Add workaround for possible classloader deadlock when trying to load JNI code (#10190)

Motivation:

netty_epoll_linuxsocket_JNI_OnLoad(...) may produce a deadlock with another thread that will load IOUtil in a static block. This seems to be a JDK bug which is not yet fixed. To workaround this we force IOUtil to be loaded from without java code before init the JNI code

Modifications:

Use Selector.open() as a workaround to load IOUtil

Result:

Fixes https://github.com/netty/netty/issues/10187

transport-native-epoll/src/main/java/io/netty/channel/epoll/Native.java

@@ -25,6 +25,7 @@ import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
 
 import java.io.IOException;
+import java.nio.channels.Selector;
 import java.util.Locale;
 
 import static io.netty.channel.epoll.NativeStaticallyReferencedJniMethods.epollerr;
@@ -49,6 +50,16 @@ public final class Native {
     private static final InternalLogger logger = InternalLoggerFactory.getInstance(Native.class);
 
     static {
+        Selector selector = null;
+        try {
+            // We call Selector.open() as this will under the hood cause IOUtil to be loaded.
+            // This is a workaround for a possible classloader deadlock that could happen otherwise:
+            //
+            // See https://github.com/netty/netty/issues/10187
+            selector = Selector.open();
+        } catch (IOException ignore) {
+            // Just ignore
+        }
         try {
             // First, try calling a side-effect free JNI method to see if the library was already
             // loaded by the application.
@@ -56,6 +67,14 @@ public final class Native {
         } catch (UnsatisfiedLinkError ignore) {
             // The library was not previously loaded, load it now.
             loadNativeLibrary();
+        } finally {
+            try {
+                if (selector != null) {
+                    selector.close();
+                }
+            } catch (IOException ignore) {
+                // Just ignore
+            }
         }
         Socket.initialize();
     }