add async benchmark

Author: madsodgaard

Samples/SwiftJavaExtractJNISampleApp/Sources/MySwiftLibrary/Async.swift

@@ -28,3 +28,28 @@ public func asyncCopy(myClass: MySwiftClass) async throws -> MySwiftClass {
   try await Task.sleep(for: .milliseconds(500))
   return new
 }
+
+public func asyncRunningSum() async -> Int64 {
+    let totalSum = await withTaskGroup(of: Int64.self) { group in
+        // 1. Add child tasks to the group
+        for number in stride(from: Int64(1), through: 100, by: 1) {
+            group.addTask {
+                try? await Task.sleep(for: .milliseconds(number))
+                return number
+            }
+        }
+
+        var collectedSum: Int64 = 0
+
+        // `for await ... in group` loops as each child task completes,
+        // (not necessarily in the order they were added).
+        for await number in group {
+            collectedSum += number
+        }
+
+        return collectedSum
+    }
+
+    // This is the value returned by the `withTaskGroup` closure.
+    return totalSum
+}

Samples/SwiftJavaExtractJNISampleApp/src/jmh/java/com/example/swift/AsyncBenchmark.java

@@ -0,0 +1,40 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+package com.example.swift;
+
+import org.openjdk.jmh.annotations.*;
+import org.openjdk.jmh.infra.Blackhole;
+import org.swift.swiftkit.core.ClosableSwiftArena;
+import org.swift.swiftkit.core.ConfinedSwiftMemorySession;
+import org.swift.swiftkit.core.SwiftArena;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+import java.util.OptionalInt;
+import java.util.concurrent.TimeUnit;
+
+@BenchmarkMode(Mode.AverageTime)
+@Warmup(iterations = 5, time = 200, timeUnit = TimeUnit.MILLISECONDS)
+@Measurement(iterations = 10, time = 500, timeUnit = TimeUnit.MILLISECONDS)
+@OutputTimeUnit(TimeUnit.SECONDS)
+@Fork(value = 3, jvmArgsAppend = { "--enable-native-access=ALL-UNNAMED" })
+public class AsyncBenchmark {
+
+    @Benchmark
+    public long asyncSum() {
+        return MySwiftLibrary.asyncRunningSum().join();
+    }
+}