Simplify the exception handling of ChannelOutboundHandler.write()

DefaultChannelHandlerContext does not trigger exceptionCaught() immediately when ChannelOutboundHandler.write() raises an exception.  It just records the exception until flush() is triggered.  On invokeFlush(), if there's any exception recorded, DefaultChannelHandlerContext will fail the promise without calling ChannelOutboundHandler.flush().  If more than one exception were raised, only the first exception is used as the cause of the failure and the others will be logged at warn level.

codec-http/src/main/java/io/netty/handler/codec/spdy/SpdySessionHandler.java

@@ -22,8 +22,6 @@ import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelPromise;
 import io.netty.util.internal.EmptyArrays;
 
-import java.util.ArrayDeque;
-import java.util.Queue;
 import java.util.concurrent.atomic.AtomicInteger;
 
 /**
@@ -55,8 +53,6 @@ public class SpdySessionHandler
 
     private final AtomicInteger pings = new AtomicInteger();
 
-    private final Queue<Object> outboundBuffer = new ArrayDeque<Object>();
-
     private boolean sentGoAwayFrame;
     private boolean receivedGoAwayFrame;
 
@@ -397,18 +393,6 @@ public class SpdySessionHandler
 
     @Override
     public void write(ChannelHandlerContext ctx, Object msg) throws Exception {
-        outboundBuffer.add(msg);
-    }
-
-    @Override
-    public void flush(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception {
-        try {
-            for (;;) {
-                Object msg = outboundBuffer.poll();
-                if (msg == null) {
-                    break;
-                }
-
         if (msg instanceof SpdyDataFrame ||
             msg instanceof SpdySynStreamFrame ||
             msg instanceof SpdySynReplyFrame ||
@@ -418,25 +402,12 @@ public class SpdySessionHandler
             msg instanceof SpdyGoAwayFrame ||
             msg instanceof SpdyHeadersFrame ||
             msg instanceof SpdyWindowUpdateFrame) {
-                    try {
+
             handleOutboundMessage(ctx, msg);
-                    } catch (SpdyProtocolException e) {
-                        if (e == PROTOCOL_EXCEPTION) {
-                            // On the case of PROTOCOL_EXCEPTION, fail the promise directly
-                            // See #1211
-                            promise.setFailure(PROTOCOL_EXCEPTION);
-                            return;
-                        }
-                    }
         } else {
             ctx.write(msg);
         }
     }
-            ctx.flush(promise);
-        } finally {
-            outboundBuffer.clear();
-        }
-    }
 
     private void handleOutboundMessage(ChannelHandlerContext ctx, Object msg) throws Exception {
         if (msg instanceof SpdyDataFrame) {

transport/src/main/java/io/netty/channel/DefaultChannelHandlerContext.java

@@ -19,6 +19,7 @@ import io.netty.buffer.ByteBufAllocator;
 import io.netty.util.DefaultAttributeMap;
 import io.netty.util.concurrent.EventExecutor;
 import io.netty.util.concurrent.EventExecutorGroup;
+import io.netty.util.internal.StringUtil;
 
 import java.net.SocketAddress;
 
@@ -33,6 +34,7 @@ final class DefaultChannelHandlerContext extends DefaultAttributeMap implements
     private final DefaultChannelPipeline pipeline;
     private final String name;
     private final ChannelHandler handler;
+    private Throwable lastWriteException;
     private boolean removed;
 
     // Will be set to null if no child executor should be used, otherwise it will be set to the
@@ -696,7 +698,13 @@ final class DefaultChannelHandlerContext extends DefaultAttributeMap implements
         try {
             handler.write(this, msg);
         } catch (Throwable t) {
-            notifyHandlerException(t);
+            if (lastWriteException == null) {
+                lastWriteException = t;
+            } else if (logger.isWarnEnabled()) {
+                logger.warn(
+                        "More than one exception was raised by " + StringUtil.simpleClassName(handler) + ".write()." +
+                        "Will fail the subsequent flush() with the first one and log others.", t);
+            }
         }
     }
 
@@ -723,6 +731,13 @@ final class DefaultChannelHandlerContext extends DefaultAttributeMap implements
     }
 
     private void invokeFlush0(ChannelPromise promise) {
+        Throwable lastWriteException = this.lastWriteException;
+        if (lastWriteException != null) {
+            this.lastWriteException = null;
+            promise.setFailure(lastWriteException);
+            return;
+        }
+
         try {
             ((ChannelOutboundHandler) handler()).flush(this, promise);
         } catch (Throwable t) {