Play slick and Async - is it a race condition?

Question

Reading Play-Slick DBAction code, I thought that this code might contain a race condition:

object DBAction{
  // snip

  def apply(r: (RequestWithDbSession) => Result)(implicit app:Application) = {
    Action { implicit request => 
      AsyncResult {
        DB.withSession{ s:scala.slick.session.Session =>
          Future(r( RequestWithDbSession(request,s) ))(executionContext)
      }
    }
  }
}

The function r runs at a future time, after withSession has returned a Future[Result], and called session.close(). Is there a race condition in this code?

Answer 1

I am not sure if that is called a race condition. However to me it seems that you are correct that something is wrong here. The session might no longer be valid when the future executes the code.

It would be better to invert the execution and request a database session from within the future:

Async {
  Future {
    DB.withSession{ s:scala.slick.session.Session =>
      r( RequestWithDbSession(request, s) )
    }
  }
}

Answer 2

I think your are right and fix suggested by EECOLOR looks correct. We are tracking this in a ticket: https://github.com/freekh/play-slick/issues/81

Thx