Added Async benchmark for future changes

src/test/java/benchmark/AsyncBenchmark.java

@@ -0,0 +1,78 @@
+package benchmark;
+
+import graphql.execution.Async;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Level;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+import org.openjdk.jmh.runner.Runner;
+import org.openjdk.jmh.runner.options.Options;
+import org.openjdk.jmh.runner.options.OptionsBuilder;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+
+@State(Scope.Benchmark)
+@BenchmarkMode(Mode.Throughput)
+@Warmup(iterations = 2)
+@Measurement(iterations = 2, timeUnit = TimeUnit.NANOSECONDS)
+public class AsyncBenchmark {
+
+    @Param({"0", "1", "10"})
+    public int num;
+
+    List<CompletableFuture<Object>> futures;
+
+    @Setup(Level.Trial)
+    public void setUp() throws ExecutionException, InterruptedException {
+        futures = new ArrayList<>();
+        for (int i = 0; i < num; i++) {
+            futures.add(mkFuture(i));
+        }
+
+    }
+
+    private CompletableFuture<Object> mkFuture(int i) {
+        // half will take some time
+        if (i % 2 == 0) {
+            return CompletableFuture.supplyAsync(() -> sleep(i));
+        } else {
+            return CompletableFuture.completedFuture(i);
+        }
+    }
+
+    private Object sleep(int i) {
+        try {
+            Thread.sleep(i * 1000L);
+        } catch (InterruptedException e) {
+            throw new RuntimeException(e);
+        }
+        return i;
+    }
+
+    @Benchmark
+    public List<Object> benchmarkAsync() {
+        Async.CombinedBuilder<Object> builder = Async.ofExpectedSize(futures.size());
+        futures.forEach(builder::add);
+        return builder.await().join();
+    }
+
+    public static void main(String[] args) throws Exception {
+        Options opt = new OptionsBuilder()
+                .include("benchmark.AsyncBenchmark")
+                .forks(5)
+                .build();
+
+        new Runner(opt).run();
+    }
+
+}