Add support for virtual workflow threads

.github/workflows/ci.yml

@@ -60,7 +60,9 @@ jobs:
     - name: Set up Java
       uses: actions/setup-java@v4
       with:
-        java-version: "11"
+        java-version: |
+          11
+          21
         distribution: "temurin"
 
     - name: Set up Gradle

temporal-sdk/build.gradle

@@ -31,6 +31,36 @@ dependencies {
     testImplementation group: 'ch.qos.logback', name: 'logback-classic', version: "${logbackVersion}"
 }
 
+// Temporal SDK supports Java 8 or later so to support virtual threads
+// we need to compile the code with Java 21 and package it in a multi-release jar.
+sourceSets {
+    java21 {
+        java {
+            srcDirs = ['src/main/java21']
+        }
+    }
+}
+
+dependencies {
+    java21Implementation files(sourceSets.main.output.classesDirs) { builtBy compileJava }
+}
+
+tasks.named('compileJava21Java') {
+    javaCompiler = javaToolchains.compilerFor {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+    options.release = 21
+}
+
+jar {
+    into('META-INF/versions/21') {
+        from sourceSets.java21.output
+    }
+    manifest.attributes(
+            'Multi-Release': 'true'
+    )
+}
+
 task registerNamespace(type: JavaExec) {
     getMainClass().set('io.temporal.internal.docker.RegisterTestNamespace')
     classpath = sourceSets.test.runtimeClasspath
@@ -49,4 +79,40 @@ task testResourceIndependent(type: Test) {
         includeCategories 'io.temporal.worker.IndependentResourceBasedTests'
         maxParallelForks = 1
     }
+}
+
+// To test the virtual thread support we need to run a seprate test suite with Java 21
+testing {
+    suites {
+        virtualThreadTests(JvmTestSuite) {
+            useJUnit(junitVersion)
+            dependencies {
+                implementation project()
+                implementation "ch.qos.logback:logback-classic:${logbackVersion}"
+                implementation project(':temporal-testing')
+
+                implementation "junit:junit:${junitVersion}"
+                implementation "org.mockito:mockito-core:${mockitoVersion}"
+                implementation 'pl.pragmatists:JUnitParams:1.1.1'
+                implementation("com.jayway.jsonpath:json-path:$jsonPathVersion"){
+                    exclude group: 'org.slf4j', module: 'slf4j-api'
+                }
+            }
+
+            targets {
+                all {
+                    testTask.configure {
+                        javaLauncher = javaToolchains.launcherFor {
+                            languageVersion = JavaLanguageVersion.of(21)
+                        }
+                        shouldRunAfter(test)
+                    }
+                }
+            }
+        }
+    }
+}
+
+tasks.named('check') {
+    dependsOn(testing.suites.virtualThreadTests)
 }

temporal-sdk/src/main/java/io/temporal/internal/task/ThreadConfigurator.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright (C) 2022 Temporal Technologies, Inc. All Rights Reserved.
+ *
+ * Copyright (C) 2012-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Modifications copyright (C) 2017 Uber Technologies, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this material 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 io.temporal.internal.task;
+
+/**
+ * Function interface for {@link VirtualThreadDelegate#newVirtualThreadExecutor(ThreadConfigurator)}
+ * called for every thread created.
+ */
+@FunctionalInterface
+public interface ThreadConfigurator {
+  /** Invoked for every thread created by {@link VirtualThreadDelegate#newVirtualThreadExecutor}. */
+  void configure(Thread t);
+}

temporal-sdk/src/main/java/io/temporal/internal/task/VirtualThreadDelegate.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2022 Temporal Technologies, Inc. All Rights Reserved.
+ *
+ * Copyright (C) 2012-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Modifications copyright (C) 2017 Uber Technologies, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this material 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 io.temporal.internal.task;
+
+import java.util.concurrent.ExecutorService;
+
+/**
+ * Internal delegate for virtual thread handling on JDK 21. This is a dummy version for reachability
+ * on JDK <21.
+ */
+public final class VirtualThreadDelegate {
+  public static ExecutorService newVirtualThreadExecutor(ThreadConfigurator configurator) {
+    throw new UnsupportedOperationException("Virtual threads not supported on JDK <21");
+  }
+
+  private VirtualThreadDelegate() {}
+}

temporal-sdk/src/main/java/io/temporal/internal/worker/ActivityWorker.java

@@ -104,7 +104,8 @@ public boolean start() {
               new TaskHandlerImpl(handler),
               pollerOptions,
               slotSupplier.maximumSlots().orElse(Integer.MAX_VALUE),
-              true);
+              true,
+              options.isUsingVirtualThreads());
       poller =
           new Poller<>(
               options.getIdentity(),

temporal-sdk/src/main/java/io/temporal/internal/worker/LocalActivityWorker.java

@@ -688,7 +688,8 @@ public boolean start() {
               new AttemptTaskHandlerImpl(handler),
               pollerOptions,
               slotSupplier.maximumSlots().orElse(Integer.MAX_VALUE),
-              false);
+              false,
+              options.isUsingVirtualThreads());
 
       this.workerMetricsScope.counter(MetricsType.WORKER_START_COUNTER).inc(1);
       this.slotQueue.start();

temporal-sdk/src/main/java/io/temporal/internal/worker/NexusWorker.java

@@ -102,7 +102,8 @@ public boolean start() {
               new TaskHandlerImpl(handler),
               pollerOptions,
               slotSupplier.maximumSlots().orElse(Integer.MAX_VALUE),
-              true);
+              true,
+              options.isUsingVirtualThreads());
       poller =
           new Poller<>(
               options.getIdentity(),

temporal-sdk/src/main/java/io/temporal/internal/worker/PollTaskExecutor.java

@@ -22,8 +22,10 @@
 
 import com.google.common.base.Preconditions;
 import io.temporal.internal.logging.LoggerTag;
+import io.temporal.internal.task.VirtualThreadDelegate;
 import java.util.Objects;
 import java.util.concurrent.*;
+import java.util.concurrent.atomic.AtomicInteger;
 import javax.annotation.Nonnull;
 import org.slf4j.MDC;
 
@@ -41,7 +43,7 @@ public interface TaskHandler<TT> {
   private final TaskHandler<T> handler;
   private final PollerOptions pollerOptions;
 
-  private final ThreadPoolExecutor taskExecutor;
+  private final ExecutorService taskExecutor;
   private final String pollThreadNamePrefix;
 
   PollTaskExecutor(
@@ -51,35 +53,46 @@ public interface TaskHandler<TT> {
       @Nonnull TaskHandler<T> handler,
       @Nonnull PollerOptions pollerOptions,
       int workerTaskSlots,
-      boolean synchronousQueue) {
+      boolean synchronousQueue,
+      boolean useVirtualThreads) {
     this.namespace = Objects.requireNonNull(namespace);
     this.taskQueue = Objects.requireNonNull(taskQueue);
     this.identity = Objects.requireNonNull(identity);
     this.handler = Objects.requireNonNull(handler);
     this.pollerOptions = Objects.requireNonNull(pollerOptions);
 
-    this.taskExecutor =
-        new ThreadPoolExecutor(
-            // for SynchronousQueue we can afford to set it to 0, because the queue is always full
-            // or empty
-            // for LinkedBlockingQueue we have to set slots to workerTaskSlots to avoid situation
-            // when the queue grows, but the amount of threads is not, because the queue is not (and
-            // never) full
-            synchronousQueue ? 0 : workerTaskSlots,
-            workerTaskSlots,
-            10,
-            TimeUnit.SECONDS,
-            synchronousQueue ? new SynchronousQueue<>() : new LinkedBlockingQueue<>());
-    this.taskExecutor.allowCoreThreadTimeOut(true);
-
     this.pollThreadNamePrefix =
         pollerOptions.getPollThreadNamePrefix().replaceFirst("Poller", "Executor");
-
-    this.taskExecutor.setThreadFactory(
-        new ExecutorThreadFactory(
-            pollerOptions.getPollThreadNamePrefix().replaceFirst("Poller", "Executor"),
-            pollerOptions.getUncaughtExceptionHandler()));
-    this.taskExecutor.setRejectedExecutionHandler(new BlockCallerPolicy());
+    // If virtual threads are enabled, we use a virtual thread executor.
+    if (useVirtualThreads) {
+      AtomicInteger threadIndex = new AtomicInteger();
+      this.taskExecutor =
+          VirtualThreadDelegate.newVirtualThreadExecutor(
+              (t) -> {
+                t.setName(this.pollThreadNamePrefix + ": " + threadIndex.incrementAndGet());
+                t.setUncaughtExceptionHandler(pollerOptions.getUncaughtExceptionHandler());
+              });
+    } else {
+      ThreadPoolExecutor threadPoolTaskExecutor =
+          new ThreadPoolExecutor(
+              // for SynchronousQueue we can afford to set it to 0, because the queue is always full
+              // or empty
+              // for LinkedBlockingQueue we have to set slots to workerTaskSlots to avoid situation
+              // when the queue grows, but the amount of threads is not, because the queue is not
+              // (and
+              // never) full
+              synchronousQueue ? 0 : workerTaskSlots,
+              workerTaskSlots,
+              10,
+              TimeUnit.SECONDS,
+              synchronousQueue ? new SynchronousQueue<>() : new LinkedBlockingQueue<>());
+      threadPoolTaskExecutor.allowCoreThreadTimeOut(true);
+      threadPoolTaskExecutor.setThreadFactory(
+          new ExecutorThreadFactory(
+              this.pollThreadNamePrefix, pollerOptions.getUncaughtExceptionHandler()));
+      threadPoolTaskExecutor.setRejectedExecutionHandler(new BlockCallerPolicy());
+      this.taskExecutor = threadPoolTaskExecutor;
+    }
   }
 
   @Override

temporal-sdk/src/main/java/io/temporal/internal/worker/Poller.java

@@ -25,10 +25,12 @@
 import io.grpc.StatusRuntimeException;
 import io.temporal.internal.BackoffThrottler;
 import io.temporal.internal.common.GrpcUtils;
+import io.temporal.internal.task.VirtualThreadDelegate;
 import io.temporal.worker.MetricsType;
 import java.time.Duration;
 import java.util.Objects;
 import java.util.concurrent.*;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -57,7 +59,7 @@ interface ThrowingRunnable {
   private final PollTask<T> pollTask;
   private final PollerOptions pollerOptions;
   private static final Logger log = LoggerFactory.getLogger(Poller.class);
-  private ThreadPoolExecutor pollExecutor;
+  private ExecutorService pollExecutor;
   private final Scope workerMetricsScope;
 
   private final AtomicReference<CountDownLatch> suspendLatch = new AtomicReference<>();
@@ -97,20 +99,34 @@ public boolean start() {
               pollerOptions.getMaximumPollRatePerSecond(),
               pollerOptions.getMaximumPollRateIntervalMilliseconds());
     }
-
-    // It is important to pass blocking queue of at least options.getPollThreadCount() capacity. As
-    // task enqueues next task the buffering is needed to queue task until the previous one releases
-    // a thread.
-    pollExecutor =
-        new ThreadPoolExecutor(
-            pollerOptions.getPollThreadCount(),
-            pollerOptions.getPollThreadCount(),
-            1,
-            TimeUnit.SECONDS,
-            new ArrayBlockingQueue<>(pollerOptions.getPollThreadCount()));
-    pollExecutor.setThreadFactory(
-        new ExecutorThreadFactory(
-            pollerOptions.getPollThreadNamePrefix(), pollerOptions.getUncaughtExceptionHandler()));
+    // If virtual threads are enabled, we use a virtual thread executor.
+    if (pollerOptions.isUsingVirtualThreads()) {
+      AtomicInteger threadIndex = new AtomicInteger();
+      pollExecutor =
+          VirtualThreadDelegate.newVirtualThreadExecutor(
+              (t) -> {
+                // TODO: Consider using a more descriptive name for the thread.
+                t.setName(
+                    pollerOptions.getPollThreadNamePrefix() + ": " + threadIndex.incrementAndGet());
+                t.setUncaughtExceptionHandler(uncaughtExceptionHandler);
+              });
+    } else {
+      // It is important to pass blocking queue of at least options.getPollThreadCount() capacity.
+      // As task enqueues next task the buffering is needed to queue task until the previous one
+      // releases a thread.
+      ThreadPoolExecutor threadPoolPoller =
+          new ThreadPoolExecutor(
+              pollerOptions.getPollThreadCount(),
+              pollerOptions.getPollThreadCount(),
+              1,
+              TimeUnit.SECONDS,
+              new ArrayBlockingQueue<>(pollerOptions.getPollThreadCount()));
+      threadPoolPoller.setThreadFactory(
+          new ExecutorThreadFactory(
+              pollerOptions.getPollThreadNamePrefix(),
+              pollerOptions.getUncaughtExceptionHandler()));
+      pollExecutor = threadPoolPoller;
+    }
 
     for (int i = 0; i < pollerOptions.getPollThreadCount(); i++) {
       pollExecutor.execute(new PollLoopTask(new PollExecutionTask()));