ctx.writeAndFlush throws BlockingOperationException even channel handler is in separate EventExecutorGroup

Expected behavior

BlockingOperationException only need to be thrown when calling await inside IO thread

Actual behavior

This is exception is thrown even when doing this:

ChannelInitializer(){
      initChannel(...){
           addLast(....)
           addLast(eventExecutorGroup,"businessExecutor", new SimpleChannelInboundHandler(){
                 channelRead0(...){
                        val p = ctx.writeAndFlush(msg)
                        p.await()
                 }  
           })
      }
}

Steps to reproduce

Minimal yet complete reproducer code (or URL to code)

Netty version

4.1.36

JVM version (e.g. java -version)

OS version (e.g. uname -a)

[normanmaurer]

@qeesung I think it is still necessary as you could still end up with a deadlock if another handler that is in from of the handler and uses the same EventExecutorGroup will delay the notification of the promise.

[qeesung]

@baijianhua As @normanmaurer said, If the same EventGroupExecutor is bound to different handlers on the same Pipeline, calling await can cause deadlock, although the thread calling await and the IO thread are not the same thread.

Like the following

pipe.addLast(executorGroup1, handler1);
pipe.addLast(executorGroup2, handler2);
pipe.addLast(executorGroup1, new SimpleChannelInboundHandler<String>() {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        ChannelFuture f = ctx.writeAndFlush("hello world");
        f.await();
    }
});

Instead, I recommend adding listener, or await it it in a custom thread (pool).