++++++++++++++--
 3 files changed, 89 insertions(+), 5 deletions(-)

diff --git a/microprofile/server/src/main/java/io/helidon/microprofile/server/ServerCdiExtension.java b/microprofile/server/src/main/java/io/helidon/microprofile/server/ServerCdiExtension.java
index 417c6764f..0ddc0fdbb 100644
--- a/microprofile/server/src/main/java/io/helidon/microprofile/server/ServerCdiExtension.java
+++ b/microprofile/server/src/main/java/io/helidon/microprofile/server/ServerCdiExtension.java
@@ -27,6 +27,7 @@ import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Supplier;
@@ -108,10 +109,34 @@ public class ServerCdiExtension implements Extension {
 
         // make sure all configuration is in place
         if (null == jaxRsExecutorService) {
-            jaxRsExecutorService = ServerThreadPoolSupplier.builder()
+            Config serverConfig = config.get("server");
+            final java.lang.reflect.Method m;
+            if (serverConfig.get("virtual-threads").asBoolean().orElse(false)) {
+                java.lang.reflect.Method temp = null;
+                try {
+                    temp = Executors.class.getDeclaredMethod("newVirtualThreadExecutor");
+                } catch (final ReflectiveOperationException notLoomEarlyAccess) {
+                    temp = null;
+                } finally {
+                    m = temp;
+                }
+            } else {
+                m = null;
+            }
+            if (m != null) {
+                jaxRsExecutorService = () -> {
+                    try {
+                        return (ExecutorService) m.invoke(null);
+                    } catch (final ReflectiveOperationException reflectiveOperationException) {
+                        throw new IllegalStateException(reflectiveOperationException.getMessage(), reflectiveOperationException);
+                    }
+                };
+            } else {
+                jaxRsExecutorService = ServerThreadPoolSupplier.builder()
                     .name("server")
-                    .config(config.get("server.executor-service"))
+                    .config(serverConfig.get("server.executor-service"))
                     .build();
+            }
         }
 
         // redirect to the first page when root is accessed (if configured)
diff --git a/pom.xml b/pom.xml
index bd950db35..17d27d363 100644
--- a/pom.xml
+++ b/pom.xml
@@ -1456,5 +1456,34 @@ helidon-parent,helidon-dependencies,helidon-bom,helidon-se,helidon-mp,io.grpc,he
                 </plugins>
             </build>
         </profile>
+        <profile>
+            <id>loom</id>
+            <activation>
+                <jdk>16-loom</jdk>
+            </activation>
+            <build>
+                <pluginManagement>
+                    <plugins>
+                        <plugin>
+                            <groupId>org.apache.maven.plugins</groupId>
+                            <artifactId>maven-compiler-plugin</artifactId>
+                            <configuration>
+                                <source>16</source>
+                                <target>16</target>
+                                <release>16</release>
+                            </configuration>
+                        </plugin>
+                        <plugin>
+                            <groupId>org.apache.maven.plugins</groupId>
+                            <artifactId>maven-javadoc-plugin</artifactId>
+                            <configuration>
+                                <source>16</source>
+                                <release>16</release>
+                            </configuration>
+                        </plugin>
+                    </plugins>
+                </pluginManagement>
+            </build>
+        </profile>
     </profiles>
 </project>
diff --git a/webserver/jersey/src/main/java/io/helidon/webserver/jersey/AsyncExecutorProvider.java b/webserver/jersey/src/main/java/io/helidon/webserver/jersey/AsyncExecutorProvider.java
index dca99048c..a1236cd96 100644
--- a/webserver/jersey/src/main/java/io/helidon/webserver/jersey/AsyncExecutorProvider.java
+++ b/webserver/jersey/src/main/java/io/helidon/webserver/jersey/AsyncExecutorProvider.java
@@ -16,7 +16,9 @@
 
 package io.helidon.webserver.jersey;
 
+import java.util.Objects;
 import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.function.Supplier;
 
 import io.helidon.common.configurable.ThreadPoolSupplier;
@@ -30,23 +32,51 @@ class AsyncExecutorProvider implements ExecutorServiceProvider {
     private final Supplier<ExecutorService> executorServiceSupplier;
 
     AsyncExecutorProvider(Supplier<ExecutorService> supplier) {
-        this.executorServiceSupplier = supplier;
+        this.executorServiceSupplier = Objects.requireNonNull(supplier);
     }
 
     static ExecutorServiceProvider create(Config config) {
-        return new AsyncExecutorProvider(ThreadPoolSupplier.builder()
+        Config asyncExecutorServiceConfig = config.get("async-executor-service");
+        final java.lang.reflect.Method m;
+        if (asyncExecutorServiceConfig.get("virtual-threads").asBoolean().orElse(false)) {
+            java.lang.reflect.Method temp = null;
+            try {
+                temp = Executors.class.getDeclaredMethod("newVirtualThreadExecutor");
+            } catch (final ReflectiveOperationException notLoom) {
+                temp = null;
+            } finally {
+                m = temp;
+            }
+        } else {
+            m = null;
+        }
+        if (m != null) {
+            return new AsyncExecutorProvider(() -> {
+                try {
+                    return (ExecutorService) m.invoke(null);
+                } catch (final ReflectiveOperationException reflectiveOperationException) {
+                    throw new IllegalStateException(reflectiveOperationException.getMessage(), reflectiveOperationException);
+                }
+            });
+        } else {
+            return new AsyncExecutorProvider(ThreadPoolSupplier.builder()
                                                  .corePoolSize(1)
                                                  .maxPoolSize(10)
                                                  .prestart(false)
                                                  .threadNamePrefix("helidon-jersey-async")
-                                                 .config(config.get("async-executor-service"))
+                                                 .config(asyncExecutorServiceConfig)
                                                  .build());
+        }
     }
 
     static ExecutorServiceProvider create(ExecutorService executor) {
         return new AsyncExecutorProvider(() -> executor);
     }
 
+    static ExecutorServiceProvider create(Supplier<ExecutorService> executorServiceSupplier) {
+        return new AsyncExecutorProvider(executorServiceSupplier);
+    }
+
     @Override
     public ExecutorService getExecutorService() {
         return executorServiceSupplier.get();