netty: not using reflection to create NioEventLoopGroup (#5630)

netty/src/main/java/io/grpc/netty/Utils.java

@@ -16,6 +16,7 @@
 
 package io.grpc.netty;
 
+import static com.google.common.base.Preconditions.checkState;
 import static io.grpc.internal.GrpcUtil.CONTENT_TYPE_KEY;
 import static io.grpc.internal.TransportFrameUtil.toHttp2Headers;
 import static io.grpc.internal.TransportFrameUtil.toRawSerializedHeaders;
@@ -46,6 +47,7 @@ import io.netty.handler.codec.http2.Http2Headers;
 import io.netty.util.AsciiString;
 import io.netty.util.concurrent.DefaultThreadFactory;
 import java.io.IOException;
+import java.lang.reflect.Constructor;
 import java.nio.channels.ClosedChannelException;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -73,31 +75,35 @@ class Utils {
   public static final AsciiString TE_TRAILERS = AsciiString.of(GrpcUtil.TE_TRAILERS);
   public static final AsciiString USER_AGENT = AsciiString.of(GrpcUtil.USER_AGENT_KEY.name());
   public static final Resource<EventLoopGroup> NIO_BOSS_EVENT_LOOP_GROUP
-      = new DefaultEventLoopGroupResource(1, "grpc-nio-boss-ELG", NioEventLoopGroup.class);
+      = new DefaultEventLoopGroupResource(1, "grpc-nio-boss-ELG", EventLoopGroupType.NIO);
   public static final Resource<EventLoopGroup> NIO_WORKER_EVENT_LOOP_GROUP
-      = new DefaultEventLoopGroupResource(0, "grpc-nio-worker-ELG", NioEventLoopGroup.class);
+      = new DefaultEventLoopGroupResource(0, "grpc-nio-worker-ELG", EventLoopGroupType.NIO);
   public static final Resource<EventLoopGroup> DEFAULT_BOSS_EVENT_LOOP_GROUP;
   public static final Resource<EventLoopGroup> DEFAULT_WORKER_EVENT_LOOP_GROUP;
 
   public static final Class<? extends ServerChannel> DEFAULT_SERVER_CHANNEL_TYPE;
   public static final Class<? extends Channel> DEFAULT_CLIENT_CHANNEL_TYPE;
 
+  @Nullable
+  private static final Constructor<? extends EventLoopGroup> EPOLL_EVENT_LOOP_GROUP_CONSTRUCTOR;
+
   static {
     // Decide default channel types and EventLoopGroup based on Epoll availability
     if (isEpollAvailable()) {
       DEFAULT_SERVER_CHANNEL_TYPE = epollServerChannelType();
       DEFAULT_CLIENT_CHANNEL_TYPE = epollChannelType();
-      Class<? extends EventLoopGroup> eventLoopGroupType = epollEventLoopGroupType();
+      EPOLL_EVENT_LOOP_GROUP_CONSTRUCTOR = epollEventLoopGroupConstructor();
       DEFAULT_BOSS_EVENT_LOOP_GROUP
-        = new DefaultEventLoopGroupResource(1, "grpc-default-boss-ELG", eventLoopGroupType);
+        = new DefaultEventLoopGroupResource(1, "grpc-default-boss-ELG", EventLoopGroupType.EPOLL);
       DEFAULT_WORKER_EVENT_LOOP_GROUP
-        = new DefaultEventLoopGroupResource(0,"grpc-default-worker-ELG", eventLoopGroupType);
+        = new DefaultEventLoopGroupResource(0,"grpc-default-worker-ELG", EventLoopGroupType.EPOLL);
     } else {
       logger.log(Level.FINE, "Epoll is not available, using Nio.", getEpollUnavailabilityCause());
       DEFAULT_SERVER_CHANNEL_TYPE = NioServerSocketChannel.class;
       DEFAULT_CLIENT_CHANNEL_TYPE = NioSocketChannel.class;
       DEFAULT_BOSS_EVENT_LOOP_GROUP = NIO_BOSS_EVENT_LOOP_GROUP;
       DEFAULT_WORKER_EVENT_LOOP_GROUP = NIO_WORKER_EVENT_LOOP_GROUP;
+      EPOLL_EVENT_LOOP_GROUP_CONSTRUCTOR = null;
     }
   }
 
@@ -246,12 +252,15 @@ class Utils {
   }
 
   // Must call when epoll is available
-  private static Class<? extends EventLoopGroup> epollEventLoopGroupType() {
+  private static Constructor<? extends EventLoopGroup> epollEventLoopGroupConstructor() {
     try {
       return Class
-          .forName("io.netty.channel.epoll.EpollEventLoopGroup").asSubclass(EventLoopGroup.class);
+          .forName("io.netty.channel.epoll.EpollEventLoopGroup").asSubclass(EventLoopGroup.class)
+          .getConstructor(Integer.TYPE, ThreadFactory.class);
     } catch (ClassNotFoundException e) {
       throw new RuntimeException("Cannot load EpollEventLoopGroup", e);
+    } catch (NoSuchMethodException e) {
+      throw new RuntimeException("EpollEventLoopGroup constructor not found", e);
     }
   }
 
@@ -268,16 +277,16 @@ class Utils {
     }
   }
 
-  private static EventLoopGroup createEventLoopGroup(
-      Class<? extends EventLoopGroup> eventLoopGroupType,
+  private static EventLoopGroup createEpollEventLoopGroup(
       int parallelism,
       ThreadFactory threadFactory) {
+    checkState(EPOLL_EVENT_LOOP_GROUP_CONSTRUCTOR != null, "Epoll is not available");
+
     try {
-      return eventLoopGroupType
-          .getConstructor(Integer.TYPE, ThreadFactory.class)
+      return EPOLL_EVENT_LOOP_GROUP_CONSTRUCTOR
           .newInstance(parallelism, threadFactory);
     } catch (Exception e) {
-      throw new RuntimeException("Cannot create EventLoopGroup for " + eventLoopGroupType, e);
+      throw new RuntimeException("Cannot create Epoll EventLoopGroup", e);
     }
   }
 
@@ -309,10 +318,10 @@ class Utils {
   private static final class DefaultEventLoopGroupResource implements Resource<EventLoopGroup> {
     private final String name;
     private final int numEventLoops;
-    private final Class<? extends EventLoopGroup> eventLoopGroupType;
+    private final EventLoopGroupType eventLoopGroupType;
 
     DefaultEventLoopGroupResource(
-        int numEventLoops, String name, Class<? extends EventLoopGroup> eventLoopGroupType) {
+        int numEventLoops, String name, EventLoopGroupType eventLoopGroupType) {
       this.name = name;
       this.numEventLoops = numEventLoops;
       this.eventLoopGroupType = eventLoopGroupType;
@@ -322,7 +331,14 @@ class Utils {
     public EventLoopGroup create() {
       // Use Netty's DefaultThreadFactory in order to get the benefit of FastThreadLocal.
       ThreadFactory threadFactory = new DefaultThreadFactory(name, /* daemon= */ true);
-      return createEventLoopGroup(eventLoopGroupType, numEventLoops, threadFactory);
+      switch (eventLoopGroupType) {
+        case NIO:
+          return new NioEventLoopGroup(numEventLoops, threadFactory);
+        case EPOLL:
+          return createEpollEventLoopGroup(numEventLoops, threadFactory);
+        default:
+          throw new AssertionError("Unknown/Unsupported EventLoopGroupType: " + eventLoopGroupType);
+      }
     }
 
     @Override
@@ -375,6 +391,11 @@ class Utils {
     return b.build();
   }
 
+  private enum EventLoopGroupType {
+    NIO,
+    EPOLL
+  }
+
   private Utils() {
     // Prevents instantiation
   }