Large response - how to handle asynchronously

[Don Park]

Łukasz,

It seems to me that you are trying to do too much within messageReceived.

I would just queue the request somewhere then handle it in another thread.

You can implement blocking behavior around that queue too.

Best,

- Don

On Mar 28, 2010, at 1:27 AM, Łukasz Osipiuk wrote:

> Hi!
> 
> We really need this solved.
> If anybody had similar problem and have some thoughts on it we would
> really appreciate help.
> 
> Best regards, Łukasz Osipiuk
> 
> On Thu, Mar 25, 2010 at 16:14, Łukasz Osipiuk <lukasz at osipiuk.net> wrote:
>> Hi guys,
>> 
>> We are implementing server application using Netty protocol framework
>> and we have problem implementing handling of large responses.
>> We will be handling many simultaneously connected clients.
>> In protocol we are implementing, responses to client requests can be
>> huge (lets assume that larger than server memory).
>> While handling request we have to read part of response data from
>> external storage - send it to client - wait until he receives the data
>> and continue with next part.
>> 
>> We approached problem with following code in handler (simplified
>> version, no error handling and so on):
>> 
>>   @Override
>>   public void messageReceived(ChannelHandlerContext ctx, MessageEvent
>> e) throws Exception {
>>       XXXRequest req = (XXXRequest) e.getMessage();
>>       writePartResponse(ctx, req);
>>   }
>> 
>>    private void writePartResponse(final ChannelHandlerContext ctx,
>> final XXXRequest req) {
>>        if (moreDataToBeRead(req)) {// anything more to be done?
>>            XXXPartResponse resPart = readSomeData(req); // read some
>> data from storage
>>            ChannelFuture f = ctx.getChannel().write(resPart);
>>            f.addListener(new ChannelFutureListener() {
>>                public void operationComplete(ChannelFuture f_) throws
>> Exception {
>>                    writePartResponse(ctx, req);
>>                }
>>            });
>>        }
>>    }
>> 
>> Above approach does not work.
>> 
>> Problem 1.
>> 
>> While handling request we have to block other client's requests  so
>> they are not handled simultaneously.
>> In above code when messageReceived() method terminates any pending
>> client requests are delivered to handler and handled even though
>> asynchronous handling of previous request might still be in progress.
>> We do not know how to block handling of any pending requests.
>> 
>> Problem 2.
>> 
>> I client is quick enough to read data from socket f.addListener
>> immediatelly triggers calling of futer.operationComplete in the same
>> thread.
>> This leads to StackOverflowError.
>> (btw. It appears that StackOverflowError it is not handled correctly
>> by netty in this place and application is not notified about it being
>> thrown - handling of request is just silently terminated).
>> 
>> Any way to avoid above problems?
>> I guess the approach is broken - can anybody lead us how to implement
>> such (trivial one might think) behaviour?
>> 
>> Best regards, Łukasz Osipiuk
>> 
>> 
>> --
>> --
>> Łukasz Osipiuk
>> mailto:lukasz at osipiuk.net
>> 
> 
> 
> 
> -- 
> -- 
> Łukasz Osipiuk
> mailto:lukasz at osipiuk.net
> 
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