[NO-TICKET] Use virtual threads (better solution without a pool)

Author: pboos

openapi-validation-core/src/main/java/com/getyourguide/openapi/validation/core/executor/VirtualThreadLimitedExecutor.java

@@ -0,0 +1,54 @@
+package com.getyourguide.openapi.validation.core.executor;
+
+import java.util.concurrent.Executor;
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class VirtualThreadLimitedExecutor implements Executor {
+    private static final int DEFAULT_MAX_CONCURRENT = 2;
+    private final int maxConcurrent;
+    private final AtomicInteger runningCount = new AtomicInteger(0);
+
+    public VirtualThreadLimitedExecutor() {
+        this(DEFAULT_MAX_CONCURRENT);
+    }
+
+    public VirtualThreadLimitedExecutor(int maxConcurrent) {
+        checkVirtualThreadSupport();
+        this.maxConcurrent = maxConcurrent;
+    }
+
+    public static boolean isSupported() {
+        try {
+            checkVirtualThreadSupport();
+            return true;
+        } catch (UnsupportedOperationException | NoSuchMethodError e) {
+            return false;
+        }
+    }
+
+    private static void checkVirtualThreadSupport() {
+        // This will throw NoSuchMethodError on Java < 21
+        //noinspection ResultOfMethodCallIgnored
+        Thread.ofVirtual();
+    }
+
+    @Override
+    public void execute(Runnable command) {
+        if (runningCount.get() >= maxConcurrent) {
+            return;
+        }
+
+        if (runningCount.incrementAndGet() > maxConcurrent) {
+            runningCount.decrementAndGet();
+            return;
+        }
+
+        Thread.ofVirtual().start(() -> {
+            try {
+                command.run();
+            } finally {
+                runningCount.decrementAndGet();
+            }
+        });
+    }
+}

spring-boot-starter/spring-boot-starter-core/src/main/java/com/getyourguide/openapi/validation/autoconfigure/LibraryAutoConfiguration.java

@@ -19,6 +19,7 @@
 import com.getyourguide.openapi.validation.core.OpenApiInteractionValidatorFactory;
 import com.getyourguide.openapi.validation.core.OpenApiRequestValidator;
 import com.getyourguide.openapi.validation.core.exclusions.InternalViolationExclusions;
+import com.getyourguide.openapi.validation.core.executor.VirtualThreadLimitedExecutor;
 import com.getyourguide.openapi.validation.core.log.DefaultOpenApiViolationHandler;
 import com.getyourguide.openapi.validation.core.log.ExclusionsOpenApiViolationHandler;
 import com.getyourguide.openapi.validation.core.log.ThrottlingOpenApiViolationHandler;
@@ -118,28 +119,18 @@ public OpenApiRequestValidator openApiRequestValidator(
     }
 
     private Executor createThreadPoolExecutor() {
-        try {
-            // Try to use virtual threads if available (Java 21+)
-            var virtualThreadFactory = Thread.ofVirtual().factory();
-            return new ThreadPoolExecutor(
-                2,
-                2,
-                1000L,
-                TimeUnit.MILLISECONDS,
-                new LinkedBlockingQueue<>(10),
-                virtualThreadFactory,
-                new ThreadPoolExecutor.DiscardPolicy()
-            );
-        } catch (UnsupportedOperationException | NoSuchMethodError e) {
-            // Fallback to ThreadPoolExecutor with regular threads for older Java versions
-            return new ThreadPoolExecutor(
-                2,
-                2,
-                1000L,
-                TimeUnit.MILLISECONDS,
-                new LinkedBlockingQueue<>(10),
-                new ThreadPoolExecutor.DiscardPolicy()
-            );
+        if (VirtualThreadLimitedExecutor.isSupported()) {
+            return new VirtualThreadLimitedExecutor();
         }
+
+        // Fallback to ThreadPoolExecutor with regular threads for older Java versions
+        return new ThreadPoolExecutor(
+            2,
+            2,
+            1000L,
+            TimeUnit.MILLISECONDS,
+            new LinkedBlockingQueue<>(10),
+            new ThreadPoolExecutor.DiscardPolicy()
+        );
     }
 }