Create Virtual Thread worker pool metrics only if needed (#5719)

* Create Virtual Thread worker pool metrics only if needed

Follows-up on #5705

Without this change, virtual thread worker pool metrics are registered and published, even when the applications run on JVM without VT support.

Signed-off-by: Thomas Segismont <[email protected]>

* Fix testVirtualThreadWorkerPoolMetrics

Signed-off-by: Thomas Segismont <[email protected]>

---------

Signed-off-by: Thomas Segismont <[email protected]>

Author: tsegismont

vertx-core/src/main/java/io/vertx/core/impl/VertxImpl.java

@@ -203,7 +203,7 @@ private static ThreadFactory virtualThreadFactory() {
     PoolMetrics internalBlockingPoolMetrics = metrics != null ? metrics.createPoolMetrics("worker", "vert.x-internal-blocking", internalBlockingPoolSize) : null;
 
     ThreadFactory virtualThreadFactory = virtualThreadFactory();
-    PoolMetrics virtualThreadWorkerPoolMetrics = metrics != null ? metrics.createPoolMetrics("worker", "vert.x-virtual-thread", -1) : null;
+    PoolMetrics virtualThreadWorkerPoolMetrics = metrics != null && virtualThreadFactory != null ? metrics.createPoolMetrics("worker", "vert.x-virtual-thread", -1) : null;
 
     contextLocals = LocalSeq.get();
     contextLocalsList = Collections.unmodifiableList(Arrays.asList(contextLocals));

vertx-core/src/test/java/io/vertx/tests/metrics/MetricsTest.java

@@ -1255,7 +1255,13 @@ public void close() {
   @Test
   public void testVirtualThreadWorkerPoolMetrics() {
     Map<String, FakePoolMetrics> all = FakePoolMetrics.getMetrics();
-    assertTrue(all.containsKey("vert.x-virtual-thread"));
-    assertNotNull(all.get("vert.x-virtual-thread"));
+    VertxInternal vertxInternal = (VertxInternal) vertx;
+    if (vertxInternal.isVirtualThreadAvailable()) {
+      assertTrue(all.containsKey("vert.x-virtual-thread"));
+      assertNotNull(all.get("vert.x-virtual-thread"));
+    } else {
+      assertFalse(all.containsKey("vert.x-virtual-thread"));
+      assertNull(all.get("vert.x-virtual-thread"));
+    }
   }
 }