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/*
* Copyright (C) 2012 Typesafe Inc. <http://www.typesafe.com>
*/
package scala.async
import scala.language.higherKinds
import scala.reflect.macros.Context
/**
* An abstraction over a future system.
*
* Used by the macro implementations in [[scala.async.AsyncBase]] to
* customize the code generation.
*
* The API mirrors that of `scala.concurrent.Future`, see the instance
* [[scala.async.ScalaConcurrentFutureSystem]] for an example of how
* to implement this.
*/
trait FutureSystem {
/** A container to receive the final value of the computation */
type Prom[A]
/** A (potentially in-progress) computation */
type Fut[A]
/** An execution context, required to create or register an on completion callback on a Future. */
type ExecContext
trait Ops {
val context: reflect.macros.Context
import context.universe._
/** Lookup the execution context, typically with an implicit search */
def execContext: Expr[ExecContext]
def promType[A: WeakTypeTag]: Type
def execContextType: Type
/** Create an empty promise */
def createProm[A: WeakTypeTag]: Expr[Prom[A]]
/** Extract a future from the given promise. */
def promiseToFuture[A: WeakTypeTag](prom: Expr[Prom[A]]): Expr[Fut[A]]
/** Construct a future to asynchronously compute the given expression */
def future[A: WeakTypeTag](a: Expr[A])(execContext: Expr[ExecContext]): Expr[Fut[A]]
/** Register an call back to run on completion of the given future */
def onComplete[A, U](future: Expr[Fut[A]], fun: Expr[scala.util.Try[A] => U],
execContext: Expr[ExecContext]): Expr[Unit]
/** Complete a promise with a value */
def completeProm[A](prom: Expr[Prom[A]], value: Expr[scala.util.Try[A]]): Expr[Unit]
def spawn(tree: context.Tree): context.Tree =
future(context.Expr[Unit](tree))(execContext).tree
def castTo[A: WeakTypeTag](future: Expr[Fut[Any]]): Expr[Fut[A]]
}
def mkOps(c: Context): Ops { val context: c.type }
}
object ScalaConcurrentFutureSystem extends FutureSystem {
import scala.concurrent._
type Prom[A] = Promise[A]
type Fut[A] = Future[A]
type ExecContext = ExecutionContext
def mkOps(c: Context): Ops {val context: c.type} = new Ops {
val context: c.type = c
import context.universe._
def execContext: Expr[ExecContext] = c.Expr(c.inferImplicitValue(c.weakTypeOf[ExecutionContext]) match {
case EmptyTree => c.abort(c.macroApplication.pos, "Unable to resolve implicit ExecutionContext")
case context => context
})
def promType[A: WeakTypeTag]: Type = c.weakTypeOf[Promise[A]]
def execContextType: Type = c.weakTypeOf[ExecutionContext]
def createProm[A: WeakTypeTag]: Expr[Prom[A]] = reify {
Promise[A]()
}
def promiseToFuture[A: WeakTypeTag](prom: Expr[Prom[A]]) = reify {
prom.splice.future
}
def future[A: WeakTypeTag](a: Expr[A])(execContext: Expr[ExecContext]) = reify {
Future(a.splice)(execContext.splice)
}
def onComplete[A, U](future: Expr[Fut[A]], fun: Expr[scala.util.Try[A] => U],
execContext: Expr[ExecContext]): Expr[Unit] = reify {
future.splice.onComplete(fun.splice)(execContext.splice)
}
def completeProm[A](prom: Expr[Prom[A]], value: Expr[scala.util.Try[A]]): Expr[Unit] = reify {
prom.splice.complete(value.splice)
context.literalUnit.splice
}
def castTo[A: WeakTypeTag](future: Expr[Fut[Any]]): Expr[Fut[A]] = reify {
future.splice.asInstanceOf[Fut[A]]
}
}
}
/**
* A trivial implementation of [[scala.async.FutureSystem]] that performs computations
* on the current thread. Useful for testing.
*/
object IdentityFutureSystem extends FutureSystem {
class Prom[A](var a: A)
type Fut[A] = A
type ExecContext = Unit
def mkOps(c: Context): Ops {val context: c.type} = new Ops {
val context: c.type = c
import context.universe._
def execContext: Expr[ExecContext] = c.literalUnit
def promType[A: WeakTypeTag]: Type = c.weakTypeOf[Prom[A]]
def execContextType: Type = c.weakTypeOf[Unit]
def createProm[A: WeakTypeTag]: Expr[Prom[A]] = reify {
new Prom(null.asInstanceOf[A])
}
def promiseToFuture[A: WeakTypeTag](prom: Expr[Prom[A]]) = reify {
prom.splice.a
}
def future[A: WeakTypeTag](t: Expr[A])(execContext: Expr[ExecContext]) = t
def onComplete[A, U](future: Expr[Fut[A]], fun: Expr[scala.util.Try[A] => U],
execContext: Expr[ExecContext]): Expr[Unit] = reify {
fun.splice.apply(util.Success(future.splice))
context.literalUnit.splice
}
def completeProm[A](prom: Expr[Prom[A]], value: Expr[scala.util.Try[A]]): Expr[Unit] = reify {
prom.splice.a = value.splice.get
context.literalUnit.splice
}
def castTo[A: WeakTypeTag](future: Expr[Fut[Any]]): Expr[Fut[A]] = ???
}
}
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