Fix NioEventLoopTest#testChannelsRegistered flakiness (#9650)

Motivation

NioEventLoopTest#testChannelsRegistered() fails intermittently due to
use of SingleThreadEventLoop#channelsRegistered() which is not
threadsafe and unreliable when called from outside the event loop.

Modifications

Add static registeredChannels method to NioEventLoopTest and
AbstractSingleThreadEventLoopTest to call from the tests via event loop
instead of directly.

Result

Hopefully fewer test failures

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

@@ -20,6 +20,7 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
+import java.util.concurrent.Callable;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.TimeUnit;
@@ -42,7 +43,7 @@ import io.netty.util.concurrent.Future;
 public abstract class AbstractSingleThreadEventLoopTest {
 
     @Test
-    public void testChannelsRegistered()  {
+    public void testChannelsRegistered() throws Exception {
         EventLoopGroup group = newEventLoopGroup();
         final SingleThreadEventLoop loop = (SingleThreadEventLoop) group.next();
 
@@ -50,28 +51,38 @@ public abstract class AbstractSingleThreadEventLoopTest {
             final Channel ch1 = newChannel();
             final Channel ch2 = newChannel();
 
-            int rc = loop.registeredChannels();
+            int rc = registeredChannels(loop);
             boolean channelCountSupported = rc != -1;
 
             if (channelCountSupported) {
-                assertEquals(0, loop.registeredChannels());
+                assertEquals(0, registeredChannels(loop));
             }
 
             assertTrue(loop.register(ch1).syncUninterruptibly().isSuccess());
             assertTrue(loop.register(ch2).syncUninterruptibly().isSuccess());
             if (channelCountSupported) {
-                assertEquals(2, loop.registeredChannels());
+                assertEquals(2, registeredChannels(loop));
             }
 
             assertTrue(ch1.deregister().syncUninterruptibly().isSuccess());
             if (channelCountSupported) {
-                assertEquals(1, loop.registeredChannels());
+                assertEquals(1, registeredChannels(loop));
             }
         } finally {
             group.shutdownGracefully();
         }
     }
 
+    // Only reliable if run from event loop
+    private static int registeredChannels(final SingleThreadEventLoop loop) throws Exception {
+        return loop.submit(new Callable<Integer>() {
+            @Override
+            public Integer call() {
+                return loop.registeredChannels();
+            }
+        }).get(1, TimeUnit.SECONDS);
+    }
+
     @Test
     @SuppressWarnings("deprecation")
     public void shutdownBeforeStart() throws Exception {

transport/src/test/java/io/netty/channel/nio/NioEventLoopTest.java

@@ -23,6 +23,7 @@ import io.netty.channel.EventLoopGroup;
 import io.netty.channel.EventLoopTaskQueueFactory;
 import io.netty.channel.SelectStrategy;
 import io.netty.channel.SelectStrategyFactory;
+import io.netty.channel.SingleThreadEventLoop;
 import io.netty.channel.socket.ServerSocketChannel;
 import io.netty.channel.socket.nio.NioServerSocketChannel;
 import io.netty.util.IntSupplier;
@@ -42,6 +43,7 @@ import java.nio.channels.Selector;
 import java.nio.channels.SocketChannel;
 import java.nio.channels.spi.SelectorProvider;
 import java.util.Queue;
+import java.util.concurrent.Callable;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.RejectedExecutionException;
@@ -269,7 +271,7 @@ public class NioEventLoopTest extends AbstractEventLoopTest {
 
     @Ignore
     @Test
-    public void testChannelsRegistered()  {
+    public void testChannelsRegistered() throws Exception {
         NioEventLoopGroup group = new NioEventLoopGroup(1);
         final NioEventLoop loop = (NioEventLoop) group.next();
 
@@ -277,19 +279,29 @@ public class NioEventLoopTest extends AbstractEventLoopTest {
             final Channel ch1 = new NioServerSocketChannel();
             final Channel ch2 = new NioServerSocketChannel();
 
-            assertEquals(0, loop.registeredChannels());
+            assertEquals(0, registeredChannels(loop));
 
             assertTrue(loop.register(ch1).syncUninterruptibly().isSuccess());
             assertTrue(loop.register(ch2).syncUninterruptibly().isSuccess());
-            assertEquals(2, loop.registeredChannels());
+            assertEquals(2, registeredChannels(loop));
 
             assertTrue(ch1.deregister().syncUninterruptibly().isSuccess());
-            assertEquals(1, loop.registeredChannels());
+            assertEquals(1, registeredChannels(loop));
         } finally {
             group.shutdownGracefully();
         }
     }
 
+    // Only reliable if run from event loop
+    private static int registeredChannels(final SingleThreadEventLoop loop) throws Exception {
+        return loop.submit(new Callable<Integer>() {
+            @Override
+            public Integer call() {
+                return loop.registeredChannels();
+            }
+        }).get(1, TimeUnit.SECONDS);
+    }
+
     @Test
     public void testCustomQueue()  {
         final AtomicBoolean called = new AtomicBoolean();