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/*
* Copyright (C) 2012 Typesafe Inc. <http://www.typesafe.com>
*/
package scala.async
package continuations
import scala.language.experimental.macros
import scala.reflect.macros.Context
import scala.util.continuations._
trait AsyncBaseWithCPSFallback extends AsyncBase {
/* Fall-back for `await` using CPS plugin.
*
* Note: This method is public, but is intended only for internal use.
*/
def awaitFallback[T](awaitable: futureSystem.Fut[T]): T @cps[futureSystem.Fut[Any]]
override protected[async] def fallbackEnabled = true
/* Implements `async { ... }` using the CPS plugin.
*/
protected def cpsBasedAsyncImpl[T: c.WeakTypeTag](c: Context)(body: c.Expr[T]): c.Expr[futureSystem.Fut[T]] = {
import c.universe._
def lookupMember(name: String) = {
val asyncTrait = c.mirror.staticClass("scala.async.continuations.AsyncBaseWithCPSFallback")
val tpe = asyncTrait.asType.toType
tpe.member(newTermName(name)).ensuring(_ != NoSymbol)
}
AsyncUtils.vprintln("AsyncBaseWithCPSFallback.cpsBasedAsyncImpl")
val utils = TransformUtils[c.type](c)
val futureSystemOps = futureSystem.mkOps(c)
val awaitSym = utils.defn.Async_await
val awaitFallbackSym = lookupMember("awaitFallback")
// replace `await` invocations with `awaitFallback` invocations
val awaitReplacer = new Transformer {
override def transform(tree: Tree): Tree = tree match {
case Apply(fun @ TypeApply(_, List(futArgTpt)), args) if fun.symbol == awaitSym =>
val typeApp = treeCopy.TypeApply(fun, Ident(awaitFallbackSym), List(TypeTree(futArgTpt.tpe)))
treeCopy.Apply(tree, typeApp, args.map(arg => c.resetAllAttrs(arg.duplicate)))
case _ =>
super.transform(tree)
}
}
val bodyWithAwaitFallback = awaitReplacer.transform(body.tree)
/* generate an expression that looks like this:
reset {
val f = future { ... }
...
val x = awaitFallback(f)
...
future { expr }
}.asInstanceOf[Future[T]]
*/
val bodyWithFuture = {
val tree = bodyWithAwaitFallback match {
case Block(stmts, expr) => Block(stmts, futureSystemOps.spawn(expr))
case expr => futureSystemOps.spawn(expr)
}
c.Expr[futureSystem.Fut[Any]](c.resetAllAttrs(tree.duplicate))
}
val bodyWithReset: c.Expr[futureSystem.Fut[Any]] = reify {
reset { bodyWithFuture.splice }
}
val bodyWithCast = futureSystemOps.castTo[T](bodyWithReset)
AsyncUtils.vprintln(s"CPS-based async transform expands to:\n${bodyWithCast.tree}")
bodyWithCast
}
override def asyncImpl[T: c.WeakTypeTag](c: Context)(body: c.Expr[T]): c.Expr[futureSystem.Fut[T]] = {
AsyncUtils.vprintln("AsyncBaseWithCPSFallback.asyncImpl")
val analyzer = AsyncAnalysis[c.type](c, this)
if (!analyzer.reportUnsupportedAwaits(body.tree))
super.asyncImpl[T](c)(body) // no unsupported awaits
else
cpsBasedAsyncImpl[T](c)(body) // fallback to CPS
}
}
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