Try to reduce GC produced while writing headers (#9682)

Motivation:

bbc34d0eda introduced correct handling of "in process" setup of streams but there is some room for improvements. Often the writeHeaders(...) is completed directly which means there is not need to create the extra listener object.

Modifications:

- Only create the listener if we really need too.

Result:

Less GC

codec-http2/src/main/java/io/netty/handler/codec/http2/Http2FrameCodec.java

@@ -17,7 +17,6 @@ package io.netty.handler.codec.http2;
 
 import io.netty.buffer.ByteBuf;
 import io.netty.channel.Channel;
-import io.netty.channel.ChannelFutureListener;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelInboundHandler;
 import io.netty.channel.ChannelPromise;
@@ -31,6 +30,7 @@ import io.netty.util.ReferenceCountUtil;
 import io.netty.util.ReferenceCounted;
 import io.netty.util.collection.IntObjectHashMap;
 import io.netty.util.collection.IntObjectMap;
+import io.netty.util.concurrent.Future;
 import io.netty.util.internal.UnstableApi;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
@@ -158,7 +158,6 @@ public class Http2FrameCodec extends Http2ConnectionHandler {
     private int numBufferedStreams;
     private final IntObjectMap<DefaultHttp2FrameStream> frameStreamToInitializeMap =
             new IntObjectHashMap<DefaultHttp2FrameStream>(8);
-    private final ChannelFutureListener bufferedStreamsListener = future -> numBufferedStreams--;
 
     Http2FrameCodec(Http2ConnectionEncoder encoder, Http2ConnectionDecoder decoder, Http2Settings initialSettings,
                     boolean decoupleCloseAndGoAway) {
@@ -412,23 +411,30 @@ public class Http2FrameCodec extends Http2ConnectionHandler {
             // We should not re-use ids.
             assert old == null;
 
-            // Clean up the stream being initialized if writing the headers fails.
-            promise.addListener(channelFuture -> {
-                if (!channelFuture.isSuccess()) {
-                    frameStreamToInitializeMap.remove(streamId);
-                }
-            });
-
             encoder().writeHeaders(ctx, streamId, headersFrame.headers(), headersFrame.padding(),
                     headersFrame.isEndStream(), promise);
 
             if (!promise.isDone()) {
                 numBufferedStreams++;
-                promise.addListener(bufferedStreamsListener);
+                // Clean up the stream being initialized if writing the headers fails and also
+                // decrement the number of buffered streams.
+                promise.addListener(channelFuture -> {
+                    numBufferedStreams--;
+
+                    handleHeaderFuture(channelFuture, streamId);
+                });
+            } else {
+                handleHeaderFuture(promise, streamId);
             }
         }
     }
 
+    private void handleHeaderFuture(Future<?> channelFuture, int streamId) {
+        if (!channelFuture.isSuccess()) {
+            frameStreamToInitializeMap.remove(streamId);
+        }
+    }
+
     private void onStreamActive0(Http2Stream stream) {
         if (stream.id() != Http2CodecUtil.HTTP_UPGRADE_STREAM_ID &&
                 connection().local().isValidStreamId(stream.id())) {