[undertow-dev] scala, activate, nio, async jdbc, future, threads

[Laurent Bedubourg]

Ok, I think my mail could be reduced to :

Is it possible possible to transfer the HttpServerExchange responsibility to
another thread ?

Regards
Laurent


On Fri Dec 12 2014 at 7:11:01 PM Laurent Bedubourg <laurent at labe.me> wrote:

> Hello,
>
> I am evaluating Undertow and trying to fit an async database (with scala,
> Activate and https://github.com/mauricio/postgresql-async which use netty
> and nio).
>
> The good news is that it more or less works.
>
> My main concern is that the database system create threads using scala
> futures and that I am forced to "Await" for the result of my Futures to
> send the result to the HttpServerExchange.
>
> I am forced to dispath() the request because Await locks the current
> thread and I shouldn't lock the IO thread from my Handler, should I?
>
> It made me wondering : is is really a good idea to use futures + Await
> with undertow and more generaly nio?
>
> If the thread pool is limited and I lock threads, even if the database
> driver is async and uses nio, am I bitting my own leg?
>
> Thanks for any input you can give me and sorry if it's too scala related :)
>
> Regards
> Laurent
>
> PS: Here's the handleRequest I am using to test this, any comment or help
> welcome too since I am discovering the API.
>
> def handleRequest(x:io.undertow.server.HttpServerExchange){
>   if (x.isInIoThread()){
>     x.dispatch(this)
>     return
>   }
>   // useful or not? no change
>   // x.startBlocking()
>
>   // Ok, we are in worker thread we can work a little with database
>   // val f = asyncTransactionalChain { implicit context =>
>   //   for (
>   //     a <- asyncTransactional { new AMember("aaa") };
>   //     b <- asyncById[AMember](a.id)
>   //   ) yield b
>   // }
>
>   // Simulate database work with just a future
>   val f = future {
>     Some(1)
>   }(scala.concurrent.ExecutionContext.Implicits.global)
>
>   // send string to xchange
>   def sendReply(str:String){
>     x.getResponseHeaders().put(io.undertow.util.Headers.CONTENT_TYPE,
> "text/plain")
>     x.getResponseSender().send(str)
>     // x.endExchange()
>   }
>
>   // // this fails
>   // f.onSuccess {
>   //   case Some(result) => sendReply(result.toString)
>   // }(scala.concurrent.ExecutionContext.Implicits.global)
>
>   // // this works
>   val result = Await.result(f, Duration(1000, MILLISECONDS))
>   sendReply(result.toString)
> }
>
>
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