Play framework async processing and blocking I/O in Java

Question

My application uses Play framework to process REST requests. I need to perform some potentially long lasting blocking I/O operation in http request handler. In parallel I\'d

Answer 1

I would recommend that you set up your own context and run your blocking/cpu-intensive operations there using Plays F.Promise. As always with threads, the optimal solution depends on numerous of things like number of cores etc.

First set up your context in applications.conf:

play {
  akka {
    akka.loggers = ["akka.event.Logging$DefaultLogger", "akka.event.slf4j.Slf4jLogger"]
    loglevel = WARNING
    actor {
      default-dispatcher = {
        fork-join-executor {
          parallelism-min = 1
          parallelism-factor = 2
          parallelism-max = 6
        }
      }
      my-context {
        fork-join-executor {
          parallelism-min = 1
          parallelism-factor = 4
          parallelism-max = 16
        }
      }
    }
  }
}

Then in your controller, make use of your context using Plays Promises (I'm using Java 8):

public static F.Promise love() {
    ExecutionContext myExecutionContext = Akka.system().dispatchers().lookup("play.akka.actor.my-context");

    F.Promise integerPromise = F.Promise.promise(() ->
            LongRunningProcess.run(10000L)
    , myExecutionContext);

    F.Promise integerPromise2 = F.Promise.promise(() ->
            LongRunningProcess.run(10000L)
    , myExecutionContext);

    return integerPromise.flatMap(i -> integerPromise2.map(x -> ok()));
}

This way your Play app will still handle short lasting requests on the default-dispatcher execution context and the blocking/cpu-intensive will run in my-context.

I made a very short example for you demonstrating this, check it out on github.