netty: add internal API to fall back to NIO transport (#5611)

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

@@ -18,6 +18,8 @@ package io.grpc.netty;
 
 import io.grpc.Internal;
 import io.grpc.internal.ClientTransportFactory;
+import io.grpc.internal.SharedResourcePool;
+import io.netty.channel.socket.nio.NioSocketChannel;
 
 /**
  * Internal {@link NettyChannelBuilder} accessor.  This is intended for usage internal to the gRPC
@@ -70,6 +72,17 @@ public final class InternalNettyChannelBuilder {
     builder.setStatsRecordRealTimeMetrics(value);
   }
 
+  /**
+   * Sets {@link io.grpc.Channel} and {@link io.netty.channel.EventLoopGroup} to Nio. A major
+   * benefit over using setters is gRPC will manage the life cycle of {@link
+   * io.netty.channel.EventLoopGroup}.
+   */
+  public static void useNioTransport(NettyChannelBuilder builder) {
+    builder.channelType(NioSocketChannel.class);
+    builder
+        .eventLoopGroupPool(SharedResourcePool.forResource(Utils.NIO_WORKER_EVENT_LOOP_GROUP));
+  }
+
   public static ClientTransportFactory buildTransportFactory(NettyChannelBuilder builder) {
     return builder.buildTransportFactory();
   }

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

@@ -17,6 +17,8 @@
 package io.grpc.netty;
 
 import io.grpc.Internal;
+import io.grpc.internal.SharedResourcePool;
+import io.netty.channel.socket.nio.NioServerSocketChannel;
 
 /**
  * Internal {@link InternalNettyServerBuilder} accessor.  This is intended for usage internal to
@@ -41,5 +43,19 @@ public final class InternalNettyServerBuilder {
     builder.setTracingEnabled(value);
   }
 
+  /**
+   * Sets {@link io.grpc.Channel} and {@link io.netty.channel.EventLoopGroup}s to Nio. A major
+   * benefit over using existing setters is gRPC will manage the life cycle of {@link
+   * io.netty.channel.EventLoopGroup}s.
+   */
+  public static void useNioTransport(NettyServerBuilder builder) {
+    builder.channelType(NioServerSocketChannel.class);
+    builder
+        .bossEventLoopGroupPool(SharedResourcePool.forResource(Utils.NIO_BOSS_EVENT_LOOP_GROUP));
+    builder
+        .workerEventLoopGroupPool(
+            SharedResourcePool.forResource(Utils.NIO_WORKER_EVENT_LOOP_GROUP));
+  }
+
   private InternalNettyServerBuilder() {}
 }

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

@@ -218,10 +218,13 @@ public final class NettyChannelBuilder
    */
   public NettyChannelBuilder eventLoopGroup(@Nullable EventLoopGroup eventLoopGroup) {
     if (eventLoopGroup != null) {
-      this.eventLoopGroupPool = new FixedObjectPool<>(eventLoopGroup);
-    } else {
-      this.eventLoopGroupPool = DEFAULT_EVENT_LOOP_GROUP_POOL;
+      return eventLoopGroupPool(new FixedObjectPool<>(eventLoopGroup));
     }
+    return eventLoopGroupPool(DEFAULT_EVENT_LOOP_GROUP_POOL);
+  }
+
+  NettyChannelBuilder eventLoopGroupPool(ObjectPool<? extends EventLoopGroup> eventLoopGroupPool) {
+    this.eventLoopGroupPool = checkNotNull(eventLoopGroupPool, "eventLoopGroupPool");
     return this;
   }
 

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

@@ -81,7 +81,7 @@ public final class NettyServerBuilder extends AbstractServerImplBuilder<NettySer
       SharedResourcePool.forResource(Utils.DEFAULT_WORKER_EVENT_LOOP_GROUP);
 
   private final List<SocketAddress> listenAddresses = new ArrayList<>();
-  private Class<? extends ServerChannel> channelType = Utils.DEFAULT_SERVER_CHANNEL_TYPE;
+  private Class<? extends ServerChannel> channelType = null;
   private final Map<ChannelOption<?>, Object> channelOptions = new HashMap<>();
   private ObjectPool<? extends EventLoopGroup> bossEventLoopGroupPool =
       DEFAULT_BOSS_EVENT_LOOP_GROUP_POOL;
@@ -193,10 +193,14 @@ public final class NettyServerBuilder extends AbstractServerImplBuilder<NettySer
    */
   public NettyServerBuilder bossEventLoopGroup(EventLoopGroup group) {
     if (group != null) {
-      this.bossEventLoopGroupPool = new FixedObjectPool<>(group);
-    } else {
-      this.bossEventLoopGroupPool = DEFAULT_BOSS_EVENT_LOOP_GROUP_POOL;
+      return bossEventLoopGroupPool(new FixedObjectPool<>(group));
     }
+    return bossEventLoopGroupPool(DEFAULT_BOSS_EVENT_LOOP_GROUP_POOL);
+  }
+
+  NettyServerBuilder bossEventLoopGroupPool(
+      ObjectPool<? extends EventLoopGroup> bossEventLoopGroupPool) {
+    this.bossEventLoopGroupPool = checkNotNull(bossEventLoopGroupPool, "bossEventLoopGroupPool");
     return this;
   }
 
@@ -225,10 +229,15 @@ public final class NettyServerBuilder extends AbstractServerImplBuilder<NettySer
    */
   public NettyServerBuilder workerEventLoopGroup(EventLoopGroup group) {
     if (group != null) {
-      this.workerEventLoopGroupPool = new FixedObjectPool<>(group);
-    } else {
-      this.workerEventLoopGroupPool = DEFAULT_WORKER_EVENT_LOOP_GROUP_POOL;
+      return workerEventLoopGroupPool(new FixedObjectPool<>(group));
     }
+    return workerEventLoopGroupPool(DEFAULT_WORKER_EVENT_LOOP_GROUP_POOL);
+  }
+
+  NettyServerBuilder workerEventLoopGroupPool(
+      ObjectPool<? extends EventLoopGroup> workerEventLoopGroupPool) {
+    this.workerEventLoopGroupPool =
+        checkNotNull(workerEventLoopGroupPool, "workerEventLoopGroupPool");
     return this;
   }
 
@@ -506,7 +515,7 @@ public final class NettyServerBuilder extends AbstractServerImplBuilder<NettySer
               + "neither should be, otherwise server may not start. Missing values will use Nio "
               + "(NioServerSocketChannel, NioEventLoopGroup) for backward compatibility. "
               + "This will cause an Exception in the future.");
-      if (channelType == Utils.DEFAULT_SERVER_CHANNEL_TYPE) {
+      if (channelType == null) {
         resolvedChannelType = NioServerSocketChannel.class;
         logger.log(Level.FINE, "One or more EventLoopGroup is provided, but Channel type is "
             + "missing. Fall back to NioServerSocketChannel.");
@@ -522,6 +531,9 @@ public final class NettyServerBuilder extends AbstractServerImplBuilder<NettySer
             + "BossEventLoopGroup is missing. Fall back to NioEventLoopGroup.");
       }
     }
+    if (resolvedChannelType == null) {
+      resolvedChannelType = Utils.DEFAULT_SERVER_CHANNEL_TYPE;
+    }
 
     List<NettyServer> transportServers = new ArrayList<>(listenAddresses.size());
     for (SocketAddress listenAddress : listenAddresses) {
@@ -539,10 +551,10 @@ public final class NettyServerBuilder extends AbstractServerImplBuilder<NettySer
 
   @VisibleForTesting
   boolean shouldFallBackToNio() {
-    boolean hasNonDefault = channelType != Utils.DEFAULT_SERVER_CHANNEL_TYPE
+    boolean hasNonDefault = channelType != null
         || bossEventLoopGroupPool != DEFAULT_BOSS_EVENT_LOOP_GROUP_POOL
         || workerEventLoopGroupPool != DEFAULT_WORKER_EVENT_LOOP_GROUP_POOL;
-    boolean hasDefault = channelType == Utils.DEFAULT_SERVER_CHANNEL_TYPE
+    boolean hasDefault = channelType == null
         || bossEventLoopGroupPool == DEFAULT_BOSS_EVENT_LOOP_GROUP_POOL
         || workerEventLoopGroupPool == DEFAULT_WORKER_EVENT_LOOP_GROUP_POOL;
     return hasNonDefault && hasDefault;

netty/src/test/java/io/grpc/netty/NettyChannelBuilderTest.java

@@ -248,4 +248,13 @@ public class NettyChannelBuilderTest {
 
     assertFalse(builder.shouldFallBackToNio());
   }
+
+  @Test
+  public void useNioTransport_shouldNotFallBack() {
+    NettyChannelBuilder builder = NettyChannelBuilder.forTarget("fakeTarget");
+
+    InternalNettyChannelBuilder.useNioTransport(builder);
+
+    assertFalse(builder.shouldFallBackToNio());
+  }
 }

netty/src/test/java/io/grpc/netty/NettyServerBuilderTest.java

@@ -173,4 +173,11 @@ public class NettyServerBuilderTest {
 
     assertFalse(builder.shouldFallBackToNio());
   }
+
+  @Test
+  public void useNioTransport_shouldNotFallBack() {
+    InternalNettyServerBuilder.useNioTransport(builder);
+
+    assertFalse(builder.shouldFallBackToNio());
+  }
 }