Be more lenient when check the number of registered channels (#11194)

Motivation:

Some SingleEventLoop implementations may need some "time" to update the number of registered Channels. We should loop until we see the correct value or timeout if we did not observe the correct value.

Modifications:

- Loop until we see the correct value
- add test timeout

Result:

Fixes https://github.com/netty/netty/issues/11169

testsuite/src/main/java/io/netty/testsuite/transport/AbstractSingleThreadEventLoopTest.java

@@ -42,7 +42,7 @@ import io.netty.util.concurrent.Future;
 
 public abstract class AbstractSingleThreadEventLoopTest {
 
-    @Test
+    @Test(timeout = 5000)
     public void testChannelsRegistered() throws Exception {
         EventLoopGroup group = newEventLoopGroup();
         final SingleThreadEventLoop loop = (SingleThreadEventLoop) group.next();
@@ -61,18 +61,25 @@ public abstract class AbstractSingleThreadEventLoopTest {
             assertTrue(loop.register(ch1).syncUninterruptibly().isSuccess());
             assertTrue(loop.register(ch2).syncUninterruptibly().isSuccess());
             if (channelCountSupported) {
-                assertEquals(2, registeredChannels(loop));
+                checkNumRegisteredChannels(loop, 2);
             }
 
             assertTrue(ch1.deregister().syncUninterruptibly().isSuccess());
             if (channelCountSupported) {
-                assertEquals(1, registeredChannels(loop));
+                checkNumRegisteredChannels(loop, 1);
             }
         } finally {
             group.shutdownGracefully();
         }
     }
 
+    private static void checkNumRegisteredChannels(SingleThreadEventLoop loop, int numChannels) throws Exception {
+        // We need to loop as some EventLoop implementations may need some time to update the counter correctly.
+        while (registeredChannels(loop) != numChannels) {
+            Thread.sleep(50);
+        }
+    }
+
     // Only reliable if run from event loop
     private static int registeredChannels(final SingleThreadEventLoop loop) throws Exception {
         return loop.submit(new Callable<Integer>() {