Futures

Contents

Index

Futures

The ReplyReactor and Actor traits support result-bearing message send operations (the !! methods) that immediately return a future. A future, that is, an instance of the Future trait, is a handle that can be used to retrieve the response to such a message send-with-future.

The sender of a message send-with-future can wait for the future's response by applying the future. For example, sending a message using val fut = a !! msg allows the sender to wait for the result of the future as follows: val res = fut().

In addition, a Future can be queried to find out whether its result is available without blocking using the isSet method.

A message send-with-future is not the only way to obtain a future. Futures can also be created from computations using the future method. In the following example, the computation body is started to run concurrently, returning a future for its result:

val fut = future { body }
// ...
fut() // wait for future

What makes futures special in the context of actors is the possibility to retrieve their result using the standard actor-based receive operations, such as receive etc. Moreover, it is possible to use the event-based operations react and reactWithin. This enables an actor to wait for the result of a future without blocking its underlying thread.

The actor-based receive operations are made available through the future's inputChannel. For a future of type Future[T], its type is InputChannel[T]. Example:

val fut = a !! msg
// ...
fut.inputChannel.react {
  case Response => // ...
}

Futures

Contents

Index