Remove Frame class from DefaultHttp2RemoteFlowController. Fixes #3488

Motivation:

For every write of a flow controlled frame (HEADERS, DATA) we are allocating
a Frame object that is not necessary anymore as it does not maintain any
state, besides the payload.

Modifications:

Remove the Frame class and directly add the payload to the pending write queue.

Result:

One few object allocation per write of a flow controlled frame.

codec-http2/src/main/java/io/netty/handler/codec/http2/DefaultHttp2RemoteFlowController.java

@@ -166,10 +166,9 @@ public class DefaultHttp2RemoteFlowController implements Http2RemoteFlowControll
     }
 
     @Override
-    public void sendFlowControlled(ChannelHandlerContext ctx, Http2Stream stream,
+    public void sendFlowControlled(ChannelHandlerContext ctx, Http2Stream stream, FlowControlled frame) {
-                                   FlowControlled payload) {
         checkNotNull(ctx, "ctx");
-        checkNotNull(payload, "payload");
+        checkNotNull(frame, "frame");
         if (this.ctx != null && this.ctx != ctx) {
             throw new IllegalArgumentException("Writing data from multiple ChannelHandlerContexts is not supported");
         }
@@ -178,16 +177,16 @@ public class DefaultHttp2RemoteFlowController implements Http2RemoteFlowControll
         FlowState state;
         try {
             state = state(stream);
-            state.newFrame(payload);
+            state.enqueueFrame(frame);
         } catch (Throwable t) {
-            payload.error(t);
+            frame.error(t);
             return;
         }
         state.writeBytes(state.writableWindow());
         try {
             flush();
         } catch (Throwable t) {
-            payload.error(t);
+            frame.error(t);
         }
     }
 
@@ -335,8 +334,8 @@ public class DefaultHttp2RemoteFlowController implements Http2RemoteFlowControll
     /**
      * The outbound flow control state for a single stream.
      */
-    final class FlowState {
+    private final class FlowState {
-        private final Deque<Frame> pendingWriteQueue;
+        private final Deque<FlowControlled> pendingWriteQueue;
         private final Http2Stream stream;
         private int window;
         private int pendingBytes;
@@ -350,7 +349,7 @@ public class DefaultHttp2RemoteFlowController implements Http2RemoteFlowControll
         FlowState(Http2Stream stream, int initialWindowSize) {
             this.stream = stream;
             window(initialWindowSize);
-            pendingWriteQueue = new ArrayDeque<Frame>(2);
+            pendingWriteQueue = new ArrayDeque<FlowControlled>(2);
         }
 
         int window() {
@@ -424,13 +423,12 @@ public class DefaultHttp2RemoteFlowController implements Http2RemoteFlowControll
         }
 
         /**
-         * Creates a new payload with the given values and immediately enqueues it.
+         * Adds the {@code frame} to the pending queue and increments the pending
+         * byte count.
          */
-        Frame newFrame(FlowControlled payload) {
+        void enqueueFrame(FlowControlled frame) {
-            // Store this as the future for the most recent write attempt.
+            incrementPendingBytes(frame.size());
-            Frame frame = new Frame(payload);
             pendingWriteQueue.offer(frame);
-            return frame;
         }
 
         /**
@@ -443,7 +441,7 @@ public class DefaultHttp2RemoteFlowController implements Http2RemoteFlowControll
         /**
          * Returns the the head of the pending queue, or {@code null} if empty.
          */
-        Frame peek() {
+        FlowControlled peek() {
             return pendingWriteQueue.peek();
         }
 
@@ -458,11 +456,11 @@ public class DefaultHttp2RemoteFlowController implements Http2RemoteFlowControll
                 return;
             }
             for (;;) {
-                Frame frame = pendingWriteQueue.poll();
+                FlowControlled frame = pendingWriteQueue.poll();
                 if (frame == null) {
                     break;
                 }
-                frame.writeError(streamError(stream.id(), INTERNAL_ERROR,
+                writeError(frame, streamError(stream.id(), INTERNAL_ERROR,
                                               "Stream closed before write could take place"));
             }
         }
@@ -476,7 +474,7 @@ public class DefaultHttp2RemoteFlowController implements Http2RemoteFlowControll
             int bytesAttempted = 0;
             while (hasFrame()) {
                 int maxBytes = min(bytes - bytesAttempted, writableWindow());
-                bytesAttempted += peek().write(maxBytes);
+                bytesAttempted += write(peek(), maxBytes);
                 if (bytes - bytesAttempted <= 0) {
                   break;
                 }
@@ -484,6 +482,50 @@ public class DefaultHttp2RemoteFlowController implements Http2RemoteFlowControll
             return bytesAttempted;
         }
 
+        /**
+         * Writes the frame and decrements the stream and connection window sizes. If the frame is in the pending
+         * queue, the written bytes are removed from this branch of the priority tree.
+         * <p>
+         * Note: this does not flush the {@link ChannelHandlerContext}.
+         * </p>
+         */
+        int write(FlowControlled frame, int allowedBytes) {
+            int before = frame.size();
+            int writtenBytes = 0;
+            try {
+                assert !writing;
+
+                // Write the portion of the frame.
+                writing = true;
+                needFlush |= frame.write(Math.max(0, allowedBytes));
+                if (!cancelled && frame.size() == 0) {
+                    // This frame has been fully written, remove this frame
+                    // and notify it. Since we remove this frame
+                    // first, we're guaranteed that its error method will not
+                    // be called when we call cancel.
+                    pendingWriteQueue.remove();
+                    frame.writeComplete();
+                }
+            } catch (Throwable e) {
+                // Mark the state as cancelled, we'll clear the pending queue
+                // via cancel() below.
+                cancelled = true;
+            } finally {
+                writing = false;
+                // Make sure we always decrement the flow control windows
+                // by the bytes written.
+                writtenBytes = before - frame.size();
+                decrementFlowControlWindow(writtenBytes);
+                decrementPendingBytes(writtenBytes);
+                // If a cancellation occurred while writing, call cancel again to
+                // clear and error all of the pending writes.
+                if (cancelled) {
+                    cancel();
+                }
+            }
+            return writtenBytes;
+        }
+
         /**
          * Recursively increments the streamable bytes for this branch in the priority tree starting at the current
          * node.
@@ -495,24 +537,12 @@ public class DefaultHttp2RemoteFlowController implements Http2RemoteFlowControll
             }
         }
 
-        /**
-         * A wrapper class around the content of a data frame.
-         */
-        private final class Frame {
-            final FlowControlled payload;
-
-            Frame(FlowControlled payload) {
-                this.payload = payload;
-                // Increment the number of pending bytes for this stream.
-                incrementPendingBytes(payload.size());
-            }
-
         /**
          * Increments the number of pending bytes for this node. If there was any change to the number of bytes that
-             * fit into the stream window, then {@link #incrementStreamableBytesForTree} to recursively update this
+         * fit into the stream window, then {@link #incrementStreamableBytesForTree} is called to recursively update
-             * branch of the priority tree.
+         * this branch of the priority tree.
          */
-            private void incrementPendingBytes(int numBytes) {
+        void incrementPendingBytes(int numBytes) {
             int previouslyStreamable = streamableBytes();
             pendingBytes += numBytes;
 
@@ -523,47 +553,10 @@ public class DefaultHttp2RemoteFlowController implements Http2RemoteFlowControll
         }
 
         /**
-             * Writes the frame and decrements the stream and connection window sizes. If the frame is in the pending
+         * If this frame is in the pending queue, decrements the number of pending bytes for the stream.
-             * queue, the written bytes are removed from this branch of the priority tree.
-             * <p>
-             * Note: this does not flush the {@link ChannelHandlerContext}.
          */
-            int write(int allowedBytes) {
+        void decrementPendingBytes(int bytes) {
-                int before = payload.size();
+            incrementPendingBytes(-bytes);
-                int writtenBytes = 0;
-                try {
-                    if (writing) {
-                        throw new IllegalStateException("write is not re-entrant");
-                    }
-                    // Write the portion of the frame.
-                    writing = true;
-                    needFlush |= payload.write(Math.max(0, allowedBytes));
-                    if (!cancelled && payload.size() == 0) {
-                        // This frame has been fully written, remove this frame
-                        // and notify the payload. Since we remove this frame
-                        // first, we're guaranteed that its error method will not
-                        // be called when we call cancel.
-                        pendingWriteQueue.remove();
-                        payload.writeComplete();
-                    }
-                } catch (Throwable e) {
-                    // Mark the state as cancelled, we'll clear the pending queue
-                    // via cancel() below.
-                    cancelled = true;
-                } finally {
-                    writing = false;
-                    // Make sure we always decrement the flow control windows
-                    // by the bytes written.
-                    writtenBytes = before - payload.size();
-                    decrementFlowControlWindow(writtenBytes);
-                    decrementPendingBytes(writtenBytes);
-                    // If a cancellation occurred while writing, call cancel again to
-                    // clear and error all of the pending writes.
-                    if (cancelled) {
-                        cancel();
-                    }
-                }
-                return writtenBytes;
         }
 
         /**
@@ -571,28 +564,22 @@ public class DefaultHttp2RemoteFlowController implements Http2RemoteFlowControll
          */
         void decrementFlowControlWindow(int bytes) {
             try {
-                    connectionState().incrementStreamWindow(-bytes);
+                int negativeBytes = -bytes;
-                    incrementStreamWindow(-bytes);
+                connectionState().incrementStreamWindow(negativeBytes);
-                } catch (Http2Exception e) { // Should never get here since we're decrementing.
+                incrementStreamWindow(negativeBytes);
-                    throw new RuntimeException("Invalid window state when writing frame: " + e.getMessage(), e);
+            } catch (Http2Exception e) {
+                // Should never get here since we're decrementing.
+                throw new IllegalStateException("Invalid window state when writing frame: " + e.getMessage(), e);
             }
         }
 
         /**
-             * Discards this frame, writing an error. If this frame is in the pending queue, the unwritten bytes are
+         * Discards this {@link FlowControlled}, writing an error. If this frame is in the pending queue,
-             * removed from this branch of the priority tree.
+         * the unwritten bytes are removed from this branch of the priority tree.
          */
-            void writeError(Http2Exception cause) {
+        void writeError(FlowControlled frame, Http2Exception cause) {
-                decrementPendingBytes(payload.size());
+            decrementPendingBytes(frame.size());
-                payload.error(cause);
+            frame.error(cause);
-            }
-
-            /**
-             * If this frame is in the pending queue, decrements the number of pending bytes for the stream.
-             */
-            void decrementPendingBytes(int bytes) {
-                incrementPendingBytes(-bytes);
-            }
         }
     }
 }